Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly 2 br

[DeaconBlues]

So I had problems like this last year and had the carb rebuilt in the off season. The boat ran great for the first 2 months of the season. Last weekend it got hot (upper 90's) and the problem is back. I know vapor lock is uncommon, but something fishy is going on related to heat. It runs great in the morning.. by late afternoon I start having problems getting it started and keeping it running at idle or low RPMs. If I can get it to WOT, it runs fine (maybe a little power loss hiccup, but doesn't die).

I did run it totally out of fuel last week, so I know I ran the risk of sucking crap out of the tank, but the filter looked clean when I checked it. Plus, I can't imagine I have gummed up jets when you consider that the problem is intermitant and I just had it rebuilt.

Can a mechanical pump run poorly when its hot? Am I having some degree of Vapor lock? Am I way off and just jacked up my carb when I ran it dry? Thoughts?

 

[DeaconBlues]

Re: Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly

Oh.. and I know the first answer is going to be to run through tests, but I can't seem to duplicate the problem consistently enough to think those tests will give me an answer. This is also why I don't want to take it to a mechanic who may charge me 2 hours of service to tell me he isn't having any issue.

 

[Don S]

Re: Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly

Next time it's real not like that, open the engine hatch and keep running and see if the problem cures itself. If it clears up, put the cover back down and continue and see if the problem comes back.

Might want to stick a thermometer in the engine compartment and see what the temp goes up to when it's closed.

 

[DeaconBlues]

Re: Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly

Will do. I read somewhere to open the fuel cap as well.

I'll do both and see if it solves it.

 

[Don S]

Re: Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly

That has nothing to do with heat, that is to check if the vent was plugged up. If the vent was plugged up, it would fail every time, hot or cold.

You have to be careful "WHAT YOU READ", I would hate to think what would happen if people tried some of the crap people recommend on forums when they don't have a clue what they are talking about.

 

[DeaconBlues]

Re: Fuel issues at low RPMS. 97' Larson, 3.0 Volvo Penta, Mechanic Fuel Pump, Holly

ok so opening the doghouse made not difference and the problem is far worse now.

I'm basing some of this on my buddy who was out with me to today and does drive train work for a race team, but I'll admit, that doesn't make him right.

According to what he saw, no fuel issue, no pump issue, no vapor issue, no fire issue. Carb is pumping fuel as expected, sparks good, plugs look good and are getting fuel, etc.

so on to electrical.

Here's the deal.... when you turn the key to start, if you keep it there, boat runs, but when you let the key go... back to run, it dies. Took the wires off the ignition switch and connected the old fashion way, same result. Checked the kill "tether" switch, bypassed it, no change. So it has to be the "run" wire (the purple one I believe) breaking circuit somewhere. Um... ok... i'll stop here, because I'm a weekend warrior and could be way off base.

Help please, I can't put anymore money into this boat, but we go out 3-4 times a week. My kids will be so down if I can't fix this thing.

Thanks,
Joe