Cornering hard, fuel starvation?

[Per]

last summer finally got my 15' TigerCat back on the water after a long restoration.
I riggged it with one of my somewhat modified Volvo Penta VP700 engines.
The powerhead came loose during the first race and that caused a major lack of cooling, we all know what that means...
Right now the powerheas is back on the bench waiting for two new pistons, good thing I keep some spare engines!

Now to my problem, when cornering hard the engine cuts out. The problem only occur when performing a left hand turn (or was it right, why didn't i write it down...)
I'm pretty sure the problem is fuel related.
I don't think the problem lies in the tank since I've tested with full tank as well as low fuel level.

Any toughts on what might cause this?

Pics showing what the fuel system looks like (and two very disappointed racer wannabes:( )

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ADD: In picture below the top carb is missing and therefore two of the fuel lines are left dangling.
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[Ron Hill]

When we were running MOD VP, we ran a Holly fuel pump, with a pressure regulator, seems at 2 1/2 pounds (Not sure on that) and we ran the evinrude fuel pumps. Now, maybe, I didn't go around the corners fast enough, but our motors ran great in the corners. What we "ASSUMED" was at 2 1/2 pounds of pressure, you would not "OVER RUN" the float seats, but when you came to the corner and tried to throw the gas out of the carbs, the fuel pump would keep the bowls full.

I think, Tim Soares figured this out, not me. But I know without the fuel pump, we stalled in the corners!

ADD:

Understand, that with too much pressure your "TOILET" will be over flwoing all the time... (A carb is basically a toilet)...

[Bill Van Steenwyk]

Those look to be "Bing" carbs. If that is the case, they were well known for giving problems when the float level was not correct.

I never used them on gasoline, only methanol, so do not have any idea what is the correct float level, but you adjust it by removing the carb top and bending the brass tab that covers the inlet needle valve. Might also check to be sure that the needle/seats are clean and not blocked by dirt or trash of some sort. I also notice that there is no clamp securely fastening the fuel line to the fuel inlet on the carb top. You might possibly be sucking air around the hose ID/inlet pipe OD with no clamp to secure it which could cause fuel starvation, although don't see what turning the boat would have to do with that type problem unless the fuel line is being "pinched" under the cowling when the motor is cranked over either direction in a turn.

Good Luck

ADD: If that fuel pump is vacuum operated with a line to the pump from the crankcase, check to be sure the line is unobstructed. Also check what seems to be a filter on the pump under the plastic cover with the screw in the middle of it.

[Per]

Thanks for sharing your ideas guys!

3030:
Is there any chance that you have a picture or sketch showing how the baffels were arranged? To me fuel getting pushed away from the jet seems like a very plausible explanation!

Ron:
Are you saying you were running the Holley pump in series with the OMC one?
I might be able to add a second vacuum operated pump on the crank case for the upper cylinder, there is a cast boss there so all I would have to do is drilling and tapping the holes necessary. If loss of pressure is a contributing factor that might solve my problem.
T-ing in a fuel pressure gauge before the carbs is probably a good idea...

Bill:
Yes, that is Bing carbs!
I know that they are sensitive when it comes to float heigth, they might not be perfect but certainly well within spec.
Before I use them again I will go through the needle valve and check for blockage. One would think that a problem like that would also be noticed when going WOT for some period?
The pump is vacuum operated but is mounted directly on the crank case, the filter is clean.

I have given the engine slightly longer intake timing though so that might lower the pressure pulses driving the pump?


Again, thanks for helping!

//Per

[Per]

Thanks!

That picture gave me some ideas:)

Belive it or not but the lenght and diameter of the different lines is according to the work shop manual, it states that the routing of the longest one (from the divider to the bottom carb) is very important. It seems to work and therefor I left it as it is. But I agree that it looks really bad...

I will do some changes to the tanks and fuel lines aswell, today I'm using two OMC tanks wich fits quite well under the deck. Unfortunally they come with the normal OMC connectors wich sometimes leak and I feel that they must be a real restriction. I will remove the connectors and replace the pickup with bigger tubing.
Maybe this doesn't help the specific problem with the engine cutting out but the present arrangement is not good anyway.

I would prefer not to go to an electric pump if that could be avoided. I'm having a small battery and the trim pump is using quite a lot of current, besides the engine's charging system have never been really great either. Guess I can try to add a second vacuum operated pump and see if that helps, switching to a electric is easy if it doesn't work!

//Per

[Bill Van Steenwyk]

Thanks!

That picture gave me some ideas:)

Belive it or not but the lenght and diameter of the different lines is according to the work shop manual, it states that the routing of the longest one (from the divider to the bottom carb) is very important. It seems to work and therefor I left it as it is. But I agree that it looks really bad...

I will do some changes to the tanks and fuel lines aswell, today I'm using two OMC tanks wich fits quite well under the deck. Unfortunally they come with the normal OMC connectors wich sometimes leak and I feel that they must be a real restriction. I will remove the connectors and replace the pickup with bigger tubing.
Maybe this doesn't help the specific problem with the engine cutting out but the present arrangement is not good anyway.

I would prefer not to go to an electric pump if that could be avoided. I'm having a small battery and the trim pump is using quite a lot of current, besides the engine's charging system have never been really great either. Guess I can try to add a second vacuum operated pump and see if that helps, switching to a electric is easy if it doesn't work!

//Per



Per:

I may be looking at this picture of the fuel hose/crankcase vacuum pulse hose routing wrong, or possibly where the hose that is coming from the fuel pump goes into the 4-way fitting and then back behind the top carb is not clear in the photo, BUT I see a potential problem with that routing unless my idea of how the pump and routing to the carbs works is incorrect.

I will qualify what I am about to say by stating that I never used a fuel pump operated by crankcase pulse on any of my racing engines. The fuel system always in use on my engines was a pressure system that was tapped into crankcase pressure and merely took that pressure and pressurized the fuel tank, causing fuel to be forced out of the tank thru an outlet to carb/carbs hose, with a check valve set at a specific pressure so as to "blow off" and vent the pressure before it reached the carbs so as to keep the carbs either from flooding from too much pressure or "locking the floats up" with the same condition, depending on how the floats worked, and where the inlet was in the carb, top or bottom of the float. Normally on my engines with the Bing carb that was 1 1/2 - 2lbs pressure.

That being said, in the pictures you have posted, unless I am completely not looking at them correctly, you have a line coming from the tank which is the grey line going into the pump Then you have the lines going carrying fuel to the carbs. The vacuum line coming from the crankcase is plumbed into the same fitting coming from the crankcase going to the pump, as the lines carrying fuel to the carbs. Unless there is something I do not understand or am not seeing something, I don't understand how this would work properly, as it looks as though you have fuel and crankcase pressure all going in the same circuit (hoses) when you should have the pressure to work the pump going in one side, and fuel to the carbs on another circuit (hoses) going from the pump to the carbs with NO mixing of the pressure from the crankcase with the fuel coming from the pump. I hope I am making myself clear, but as stated, unless something is not clear in the photos I do not see how it would work the way the hoses are run. In my mind you need a hose from the crankcase to the pump, to provide pressure to operate the pump to pump the fuel from tank to pump, through the pump and on to the carbs. Also when you re-hose the system if you use clear transparent hose, at least under the cowling, you will always be able to visually see the fuel flow and be able to diagnose any fuel problems easier.

If you think what I am saying makes sense, try plumbing the crankcase to the pump, and then go to the carbs with one line and divide that in two close to the carbs with a fitting that has only three outlets, one for fuel from the pump, and two out, one each to each carb.

Hope this all made sense to you.



Added later:
After looking at these pictures again, and then some more, I am convinced that the line you have running from the crankcase fitting to the fuel pump is not the way the pump is intended to work. I would almost bet if you removed the fuel pump from the crankcase, you would find that there is a port, or ports that allow the fuel pump to operate by taking pressure DIRECTLY off the mounting on the crankcase. If that is correct, the way you need to plumb the system, is remove the hose from the bottom of the pump to the crankcase, and go to the carbs from that fitting with a single hose that divides into two hoses as close to the carbs as possible. I am positive that pump is not designed to pump fuel with a hose going to it from the crankcase like you show in you photo. You are putting pressure into the same lines you have fuel in going to the carbs the way you are hooked up now. In other words, you are pumping both to the carb and then away from it the way you are hooked up. That would certainly cause fuel problelms.

If I am correct and there are ports behind the fuel pump that provide pressure to operate it, then the fitting you are taking pressure from and going to the pump with a hose is for another purpose, NOT to provide pressure to the pump. I can almost guarantee if you hook up a simple pressure system as mentioned earlier, that would both prove the pump is incorrectly plumbed, and solve your problem. Then the only decision is to decide whether you want to leave it that way.

[Per]

Now I understand what is causing the confusion!
My second picture showing the pump is from when I bought the engine and in that pic it is missing the top carb, therefore one of the hoses appear to be connected to the crank case.
I didn't noticed it until now, I'm really sorry to cause the confusion :o

Bill, you are absolutely right, the pump gets it's pressure pulses from a hole in crank case, take a look at the picture in the link below.

This is the actual pump.
http://www.bingpower.de/download/datenblaetter/type08080.pdf

The pump gets pressure pulses through the 4mm hole shown in the view with dimensions on page #2.


The routing of the hoses might look odd but is according to the work shop manual.

The hose that goes down from the four way fitting and behind the top carb is the supply line for the solenoid operated choke / cold start enrichment. It is not connected to the crank case in any way.

I don't think there is something wrong with the routing of hoses, maybe the changed intake timimg makes the pressure pulses to the pump weaker and in that way contributing to my problem.

This routing and dimensions have worked well earlier when I've used this kind of engine on V-bottom boats. My own idea is that when I'm now uses the engine on a cat that is turning flat or leaning slightly outwards through the turn it is what causing my problem. When I used it on a V-bottom the boat leaned inwards and the engines worked flawless...

Thanks for helping out!

//Per

[shenders]

Gentlemen
That looks like an OMC fuel pump. Does it have 2 ports on the bottom? One in the
center. One on the bottom is fuel in from the tank. The other goes to the crankcase pressure
port. The out let is the one coming from the cover. In the second picture your looking
straight at it. It goes to the carbs. Simple deal.
IF-it only has one port on the bottom then that hose would go to the fuel tank.

[Per]

shenders:
My German is not the best but I think that the view on page two in the Bing pdf is describing three different ways to connect the pressure pulses from the crank case.
In the Volvo Penta case the hole marked 2b is used. There is no separate hose fitting for crank case connection...

Well, belive it or not but the pump on my power head is a Bing pump:)

Let us for a moment assume that the routing of the fuel lines and mounting of the pump is correct:D

In that case it should be a good idea to start with baffels in the float bowl and raising the fuel pressure (and flow), right?

Just for the fun of it, here is a view from the work shop manual;)
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[Mike Schmidt]

We raced a 350 4 cylinder Yamato with the same style Bing carbs. With motor mounted as it came from the factory it ran good. Looking for more speed we turned the powerhead 90 degrees so the pipes went straight out the back. Ran feaster, but as soon as I turned left, it died. All the fuel was sloshing away from the main jet. We put Mikuni flatslides on it and it worked great. When Rex Hall turned his 700 Konig 90 degrees he ran into the same problem. He put some FA Konig floats on the right side of the carbs and it worked GREAT !

I would also check the fuel tank to see if it is mounted in its normal position. I have run into people that put the fuel tank in backwards, so the pickup is in the front left of the tank rather than the back right side.

Keep us posted as to what you find.

Michael D-1

[shenders]

Well I guess I’m way off base here. The pump does look like the old type (omc) pump. I would
hook it up like your manual shows. Float level and the baffles I guess is your next place to ck.
Not sure how your going to get more fuel pressure or flow. The pump is only going to pump
so much.

[Ron Hill]

We never disconnected the OMC pumps, we just added a Holly between the tank and the fuel pumps. The Holly just "OVER RODE" the OMC pumps, and we ran low enough pressure that they basically worked like "Floatless" carbs. I know our 235's would die in the corner without a Holly pump!

Tim Soares actually plumbed the line around the pump, so if the pump quit the omc pumps could still suck the fuel around the pumps. OLD Enduro racers knew finishing was half of winning.

I just put in a call for Tim to see if he remembers what pressure we set the props!

[whiplash]

we run a holly blue top at between 3.5psi and 4.5psi on our tunnel with a omc115 as we had the same issues in the corners and at the end of the straights. The other thing you can do is fill the top of the carb with a layer of epoxy reisin to stop the slosh around the air vents.

[Yellowjacket]

Is it starving or flooding??? If you don't know you can run it into the corner and as it dies hit the enrichment device. If it picks back up, it's starving, if it's flooding it will get worse.

Some carbs just aren't built for high lateral g loads and these floats may be just not designed for what you are doing. You also want to make sure the floats aren't sticking or binding when the lateral load is applied. Depends on how the floats are swinging in the bowl and where the float is relative to the jets.

At this point it may be a lot easier to replace the carbs than fooling around and trying to get something that works. Look as weather or not the g loads are causing the float to cut off fuel (heigth of the fuel in the float bowl relative to the main jet), or flood (fuel level is dropping at the float relative to the jet) and go from there. I doubt that it's as much a fuel pressure thing as it is a float level relative to the jet problem and that might not be solvable.

[Per]

Thanks everybody!!

Mike Schmidt:
I would really love to put a set of Mikuni carbs on that engine! I have already found what I think would be a good candidate for the swap, carbs from Yamaha RD 350LC should be perfect.
Fitting them to the engine and jetting them correctly would on the other hand take ages for me since work / family takes most of my time right now:(

The fuel pickups in the tanks will be changed to next summer and I will bear in mind what you wrote about it!
I will keep you posted, the result will show first in a couple of month though, the lake here is more suited to ice skates right now:)

shenders:
I was thinking maybe adding another vacuum operated pump on the top crank case would help. Maybe I'm wrong here but plumbing in a pump in series should raise the pressure if the "resistance" from the carbs are the same. If plumbed in in parallell the two pumps should together have a larger capacity:rolleyes:
Than again, reading Yellowfjacket's post made me really think...

Ron:
Perfect! If dual vacuum operated pumps won't work I now were to find a really cheap electric one that probably have the roughly the right pressure for the task. Soo true what you wrote about winning, in our first and so far only race we only made it halfways...

Whiplash:
I'll take a look at the top portion of the float bowl and see if there is any place that the fuel might escape, good info about the pressure levels!

Yellowjacket:
You raised a few very interesting question! I have assumed that the engine died from fuel starvation since that is what have happend to me before:o
It could of course be flooding aswell but my gut feeling says starving, right now I feel a bit stupid for not making such an easy check...
The float is guided by a vertical shaft, maybe the lateral forces make it stick a bit...
After your post there is several things I need to check.
The carbs might not be built for this kind of use but I seems to remember that the Crescent CS 500 engine used the same type, maybe I should talk to some of the guys running those engines on the classic cabover hydros....
Changing carbs will however be a last resort and if nothing helps I can always put an OMC 56CI triple on the boat, probably a lot less hassle:rolleyes:

//Per
PS: English is not my native language, excuse my spelling and grammar...

[Yellowjacket]

In looking at the outside of the float bowls I was thinking that the floats were probably not swinging, but were a guided on a rod type deal. Those type of rigs are much more prone to sticking than swinging floats.

If it's starving from sticking, then the float is sticking in the top position. Hard to think that they would stick with oil in the fuel but some designs suck. You might try some more fuel pressure and that may help, but I doubt it. A very light spring on the top of the float also might help but it's going to have to be really light not to screw things up.

What is likely happening is that the fuel in the float chamber is climbing the wall and the float has a lot of extra bouyancy and, even though the bowl level is getting lower, the jet is starving since the distance the fuel has to get pulled up is higher and there isn't enough suction to do that. If that's the case, then adding a spring (again, a really soft one) on top of the float might help reduce the extra bouyancy and get you where you need to be.

Lastly, if you really are starving, adjusting the float to the highest level allowed, or a bit more may help too, since that opens the needle sooner and doesn't starve as soon.

[shenders]

I think at this point, if it was me I would raise the float level 1/16 “ just to see what would
happen. Gotta do something, can’t just keep talking about the problem.

[Per]

shenders:
I will have to make you disapointed, we have 8" of snow and roughly the same amount of ice on the lake:D
In about two month the snow and ice is hopefully gone and testing season begins.
Right now it is only planning and some work shop time, but I think it is better to ask questions in the winter time when people have time to discuss:)
I have alot of good suggestions from all of you guys, some of them will certainly be incorporated in the rebuild of the blown engine!
I will let you now how things turn out

Once again, thanks for all good suggestions!

//Per

Short video from the first test last summer...
http://www.youtube.com/watch?v=tfrttFpzzTo