1993 Volvo Penta 500B runs great for about 30 minutes then .... Please Help !!

M2bsing

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I'll have to try and borrow a gauge from someone, but I do have 1 question. If the pressure tests fine, what does that tell me? Rebuild carb? Look for something in the electrical category? I'm stumped.
 

alldodge

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Probably isn't fuel pressure and just read back thru everything again, It runs fine with the seat open and does not when its closed, it has to be the motor is not getting enough air, or there are other fumes building up and the motor cannot run.

As an example: Buddy just filled his house boat up and turned on the blower. Started the motor and pulled away from the dock. Got just a bit away and the motor starts choking down and will hardly run. He is getting into trouble and I go back and lift the engine hatch and motor revs up and takes off. Well the engine room was full of gas fumes, and we were lucky it didn't blow up. So if your getting exhaust or gas fumes building up, or if the motor is just not getting enough air this can happen.

So look close at your vents and blower hoses. Don't want to have a bird or something build a nest in them. If all that checks out, maybe add another vent. Adding another vent should not be necessary because the boat was doing fine before all this started.
 

M2bsing

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Thanks again for the response!! I don't ever smell any fumes and I did take a shop vac and put it on " Blower" and shot it down all 4 hoses. Nothing but some sediment came through it. I did install an extra blower and there is plenty of air ( just a bit warmer that the outside air temp ) coming out of the exhaust side of the vents.
 

M2bsing

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Yes, but it will run fine until I go through a long no wake zone after it's warmed up. When it's running poorly , and I open engine compartment, it may take 15 minutes or so to start running well. One day I just ran it for an hour with the engine compartment open and it never ran bad.
 

alldodge

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Sorry to say but what you have makes no since to me, so either I'm to dumb to understand what your saying or something is missing. What we need more then anything else is what is changing during the time it no longer runs correctly. Need to know fuel pressure and spark quality but I don't see spark
 

M2bsing

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I totally agree that something is missing. I wonder if the carb is partially flooding as it is a consistent condition after I go through a long no wake zone. Recently I ran it without a long idle period for almost an hour and it did fine.
 

M2bsing

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Well I recently ran the boat without the flame arrestor ( fire extinguisher close by ) to see if it were an air flow problem at the carb. Basically same symptoms after 40-min. run . After a long no wake zone, boat was starving for something. I ran it with the engine cover closed. I did notice that the distributor base was very hot !!

Maybe running it with the cover open helps cool that part down?

Thoughts?
 

alldodge

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I'm out of ideas, it just does not make since. The base of the distributor would be as hot as the motor block, so not really seeing anything
 

alldodge

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Are we sure the reason for no start is fuel and not spark?
 

Lou C

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What do the plugs look like? Black from rich running? Is the choke sticking closed or not opening all the way?
 

M2bsing

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I'll pull the plugs and check them next. They are new this season and the problem started at the end of last season. I did check the flap on carb and it is straight up after warm up.
 

M2bsing

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Noticed yesterday that the tach goes spastic when running poorly at full throttle. Boat jerks until I bring it down to mid throttle.
 

M2bsing

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Well after a year of trying to problem solve, I replace the ignition module this morning and ran it for over an hour. I stopped, started, ran through no wake zones and no issues !!! I'm excited but still not too confident!! I will post again if any issues come back.

Thank god I think that it's possibly fixed. Thanks for all of the responses.
 

M2bsing

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