Fuel Problem??

[doorman111]

I have twin 1986 Merc 260 inboard with thunderbolt ignition. Problem started (port engine only) with water and junk in gas. Now have fresh gas, seperators, fuel filters, plugs, wires, dist cap, rotor, efi module in dist. Put on new rebuilt Rochester Quadrajunk, ran at idle for a while, let warm up, popped open 4-barrel, then flooded out to the point of filling crankcase with gas!( I pumped 10 Qts total of gas-oil mix out of engine)I changed oil, filter, & plugs again, and then sent for a second rebuilt carb & installed it. Could not properly set idle(stalling under 900rpm), so I thought I would take it out to burn off any leftovers. Engine now seems to have no power under a load only gets 2600rpm, still seems to be dumping excessive gas through exhaust. My next thought was to take the carb & fuel pump off the good running starboard engine , but if anyone has any ideas, or has come across this problem, PLEASE help, Thanx in advance - D3

 

[Reel Poor]

Re: Fuel Problem??

It may be that the fuel pump diaphram has failed. The gas may be getting into the carb via the clear plastic hose that runs from the fuel pump to the carb. There should be no fuel in that hose. If there is it's due to a faulty fuel pump.

BTW Welcome to iboats

 

[doorman111]

Re: Fuel Problem??

Thanx Reel Poor - The hose is clear-no fuel coming back to carb, must be something else

 

[Reel Poor]

Re: Fuel Problem??

It sounds like a carb problem. You could pull a spark plug or two and look at them to see how they're burning. If they're black it running rich. That would confirm a possible carb problem. If you do switch the carbs from one engine to the other, don;t put the suspected bad carb on the good running engine. Put the good carb on the bad running moter and see what the results are.

 

[Coors]

Re: Fuel Problem??

Like Reel Poor said, seems the float is stuck. I have rebuilt a lot of q-jets; if the 2 internal plugs are not leaking, which you only get after a hot start, the problem seems to be a bad float, as the secondaries have no float.

 

[doorman111]

Re: Fuel Problem??

Thanx for the input - I will switch out the carb this weekend. The plugs are definatly black and fouled. I had an outfit in Cal send me the rebuilt carb - twice with the same result -no good( I had rebuilt the original carb myself last season,it worked ok, but I couldn't get it to idle right - when I put it in gear , it would stall,had to keep it at 1000rpm, if some one would hold the choke just slightly, it worked great at idle, no stall, that one ran great at any load speed) I will post results after the test -D3

 

[doorman111]

Re: Fuel Problem??

Switched carbs over the weekend, the engine purrs like a kitten, runs perfect. I tore apart my old original carb, soaked & and cleared out best as possible,put it on my starboard engine. Runs great EXCEPT when I put it in gear at 800rpm, it stalls. If I hold the butterfly just slightly and had someone put it in gear, it did not stall. Getting closer!
It's a shame you put your faith in buying products (carbs from 2 differant places) and you find out after much trial & error (and $$$)that they were rebuilt wrong!
Thanx for your help, any suggestions about the idle problem would be great -D3

 

[Reel Poor]

Re: Fuel Problem??

If your holding the choke butterfly the carb is running a little lean. You maybe able to adjust that out with the idle mixture screws. If not, there is a problem in the idle circuit in the carb, ie, wrong gasket or stopped up somewhere.

 

[doorman111]

Re: Fuel Problem??

I have tried to adjust both the mixture screws, don't seem to respond at idle.
set them at 2-1/2 turns out , to richen, should I turn them out further?
The good carb is set at about 5-1/2 out D#