carburetor question

[sean169211]

hi guys i have a 1988 sunrunner with the volvo penta aq271 engine and 290 duo prop outdrive right now i have a 715cfm double pumper holley carb. I know this carb is too big but my question is what size should i be looking at 600cfm? I imagine i should go to a single feed? also where i can purchase a new one would be appreciated thanks!

 

[Maclin]

Re: carburetor question

Is that the stock carb?

The reason I ask is because I have the same engine. Mine has a Holley carb with secondary metering block but is still vacuum secondary. When I ran the listing number on mine it came up as a 735 cfm vacuum secondary. I know it is the original carb.

If yours is the stock carb it would be best to rebuild it to specs. That is what I did with mine and it works great.

I am not sure how to acquire one if yours is not the stock unit.

 

[sean169211]

Re: carburetor question

thanks for the reply i dont know if its the stock carb but at the begining of the season i bought the exact carburetor that was on the boat but the thing is i bought the boat used and i dont know if its the original or not. i thought that volvo pentas used quadrajets but maybe im wrong? also i put the gas level to as low as it goes and it still seems to shoot quite a bit of gas.

 

[Maclin]

Re: carburetor question

The AQ271C's were Holleys, but not double pumpers.

Do u still have the one that was on there? and any chance of Pics?

The carb would have been painted red from VP.

Double pumper and Vac secondary Holleys adjust the fuel level the same way with the sight plugs.

Now, what do you mean by "shoot quite a bit of gas". The fuel bowl level has little to do with how much the accelerator pump squirts out. If there is enough fuel in the bowl the pump will shoot the same amount as if it was overfull. The accelerator pump diaphragm housing determines the volume and the squirters determine the duration of the shot.

I think a double pumper is too much for that engine. The original carb had quick opening secondaries due to the vacuum diaphragm spring the spec calls for. Also the power valve in the primaries is a 2.5hg so it will open sooner under load, and the jets are staggered (not the same size side to side) and larger than "stock". The secondary metering plate does not have jets or a powervalve even though there is a metering block. I can't remember the size of the squirters called out, probably 30's or 31's but the accelerator pump diaphragm housing is the smaller 30cc and not the 50cc that is usually found on double pumpers.

 

[Maclin]

Re: carburetor question

This is a pic of a Holley on the AQ271 (aka 570) engines. You can see the secondary has a metering block with the idle air screw holes and vac ports blocked. The vacuum secondary can is on the other side and not visible here but you can see the slotted and curved linkage plate that is connected on a shaft to the vacuum can's linkage on the other side. A rod from the throttle lever fits thru the slot and controls when the secondaries can open as the throttle is opened and also pulls them closed as the throttle returns. This linkage does not exist on the double pumpers.

 

[Maclin]

Re: carburetor question

The secondary metering plate does have jets, sorry for the misinfo in the other post.

Many people see the two metering blocks and immediately think or assume double pumper, but there are some like this that are vac sec.

 

[sean169211]

Re: carburetor question

that carb posted looks like the one on my boat right now its red but i dont know if it was stock assuming that what one of the other replys said it must not be stock since it is a double pumper

 

[Maclin]

Re: carburetor question

Are you sure the one you have is a double pumper? The one in the pic is not a double pumper. Can u post a pic or two of yours? One from the top will tell the tale.