This one got me

[Trent]

Been doing this for along time but this one has got me pullin my hair out.<br /><br />1983 Mercrusier 3.0 with a two barrel Mercarb.. Runs great if I slowly increase the throttle. Punch it and it either goes or lean pops and dies. So I clean the carb and install a kit. Power valve, needle and seat and accelerator pump. Problem gets a little better but its still doing it. I know Im missing something but this one has got me so far. Checked the service bullitins and also the float and pump are spot on to the manual. Any of you guys seen this one?<br /><br />Oh forgot to say that Im getting a good stream of fuel out of the venturi cluster when I pump the throttle. This Mercarb does not have the three holes for adjusting the accel pump. Think if I add it that might help? Guess I could try bending the linkage... Customer complains this problem has been with him since he has had the boat...three years

 

[marinemech1]

Re: This one got me

about the only thing i can think of is distributer may be messed up pins for return springs loose springs broken or weights going out too far

 

[trog100]

Re: This one got me

pure guess this.. but how about an air pocket in the fuel line.. just enough to cause that weak spot when u hit the gas hard.. once its gone everything runs okay till the engine is throttled back then it forms again..<br /><br />as i say.. a pure guess..<br /><br />trog100

 

[achris]

Re: This one got me

Trent,<br /><br />My first thought was accel pump, and I guess it was yours too. Check that the timing is advancing correctly. Retarded timing will also cause the problem you've got. You could have a sticky weight.<br /><br />Chris..........

 

[Trent]

Re: This one got me

Ok... Guess Iv got to go back to the basics? Ill check the compression and the timing and the flyweights. But it just seems like a carb issue? It runs sweet. Just try to pull up a skier and your screwed. Fuel lines and fuel pump are new. Same problem. Boat has been sitting for three years. It had the same problem before, customer says. New fuel pump was because it would not start. Bad diaphram.

 

[achris]

Re: This one got me

Boat has been sitting for three years

Might have something to do with it. Something that should be moving isn't.

 

[TilliamWe]

Re: This one got me

Hmmm, been sitting, but the problem existed even before that?<br />Check that the valve from the gas tank is clear. We had some debris in a screen that we didn't know existed, and it caused a very, very similiar problem as to what you are describing.

 

[Richard Petersen]

Re: This one got me

Possibles. Low float level. Permenantly reduced main jet bores or dirt stuck in them. ORR. Wrong main jet. Ignition problems NEVER remain constant for this long. Unless it is really retarded. NAAAH. Quick timeing check. Back to main fuel stuff. Dammm, I almost forgot. See if the float arm has a pull off spring on it. If missing or not standard, the needles can stick up and run the bowl low fast. With fuel pressure OK. Rare. But found that 2 X in my life.

 

[Bondo]

Re: This one got me

Vacuum Leak ??

 

[bigbrownbuku]

Re: This one got me

my thought bondo. setup a vacuum guage to the intake.

 

[trog100]

Re: This one got me

my "guess" answer was based on trent already having done all the basic checks and not found any problems by the way.. just in case anyone wonders why it was so off-beat..<br /><br />i nearly just replied.. "it would have me beat too".. but i dragged the depths of possibilities.. he he..<br /><br />it would also be caused by an air leak... but an air leak on the tank side of the fuel pump..<br /><br />trog100

 

[ahein]

Re: This one got me

I'd pull the distributor cap off and check your advance weights. I had a similar problem with my Volvo AQ-260 (GM350). It would idle great and was fine at low speeds, but as soon as I tried to open it up past 3500 rpm it would bog and backfire through the carburator.<br /><br />I checked everything, starting with the fuel/water seperator, inline fuel filter, and even ran it off a portable fuel tank with new gas. No change in the symptoms. Had the carb rebuilt. Still no change. Replaced plugs and wires, checked the cap and rotor, double checked the timing. Everything looked ok, but it still would not go past 3500 rpm without misfiring.<br /><br />Finally found the problem when we checked the timing during accelleration. Found out that it wouldn't advance to 28 degrees as specified by the manual (it would only get to about 18 degrees). Pulled the cap again and noticed corrosion on the undersides advance weights that was preventing them from fully swinging open. Cleaned and lubed everthing really well, put it back together, and took the boat for a run. Ran like a champ. Timing advanced to 28 degrees at full throttle without missing a beat.<br /><br />Just something to check. Sometimes the simplest things can cause the biggest headaches.<br /><br />Good luck!

 

[DaveM]

Re: This one got me

It sounds like the vacuum leak theory might be worth exploring. I found one once by spraying carb. cleaner around the base and intake manifold to see of the engine would cough. Crude, but effective

 

[SeattleMatt]

Re: This one got me

sounds exaclty like what mine did with bad gas and a clogged fuel filter.

 

[rodbolt]

Re: This one got me

trent<br /> look for a bulliten on the venturi cluster. I know there was one for the mercarb and a 305. I think there were sevreal possibilities of wrong venturi cluster installed. also sometimes I have has to use a long thin punc and "seat" the pump chek ball assy under the venturi areaa. seems it will leak down and the pump passages will be dry. if you tap on the ball to insure its seated you will need a new ball. I always measue the new check balls against the old with calipers.if the fuel bowl is at the proer level and the accelerator check balls, and some used two, are seating then look for an incorrect or faulty venturi cluster.<br /> unless its a deal I got last year where someone had installed a 3.0 manifold with a mercarb on an 83 120 that had originally had a 2bbl rochester. seems the later style manifold has a larger phlenum area and larger intake ports and the mercarb will bog. took me a while to finally catch it.was a case of everything fit yet nothing worked. but all the other mechanical problems must be checked and addressed as nessasary or a carb will never work correctly.

 

[Trent]

Re: This one got me

I actually dont want to tell you the truth! Last night I said I have to go back and do the basics! Never should I have taken a persons word and thats my fault. I thought the guy knew what he was doing. <br /> So I went back to the basics. Check compression, fuel flow and vacuum. Then timing.. Crap....Way the heck off. Called the guy and he said it was spot on. I said no. He showed me. He had timed the engine to a "tool mark" on the pully and not the correct timing mark. Im speechless. Sorry guys I feel bad. But its fixed. Ok I screwed up. I should have done the basics first!! I a dummy. And you have never been wrong!! Thanks for your help!

 

[achris]

Re: This one got me

Well done. And man enough to admit the real fault. Brownie points all round.<br /><br />Chris..........

 

[Dunaruna]

Re: This one got me

Been caught with that one myself. Now, I always nod and praise the owner for his extensive (not!) mechanical knowledge - then I check everything he's touched. <br /><br />And charge accordingly.<br /><br />Aldo

 

[Trent]

Re: This one got me

Thanks guys....But Im still mad at myself! Dummy me.........

 

[Bondo]

Re: This one got me

Believe Me,........ We've ALL Done Worse..............