Jerky Runner
 

No I do not mean the guy behind the wheel! It is the car that is jerking around.


To fill you in on the problem. My 1929 coupe has sat in the garage since the 4th of July parade. I started it up to take it for a drive. When I took off is 1st gear, it had a bad jerking or stalling when I started off and pressed the gas. Another way to describe the problem is that I would press on the gas, it would take off and then almost kill the motor but would pick up again and continue on doing the same thing over and over again. Also sometimes would backfire through the carb. But it had run great last time I had it out!


What I have done to try to fix it. I replace the carb with a known good carb. Still same problem. I replaced the distributor with a known good distributor. Still the same problem. So where do I go from here???


Due to the fact the rig had sat for almost 2 months without being run, could it be a sticking valve? Maybe an intake valve due to fact it backfires into carb??


Any ideas on what to do? Should I put some Marvel Mystery Oil in the cylinders and take it out for a run? Or just take it out and run it hard? Or does anyone have any other good ideas what to do? Would appreciate any help I can get. I am not a qualified A guy and just guess at things.

Re: Jerky Runner
 

I would check the following, gas flow, sticking valve, weak spark, clean plugs, points, distributor contacts, and rotor.

Just not running for eight weeks should not cause a problem. I leave our 29 in the garage from November until May. Have done this for almost forty years. Always started right up.

I recommend using Marvel Mystery Oil in gas. Has always worked for me. Good luck. It will not be a big problem. Enjoy.

Re: Jerky Runner
 

Thanks. You mentioned a few things I have not checked. I did notice the plugs were rather black. But I did replace the carb with good carb and the distributor with good one. And it ran great last time it was out. So I think I will work on the possible sticking valve, plugs or weak spark.

Re: Jerky Runner
 

Replacing parts before troubleshooting is a sure way to introduce more problems. Pull a spark plug wire and run the engine, is the spark hot and steady? Use an unlit propane torch around the intake manifold, does the engine RPM change? Do you have a good stream of gas at the carb inlet?

Re: Jerky Runner
 

mmmm What breaker point set up do you have. Sounds like an intermittent short. Pop out switch on the verge of going pot. Condenser or coil getting weak?

Re: Jerky Runner
 

I use 18 setting. Also as I mentioned I replaced the entire distributor with a known good distributor. So pig tail may not be the problem. Also when I put in "new" distributor I rechecked the points and re-timed it.
It could be a bad coil acting up. Never had problems last time I had it out but maybe it is failing. So will check spark at plugs. I have had coil problems on my huckster but that problem the rig completely died but would restart. This problem it just jerks and then goes on.

Gas seems to be getting to the carb OK. But could also check this.

Thanks again for ideas. I think I will try the Mystery oil also if spark checks out.

Re: Jerky Runner
 

Try driving the car with the gas cap off. If it runs ok with it off, you have the vent hole on the cap plugged off.


Tom Endy

Re: Jerky Runner
 

I would change out the coil with a known good one. I just had the same problem with a coupe and found the coil had burned itself up. Replaced and car runs fine. Mine was obvious, plastic oozing out of the bottom of it. Ate up the points also so changed all that and now have another coil. This one is oil filled instead of epoxy, so I mounted it with the high tension wire up instead of down. Should have better luck this time. Had to make up a longer high tension wire, hard to find. Old shop in town had bulk wire.

Re: Jerky Runner
 

Re: Jerky Runner
 

Carb float.

Re: Jerky Runner
 

Thanks. I had changed out the carb with a known good carb. Still same problem with good carb.

Re: Jerky Runner
 

I have considered this possibility. If some other things I need to check out don't solve it, then a new coil may be the answer. Thanks

Re: Jerky Runner
 

Well guys thanks again for the help. I have tried most of the ideas presented in your comments but still have the same old jerky problem.

I haven't checked for a leak in the intake manifold nor have I put on a different coil. When the weather around here gets back to raining or cooler, then I will get back to doing more.

I did put some Mystery oil in the cylinders but that still did not help.

I did notice that when I went along in second gear at a lower consistent speed (10 MPH), when it would jerk, it would backfire in the carb. Could this be a bad valve or a sticking one or maybe one out of adjustment???? Reason I ask about the adjustment is that I tried to adjust the valves awhile back and I may have messed them up.

Anyway thanks again for your comments and if anyone has any other ideas, please tell me how messed up I am.

Tom BTW I did check the gas cap and it was not screwed down tight and I also loosened it more. But no change in the problem.

Re: Jerky Runner
 

Maybe an idea to check out the valves would be to do a compression test. If a valve is sticking or not closing, this test should tell me. Am I thinking correctly???

Re: Jerky Runner
 

Check Compression. If just one cylinder is really low or zero it could be a valve stuck open. I put about three tablespoons of Marvels Mystery Oil in the errant cylinder when it happened to me. Put the plug back in the hole and cranked it a few revs with the key off. Next morning I put in the rest of the plugs and drove to coffee. Been driving it since for about two years or more. Comp. was 1 94, 2 0, 3 94 and 4 93. Now all are 94. Happy me.

Re: Jerky Runner
 

The best medicine for a Model A ... drive it at least once a week for 15 - 20 miles.

Re: Jerky Runner
 

How does it idle? If you do have a stuck valve and it isn't running on all cylinders shouldn't it be pretty noticeable at idle?

Re: Jerky Runner
 

Well guys (and gals) I am back again to report on this encounter with a problem A. So will give you a list of what I did now.


1. I did check the compression. Three of the cylinders measured around 75 and one was at 78. I did it with a cold engine (didn't want to put hot plugs). So this eliminates a permanent stuck valve (I guess-is this a valid assumption??)


2. This time I put about 2 oz of Mystery oil in the gas tank which was about 1/2 full. Took it for a drive around the neighborhood and reved it up to about 20 to 25 MPH in 2nd gear. Went for maybe 2-3 miles this way. I may still have a valve problem.


Well good news!!! It has seemed to have worked to stop the Jerky running!!!!!!! Will know the next time I take it out.


Have to leave it set for a few days because we are going to the Oregon coast to get away from the smoke in a lot of Oregon.


But deniskliesen you may have come up with the best answer for my problem. Because the rig had set for about 2 months without being taken out for a run.


Thank you all for your comments. It kept this old guy busy doing something. Kept out of the wife's way for a period of time!

Re: Jerky Runner
 

Fred, You might try putting oil in the accelerator bracket in the back of the motor. There are two holes for oiling this bracket. This might free up the bracket and make your acceleration smoother.

Re: Jerky Runner
 

4 oz of MMO per 10 gals of gas is the normal amout! An A will run on more MMO in the gas!

Re: Jerky Runner
 

I do: glug-glug-glug-glug whenever I get gas. Not going to hurt a thing.
Paul in CT

Re: Jerky Runner
 

Re: Jerky Runner
 

I had a similar problem on one of mine (was not running smoothly), but was not backfiring. I tried a number of things, and what finely worked for me was to reset the valve clearance on all the valves.

Re: Jerky Runner
 

Ben, this also could be my problem. I did try to adjust the valves awhile back. But I was having a problem with one of the adjustable valves and I may have messed it up. So I may need to try adjusting them again.

Re: Jerky Runner
 

I see them (cell phones) in my living room. They aren't jerky in their actions but they are "Jerks". Forgot how to communicate in this environment.

Re: Jerky Runner
 

Well back in Aug of 2018, I started this post about my jerky 29 coupe. Guess what, here it is Sept 2019 and I have the same problem. Same situation, ran it is 4th of July parade, let it set until now (sept) and the same problem started again. The problem was that when I would start to go, press on the gas it would jerk and backfire in the carb.


So I did some thinking about the situation as to what it was doing--- would "miss" when pressing on the gas starting out from a stop. Well so many people recommended Marvel Mystery Oil so I got carried away. A few days ago I took the plugs out, dumped in a bunch of MMO in each cylinder, and let it set for a few days. Today I got in it, started it up(and it did start) and I had a concern that the neighbors would call the fire department. So I backed outside and let it run for awhile blowing smoke all over the neighborhood. Then I got in it and drove it around the block a few times in 1st and 2nd. At first it still had the problem. Then after a few rounds it all cleared up-smoke and the jerk (not me).

After parking it after a few miles, I turned it off and let it set for while. They I tried to start it. I had spark up, gas lever up and just a touch of the starter, it was up and running! Wow! This start was better that it had done for years. I also pulled one of the spark plugs and looked at it. Before the MMO, when I took them out they were covered with black junk. This time the electro look nice and brown and no black stuff.


Anyway to sum up all these comments- it does look like I had a stuck valve. Putting the MMO in the cylinders and running it after that did clear up the problem of a jerky start where it would jerk and backfire in the carb.


Hope this helps someone.

Re: Jerky Runner
 

Thanks for the come back and final report. MMO seems to be a common cure and should always be the first step in solving performance problems. Go drive it like you stole it !!

Re: Jerky Runner
 

Glad it worked out for you Fred. :) This tells me that you need to start looking for more parades during the year. :D And for what it is worth, i always add about 4 oz of MMO every time i fill up on both of my A's. Mark.

Re: Jerky Runner
 

Mark, the MMO idea sounds good. Will have to do. But I think the parades may go. Hard on the old rig, clutch etc. So think I will watch parades instead of being in them!

Re: Jerky Runner
 

I am with you on that Fred. I use to do two different Christmas parades for a few years, but now i find a fold out chair and a cup of coffee just seems to fit me better. ;) Mark.

Re: Jerky Runner
 

I also think I need to change the engine oil after this situation because I did put a liberal amount of MMO in the spark holes. I am sure a lot of it got in the engine oil. Maybe that is good for the oil but it is about time to change the engine oil anyway.

Re: Jerky Runner
 

Your real problem is either wrong or faulty plugs, or most likely, your running to rich and idling to much.

Re: Jerky Runner
 

Is the ignition cable an original one ? I had a very similar experience recently with my car, and finally diagnosed the problem as an intermittent short inside the cable conduit. the wire inside was almost 90 years old and the insulation was badly cracked and falling off. Found this only after rebuilding the distributor and replacing the coil.....all the parts I replaced were working just find. Checking the ignition cable never occurred to me.

Re: Jerky Runner
 

Well I took the old jerky runner out for a drive today. About 2 weeks after the MMO treatment in the cylinders. It started better than it ever did, after warming up (46 degrees around here today) and ran like it should. No jerks and good pickup. So I again would guess that I had a stuck valve or it may have be very sooty spark plugs that cleared up with the MMO. But I am no experts on this type of thing but this is what it seemed like to me.

Re: Jerky Runner
 

Good to hear Fred. Depending on the weather, you just might have to get it out and drive it a little more often. Take the wife out to breakfast or lunch or dinner. Or maybe all three. :) Good luck with it and have a great weekend. Mark.

Re: Jerky Runner
 

The two most common problems that can happen after a car sets for a time is fuel deterioration and sticking valves.

Fuel doesn't last very long unless it is a higher quality formula like 93 octane premium. Avgas last a lot longer but it's overkill on a model A and it's not legal to run it in cars. Draining the fuel is a PITA but sometimes it's the only way to insure a clean fuel system.

MMO and running the engine regularly are the best way to prevent sticking valves. I wouldn't use any more MMO than is necessary. This isn't a 2-stroke engine and they generally get enough blow by to keep the piston rings lubed up. They don't run well on oil and solvent alone. It doesn't take all that much MMO to do the intended job.

We run the aircraft engines every 2-weeks if they are in flyable storage. This is considered the minimum interval for safe flight. Even 2 months is too long.

Re: Jerky Runner
 

Thanks, good information.
I use no crap gas in my rigs and that seems to work out great. So I think in the future I do need to use the MMO as you mentioned. Because I do leave my rigs in the shop for long periods of time and don't run them enough.

Re: Jerky Runner
 

Don't feel alone about that. Folks don't always have time or weather that coincides with opportunity. I have helicopter customers that let them set far too long. It's what keeps money in my pocket though but I worry about them too.