MF165 engine missing and back-firing

[mark christie]

Hello all,

I was lifting with my bucket on my sweet old MF165 today - heavy load and revving about 2000. The engine started missing and then backfiring (very loud) and I had to cut down the throttle and it caught up and ran again for a while. It got worse and worse until it was basically impossible to run.

I figure it must be missing spark and letting fuel into the exhaust and hence the back-fire when it gets spark again. BUT, I don't know what to check. I am not sure how to check the points gap or how to know if it is firing at the appropriate time. I cleaned and lightly sanded all the contact points on the rotor and distribiutor cap.

I welcome any assistance on this. Thanks.

Mark Christie

 

[Car Doc]

Do you have an ohm meter and can check the plug wires?

The way I check a miss is carefully so as not to get shocked un-plug one wire at a time with the engine running to find the cyl that is affected and then go from there pulling plugs checking carbon tracks in cap etc.

I have seen carbon break loose attach itself across the gap on a plug while under a load and short the plug out so that may well be what it is? hth

 

[Car Doc]

Did you figure it out yet Mark?

An old rule of thumb is the gap on points is .018-.019" and generally a matchbook cover will get you real close.

The backyard way to tell the timing is close is leave that paper or something thinner preferably in the points and rotate the engine until the #1 piston is up looking thru the spark plug hole and watching the rotor making sure its generally pointing at the tower in the cap that goes to #1, and when the paper will just start to pull out the timing marks should be pretty close.

The ideal way to get super close is cigarette paper in the points provided there isn't a peak worn into one contact as its .004-.005" thick but that's what old timers had on hand so that's what they used. hth

 

[mark christie]

Hi Car Doc,

I do have an ohm meter but I wouldn't know how to test the wires. I do know how to check the plugs and I will do that first.

The matchbook cover and the cigarette papers are also in or close to my toolbox so I will also try setting the gap. I guess that I just turn the engine over with the starter to get it as close to top dead centre as I can.

I am helping a guy repair his barn today so I won\t be able to get at it until tomorrow. Thanks for the advice. I am sure that I will have more questions for you if you have the time. Thanks.

Mark

 

[Car Doc]

Yeah go ahead ask away I will be happy to help when I can.

The rule of thumb is 5k ohms per foot on resister wires and 1-10 ohms on straight wires (basically a short in other words as a comparative to an open vs resistance) What you will be looking for is an open wire by ohming them.