1986 Mariner 8hp 6G1 won't idle without choke

[SteveVT]

I just cleaned up my low hours 1986 Mariner 8hp 6G1 manual shift (Yamaha block, I believe) after 30 years of storage. Taking off the scratched cowl, the engine looks new inside. I replaced the waterpump (though the impeller actually looked good).

I took off the carb, cleaned it -- all parts looked great, no varnish or corrosion -- it was stored dry. Float and needle drop easily. I connected a new plastic tank with new made-up lines (automotive ethanol proof fuel line) and new fittings. Added new gas from the pump to new quicksilver oil at 50:1.

Tested in 55 gallon barrel. Engine started first pull with choke out. Water jetting nicely out of the telltale. Started to slow from choking so pushed the choke in. Engine ran normally. Idle was nice and slow. "Start" position was a fast idle, I throttled up in gear as far as I could without throwing the water out of the barrel. That was fine. Back to idle, no problem. Reverse, no problem. Let her run at a fast idle for five minutes. No problems. Then back up, and down to idle, all no problems. Perfect!

Put her on the boat for a test run. Went to a local pond. Launched. Pulled the cord with choke out. Motor started first pull. Pushed choke in, all fine. Backed out of the dock at idle. No problems, turned to head down pond, forward at idle again, great. Gradual increase throttle water flowing by, telltale fine, boat moving along, then a short run at fast idle, then a run at mid speed. Finally full throttle run, boat is on plane, sounds great pond shore is passing by fast probably a good minute at high throttle, everything is great. So I slow down to turn back for another run, turn the boat, bring it all the way down to idle. That sounds a little rough, and then quits. So I pull choke, and give the cord a pull, Engine starts then dies (rich). Push choke in, Pull cord, engine starts and dies (lean). Pull choke out, pull cord, engine starts and dies (rich). Choke in, pull cord engine starts and dies (lean). Repeat as long as you want.

Fuel bulb remained hard (good fuel continuity) eventually I find that I can pull choke, pull cord, and push in the choke slightly (about 3/4 out) and the engine will sustain. The sweet spot is extremely narrow, but I know I can get back to the ramp this way.

But before heading back, I pull the cowl off, and try adjusting the idle mix screw out. Doesn't seem to make a difference. It had been out 2 turns when I had cleaned the carb, but I had adjusted it in to about 1-1/2 turns in the tank for best running (about 1/4 turn rich from the lean edge of running well). Butg now out on the water, even three turns out wouldn't keep it from dying (lean) when the choke was pushed in.

So I suspected that I'd picked up dirt somehow into the idle circuit. Brought the boat home. Pulled the carb, took it apart, found no dirt in the bowl gas, but cleaned the whole thing again with carb cleaner and compressed air, checked the float and needle movement. Checked the fuel passages. Reinstalled the idle mix needle to 2 turns. Checked the fuel filter. Reinstalled the engine in the tank.

Pulled over with choke on. Instant start, Ran for a few seconds. Then choke in, pulled again start and die.

So that's where I am now. Any ideas? Thanks in advance.

 

[PreachRick]

Just a thought, have you tried a higher octane fuel? Get some high octane fuel, put In 1/2 can of Berrymans Carb Cleaner (liquid not spray) see if any of that helps.

 

[roscoe]

High octane will do nothing for you.

Check for air leaks around the carb.
Did you use a new gasket?

Get her running and spray some starting fluid around the cab, not in the carb.
If it gets sucked into the engine you will hear the difference and know you have a leak.

 

[SteveVT]

Thank you both. I agree, I don't think higher octane will help this situation. Roscoe, thanks for that air leak test suggestion -- that's very clever. I'll try it.

At this point there seem to be the main possibilities:
Dirt in idle circuit or jets, float needle seat needs polishing, air leak at carb to manifold gasket (nope I did not replace it, but I've ordered a new one and will), float height incorrect.

If there's dirt clogging jets again (after 3 cleanings) it would have to be coming after the fuel filter. The only possibility there would be the integral fuel pump. I did not take the old one apart because I didn't have gaskets or diaphragms. Hard to find. But now these also have been ordered, and I will replace them.

 

[flyingscott]

Clean your carb again and make sure you blow air through all the passages.

 

[SteveVT]

Already done yesterday flyingscot, including polishing the float valve seat, and removing and cleaning all jets. The motor is running well in the tank.

Will need to see how she goes on water.