at my wits end with running issue

Hi there i have, a bayliner 2052 with 4.3 ltr mercruiser v6 engine- year 2000.
its the carb version with electric fuel pump, and thunderbolt ignition.

i have a problem all this season which i cant get to the bottom of. it will start and idle perfect and run at low speeds perfect, but when under load at 3/4 to full throttle i get popping from the engine like misfire, and sometimes a backfire through the carn / intake. its also down on power and sometimes hesitates when underway at speed.

i have replaced, spark plugs, ht lead, rotor arm, distributor cap, ignition sensor wheel and also ignition sensor inside the distributor. new coil, new fuel filter also fitted. tank was completley pumped out and refilled with good fresh petrol too.

basically if its revved out of gear its fine but just under load i get problems, any ideas?

fuel pump is operating as i can also hear it buzzing.

Re: at my wits end with running issue

You might want to check your fuel pressure and your float level. Maybe also look at rebuilding the carb. Also, don't run the engine to the point where it is missing and backfiring as it is probably very lean and you are asking for detonation. It will not live under those conditions.

PB

Re: at my wits end with running issue

okay thanks for that, what should i be looking for in terms of fuel pressure, or how do i check it. I was half thinking althought the pumps running its not building up enough pressure. also is a carb rebuild fairly straight forward?

Re: at my wits end with running issue

Check your timing,

Re: at my wits end with running issue

base190380 said:

okay thanks for that, what should i be looking for in terms of fuel pressure, or how do i check it. I was half thinking althought the pumps running its not building up enough pressure. also is a carb rebuild fairly straight forward?

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According to Mercruiser Service Manual #25, fuel pressure should be 3-7 PSI. This is checked at the carb, with the engine running. If it's less than 3, replace it. You should have a 2 barrel Merc Carb, which is not to hard to rebuild. The key to any rebuild is cleanliness and correct float level. Go to the ADULTS SECTION up above and go to the Mercruiser section and download Service Manual #25. That should cover the fuel system on your boat.

PB

Re: at my wits end with running issue

+1 for timing. I would also rebuild the carb.

Re: at my wits end with running issue

good advice guys thanks for that, if i rebuild the carb then is it just a case of new gaskets,and needles and correct float level therefore it will run good or does it all need to be tuned and set up after this?
Ill look into getting a fuel pressure gauge to check pressure of pump too.

Re: at my wits end with running issue

Wait, don't tear down the carb yet. Change the plug wires and check final fuel filter at the front of the carb. It's a 3 dollar screen. I had this issue with my motor and the wires solve the issue.

Re: at my wits end with running issue

Okay the other day i went down again, and have removed the final gauge filter at the carb fuel intake, it was a little dirty but wouldnt have thought it that bad, also removed spark plugs, flame arrestor, and cleaned out. I had picked up Carb intake cleaner so will spray carb out too.
Did notice that one of the spark plugs on the right side of the engine atthe very back, has a crack on thye upper ceramic, going from the metail base where the threads are up to the top where the ht lead clips on. there is a crack each side and you can open up the gap on the ceramic by twisting the cermaic from side to side, could this cause the popping through the carb and loss of power?
Have ordered new plugs online so will fit them tommorow and try again.

Re: at my wits end with running issue

base190380 said:

okay the other day i went down again, and have removed the final gauge filter at the carb fuel intake, it was a little dirty but wouldnt have thought it that bad, also removed spark plugs, flame arrestor, and cleaned out. I had picked up carb intake cleaner so will spray carb out too.
Did notice that one of the spark plugs on the right side of the engine atthe very back, has a crack on thye upper ceramic, going from the metail base where the threads are up to the top where the ht lead clips on. There is a crack each side and you can open up the gap on the ceramic by twisting the cermaic from side to side, could this cause the popping through the carb and loss of power?
Have ordered new plugs online so will fit them tommorow and try again.

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yes!!

Re: at my wits end with running issue

If you have vacum advance on your distributor,test to see if it is holding vacum...good luck.