Carb Rebuilt - Falls on its face at WOT

[trailshredder]

Had some issues toward the end of last season on my 97 Glastron/5.7L Volvo Penta. At cruising speed the engine would cut out and stall about 80 percent of time. It would start to miss terribly and If I didn?t back the throttle down right away, it would stall. Low speeds were fine. From previous experience, I decided it was time for a carb rebuild. I pulled the carb when I winterized it last fall and rebuilt it over the winter. Put the carb on this past weekend and took it for a ride. Got up to cruising speed and did great, perfect, in fact. Decided to try WOT and it fell on its face, no miss or stall, just felt like someone hooked a barge to the boat. If I would back the throttle down a little, it would pick right up and do fine. I am wondering if the accelerator pump in the rebuild kit I ordered is too small? It came with two and I used the larger one of the two. I do not recall the numbers on it though. Does this sound like an accelerator pump issue or something else?

 

[gm280]

If you ease up to WOT does if do the same thing? I don't see the accelerator pump as the issue, but maybe the high speed jet(s) system. Especially if easing up with the throttle does the same thing. Sounds like too much air and not enough gas. JMHO

 

[trailshredder]

No, as soon as I back off on the throttle, it runs fine.

 

[Scott Danforth]

Im guessing dirt still in the accelerator circuit.

Maybe dump the contents of your fuel/water filters in a clear baggy to see if you have pure gas or if there is something in your tank

 

[Bondo]

Ayuh,..... Bad carb, Bad fuel pump, or Bad gas,....

 

[Insomnium]

What size power valve did you replace it with?

 

[jimmbo]

Which carb, Holley 2bbl, Holley 4bbl, or Rochester Q-jet? Do you have a Volvo part #?

 

[211libwtfo]

I would definitely check your anti-siphon valve. It's a fitting in the gas line from tank to carb that little thing $5 part, cost me half a season last year.

 

[Lawnpro979]

Seems like I was reading about this issue in the technical info at top of page.......the do it your self items

 

[trailshredder]

What size power valve did you replace it with?

I do not recall. I have looked for pictures of the one that came out of it but can't find them. UGGHH.

 

[trailshredder]

Which carb, Holley 2bbl, Holley 4bbl, or Rochester Q-jet? Do you have a Volvo part #?

Holley 2bbl. Volvo carb part #?

 

[jimmbo]

It's on the front of the air horn. One of the numbers on it is Volvo's, the other is Holley's

 

[Insomnium]

I do not recall. I have looked for pictures of the one that came out of it but can't find them. UGGHH.

Where did you get the carb rebuild kit? If its the automotive one, I bet it had a 6.5 or higher power valve. I am willing to bet yours was a 4.5 like mine. Might want to open her up and check.

 

[trailshredder]

Which carb, Holley 2bbl, Holley 4bbl, or Rochester Q-jet? Do you have a Volvo part #?

The numbers on the carb are;
3850245
80402-1
3046

 

[trailshredder]

Where did you get the carb rebuild kit? If its the automotive one, I bet it had a 6.5 or higher power valve. I am willing to bet yours was a 4.5 like mine. Might want to open her up and check.

The kit was Holley 703-36 Marine Carburetor Rebuild Kit. The kit came with 2 power valves, thinking a 6.5 and a 4.5. I think I used the 6.5 because I couldn't read the original one.

 

[Insomnium]

I say get a vacuum gauge and see where you are at. They aren't expensive and are easy to use. Find out your vacuum and then divide it by two and thats the PV you need. If jetted properly of course.

The PV might not be opening.

 

[jimmbo]

If he used the 6.5, it should be open at WOT, that combo won't have 6.5 inches of Vacuum at WOT, I know my 5.7 would drop to 1" on the gauge then as the engine passed 4200 rpm the vacuum would start rising and peak at about 4". The 500cfm(about 380cfm when flow rated like a 4bbl) Holley just a wee bit too small for a 5.7 @4800 rpm.
If the fuel passages or metering Orifices are dirty/plugged, or gasket(s) weren't correct, it will behave like it has a stuck closed PV