Max timing advance

[Boatnut]

It seems i can't find my workshop manual.:mad:...........could someone please let me know what the max timing advance at WOT is for a 1988 3cyl 2str Yamaha.
Powerhead is standard, no work....................................yet:D

[quick2008]

What HP is it???

[Boatnut]

OOPS:o
90hp.

[mercmack]

Why Dont You Try E-bay..just Put Down Yamaha Service Manual.
Its Worth The Effort..a Lot Of Those Eng Have A Per Fixed Setting
The Computor Or Cd Box Does It..

[Fast Fred]

stock = 22deg +/-1:cool:

[Boatnut]

Thanks fred.....:):cool:

[Fast Fred]

stock timin is for stock revs (5800-6000), as rpms go up (7000-8000) timin Must go down. drag boat guys run more timin, but do not hold the moda at rpm,
as soon as it peaks it's shutoff:eek::cool:

[50sFlash]

stock timin is for stock revs (5800-6000), as rpms go up (7000-8000) timin Must go down. drag boat guys run more timin, but do not hold the moda at rpm,
as soon as it peaks it's shutoff:eek::cool:

That seems so counterproductive Fred. Back in the days of distributors and vacuum advances, they would give it max advance when the engine wasn't pulling and could handle it. The flame pattern is at the same speed whether it's at 1,000RPM or 8,000RPM (I would think) so at the higher RPM you need more lead time to get maximum expansion at or slightly after TDC. Could it be you're getting too lean a mixture at higher RPM which would cause detonation? I would think the retarded timing would hurt the low to mid-range. The oil in the fuel is already slowing the flame pattern down. What's the thought behind it?

[Fast Fred]

true, 2stroke timmin, the more timmin it has the harder it pulls,to a point.
at 22deg max that 90hp will pull nice to 6000 and stay there, make a pull to 8000 at 22deg and try to hold it thare it's guna melt the pistons out of it.:cool:

[zul8tr]

That seems so counterproductive Fred. Back in the days of distributors and vacuum advances, they would give it max advance when the engine wasn't pulling and could handle it. The flame pattern is at the same speed whether it's at 1,000RPM or 8,000RPM (I would think) so at the higher RPM you need more lead time to get maximum expansion at or slightly after TDC. Could it be you're getting too lean a mixture at higher RPM which would cause detonation? I would think the retarded timing would hurt the low to mid-range. The oil in the fuel is already slowing the flame pattern down. What's the thought behind it?

--------------------------------
I agree with you on more lead time as rpm goes up and would be supprised if contrare to this. Not sure I agree (although you hedged your thought) if the flame front spreads at the same rate at different rpms. I have never seen test results on this but I tend to think that the flame travel would be different (suspect slower) since as the rpm increases volumetric efficiency decreases in a normal aspirated engine due to reduced fuel/air charge transfer time (and other engine deficiencies) thus less fuel/air charge per intake cycle at the higher rpms.

Maybe a ME can chime in here with engine design and test specifics?:)

[Fast Fred]

?, just the way it works, not an engineer my self, but that box of melted pistons
i got is good for me. the more efficient a Moda is the less timmin it will tolerate. :cool:

[Roy Hodges]

[QUOTE=Fast Fred;70408]?, just the way it works, not an engineer my self, but that box of melted pistons
i got is good for me. the more efficient a Moda is the less timmin it will tolerate. :cool
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I'll drink to THAT . ...Frigid

[50sFlash]

WOW! Fred. TMI I just spent the last three hours going through that thread. I had a 75 Stinger that I was going to put on this boat I'm building, but decided the 2 35s would look cooler (I'm all about looks) but I could have made it fly with all that I read. In my world though if you're melting holes in pistons it's because it's running lean. I saw one place where you said you ran stock jetting which may be great for the carbs CFM at 5 grand, but as the air flow increases at 8 grand you're at max fuel flow in the hi speed tube result is a lean mixture, and a hole in the piston. But what do I know?

[Fast Fred]

when thay go lean it will burn the center of the piston, by the plug, when thay detonate from to much timin it will melt the crown at the exhaust port, stick the ring and then everybody goes right by:eek::eek::eek:

ya i know, what you said is true, but not for a outboard looper.

[50sFlash]

Thanks Fred. I know that knowledge didn't come fast or cheap. It's great that you are willing to share it with those of us that are way over our heads. Back to my little drawing board.
Jerry

[john miffco]

timing must be retarded after 6,000 rpm
on any motor 2 or 4 stroke,,,,,,,,
especially 2s cause of the burn on every stroke,,,,
piston does not get a stroke to disapate heat as in a 4 stroke motor

even on drag motors...
yes they shut down with 1 pass,,,
but that pass is very high compression,,very high rpms,,very hot burning fuel and lean for max power

a simple way to run high timing for low end and retard for high

i used a car electric solenoid with a msd timing retard box to retard timing when i ran unlimeted ob
the car solenoid was from old carb cars,,,,,was the air conditioner solenoid to raise idle when ac on,,,,,and was adjustable,,,,,,
mounted to hit the timing arm,,,,to retard when activated by rpm pill on msd

this and indexing the spark plugs stopped my piston burns and hard scuffing on the ex side,,,,,,,,,,,

plus retarding the timing adds rpm,,,,,,,
john

[Fast Fred]

i used a car electric solenoid with a msd timing retard box to retard timing when i ran unlimeted ob
the car solenoid was from old carb cars,,,,,was the air conditioner solenoid to raise idle when ac on,,,,,and was adjustable,,,,,,
mounted to hit the timing arm,,,,to retard when activated by rpm pill on msd
:cool: more good stuff, :cool:

thanks 50sFlash

[50sFlash]

I'll throw one more little tidbit out there to think about. I think that is happening because the ignition and flame pattern isn't burning until it's ready to leave the cylinder. When I ran S/B chevs in a dragster back in the late 60's we ran over 50 degrees total advance, and if I wanted to run really fast we ran regular gas because the lead in premium retarded the spark too much. One of the problems is it doesn't start with a starter real well, but we push-started the dragster, and you couldn't lug it down, the RPM had to stay above 6 grand, and you had to run very rich.

[OUTBOARDER]

timing must be retarded after 6,000 rpm
on any motor 2 or 4 stroke,,,,,,,,
especially 2s cause of the burn on every stroke,,,,
piston does not get a stroke to disapate heat as in a 4 stroke motor

even on drag motors...
yes they shut down with 1 pass,,,
but that pass is very high compression,,very high rpms,,very hot burning fuel and lean for max power

a simple way to run high timing for low end and retard for high

i used a car electric solenoid with a msd timing retard box to retard timing when i ran unlimeted ob
the car solenoid was from old carb cars,,,,,was the air conditioner solenoid to raise idle when ac on,,,,,and was adjustable,,,,,,
mounted to hit the timing arm,,,,to retard when activated by rpm pill on msd

this and indexing the spark plugs stopped my piston burns and hard scuffing on the ex side,,,,,,,,,,,

plus retarding the timing adds rpm,,,,,,,
john

That is awsome!!! Maybe I wont have to use the MSD after all!!!
I wonder if there is a off the shelf solenoid and controller that could be used?
Need to pull a few degrees out after 6K..............

[john miffco]

the 4 stroke sb chevy can go with more timing advance
its a 4 STROKE
have a full stroke for piston to cool
have valves to close precisely,,,,,
2 strokes are more non efficient
lots of raw wasted fuel runs out of the ex
the port heights regulate the flow,,,,,
the ex is always open and is regulated by the rings
can and does mix a smigin with the intake stroke
the intake has a reed valve,,,and can burn or be blown out
so timing is more critical in a 2 stroke motor
and a flash fuel is needed like unleaded and not a cooler long burning
high octane as for 4 strokes
but with the higher heat from flashier fuels
the timing at high rpms need to be shortened,,,
to have a shorter burn to get out ex before intake charge
then for less heat on the piston top to not burn top
since it does fire on each stroke
when i ran alky mixed with nitro or prope,,,,
i could not go over 18% because of the long burn
it would melt the reeds,,,,,,,,,,,
in a maxed out 2 stroke there is a finer line to deal with than a 4 stroke

also another alternative to the msd controller
is using a shift light,,,,,,,
this connects to tach lead also,,,,,
take the bulb out and use the bulb leads to active the solenoid

just my thoughts
john

[Bill Van Steenwyk]

Jerry and Anthony:

The whole length of time I ran alky motors from the late 60's to 2003 or so, timing was set staticly for as much as the engine would stand up to about 6-7 thousand or so, because if it was set any higher, at the higher RPM past that, burned or stuck pistons were sure to result. When the CD ignitions came out, even the early Phelan self excited type used on the Konigs, they supposedly had electronic means in the "porkchops" that the flywheel passed by so as to retard the spark at higher RPM electronically. In the mid 90's I had a 125 made from Honda and Yamaha road race bike cylinders, and we used an MSD ignition on it that came with small plug in modules that allowed retarding the spark at higher RPM to keep from burning/sticking. These modules allowed different degrees of retard at different RPM's, and worked very well, but for some reason MSD went away from that type system, and then you had small switches on the box itself that could be arranged in different sequences to do the same thing. If you did not use that those type devices after they became available and tried to run the same static timing (high)you set for best acceleration all the way to top RPM, without some way to retard it past 6-7 K RPM you would be replacing pistons very regularly. Most of the explanations to this point I have read on this thread say basically the same thing, more advance at lower RPM for acceleration, but it you run it high pushing the envelope too far up the RPM range without some way to retard it, either mechanically or electronically, it gets costly very quick My experience was the same as Fred's, and I am not near as smart, so I think he knows of what he speaks, cause I had those boxes of burnt pistons also, as did others that tried to push the envelope. Of course if you want to run up front, that is what you have to do.

There are several manufacturers of ignitions out there that have these features. Whether they could be adapted to work on a Yamaha of the type described is another matter, although where there is a will, there is a way most of the time, with enough money.

[50sFlash]

Thanks guys. I get the picture. I got a ton of learnin' to forget. A thought on a solenoid, OMC choke solenoids are small and might work.

[Bill Van Steenwyk]

Jerry and Anthony:

Please be sure and notice the part on my earlier post about the adjustable retard capability of the MSD boxes. Don't know if it is still availiable but their website should give your the info.

I have no interest in MSD other than knowing that they are a reputable company and their product worked well for me in the particular application I posted about earlier. One thing about them is the tech dept at the time was very willing to work with us to provide us with the components to make the ignition work after they understood what we were doing. Perhaps they could work with you in the same way if you want to try to upgrade the existing ignition you are working with. We were using a battery total loss system to fire the ignition (very small light wgt l-2 lb battery) and a trigger mounted on the flywheel. They make ignitions for both self excited and battery systems and could probably provide some type control box that would allow you to time the motor statically and then retard at higher RPM to accomplish what you want. There are probably others out there also, but this is one I am familiar with, that would probably work with a minumum of work. They also make most of the ignitions the NASCAR folks us also, so they are certainly technically capable. There is a company called Rapair that also that makes ignitions for Mercury and possibly might have something for you also.

If you are not familiar with a website called Scream and Fly, they have good tech forums for pleasure type outboards and a lot of folks that chime in with good answers to questions such as yours. Good luck.

[Powerabout]

Dont forget the exhuast pulse will be changing as the rpm changes.
This can do different things on different engines.
If it leans it out you want less timing or
if it stuffs charge back in the cylinder so the bmep goes up you also want to back off the timing.
The speed of combustion/flame front will most likely be different at different speeds as this depends on how homogenous the mixture is.
And this will all be happening at different rpms depending on the atmospheric conditions on the day...dew point/speed of sound and all that...

[50sFlash]

So it really is just a crap-shoot, and until you have a box of burnt pistons, you're just guessing?

[Bill Van Steenwyk]

As previously mentioned, MSD for one, and possibly others now, make PROGRAMMABLE ignitions that allow you to electronically set the RPM point and also the amount of degrees the timing would be retarded at top RPM, to keep from filling up those boxes with those stuck and burnt pistons.

BUT, it is like anything else in racing, testing and trial and error while figuring out what your engine likes in the way of timing depending on the pipes or exhaust tuner, porting, prop, length of course, and all the other variables involved in racing, boats or othewise. Going along with the testing, is keeping good records regards temperature, humidity, etc., so you can refer back to when you did stick or burn a piston and not run the engine at that static timing again if you dont have the capability of retarding it at top RPM, or set the retard if so equipped, to start at a lower RPM and/or retard more degrees, or a combination of both.

It is still a testing process no matter the state of the art equipment you have, test or otherwise. I think anyone who has been in this game for any length of time at all would tell you if burnt or stuck pistons scare you or you don't have time or money for them, you are wasting your time trying to get every last bit of performance out of an engine, because based on 40 years of doing and watching, they all run best right before they come to a sudden stop. The hard part is figuring out where that point is, and tuning right up to it but not beyond, no matter whether it is pipes, ignition, or carb fuel/air mixture. Nothing will tell you that like it happening to you so you recognize that point and don't go beyond it the next time.

As to calling it "guessing", I wouldn't go that far, as anyone who is familiar with engines knows the basic limits to start with, either thru someone else running the same kind of equipment, or information funrnished by a manufacturer or selling dealer of the engine. But when you get to the point where you are trying to extract that last bit of RPM and speed, then to use "guessing" implies that you have no idea what you are doing. I doubt you would be on this forum talking about your engine unless you had some basic knowledge. Better to call it "parts investment speculation". That sounds more engineering oriented, don't you think. It's probably not going to be any cheaper on you in the long run,, but like the guys on Wall Street, "Investment Consultant" sounds better than "THIEF".

[Powerabout]

"parts investment speculation"
Good one!

[50sFlash]

Been there. In our Pro/Stock Camaro we spent hundreds of hours building a 538 Cu in, "monster Motor" (1970) We had over $5,000 in heads, stroker crank, everything the best. The engine builder clearanced the deck for steel rods, and then put in M/T Aluminum. Well they stretch .005 more at 7,000 RPM. Piston, meet head. 1 full pass, box of parts. Don't need to do that again.
The good news, I'm not racing it, just trying to get a couple extra out of a 1958 Johnson. I have a lot better idea of what not to do now.

[Fastjeff57]

I hope you made those morons compensate you!

Jeff

[Powerabout]

I think only 2 hp Jonrudes had aluminium rods so no problem there

[50sFlash]

I think only 2 hp Jonrudes had aluminium rods so no problem there

Will they fit in a 35?

Sorry, shame on me.

The engine builder had done the labor for nothing as one of our sponsors. They offered to give back what we paid them.
That's racing.

[LIQUID NIRVANA]

I think only 2 hp Jonrudes had aluminium rods so no problem there

From memory, Aluminium conrods were in 1.5hp, 2hp, 3hp. 4hp. 5hp, 6hp, & 9.5hp in the 1960's. They worked great.

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