440ic "popping" at idle

[yasmar]

My 440 has developed an annoying backfire at idle. Real sharp "snap" backfire...everything's fine when I put it under load...it just happens at idle.

On a side note, she's been great pushing down trees. Push 'em high to dislodge the roots, chain 'em and drag 'em out. Luckily we're having a VERY mild winter up here (almost 60 last weekend!) so I get to play on her more often.

[hunter41mag]

yasmar,

I would check timing, maybe at idle its to retarded but when rpms are higher and under load the distributor advances it far enough. Also make sure you use the correct marks off the flywheeel, if its dirty and rusty the marks are hard to see and read.
The other possibility would be the carb idle mixture screw is set too lean. Check the manual for how far the idle needle should be backed off the seat.
The only other thing I can think of could be possibile bad valve that is not seating completely.

Don
Eastern PA
440IC

[Lavoy]

If it occured suddenly, I might lean more towards the valve idea. As a cheap test, put in plugs, points and condenser just to try it in case it is a simple fix.
Lavoy