Runs/Idles rough and what I've done so far
 

My new '31 is running rough at idle and will have a vibration in the steering wheel and body in general. It also seems to need to idle a little on the high side to stay running and not lope. While driving it will die when I come to a stop at times and also backfire on deceleration. It does seem to have adequate power. Before I got it, it saw less than a 1000 miles in the past 10 years and I believe absolutely nothing had been done to it either.

What's been done so far. Cleaned and gapped the plugs, set points, adjusted the distance of the rotor to distributor contacts, set timing, cleaned fuel filter and screen in carburetor. The timing was dead on, but all other gaps were off. It seems to have a strong spark. The cap and rotor seem old. Should I replace any of the ignition components? I also have replaced most of the fluids.


I think the carb should be rebuilt. Am I missing anything? Do you think the problem is in the carb?

I would just like to get it running well. Any suggestions will be appreciated!

Dean

Re: Runs/Idles rough and what I've done so far
 

Dean, I'm far from an expert on Model A's and a new owner myself. It sounds like the same symptoms I was just experiencing.

If so I believe it is running too rich. Try adjusting the GAV (turn cw to lean out) and adjust your idle mixture.

Do you have an air filter? You may want to try it with the air filter off. It may cause it to run rich also (as some on the Barn believe... :rolleyes:).

You also state it backfires on deceleration. This to is also a symptom of being rich, unburned gas being ignited in the exhaust.

One last thing I tried and helped was I installed a hotter heat range spark plug. I went to a hotter plug because I rarely drive far enough to get the engine warmed up. Sorry, I'm having a Brain Fart. I believe they are W18 Champions.

I'll check in the AM. I'm sure someone will chime in.

Re: Runs/Idles rough and what I've done so far
 

I am sure others on the Barn may have other ideas but I think you may be correct in thinking the carb should be rebuilt or like mentioned above, maybe just adjustment of the GAV may do it.

Re: Runs/Idles rough and what I've done so far
 

back to basics, fellas, we need diagnostics before parts changing.

start with a compression test and get back to us

did it ever run smoothly while under your ownership?

Re: Runs/Idles rough and what I've done so far
 

There is a long list of things that would create those symptoms. As mentioned above more testing needs to be done before suggestions of replacement are made.

A vacuum meter would tell us a lot as well the compression test mentioned.

Re: Runs/Idles rough and what I've done so far
 

I've only have had the car a week and have driven it about 100 miles. It seems to run rougher than when I got it. I don't think it was super smooth though. How smooth should it run?

I'll have to get the right tools to do a compression test. I don't have black or oily plugs. I sense the carburetor is gummed up though. I did notice some gas seepage out of the air intake opening after I took it around the block.

Re: Runs/Idles rough and what I've done so far
 

Where would I attach a vacuum gauge? It does suck air very strongly thru the carb.

Re: Runs/Idles rough and what I've done so far
 

Most Model A intake manifolds have a threaded port for vacuum wipers. This is where you'd attach the vacuum gauge.

You say it seems to run rougher than when you first got it, so we can assume it's a running problem, and not a mechanical inbalance. Now we need to determine if it's spark, fuel, or a mechanical problem such as burned valves.

Re: Runs/Idles rough and what I've done so far
 

I think it ran smoother when I looked at it to buy and when I first started driving it.
Playing around with it this evening, starts right up, the more the timing is advanced the better/smoother it runs. I don't know maybe this is somewhat normal. Unfortunately I have no Model A experience and don't have a bunch of friends with Model A's to compare.

Has far as carb problems when I pulled out the air idle valve it seemed gummy. I also think sitting for the past 10 years couldn't be good for the carb internally. I think I'll probably order a rebuild kit.

As far as compression test I'll order a spark plug adapter and borrow a compression gauge kit.

Dean

Re: Runs/Idles rough and what I've done so far
 

"the more the timing is advanced the better/smoother it runs."

set your points to .020
then go to Marco's site:
http://www.abarnyard.com/workshop/timing.htm

to see how to set the timing.

The method is different than any other car ever made and yet very simple.

There are timing instructions all over the place, but Marco has it the clearest

Re: Runs/Idles rough and what I've done so far
 

Another problem that may cause ruff idle is if the accelerator shaft bearings are worn and they allow air to come in around the shaft. You can check it by seeing if the shaft has play in the bearings.

Re: Runs/Idles rough and what I've done so far
 

Dont forget this wonderful website as well, ive learned a lot off it. http://modelabasics.com/

Re: Runs/Idles rough and what I've done so far
 

You might need some carb gaskets, but I wouldn't buy the rebuild kit; at least not yet. Take the carb apart and clean it with laquer thinner or a good carb cleaner. Sea Foam in the gas tank can also remove some deposits, but I'd take the carb apart and clean it first. Use compressed air to blow through the passages.

Re: Runs/Idles rough and what I've done so far
 

Thanks for the link! I set the timing yesterday and after reading this site I felt I might have set the timing a little retarded. After checking I did and reset it. It definitely seems to idle better and at a lower rpm. I'll drive it in the next day or two.

Already on my favorites list and the directions I used to set the timing.

Thanks for the tip. I think it's the way to go initially.

Re: Runs/Idles rough and what I've done so far
 

Still working on it while I wait for tools to do compression test.

Well I took it for a ride today. Still starts up quickly and idles better. While driving when coming to a stop it dies out, especially if slowing down from a higher rate of speed. It did not do this when I first started driving it. I also seems to have a very slight miss.

Dean

It's now idling/running rough like in the beginning. I have a steady flow of fuel. I did notice that the glass fuel filter bowl is about half full while running. it runs smoother when it's partially choked.

Dean

Re: Runs/Idles rough and what I've done so far
 

This is kind of what I'm dealing with at the moment as well. Paying close attention to this thread.

Re: Runs/Idles rough and what I've done so far
 

Hi Dean,

The filter bowl should be full of fuel when running the engine. Check the tank for a blockage due to rust. I installed the little finger filter in the gas shut off valve and that cured that issue-after I cleaned the tank out a bit. Also, when you come to a stop, like you are in city traffic, keep the GAV open about a 1/4 turn. Zenith carbs are famous for dying out at quick stops.

Mike

Re: Runs/Idles rough and what I've done so far
 

Great advice, you may have a dirty tank that keeps gunking up the carb. Get that fuel filter installed.

Re: Runs/Idles rough and what I've done so far
 

First, thanks for the replies and ideas.

The tank actually looks very clean with no rust floating around. The carb has been sent to Renner's for a rebuild. I will also remove the original cast iron sediment filter along with glass bowl filter installed after it and put a glass bowl sediment filter from Snyder's in its place.

Another thing I did was snug up the bolts for the exhaust and intake. The two 1/2" bolts from intake to exhaust manifold had the most movement, maybe a 1/4+ turn. The 11/16" bolts to the block maybe an 1/8 turn. Do you think I should replace the intake and exhaust gaskets?

Dean

Re: Runs/Idles rough and what I've done so far
 

After a minor hiccup with the rebuilt carb, the '31 is running very well. It seems that the carb was the major contributor to the Sedan's poor running. The carb ended up needing a throttle shaft and float valve. The drivability and idle quality has a very noticeable improvement.

I'd now like to replace the spark plugs, it currently has Champion C-16C's. Any recommendations on replacements?
Dean