2 barrel 2 banger

[JohnsonM50]

An Idea to re-ask, Ive been thinking about putting a 2 barrel carb on a '70s 31.8ci OMC twin. Ive been given some good ideas so am in progress. Ive got a 2 barrel from a 4 cyl OMC. that used 2 carbs. The throats at the rear are 1 3/8", same as a stock single for the 31.8ci motor. The venturi sizes are very close between the carbs, the 2 barrel appears to be equal side to side.
The single barrel stock carb feeds a common intake that both reed sets draw from so in effect the carb singularly feeds each cyl. Every charge to each cyl is from the full bore of the single barrel drawn back & forth thru the reeds.
If the above is correct, I theorize that if I separate the intake plenum so the each barrel feeds 1 cyl Ill essentially [short of working out bugs] have the same thing. If so then the performance.. where would be the gain? Im thinking the smaller more direct intake per cyl might cause an increase in velocity [this is a crossflow] and therefore send a better atomized, possibly slightly larger charge in. The carb would be drawing from each feed tube 1/2 as many times per barrel as the single barrel so might be more capable at top end. Im wondering if in alternate operation the feed jets would cause a siphoning effect on each other but doubt it because the air vent should cover that.
Worse case it doesnt work & I cut up a spare intake & sunk a bunch of time.
Im ready now...Point-n-Laff:D, Ask why!?:confused:, make remarks:rolleyes:,or add wisdom;) Rest assured Im enjoying try-n it & theres more to the story than just stickin this on any motor. Thanks

[JohnsonM50]

so far...
http://i35.photobucket.com/albums/d151/mes355/DSCN0382.jpg

[OUTBOARDER]

1-3/8" O.D X 1-1/4" I.D Alum tube will fit on butterfly side, drill thru hole for throttle shaft and make/get a 1-1/4" dia butterfly....................:)

oops also Drill out idle and transition holes thru sleeve

[JohnsonM50]

At 1st glance I thought to make a plate to attach to the intake but it became apparent that to thru bolt to whole thing was the only way. Ill have to go thru the carb of course, there appears to be orifices in the rear cutouts between barrels. Will separating the intake effect them is 1 concern, how to compensate the other. Im not concerned with idle/troll speed:rolleyes: so can sacrifice purr like a kitten in favor the roar.
http://i35.photobucket.com/albums/d151/mes355/DSCN0389.jpg
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Thanks Anthony, I will do that if needed but am going to test 'as is' just in case.

[Powerabout]

If you want power at high revs you will need to use reeds on a vee block not the flat ones

[zul8tr]

Thoughts

Have you checked the size of the total venturi area of the 2 x carb compared to the total venturi area of the single carb you are replacing? It appears to me that the 2x has a whole lot more area than the single. While this may be good for max high rpm output (?) it most likely will be negative for lower to mid range performance due to poor throttle response from reduced air velocity at the venturi. The new 2x carb setup would require proper jetting to obtain the correct A/F ratio but such a larger venturi area then stock might make jetting out of reasonable range.

You note correctly that each cylindere feeds on the single carb and theorize that a 2X carb divided at the plenum will allow each cylindere to use each side of the 2x carb and that should provide a more efficient intake. While it sounds reasonable the intake air still mixes atthe reed cage. I think that unless you keep the intake seperate all the way to the cylindere intake ports the 2x carb will have about 1/2 the air velocity at each venturi as the stock single venturi setup based on the similiar geometry dimensions you note.

Since you are already on the way go for it and see what happens. Edison tried 1000 filiments before he hit on carbon impregnated cotton, but he missed it on his incorrect belief that DC power was the way of the future. It took Nikola Tesla (his former employee) to set the light and gave us AC, Edison was pissed - thank you Mr Tesla.

[JohnsonM50]

Thanks for the suggestions, I will keep them in mind as I run it. Ive thought about V reeds & might later, for now Im thinkin non steel reeds.
The venturi area is slightly less than the stock single barrel & this is to be tried on a .030 over 32+ci motor with squared port tops & lighter than stock spinning mass & bumped up compression 35hp.
Im sure I run the risk of a 'fail to launch' but Im ok with that. Once the intake is made I can try different carbs or whatever. Velocity or not may well be the maker/breaker of this experiment.

[Seagull 170]

Before you follow zul8tr thoughts, who I'd guess is bang on the money, & build a dividing wall.
See if you can seperate the butterflys so that they are actuated by separate cables, if you have a spare carb.
Cable up one choke in the normal manner to give normal low & mid range performance, & the second to open when it starts to come on song, maybe 1000 revs below max, then open both together to find the limits on the second choke.
If the second choke is first tried on a lawn mower type throttle it's easy to find the start point.
I've seen this done on small single cylinders fishing motors with two seperate carbs both slightly smaller than the origonal, the second only opening almost at the previous peak revs, with a 10% gain in peak revs with the same prop.

This is another experiment where it would be good to have dyno at home.

[JohnsonM50]

Before you follow zul8tr thoughts, who I'd guess is bang on the money, & build a dividing wall.
See if you can seperate the butterflys so that they are actuated by separate cables, if you have a spare carb.
Cable up one choke in the normal manner to give normal low & mid range performance, & the second to open when it starts to come on song, maybe 1000 revs below max, then open both together to find the limits on the second choke.
If the second choke is first tried on a lawn mower type throttle it's easy to find the start point.
I've seen this done on small single cylinders fishing motors with two seperate carbs both slightly smaller than the origonal, the second only opening almost at the previous peak revs, with a 10% gain in peak revs with the same prop.

This is another experiment where it would be good to have dyno at home.
I was also thinking the secondary barrel & could maybe do something with that, would be easy to cut the shaft. [it sure works as a V8-4 barrel:D] Thanks

[zul8tr]

Before you follow zul8tr thoughts, who I'd guess is bang on the money, & build a dividing wall.
See if you can seperate the butterflys so that they are actuated by separate cables, if you have a spare carb.
Cable up one choke in the normal manner to give normal low & mid range performance, & the second to open when it starts to come on song, maybe 1000 revs below max, then open both together to find the limits on the second choke.
If the second choke is first tried on a lawn mower type throttle it's easy to find the start point.
I've seen this done on small single cylinders fishing motors with two seperate carbs both slightly smaller than the origonal, the second only opening almost at the previous peak revs, with a 10% gain in peak revs with the same prop.

This is another experiment where it would be good to have dyno at home.

----------------------------------------

That is a reasonable idea and worth a try. Like delayed secondaries on a 4 barrel carb.

I remember an older Mercury (car) I was tinkering with. It was a stock 312 c.i.V8 with a 1x four barrel so I decided to replace the stock manifold and carb with a 2x four barrel set up. It definately was too much venturie area at the low and mid range if not careful with the throttle but was a stomper :eek: at the higher revs. The only set up that worked was the stock factory setup progressive linkage system. The front 2 barrels of each four barrel were operated together and the rear 2 barrels came in at about 70% open throttle.

[JohnsonM50]

----------------------------------------

That is a reasonable idea and worth a try. Like delayed secondaries on a 4 barrel carb.

I remember an older Mercury (car) I was tinkering with. It was a stock 312 c.i.V8 with a 1x four barrel so I decided to replace the stock manifold and carb with a 2x four barrel set up. It definately was too much venturie area at the low and mid range if not careful with the throttle but was a stomper :eek: at the higher revs. The only set up that worked was the stock factory setup progressive linkage system. The front 2 barrels of each four barrel were operated together and the rear 2 barrels came in at about 70% open throttle.Yes it is. Theres a number of ways I can go with this & Im pretty sure Ill hit on something sooner or later. Ill go with simple at 1st then go into trial & error with the different ideas based on results. Ill need to test in a barrel with a test wheel at 1st then see If I can get some real test tank time with a prop on. Otherwise tho Ill be going by ear, spark plug color & seat of pants :cool: oh & some on boat testing too ;)

[zul8tr]

Yes it is. Theres a number of ways I can go with this & Im pretty sure Ill hit on something sooner or later. Ill go with simple at 1st then go into trial & error with the different ideas based on results. Ill need to test in a barrel with a test wheel at 1st then see If I can get some real test tank time with a prop on. Otherwise tho Ill be going by ear, spark plug color & seat of pants :cool: oh & some on boat testing too ;)

Post results and pics

[Fastjeff57]

That's not how dual 4 barrels were normally set up. The rear of the two (since its primary barrels were nearer the center of the manifold) was what the motor ran on most of the time. The front carb came in about half throttle, with the secondary barrels of both carbs starting to open at about 3/4 throttle. The setup was bog resistant and allowed normal running at low speed. It even idled well, as Buick "Wildcat" and Mopar "413 Ramcharger" owners can attest.

Jeff (old geezer)

[JohnsonM50]

That's not how dual 4 barrels were normally set up. The rear of the two (since its primary barrels were nearer the center of the manifold) was what the motor ran on most of the time. The front carb came in about half throttle, with the secondary barrels of both carbs starting to open at about 3/4 throttle. The setup was bog resistant and allowed normal running at low speed. It even idled well, as Buick "Wildcat" and Mopar "413 Ramcharger" owners can attest.

Jeff (old geezer)

I never saw a 2-4 barrel 413 Mopar but got to drive several 426's, I worked at a Chry-Ply dealer & grabbed every opportunity:D I remember there being alot of pedal pressure near the bottom, not gonna floor that by mistake:eek:
This little outboard Im messin with is typically designed with the single carb slightly favoring the top cyl. [position wise] If I do set this up as a 2nd-ary Id use the top side as the primary.

[zul8tr]

That's not how dual 4 barrels were normally set up. The rear of the two (since its primary barrels were nearer the center of the manifold) was what the motor ran on most of the time. The front carb came in about half throttle, with the secondary barrels of both carbs starting to open at about 3/4 throttle. The setup was bog resistant and allowed normal running at low speed. It even idled well, as Buick "Wildcat" and Mopar "413 Ramcharger" owners can attest.

Jeff (old geezer)

---------------------------------------

Well I said it was the stock factory setup and that's how Ford set up their dual 4 barrel on the 57 TBird manifold and carbs that I placed on the Merc. They were the high top Holly 4 barrels and the rears had vacuum activation . Wouldn't know about Mopar stuff. I suppose you could do as you suggest but because the Holly's had small primary venturies the car had good low end throttle response.

[Fastjeff57]

I was wondering if any olde time motorheads out there would catch my error: The 413 Ramchargers had its four barrels on a super long ram intake, one on each side of the motor, so this was NOT a progressive opening setup. I smartened up after making that goof, expecting someone would catch me on it, but...

A bunch of other factory cars also used dual 4 barrels, including Cadillac, Pontiac (421 Super Duty) Ford (427 Hi-Riser) and of course "She's real fine my 409!" All of THOSE were progressive setups. Honest!

Jeff

[JohnsonM50]

I was wondering if any olde time motorheads out there would catch my error: The 413 Ramchargers had its four barrels on a super long ram intake, one on each side of the motor, so this was NOT a progressive opening setup. I smartened up after making that goof, expecting someone would catch me on it, but...

A bunch of other factory cars also used dual 4 barrels, including Cadillac, Pontiac (421 Super Duty) Ford (427 Hi-Riser) and of course "She's real fine my 409!" All of THOSE were progressive setups. Honest!

JeffI have heard of the 413's ram intake. Id guess not that many made tho. Ive seen the 413 luxury version [Imperials] but a little before my time.

[Fastjeff57]

They were spectacular to see: The Carter AFBs were above and just to the outside of the valve covers! That's a loooong intake tract. I rode in a 300K (I think) with that engine on a date once, and the motor ran smooth as silk. The guy never jumped on it once, to my utter disgust!

Jeff

[Powerabout]

I was wondering if any olde time motorheads out there would catch my error: The 413 Ramchargers had its four barrels on a super long ram intake, one on each side of the motor, so this was NOT a progressive opening setup. I smartened up after making that goof, expecting someone would catch me on it, but...

A bunch of other factory cars also used dual 4 barrels, including Cadillac, Pontiac (421 Super Duty) Ford (427 Hi-Riser) and of course "She's real fine my 409!" All of THOSE were progressive setups. Honest!

Jeff
How about the Z28 302 dual quads.
how did they work?

[Fastjeff57]

Progressive also. I almost bought one of those cars, but the salemen at the Chevy dealership never heard of a Z28! (This was the Camaro's first year.) I bought a Firebird 400 instead--a dog.

Jeff

[JohnsonM50]

From questionable technologies* a subsidiary of Rude RaT motors.................
>>>>>>>>>>>>>>>>>> 2 banger x 2 barrel >>>>>>>>>>>>>>>>>>>>>>>>>>

Heres some pics of the maniflood project, as you can see if there is a function form follows it. Pretty aint in the picture, pun perpetuated. Im hopin to rig up a powerhead & start the process of starting the motor to see what I can see then ponder pond testing. Well, enuff of that- work or not other serious speed considerations are under delerious speed consideration. me, myself & I - Prez, V-Prez & cleanup boy of Rude Rat un-inc.:D
http://i35.photobucket.com/albums/d151/mes355/DSCN0434.jpg
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[Fast Fred]

:cool:

[JohnsonM50]

[QUOTE=Fast Fred;86867]:cool:
Thanks Fred, Just hope I get it goin ok. It'll be a novelty if it goes as good as stock, get-n more from it to any degree will be neat. Ive got a couple OMC 31.8s that are faster than stock but no great improvement yet. With the hefty crossflow pistons & the flat reed plate, limits are in place.
The carb Im working with is from a 90hp, year unknown. I found a "72 OMC 85hp carb & am glad to see the venturi is significantly smaller than the 90 while the throats & bolts are the same. With that Ive got 2 to test & theres others float-n around.
The maniflod is done, mocked up with all fasteners & the carb bolted up. If I learnt anything about fab-n, the parts need to be made to fit as well as bolt patterns worked out so they dont interfere. That determines whether or not its worth doin as much as the parts workin.

[JohnsonM50]

After some leak chasing...
http://i35.photobucket.com/albums/d151/mes355/DSCN0449.jpg
I mounted a spare powerhead on an old tower, roped to a stand [no clamps]
http://i35.photobucket.com/albums/d151/mes355/DSCN0452.jpg
Made up a couple quicky gaskets & assembled it.
http://i35.photobucket.com/albums/d151/mes355/DSCN0457.jpg
It started right up after a few 'choked with a rag pulls', idled sorta high, [the timings full]. It rev's nice..Wicked nice! So on to testing on water. Hose tests always sound good.. I know, but it shows promise as is. :D:cool:

[Fast Fred]

:cool:

[JohnsonM50]

Before running it again I cleaned the plugs real good, they came out oiled up & were old ones. Then upon re-running I found the mix to be fat at idle, it would load up & puff a cloud when cracked. I re-jetted the carb hi & low to lean it some. Now it will idle consistantly without loading. I clogged the exhaust with a rag for a few to simulate sitting in water & it didnt effect it.
Ive got a modded powerhead on a boat to run & note performance. Then without changing anything [prop/setup] Im going to put a stock powerhead on with this carb to compare to the other & see how it does in general. If I like what it does Ill put the 2 barrel on the modded powerhead [that does like more fuel] & go for it. :D

[Mark Poole]

Try velocity stacks on your tests. Someone already mentioned that the air speed will be greatly reduced because of such increased throat volume. You might also try spacers of different thickness between the carb and manifold. Normally a short intake track works best but with such a change in parameters with this carb you never know. I know my 30 Johnson with the single big bore carb will almost suck your fingers off on acceleration.

This leads me to a question for a Merc guy....why did the older Merc carbs have that little plastic "mini venturi" in the throat?

[Tim Kurcz]

Answer is to help fuel atomization during part throttle openings for the large throat carbs. At the dealer we took a set out and tank tested to find soggy acceleration. Reinstall and all was good again!


BTW: Nice project with the two bbl on your twin. If it refuses to behave, you might back up to a 1" venturi version. Good luck!

[JohnsonM50]

Try velocity stacks on your tests. Someone already mentioned that the air speed will be greatly reduced because of such increased throat volume. You might also try spacers of different thickness between the carb and manifold. Normally a short intake track works best but with such a change in parameters with this carb you never know. I know my 30 Johnson with the single big bore carb will almost suck your fingers off on acceleration.

This leads me to a question for a Merc guy....why did the older Merc carbs have that little plastic "mini venturi" in the throat?

Actually, each side of the 2 barrel is almost exactly the same as the stock single. The intake in stock form is open to both cyls & the fuel is drawn back & forth so in effect each cyl. draws from a 1-3/8 carb with a 1-3/16 venturi. What I did is fill the middle of the intake so each cyl has its own smaller intake & a carb of the same size effectivly. 2 barrels at once would definitely flood this little motor. My hope is it will have more velocity & since each barrel will pulse half the amount as a single, a more stable mixture [might be reaching here] I havent run it under load yet but am confident that if it wont 'go' at least itll idle back :rolleyes: :D
Tim, I was looking at a smaller ventury carb from an 85, reasonable on E-buy. For now Ive got this one so if it wont work after fair attempt Ill go that direction, Lean wont be a problem at least. ;)

Thanks for all the suggestions, unless Im real lucky & this flies Ill be looking back at them. :cool: :)

[JohnsonM50]

Ready to test
http://i35.photobucket.com/albums/d151/mes355/DSCN0463.jpg
http://i35.photobucket.com/albums/d151/mes355/DSCN0462.jpg
I have a 1 3/8 tube Im going to make velocity stacks out of as it seems weak mid-range but idles good & revs hi well. Soon Ill get it on H2O.:D

[Tim Kurcz]

Just in case you've never tried it, ram air actually hurts performance. You might plan on a deflector to keep air and water from those throats. Looks like fun! Keep us posted.

[JohnsonM50]

Thanks Tim, Im thinkin the single carbs have a 1 1/2 dia cylinder shaped opening and this 2 barrel is like an open box in front of the 2 venturies. Im making 2 short tubes to slide in & separate the outer openings. Im still looking into an efficient way to make a deflector but plan on something.

[David Mason]

I agree with Tim, the Ram Air hurts. In my experience it also can stick your engine. In the triple 49 cuber, we tried a while back, and the sand that gets into the boat no matter what, was sucked up byt the massive vacuum these engines have, and you can guess what happend next. So not only does it not work as Tim suggests, it can lead to other bad things as well.

Looks like a fun project, good luck. Have fun, that is the main thing.

[JohnsonM50]

Fun.. doing it & running it, thats the plan.:cool: Thanks Dave, similar problem when I had this on a shorter mod tower, it drew some of the little bit of water up from the bilge & cut out in a turn, maybe best to draw air from behind. I have some thin wall 1 1/2 pvc pipe that I cut for throat inserts. I tried once to make an airbox that was supposed to act as a stationary turbine & put a spin on the air but so far the idea itself is a spin.:rolleyes: like the 'Tornado' auto gimmick.

[JohnsonM50]

On water today. as expected.. its got bugs. 1, I need to get a spacer to run a D prop I have that will take off very well, dont even need to lean forward. That will make testing easier. 2, The most intriguing thing Ive learned since messing with go-fast boats is 'things' are often -not- what they seem they should be.
So, here it is. This is 1 of 2 of a 90hp carb set so should be about right for 45 hp. Its on a 35 twin with some work done thats confirmed to be about 10% more power with the single barrel so shouldnt be toooo far off. I thought it was running rich on numerous hose starts so went down a jet size which improved hose running. On water it would start & sputter, moving my hand close to the holes would revive it. I got it good & warm then tried to go, had to play with choking it a little then it took off & quickly cut & died. After a couple tries [& some water over the transome] I got it on plane & opened it up, it would go but no records were threatened. So realizing it needed more R&D gave it a hot run back to the ramp, shut down & pulled the plugs once out. They were dry & looked to be a little hot. From this I gather the way to go is back to the origional jets. I was short on time & need to go with stuff to make changes & play around, It still might...

[Tim Kurcz]

Ahh, the challenges of research & development. Make only one change at a time and be patient. Nothing that runs well ever happened by itself, and usually not in the first try. If so, it's just luck!

T

[JohnsonM50]

Ahh, the challenges of research & development. Make only one change at a time and be patient. Nothing that runs well ever happened by itself, and usually not in the first try. If so, it's just luck!

T Yup, nothing wrong with luck :D

[David Mason]

I will take luck over skill any day of the week.

I cringed as soon as I read your testing. I figured it was stick time. With no load on the hose test, and a good load with the in water test.... If you have to choke it to get on top most likley it will lead to problems later on.

Good luck, and keep at it. I agree with Tim, one thing changed at a time is the best approach.

[JohnsonM50]

I will take luck over skill any day of the week.

I cringed as soon as I read your testing. I figured it was stick time. With no load on the hose test, and a good load with the in water test.... If you have to choke it to get on top most likley it will lead to problems later on.

Good luck, and keep at it. I agree with Tim, one thing changed at a time is the best approach.

Thanks Tim & Dave, I keep the tests short on new stuff like this. If it isnt right [especially on the lean side].. 1st change will be to put the origional jets back. I have the insert described in & would think that should rich-en the mix but maybe not. :cool:

[JohnsonM50]

Having put the bag of jets where I wouldnt lose em :rolleyes:. I just found em & tried the richer set, theres a little better low response & is no faster on top than the single. Im thinkin a 1" ventury carb next. Since the seasons on I put the 1 barrel back on & will mess with this more late season. Now for the 1st time Ive got a known to perform very well modified single barrel on Boyesen reeds. I started it & seems good. The whole 2 barrel set up inc screws, nuts, gaskets & hose clamp are neatly boxed, marked & ready for more fun.

Any bets on if the reeds will make a big difference? :D

[David Mason]

Having put the bag of jets where I wouldnt lose em :rolleyes:.

Been down that road more than I care to admit !!

[JohnsonM50]

Been down that road more than I care to admit !!Me too, anybody seen my keys?:rolleyes:

[JohnsonM50]

Its been awhile..The whole 2 barrel set up inc screws, nuts, gaskets & hose clamp are neatly boxed, marked & ready for more fun. Since boxing it up I have found a 2 barrel from an 85 that has 1" venturis down from 1-3/16". This carb also has a choke butterfly & lever so will be easier to start than stuffing a rag in. Ive run it with a test wheel in a barrel & its better than the bigger one there which says little of how it will work on water. Ive got it on the boat now ready to test. Theres still a bit of a chill & the wind is up for a couple days so hopefully soon, I have run the boat last week exactly as is with a 1 barrel & noted rpms so I have a benchmark in case it goes well.
http://i35.photobucket.com/albums/d151/mes355/DSCN0820.jpg
A fair amount less volume of air will pass these openings so hopefully the missing velocity will be found & it runs thru its range better. Ive got to make up a spray shield but have a plan thats easy to start with.

[Roy Hodges]

It is my opinion that you will get MORE air through the 1" carbs; why? Because you will get higher velocity , therefore more air. And, that's because your motor cant suck air with the same velocity that it can with optimum sized carbs.An example I saw ,about 30 years ago , here in Napa(calif) was a moded 60" six cylinder Merc,had 3 japanese motorcycle carbs installed . Looked beautiful. Started right up, then when he cracked the throttle, it would die, every time. problem? 39 M.M. carbs ! way too big . NO velocity when throttle opened. I believe if those were about 31 or 32 M.M. it might have run GOOD !

[Fastjeff57]

Drag racers regularly over-carburate as well, using a 800 to 1,000 CFM carb on a mild 350 SB Chevy. The Nationwide NASCAR racers, by rule, use a tiny 360 CFM four barrel carb on their 350-sized motors and make over 500 hp.

Jeff

[Mark75H]

Its because carbs work by vacuum. If your carb is too big, there will be no vacuum and no fuel mixed with all that air the large hole lets in.

That is what sets the practical limit on carb size

[JohnsonM50]

That was the problem with the larger carb, it would idle & if you could get it thru the mid range it would catch & go the rest of the way up. Keep in mind the single barrel that works best is 1-3/16" at the v & 1-3/8" at the maniflod end, exactly the same as the bigger 2 barrel. The manifold is separated so 1 barrel feeds 1 cyl. & the new carb is 1" at the v, 1-3/8" at the manifold so in effect the cyls are drawing thru a smaller hole than the single & the only common aspects are the float chamber & the open common carb entry chamber. It still might get more air but im hoping with good result.

[Powerabout]

accelerator pump

[JohnsonM50]

accelerator pump Even tho neither of the carbs mentioned uses an accelerator pump, with the bigger 2 barrel it did act like a typical car motor with a bad acc. pump. Q' being how?, pressurizing the bowl vent would sure send more gas up but probably not with a good result.:D

[JohnsonM50]

Drag racers regularly over-carburate as well, using a 800 to 1,000 CFM carb on a mild 350 SB Chevy. The Nationwide NASCAR racers, by rule, use a tiny 360 CFM four barrel carb on their 350-sized motors and make over 500 hp.

Jeff The 350's are one of the best & most versatile engines made in its size class. Many unwitting rod'rs spent cash on the wrong stuff for years. Nowadays system matched kits are available & the guess-work is no longer. The big carbs would be kinda messy on a restrictor plate so that makes sense. Its the camshaft advance that really brings it up. Some newer cars have variable cam timing & are wildly quick.:cool:

[Roy Hodges]

[QUOTE=Mark75H;104695]Its because carbs work by vacuum. If your carb is too big, there will be no vacuum and no fuel mixed with all that air the large hole lets in.

That is what sets the practical limit on carb size.............................................. ............
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Years ago, Lon Stevens told me his full house Mercs had the 3 side carbs (additional,)
but they were set to open only after the main carbs were 90% open.So the motor did not bog down. Funny thing is that Rich Fushlin told me that they helped accelleration,but NOT top end ( ?). that seems strange to me .

[JohnsonM50]

Test time, went well. It was hard to start, I tried to get it to kick on trailer, pulled the plugs a couple times Then got it to go. Probably having to do with where throttle & choke wise it wants to be. In water at the same setting it kicked right up. I let it idle a few & ran it up slowly to look for flat or dead spots. That went well, its consistent there so right up on plane no problem [got my best starting prop on]. It seemed good so I took it out of the lagoon to open it up. Right up no problem, smooth & powerful like my best single barrel. The difference between going well & going great is its 70 rpm less than the single barrel test run. The only thing not exactly the same is today the water is calm, the previous test was ruff-r & its a bit faster in just the right ruff -like then. With that in mind I think its the same on top but a little better on the way up. The last thing I did was a hot run / shut down toward the ramp area & paddled in. When in I re-pulled the plugs, they were tan & dry. The single barrel usually leaves the plugs a little wet. Q' being should I mess with jets?.

[JohnsonM50]

Last time out it ran good enough for me to make up a spray shield.
http://i35.photobucket.com/albums/d151/mes355/DSCN0832.jpg
Today I put about 20-25 miles on it, It's running very good & starting's easy now that I f ound it starts well throttle down & choke 1/2 closed. The performance is the same so far on top but mid range is better than the single barrel. The single had to run fat & wet to not bog down at low speed.
http://i35.photobucket.com/albums/d151/mes355/DSCN0841.jpg
Ive been thinking about that flat 'wall' of reeds, I tried 2 stage Boyesens, they did nothing, Im thinking single stage or a new configuration next. From a failed opened reed experiment I know for sure if you can get the stiffness out of the plate reeds they will cook with fire till fail. :D:confused::eek::mad: