Engine Starting Promblem

[jpence]

Tried starting my cup today, and it would only turn over part way and stop. Charged the battery and still no luck. Put the starter generator on the 71 and it works fine. Took out the spark plug it would turn over easy (maybe a crompression release promblem ). Any help or advice would be greatly appreciated.

[mgonitzke]

Check your grounds...

[vince_o]

James

Are you saying that you swaped out the the S/G?

Maybe the spring is off the cam, comp relese, but the S/G may be week.

If you turn the eng past top dead center, will it start or spin past top dead center?

If it will you dont have enough power, like Matt said, maybe a week ground.

[jpence]

I tried the s/g on a different cub and it started up fine. I had the all wires tight and cleaned battery terminals and ground connections. (what is top dead center )

[mmzullo]

Sounds like to me is an ACR spring must be broken of fell off.

By the way what model/engine?

[vince_o]

Well if all you did is swap out the S/G, and its starts fine, then you have a bad S/g.

[Jeff in Pa]

I tried the s/g on a different cub and it started up fine. I had the all wires tight and cleaned battery terminals and ground connections. (what is top dead center )

Top Dead Center ( TDC ) is when the piston moves up in the cylinder compressing the air gas mixture.



Looking at the .gif of a single cylinder, four stroke engine.

The air is drawn thru the left side into the carb. It is then sucked into the cylinder when the intake valve opens ( by the camshaft ) . That mixture is greenish-blue. The piston then moves up to TDC where the spark plug ignites the compressed gas & air mixture. That is shown in red. The resulting (controlled )explosion drives the piston down and as it goes back up, the exhaust valve opens, venting the spent ( used or burned ) fuel mixture. As the piston starts down, the entire process starts over again.

Jeff

[F Currier Northern Maine]

Very good, Jeff! An answer like that, with its grafic, has to be noted!!
Is it time, now, to deal with the ACR setting? I could start by saying take the carburetor off, take the crankcase breather off ( the governor arm tends to get in the way and it's easier if you take the stud that holds the breather out), finding TDC and checking the intake valve clearance for .009 and the exhaust for .018.
That said, usually it's the points/points setting that causes most of my problems.

[vince_o]

jeff

cool little pic

[jpence]

I have a 72 w/ a 12hp engine from a 128, is there an 'easy' way to check if it is the points

[F Currier Northern Maine]

Take the points cover off and crank it over to see if you have a spark at the points. Turning it over by hand until the points are closed, turning the key on and opening the points by hand (long fingernail is a plus) should also show you a spark. Seems I read someplace that drawing a dollar bill 100 times (or a hundred dollar bill one time) through the closed points is a good way to clean them.

[Farmallgray]

If the condenser is doing its job, there should be very little (if any) noticable spark at the points. However, you should get a spark at the plug by manually
opening the points like that.

[jpence]

I got the problem resolved , it was a weak battery and when i changed the drive shaft i put an old bad drive shaft in causing problems.so i have to get it changed before i have to plow my drive way. thanks for all the help.