hard start and rough idle after timing set

[rca1pollock]

i have 1984 mcm 120 ser#66-----. after tune up including coil, wires, plugs, cap, rotor, change to electronic ignition..all those are to spec....engine started immediately upon cranking. after adjusting timing to 8 degrees btdc (i think i remember checking mark BEFORE loosening distributor and is was way before 8 degrees...like where 20 degrees btdc or so would be if marks went that far) now engine only barely cold starts when i add some throttle..and runs rough til it warms up, then runs fine. i know all parts that i replaced are correct even plugs are mr43t but i was told to increase gap from .035 to .040. any ideas? thanx

 

[Bondo]

i have 1984 mcm 120 ser#66-----. after tune up including coil, wires, plugs, cap, rotor, change to electronic ignition..all those are to spec....engine started immediately upon cranking. after adjusting timing to 8 degrees btdc (i think i remember checking mark BEFORE loosening distributor and is was way before 8 degrees...like where 20 degrees btdc or so would be if marks went that far) now engine only barely cold starts when i add some throttle..and runs rough til it warms up, then runs fine.i know all parts that i replaced are correct even plugs are mr43t but i was told to increase gap from .035 to .040. any ideas? thanx

Ayuh,.... Welcome Aboard,.... Fix yer Carb,.... The Choke is all messed up,.....

 

[rca1pollock]

wouldn't that have caused it to run rough before i adjusted timing also..(it started fine) . also could i just check choke by removing spark arrester at start-up

 

[rca1pollock]

anybody?

 

[thumpar]

Yes you can check the choke by removing the flame arrestor. Are you setting the choke before startup?

 

[rca1pollock]

SETTING ? the choke ..not sure what u mean?

 

[NHGuy]

Some chokes require that you pump the gas a couple of times, the pumping allows that style of choke to set. It's common in carbureted cars I grew up with. Pumping gas is standard operating procedure before starting a cold carbureted motor. Then you should have the throttle cracked open a bit so when the motor lights off it will spin up a bit. You can throttle it back once it starts but it does take a little throttle to get a good start.

 

[NHGuy]

You can pull the flame arrestor off and look at the choke plate when your engine has sat and is cold to see if it's already closed. But still pump the gas a couple times, put the stick a touch above idle and crank it.

 

[rca1pollock]

great..thanx..when i did just pull flame arrestor off the choke was stuck open til i bumped it, then it closed i will clean up linkage and pump gas cple times after it cools

 

[rca1pollock]

did not run well at first with choke closed at startup...so i adjusted choke to be open a little (maybe 1/8 inch) when its cold..seems to start better after setting choke and pumping gas two/three times. has rochester 2-barrel carb that i would like to take fuel inlet line off and clean fuel screen, but am afraid that when i try to loosen one nut while holding the other..it may twist/ruin the fuel line..leaving more fixes. something is causing only 3700rpm at wot. and i guess its not timing since ive got that at 8 degrees btdc..17 pitch prop should at least be 3900-4200 per specs. top end mcm120 17ft fourwinns low loads is only 30mph

 

[thumpar]

How did you measure your speed? If it was GPS your tach must be off. At 3700 RPM, 1.98 gear ration and a 17 pitch prop at 30mph would be 0% slip which isn't possible most are 10%+. If you use 15% slip it means you are running at about 4300 RPM when you are going 30 MPH.

 

[NHGuy]

Use "line" wrenches on those fuel fittings. It's way cheaper and faster than replacing steel fuel line due to bunged up hex heads. I know, did it wrong before and paid the price.

 

[thumpar]

Use "line" wrenches on those fuel fittings. It's way cheaper and faster than replacing steel fuel line due to bunged up hex heads. I know, did it wrong before and paid the price.

I found that out when I redid the trailer brakes.