On my 1950 331 - I replaced the rotor, coil, condenser, points, spark plugs and wires, a few months back and everything ran fine. Recently the car is shakey at idle, and runs a little messy with low throttle. Once Im going down the road it seems Okay, but at red lights it was idling low and shakey, so Id put it in neutral and hold a high idle. Ive adjusted the timing by ear. Ive tried it with more advanced and retarded timing. We noticed the rough running seemed less worse with the vacuum advance line disconnected. Does this mean my distributor is just worn out and needs a rebuild?
If the idle improves with the vacuum advance disconnected, you may have too much initial timing. Timing it by ear may have increased the odds of this happening. Try to get your hands on a timing light and try setting things to the factory specs. Make sure the centifugal and vacuum advance mechanisms are working properly and not sticking or binding. You don't mention replacing the distributor cap. You might consider doing so. Get a vacuum gauge and see what the manifold vacuum readings look like and that you've got steady readings, something around 17 to 20 inches at idle. Of course it could also be a carburetor problem, I suppose...
What Clay said and make sure the vacuum advance is working and isn't leaking giving you a vacuum leak. Yes make sure the timing is correct and advances when you race it up some.
You can check the advance diaphragm for leaking by putting a hose on the diaphragm and ****ing on the other end of the hose to see if you get vacuum and the mechanism moves. Either by sticking the end of the hose in your mouth or using a Mity-Vac style vacuum pump. That's a it doesn't leak and works or a it leaks and doesn't work deal with no in between on the good or bad. If the advance is ok and working I'd be looking in the direction of the carb as it may have picked up some crud that is plugging a low speed/idle circuit or have a leak causing the issue. Checking to make sure all the plug wires are on tight at both ends isn't a bad idea either as you may have one that came loose from the plug or pulled out of the contact in the cap causing a miss.
put a dwell meter on it and check the dwell. Both of my caddys need a little dwell adjustment every once in awhile.
How would a bad transmission effect idle? I did just change the trans fluid and this piqued my interest.
I should also note - lately when I first start it it runs kinda garbled on the high idle when warming up - smokes a little bit just like a lawn mower that you have the choke engaged too much. Does that mean its running too rich and I can just adjust the choke to a more lean setting? Its the original 2 barrel carter by the way. Also - I orginally bought a cap and rotor set from Rock Auto that fit very poorly. I had to buy a NOS rotor and leave the original cap (which looked clean) for it to run properly.
So you want to solve a problem, a problem filled with variables at every turn. If the dizzy is original from 1950 it certainly could benifit from a rebuild, no? Running an old cap - they do wear out. Timing set by ear, and removing the vac line makes it run better ??? That would point to initial timing way to high. And running with timing that far advanced , points towards all things being way out of tune. To solve any problem you need to start eliminating your variables
The timing is set quite low actually. Brought it down to where it began to run rough and then gradually brought it up slowly until it smoothed out. I bought a timing light (although 12v) today and will see what I find.
I agree with this approach, possibly a burned wire, cracked cap, sticky choke, bad vacuum connection or fouled plug.
To update: Theres two timing marks. "C" for lower octane and "A" for higher octane. It seemed below the C so I put in line with that and drove the car. It seemed alright for a bit but when coming home it started to do that rough idle again. I checked the timing and it had dropped about 1/4" below the C. I then thought Id try the A. Seemed to like that, and had more power. By the time I got home it was running rough again coming to stops and idle. So I came back and re-read it with the timing light and now it was 1/4" above the A! So I messed with the throttle adjustment on the carb itself to lower it down to where it started to huff, and then I raised it just above that. My manual calls for 375-400 rpm so I know it likes it quite lower then Im used to. What I found was I could yank the throttle lever back towards the firewall and the rpm's would drop and stay there. If i reved it up theyd stay a little bit higher. I think thats why I was getting readings all over the place. So I reset it to A with a low idle - and it still is a little huffy if I apply minimal throttle while in gear. Once Im driving in higher RPM everything is fine. Pulled number one plug and it looks fine. Checked the points gap and was a tiny under .016. So thats where I stand now. I dont own a dwell meter.
Guys - what do you think about the possibility of vapor lock? The carb heater line that runs from the exhaust manifold gets really hot - it burnt my hand several times while reaching to adjust the distributor for timing changes. It is non insulated and does cross paths with the fuel line. Not sure if this has anything to do with it but im currently not running a thermostat (long story and I have a new one just havent put it in yet)
I may be wrong but I have had a few old cars were the dwell kept changing. It turned out to be slack in the timing chain.Bring it up to top dead center on the har.balancer ,then pull the cap off and have some one turn the fan by hand. Keep an eye on the rotor. Shout when you see the rotor move and look on the balancer and see how much it moved off top dead center.If its a lot it need a timing chain.Bruce.
not familiar with that distributor , but to me it sounds like your timing is jumping all over the place , and probably your dwell too. you said you don't have a dwell meter.....i'd borrow one and see whats going on. could have bad distributor bushings causing the dwell to change. or you could have a bad ground on the point plate. is there a little wire going from the point plate to ground? i once had a broken wire on a SBC causing the dwell/timing to ****ter all over on a SBC it looks like this:
When I think of a worn timing chain, I think of the ignition timing being erratic. When the dwell gets all wonky I'd lean more toward the distributor shaft and bushings being worn. Still not a bad idea to check both of them though. And one of those ground wires in the distributor can drive you nuts chasing your tail too! Still haven't seen any mention of manifold vacuum readings.
Took some videos after installing the thermostat today. For whatever reason, it did not act up with a rough idle today once warmed up, however it was still a little jerky if I only gave minimum throttle while in gear. Cant upload the vids after multiple tries. I did take some pics of my cap and distributor for whatever its worth. Maybe your eyes will see something I dont know about. Edit: cap photo is apparently too large to upload
Sloppy timing chain is a easy physical / visual proof positive test and diagnosis. Measure crank movement cccw and Cw against rotor movement. Really worn dizzy bushings are too with the dizzy out but the slightly worn dizzy you could benefit from a dwell meter.
Hard to say for sure, but it looks like the center contact ****on in the cap is pretty well eroded away. Not sure what it's supposed to look like when it's new though.
Sorry - what do you mean by cw and cccw? I did watch an "eric the car guy" timing chain slack test on youtube today. Im ***uming youre talking about the same thing. Basically he lined up the timing marks - then manually reverse spun the engine until the rotor just began to move, followed by measuring the distance from his starting point - which was 7 degrees in his case - indicating the chain had slack. I need to do this to check. I think a good part of what was causing my timing light readings to vary was the fact that the idle wasnt returning to the identical place after revving the engine. I can always lower the rpms by actually pushing the throttle linkage back towards the firewall. Someone told me I might try a heavier throttle return spring.
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