1986 75HP A953921 - Flooding when throttling down

[turtle1173]

This motor starts and seems to run good, although the idle seems fast. After running for a bit, either WOT or just half, when throttling down towards idle it starts to sputter and dies unless you throttle back up. There's gas on top of the water. Squeezing the bulb caused even more gas to come pouring out of the carbs. The engine was clearly flooded and took a bit to clear it out and get it restarted, only to repeat the same process.

This is a friend's motor. He took it to a mechanic last year. They cleaned the carbs and told him the reeds needed to be replaced. I have a hard time thinking this is the problem. It seems to me that the float(s) are not adjusted right and/or the needle is not seating and too much fuel is entering the carbs.

Does this sound like a reed problem (mechanic wanted $1200) or just a carb/fuel issue?

Thank you for your help!

 

[carholme]

Re: 1986 75HP A953921 - Flooding when throttling down

Your s/n comes up as:

MERCURY - ( 75 H.P. (1986 ))
Serial No: 0A953921 Model No: 1075726

Parts and Service Bulletin list for s/n 0A953921:

Search Results - Crowley Marine

The service manual you require is P/N: 90-13645-2

If you do not have this manual, see my message to you in Notifications at the top of this page.

Gerry

Search Results - Crowley Marine

 

[turtle1173]

Re: 1986 75HP A953921 - Flooding when throttling down

Thanks for the information on the manual. I do have a manual for 3 & 4 cylinder Mercury's. It does cover the carbs of this motor. I currently have the carbs torn down and cleaned. We are waiting on the gasket kit & needle and seat to come in.

My opinion of the situation is that it must be the carbs causing the problem. I see no reason that the reeds would be responsible for a flooding out condition after coming down from WOT. Squeezing the bulb and fuel pouring out would indicate the needle not seating or float adjustment not proper. It bothers me some that when disassembling the carbs, they look clean and nothing stands out as being visibly wrong.

Is my opinion faulty?

 

[CharlieB]

Re: 1986 75HP A953921 - Flooding when throttling down

You are most likely correct.

The primer only needs a firm handshake, seriously squeezing it can raise the pressure over the 4 -5 psi and can overcome the float/needle and seat.

Float height can also contribute to easy flooding if set too high, very near the flood line.

I'm sure with the new carb kits and correct float settings, you will have solved most of his problems.

Idle mixture will have to be perfected again once back on the water. If float levels are lower you may have to richen the adjustment.

 

[turtle1173]

Re: 1986 75HP A953921 - Flooding when throttling down

rebuilt the carbs, including new needle and seat. Set the float level. Put it all back together and everything worked good. Took it out on the river and it ran perfect. So 2 weeks went by and my son & I planned a fishing trip. Took the boat to the ramp, pumped up the primer bulb and fuel was shooting out of both carb jets. Very frustrating!! Took the carbs apart and it looks like the bowl gasket was hitting the float. I don't know if the gasket expanded or what. Both of them were this way. But after trimming and putting back together, fuel was still shooting out of both carbs. In the process of adjusting float levels again, I broke one of the float levers. Aaahhh.

So, I've now bought 2 new complete carb kits. These include all carb parts including new floats. I just can't figure out why this is happening. For some reason, either the needle is not cutting off the fuel or the float level is not high enough to cut off the flow. Or perhaps the floats aren't functioning right.

Anything I might be missing?

 

[CharlieB]

Re: 1986 75HP A953921 - Flooding when throttling down

Are you holding the carb upside-down while checking float adjustment, then blowing into the inlet checking for a good seal?

If so then all should be well as long as the gasket does not obstruct the float AND you have a fuel filter to keep any particles out of the carbs. A water-separating filter, spin-on canister look a lot like an oil filter, is a very good investment in helping to keep carbs clean.