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'80 Mercruiser 8cyl starting issues

CaptnTony

New member
Fuel, Air, Spark, Compression.

Our boat sat last summer as we acquired a set of jetskis that occupied our time mostly last year. This year, we'd tried to get the boat going and found it's having a difficult time starting.

We've had it for about 6 years now, and it's never given us a lick of problems. Though the gentleman we purchased it from told us that he always had to put a 'spurt' of quickstart into the carb on the first start of the day. We carried that tradition on. But this year, even that isn't getting it running on it's own.

What we've encountered and what we've done so far:

1. Starter didn't engage - new starter installed
2. Weak turning over - new battery and cleaned all connections
3. Broken terminal (while cleaning everything) on slave solenoid - replaced
4. New plugs - gapped to .035
5. Flame arrester (think that's what device on top of carb is called) was cleaned out with carb cleaner and let to dry
6. Fresh fuel (only about a gallon of gas with stabilizer was left in tank for the year).

Turns strong now, but won't start w/o pouring gas into carb. If we continue to pour a bit of gas into carb it'll run strong, but as soon as we stop the engine kills out. If we put a tablespoon of gas into the carb, it'll start but kill off quickly (after gas is used up). There are no backfires but we don't see, or hear as someone else mentioned on a forum, any fuel going into the carb. We know there is gas all the way to the fuel filter in the carb and that filter is clean - not even a speck in it when we pulled it.

We're looking at doing a rebuild on the carb. It's a Rochester 4bbl. My brother in law says rebuilding them isn't that difficult and kits aren't that expensive. But I'd like to make sure we want to do that. The carb is CLEAN. I mean I've cleaned four carbs off other toys this year and this one looks better than any of the others do after I've cleaned them! Of course, I can't say if the jets are stuck or anything, but is there a way to test for that? Is there anything else I should look at before taking the carb off and rebuilding it? I'm not opposed to it, it's probably been 7 years since it was done (the original owner had total rebuild a year before we bought it).

Any ideas are appreciated. Thanks in advance.
 
Rebuild the carb, soak it good in berrymans for hours and hours. Do it right and post back.

If you do have fuel going to the carb.

You did a fuel pump psi test ?

Some fuel pumps have a filter in them.

You anti syphin valve is good, fuel pickup tube screen clean ?

Vent to tank clean, cant draw gas if it got a vacuum in the tank.
 
Unless your brother-in-law boats with you all the time AND knows how to use the oars he brings along, I'd ask him to hold off a bit.

Like Chief suggests, verify the fuel delivery system is working first. Start by making sure all the shutoff valves are ON and fully open. Then go on to the fuel pressure test.

If you were pouring the gasoline into the vent of the carb and the engine was running (until the gas was gone), I'd suspect the fuel pump. If you were pouring directly into the venturi area, it's hard to say. (Also, not good for the internals of the engine.)
 
No, I haven't ever done a fuel pressure test on the boat. How might I go about doing that? Same as with a car? I looked this morning and didn't see anyplace to attach a fuel pressure gauge, is there suppose to be one somewhere?

I'll also try to find the shut-off valves. I have a manual on order, but it hasn't arrived yet (been two weeks, arrgh). Right now I'm just doing with web searches and forums. I appreciate the tips and quick responses. Thank you!

And no more pouring gas into carb, gotcha.
 
You do it the same as a car do it after the fuel pump somewhere.

If you find the pump is giving you between 4-7 psi then your good to try running the boat off a external tank of gas.

Run a line into the fuel pump from a external tank, takes everything else out of the equation

If it runs good then you know the problem is before the pump.

Does not run good you know it's after the pump the problem.

Understand ?

This is a straight easy trouble shoot very close to a auto fuel problem.
 
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Bad weather has prevented me from getting to it the last couple of weeks. It's raining like the 40 days and nights you read about up here - every day for past two - three weeks has been 30-70% chance of thunderstorms. I just won't bring the baby outside in the rain to be worked on. Yeah, yeah, it's a boat - it's meant to get wet. I don't think the motor is meant to get water on it and I can't run the hose in the garage.

I do plan on trying to test fuel pressure this week though.

Thanks for all the ideas.
 
chief is right he knows his boat s$$t carb is where i would start sounds like the float needle is gumed up it does not take much gummy crap to stop it up!!! had a motor do the same thing!! ps i would buy a new carb if that one is very old!! just put it on and go. edlebrock makes a nice marine carb worth the money.
 
Mikey thats a nice carb but for a boat motor the rochester is bullet proof, i left mine on my boat.

My friend got maybe 25 carbs he keeps tellin me to let him install a different one says i'll get more hp i know he's right but my baby had this carb sinse it was built in 86' runs strong don't kill me on gas i'm keeping it.
 
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