Volvo penta carburrettor fueling

[shaners101]

Hi,
I have a 2001 larson boat with a 3.0 litre volvo penta inboard engine. I have rebuilt the engine and the carburetor. To start the engine I have to have the throttle in the wide open position and it will not run at small throttle positions. I also by passed the mechanical fuel pump and supplied fuel directly to the carburetor from a small tank slightly higher than than the carb. It will run but still not at idle. When it is running the is a lot of black smoke suggesting too much fuel. When it starts to run out of fuel it will run at idle for a second or 2, again suggesting too much fuel from the carburetor. The carburetor is a 2 barrel Holley. Is there some way that the fuel can get in to the airflow without been metered through the carburetor? If I close the choke it makes the engine running worse.
Any ideas what to do next?
Thanks,
Shane.

 

[Bondo]

Re: Volvo penta carburrettor fueling

I have rebuilt the engine and the carburetor.

Ayuh,.... My guess is,... Either you screwed up the carb Rebuild, or the carb is just plain Junk...

 

[Don S]

Re: Volvo penta carburrettor fueling

Lots of possibilities.
Since you rebuilt the engine too, how about the valve adjustment? Timing, firing order.
Have you ever rebuilt carbs and engines before?

 

[shaners101]

Re: Volvo penta carburrettor fueling

I have rebuilt 2 stroke engines and diaphragm carbs.
I am happy with the ignition tiiming and valve timing. In the yard it runs ok with the throttle open. The engine will tick over when its running low on fuel from the tank.

 

[Maclin]

Re: Volvo penta carburrettor fueling

The carburetor is a 2 barrel Holley. Is there some way that the fuel can get in to the airflow without been metered through the carburetor?

There is a powervalve with a rubber diaphragm, if that is compromised then fuel runs directly into the intake from the carb fuel bowl. But all of that should have been taken care of in the carb rebuild if all new and correct parts were used. There are different powervalves, they designed to allow more fuel thru the metering block when the engine is under load (lower vacuum). They are rated by how much vacuum it takes to keep it closed when the engine is running, if the engine vacuum at idle is lower than the rating then the valve will not stay closed and that can will richen the mix and idle will be very poor.

 

[ENSIGN]

Re: Volvo penta carburrettor fueling

Sounds like a misadjusted float,heavy float or leaky neddle valve and seat.Also,is the choke opening all the way?

 

[shaners101]

Re: Volvo penta carburrettor fueling

I checked the float high and inlet was closing when I held the float bowl upside down. The powervalve suggested by Maclin seems the most likely as I think the fuel in getting in the the airstream without been metered.
I can strip the carb again and have a look as I rebuilt it with new parts. Is there a test that I can do on the carburettot to check that the powervalve is closing? When the engine is running an I put more vacuum onto to the carburettor to prove that it is the power valve?

 

[Maclin]

Re: Volvo penta carburrettor fueling

The vacuum applied to the powervalve is thru internal passages in the carb, no real test once it is in the carb. You may have left the powervalve gasket out or used the wrong one, that can lead to the same type of symptoms.

One good backfire thru the carb can rupture the diaphragm, this is a common problem in older Holleys.

You can hold the powervalve and work the diaphragm against the spring then block the hole on the other side with a finger and slowly release the spring, the spring should not be able to open it all the way if the diaphragm is intact. You should be able to feel a slight vacuum pull on your finger that is blocking the hole.

It is very important to have the right powervalve in there. It is related to the vacuum that you engine sees when running, go with what the carb spec shows. Marine applications usually us a lower number than automotive. The one that comes with the Holley kit is probably not the right one unless the kit is very specific to that marine application. A more generic Holley kit will have a powervalve with too high a number in all likelihood.

 

[Jeepster04]

Re: Volvo penta carburrettor fueling

Hi, I also by passed the mechanical fuel pump and supplied fuel directly to the carburetor from a small tank slightly higher than than the carb.

A little confused by this. Are you saying you by passed the fuel pump and the fuel is gravity feed into the carb?

 

[shaners101]

Re: Volvo penta carburrettor fueling

Yes I had I have the fuel gravity feeding to the carburettor (at 2 or 3 psi).
Its a 2001 engine. I found the problem, it was with the gaskets supplied between the metering block and carb. body. One of the gaskets had the transfer hole from the accelerater pump in the same "mouse hole" cut out as the power value. This was then allowing fuel to be sucked out of the accelerator pump chamber. This fuel collected in the chamber in front of the power valve diaphram flooding the engine and also seeping into the engine overnight! (the carb. doesn't have a transfer tube). The replacement power value was the correct one. With the correct gasket (as told by Holley) there is no fuel been sucked from the carb. I pour fuel into the intake and the engine starts but wont keep running. There is fuel in the float. The acelerater pump works before I bolt it to the carb body but after I bolt it all together and fill the float the accelerater chamber does not refill with fuel. Still investigating??

 

[shaners101]

Re: Volvo penta carburrettor fueling

The accelerator pump check valve is completely corroded up and can't get it out. I took it to a carburettor specialists. He got the check ball free by soaking it and sand blasting it. Very expensive ?280.