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Pulling My Hair Out! Merc 260 With Quardajet 4 Barrel Carb

J

JBraden

New member
Hey all. Im Pulling my hair out with this darn port engine on my 88 Sea Ray 300 with twin 260s. Ive rebuilt the port side carb 3 times now and finally gave up and took it to a pro. I got Both carbs back and still am having the same issue out of my port side engine. I can fire it up and warm it up and it runs great 90% of the time. When it finally gets up to temp and I pull the throttle back from 1100ish rpm it will load up with fuel and stall. I can hold it wide open and it will restart and clean up and be fine. So ill be on my way to our hangout spot (the engine performs as it should above 1000 RPM in gear) and when I pull the throttle back it will load up with fuel and stall. So the other day while beached i pulled the hatch and tapped the carb with a screwdriver handle a few times. I cranked the engine and it fired up and idled great for 10 minutes. So i took it for a cruise for about 10 minutes and came back to the beach, pulled the throttle back and it stalled again. Does this sound like a carb issue or possibly a pump issue? Ive checked the sight tube and there doesnt appear to be any fuel in it from a busted diaphragm.
 
Next time you are about to slow down and pull throttle back. Have the flame arrester off and have a second person throttle down while you look intro carb with a flash light and watch what happens. I would suggest doing this to both engines for comparison.

take note of anything,
where is the choke butterfly?
Any fuel dripping when desired rpm is reached?
weird noise (s)?


also if not to difficult you should confirm timing on both engines to be the exact same. ~ 6-8 degrees BTDC at idle (650-750rpm)

If engine in questions timing is retarded more than normal running engine then this may lead to issue with carb.

One last thought, have you swapped carbs for testing? if starb carb seems to work correct and you ry it on port and its not, then its not the carb!
 
Like that last suggestion. Swap the carbs and see if the problem follows.

Jeff

PS: I assume you have mechanical fuel pumps. I've seen wide pressure fluctuations with them (and even electric pumps). You might have way too high fuel pressure developing from a bad pump that overwhelms the carb AFTER you slow down. Swapping the carbs will illustrate that.
 
So I talked to my buddy, he has a known good spare quadrajet that he just pulled off one of his spare 260s for me to try. I'm heading to the boat now to swap them out. I will report back if that solved my issue or not. If it doesn't most likely I'll be looking at a fuel pump issue? It does seem to be worse with the more fuel I have in it, which sounds like some kind of pressure issue. But I'll try swapping the carbs and see what happens.
 
Well I went to the boat today just to see what the original carb would do. It fired right up but as I watched everything the fuel level kept rising and eventually was coming out the top of the carb and around the accelerator pump. And it stalled . So I swapped the carbs with the known good one and it fired right up no issues. I'm thinking that the bad carb has the wrong float setting. So for now my issue is solved at the carb that was on it is now at the marina repair shop so they can figure out what's wrong with it. I'll report back what they find. Thanks everyone for all your suggestions and info. I really appreciate it!
 
Well I spoke too soon. I took the boat out for a cruise yesterday and it stalled again while coming off plane into the channel. ��. I guess I will start with checking the timing.
 
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