Robb
Well-Known Member
This is my first 340, and I am not familiar with any of their running characteristics (if any), and I have some tuning questions
Motor Info/History
The motor is a stock bore 69, and I am told it was a low mileage stock rebuild (X heads, stock intake, and manifolds) with a mild mopar cam. It has about 10-15k on the rebuild. I have receipts verifying the bottom end rebuild, but I have no details on the cam or head work. Its running mopar elec ignition, with all new stock replacement tune up parts. The old plugs seemed a tad rich, but none were fouled or oiled. Also new is a 650 edelbrock AVS w/elect choke.
Issues and Questions
It has ran with what seems like a slight miss (seems shaky or shuddery for lack of a better description) and poor hot starting since I bought it. The new carb and tune up has helped (mainly with the throttle bushing gas leak), but it still has a rough idle. We have verified that the vac advance is working, firing order is correct and the timing is at 10 degrees. Where do we go from here? We have a few theories, but my first question is should we assume a smooth steady idle without shaking/looping is possible, or is this just how a 340 runs? I hope thats not too dumb of a question.
Any additional recommendations on timing?
Could we have a vacuum leak or intake leak?
Worn timing chain?
Harmonics issues?
Valve adjustments?
All of the above?
Are we just over thinking it?
Keep in mind, I am a novice mechanic and a lone mopar owner surrounded by GM people, but my main help is my buddy who is a marine mechanic by profession, so he has a lot of experience with all sorts of naturally aspirated V8s, the least of which are unfortunately mopars!
Motor Info/History
The motor is a stock bore 69, and I am told it was a low mileage stock rebuild (X heads, stock intake, and manifolds) with a mild mopar cam. It has about 10-15k on the rebuild. I have receipts verifying the bottom end rebuild, but I have no details on the cam or head work. Its running mopar elec ignition, with all new stock replacement tune up parts. The old plugs seemed a tad rich, but none were fouled or oiled. Also new is a 650 edelbrock AVS w/elect choke.
Issues and Questions
It has ran with what seems like a slight miss (seems shaky or shuddery for lack of a better description) and poor hot starting since I bought it. The new carb and tune up has helped (mainly with the throttle bushing gas leak), but it still has a rough idle. We have verified that the vac advance is working, firing order is correct and the timing is at 10 degrees. Where do we go from here? We have a few theories, but my first question is should we assume a smooth steady idle without shaking/looping is possible, or is this just how a 340 runs? I hope thats not too dumb of a question.
Any additional recommendations on timing?
Could we have a vacuum leak or intake leak?
Worn timing chain?
Harmonics issues?
Valve adjustments?
All of the above?
Are we just over thinking it?
Keep in mind, I am a novice mechanic and a lone mopar owner surrounded by GM people, but my main help is my buddy who is a marine mechanic by profession, so he has a lot of experience with all sorts of naturally aspirated V8s, the least of which are unfortunately mopars!