Long opening statement, thank you to those who are willing to read through all this and give feedback…..

I’ve had my share of dealings with this generation of motors, but am particularly frustrated with this one so figured I’d throw out the problem to the panel for feedback.

This motor will not idle without sneezing and stopping abruptly. The carb is not responding the way it should and from all accounts this motor is running lean. At 3 turns out, it runs a little better at a high idle, but at the factory recommended 1 turn it will not stay running. 2 turns it will sneeze repeatedly. Anything above 1/4 idle it works just fine with a normal power curve and no missing.

I can get it to hold a high idle in gear but it slowly starts to get leaner and leaner, eventually sneezing, then an abrupt stop.

I’ve replaced the low speed needle bearing and little cup (basically the two plastic pieces to keep air from getting in that way), pulled the low-speed circuit welch plug to inspect (OK), and the carb is completely clean.

I’ve tried changing the cam follower pickup timing to favor more fuel at low timing, and more fuel at a little faster timing, really hasn’t made any difference.

I’ve installed a new carb to manifold gasket.

Leaf plates are all seated properly with no appearance of distortion.

Compression is pretty good on this powerhead (120-130 range).

No evidence of air leaks on the powerhead. I even went so far as to plug the manifold oil recirculator hose (tied it off) and switch out the intake bypass nipple cover with an older style which does not have one. Why? Initially, the motor was sneezing so much that the back fire was repeatedly melting that recirculating hose and then of course would create an air leak or flat out fuel spraying out that crack in the hose.

IN OTHER NEWER 25HP MOTORS (post 1976), I’ve found switching the carb solves the problem, as some sort of fouling of the low-speed circuit was present. In this case, I don’t have another one to swap from a known working motor for comparisons.

Seems the only motors I run into with this issue is 1973-76 models with the low-tension magneto. Any recommendations? I’ve already cancelled the order with the customer because I’ve had enough of this engine, but would like to use it as a learning opportunity.