Rough Idle and Hard Advance

[pwilliam]

72 BS1 - 1608. Bought the car and replaced the timing belt, water pump and tensioner bearing as soon as I got it. Although an aspiring mechanic I often forget really important things...like setting the timing. However, the car started up and ran perfectly well, exactly the same as before the belt removal. Car did have a rough time warming up occasional and once and a while would desire to stall out on me at a stop sign, occurring before and after the belt change. This symptom became somewhat worse after the belt change and i would have to pull out the choke to keep it from stalling.

The carb was leaking fuel and was comprised of multiple types of bolts from hex heads to phillips to flat heads, and a screw had worked itself out so one of the pieces of the carb was just dangling. So i figured it was probably just best to swap to an alternate dhsa3 that my Dad had available. Made the swap and cleaned all the jets to be safe. The car now idles terribly although having identical jets to the previous carb.

The float is not sticking so I have eliminated that. I have tried tuning the car per the Artigue guide. Choke plates open, 1 1/2 turns in on the idle speed screw and 2 turns out on the mixture screw. Set the idle to 850 via the idle speed screw then adjust the mixture screw to optimal speed, etc., etc. I feel pretty comfortable with this process. However the idle is never constant. It will occasionally surge then resume, dip to a stall or near stall and then resume. Very frustrating. Got the car to a point where i could drive it but it would want to stall out on me at stop signs and it would hesitate under acceleration. If i mash on it, it'll go though. Also spark plugs are very dark, covered in soot and a little wet at times. it seems the car is running way too rich. Since i had been through the adjusting process several times on the carb i though perhaps the timing was the issue so i finally took a look. The car was advanced by about 20 degrees, however if i tune it by ear - searching for the highest rpm its about right. If i turn the car to 5 degrees advance per the 1608 requirements, the car will barely just run with the idle speed screw all the way in.

Very flummoxed here. Is it possible the belt skipped a tooth? i feel confident the belt alignment is correct.

[pwilliam]

As a follow up - the points needed adjusting. This has helped some but not entirely. Still some rough idling at start up until the engine warms and the occasional backfiring/puffing under hard acceleration.

Still flummoxed though. Set cylinder 1 to TDC. Set points gap with the points fully opened (widest part of the distributor cam lobe) and the engine is happiest at 20 degrees before TDC when i hit it with the timing light. Is it possible the PO pulled the distributor and put it back a tooth or two off?

If I turn the distributor to get the car to 5 degrees advance it just barely runs. It will not run at 0 degrees advance.

[carl]

Check the cams are timed correctly, really easy to get this off when changing timing belts. Then reset the ignition timing as odds are this got off spec when changing timing belts.

[pwilliam]

Cams look OK. If I turn the exhaust cam, shouldnt the dizzy cam be turning with it and therefor shouldnt come out of synch?

[dom]

It sounds like you have more than one problem. Check for air leaks or vacuum leaks around the carb. Also wiggle the rotor when you have he cap off to see if there is play in the shaft if so you a dwell meter to set he gap or just reduce the gap below spec and see if it changes performance.

[bluespider262]

Po mounted the timing mark on my 79 backwards. It fits either way. Make sure yours isn't the same.