1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

[Augoose]

My issue is that during moderate to heavy throttle increase, the engine dies- almost instantly. It idles well in neutral and if I slowly increase the throttle, it increases in rpms nice and smooth throughout the power band as if nothing is wrong.

I've yet to be able to identify the Holley carb which sits on it because I can't find the model or any number for that matter stamped anywhere on it- nothing that I can see on the fuel bowl either. I changed the plugs today and the old ones were pretty black and sooty, however I was previously dealing with bad gas so that adds a variable. The poor combustion could leave the soot as could a rich mixture due to a failed powervalve- now its hard to tell. I let it idle for about 20 minutes today and it didn't smell or appear to be running rich at all.

My last dealings with Holleys were some time ago, but I'm leaning towards a failed or out of adjustment accelerator pump. I know lots of other issues can cause this problem, but I think mine are symptoms of a failing accelerator pump are they not?

I've not detected any vac leaks around the carb. I plan on closing the mixture screws to see if it kills the engine to rule out a failed powervalve as well as pulling the flame arrestor and looking for the accelerator pump shot down in the throat of the carb.

I'm not near the boat now and just wanted to run through a couple of variables.
Any suggestions?

 

[Don S]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

Just watch the carb (Engine not running) and operate the throttle and see if you get 2 nice streams of gas squirting gas into the throttle bores.

 

[bnicov]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

Do what Don said. If you aren't getting a couple of good streams, then a rebuild is in order. The kit is only around $40 or so and a few hours of your time.

 

[Augoose]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

Thanks guys- that's on my list of things to check. I'll find out and report back.

 

[Augoose]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

Well, upon hitting the throttle, I do get two streams of gas, but they are not a pressured spray like I see with my jeep. Instead, they are kind of like slow squirts, but the volume of fuel seems to be decent. What I did notice is that the accelerator pump linkage does not return to the starting postion easily. It seems there is a lot of binding with the linkage so I think that not only is it staying open after the initial shot, when the throttle linkage initiates the accelerator pump linkage via the cam, its so resistant that I don't think its getting the full shot that it could if the linkage were to aggresively pump the accelerator bladder - at least that's what I'm assuming.
Since the carb is covered in oil and gunk, I've decided to rebuild it. I've pulled it out and torn it down, ordered a new renew kit (http://www.holley.com/703-36.asp) and worked on the accelerator pump linkage which is now nice and smooth. After the kit gets here I'll put it all back together and test it out. The numbers on my carb were 3858334, 75004-1 which is the "list" number, and 2208 which I'm told by Holley is the date. When I called Holley, they told me the rebuild kit for list 75004-1 is the 703-36.

Question - does the return pressure which causes the accelerator pump to come back to "rest" position come from the spring which is inside the accelerator pump? I ask this because I see no return spring on the exterior of the accelerator pump linkage.

 

[Maclin]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

The accel pump linkage arm pushes against a spring loaded post that pushes on the diaphragm, this post is adjustable. This is designed to provide a more consistent pump shot and also to not break the diaphragm when the throttle is moved rapidly. The spring is what keeps the linkage arm "connected" at both ends (diaphragm and throttle linkage cam).

The adjustment for the pump linkage is set at fully open throttle, there is a gap that needs to be observed. If it is not set correctly the linkage can cause the diapghragm to bottom out and could bend the linkage arm or worse.

The duration of the pump shot is determined by the squirter nozzle size.

The voume of the shot is determined by the accel pump housing size.

Be sure to have the check balls in place in the pump housing inlet and at the bottom of the squirter body. The one at the inlet for the pump housing is usually staked in. The one at the bottom of where the nozzle screws into can easily be left out.

 

[Augoose]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

Thanks Maclin,
I do have the instructions on how to set the gap on the linkage arm, I think I recall .030" or so, but I'll confirm that when I put it all back together. That also makes sense with the spring keeping the whole linkage connected- so I'm assuming that that spring also pushes the pump operating lever off the cam and back into the original rest or neutral position? My pump operating lever was frozen and was very hard to move so I'm confident that that was at least part of my issue. The red circle and arrow shows where the pump operating lever was binding on the mounting post.

Now I realize I might have another issue. When I removed the accelerator pump and removed the diaphragm I did not see any check balls. I'm actually missing #24 and #25. I do have the umbrella check valve which isn't on the schematic - did that replace the check balls?

 

[Maclin]

Re: 1999 Volvo Penta 5.0GL PWTR acceleration/bogging/dies

The check ball for the pump housing inlet is up in the fuel bowl. It is usually staked in. The info I am accessing (memory) may have been superseded!