VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 rough acceleration - UPDATE

UPDATE: Since my last post I have replaced the fuel tank, sending unit, fuel pump and filter. All of the lines have been cleaned out, the carb was professionaly rebuilt...I think I can positively rule out the fuel system as the problem. Next I replaced the vacume advance. The distributor is moving slightly now when accelerating as it should...unfortunatley I'm still having the same problem. It idles PERFECT but once I rev it up high or attempt to drive and get to 10mph it stumbles, won't accelerate and feels like it has a bad miss. All of the plugs, wires, cap and rotor are new, gapped correctly and good to go so I'm stumped. Any other suggestions?

Replace the condenser. If the problem persists, remove and clean the carburetor.

Seeings how the fuel system is in good order and the ignition is in good order. About the only thing left is the choke and timing.How about the choke? Timing?
Charlie

Check the wire that goes from coil to points. I had one with an open inside the distributor. It would cut out when the vacume moved the distributor.

In addition to the condenser, check the dwell. Insure everything in the distributor is secure.

I have had bad spark coils act just like that, the engine would idle but not rev up or pull. Try another coil to rule out that possibility.

I'm running out of options...I oiled the fuzzy under the rotor in the distributor, replaced the condensor, checked the timing (dead on), the coil is fairly new but tomorrow I will try another and see if it makes a difference. Someone mentioned possibly a head gasket? It's never overheated. The only work that was done prior to this problem was the rocker arm and push rod replacement. The rocker arm was replaced with one of an identical number for that location, push rod replaced with one of identical size / shape...it ran fine just after that but can't remember if I took it out on the highway. I'm sure I at least went to Sonic after that repair so it would have gotten up to 30mph fine. If memory serves me though, that was the last time it was on the road. When replacing the rocker arm and pushrod I used some marvel mystery oil to sit in that valve for a few days prior to the repair...hmmm

I recently had what sounds like the same problem develop on my '52 while on a short freeway drive. Thought I wasn't going to get it home, but finally did. Went through every system, just as you have done, with no sucess. Out of ideas, I removed the carb and replaced it with another, and, the problem was gone. I haven't determined what the problem was; previously ran fine; intermediate curcuit had to fail. I'm now adding a product to remove and minimize varnish buildup to my fuel. Guess only time will tell if the problem reoccurs.

Had the same problem with my 48.

After pulling out the last hair on my head, also had 2 "professional" rebuilt carbs on car and to no avail. Ended up buying used carb and problems were solved.

Will agree 100% with Ray (he is top notch) and gpallen2. Probably should try different carb. Know anyone that has a good running car with 216 in it that would let you swap carbs to try it?? Doesn't take very long. Just a thought and LOL.

Jim.

I did some more testing...the car is tuned in great, like I said it idles like a champ and starts on a dime every time but upon acceleration it feels like it's missing. The tailpipe sputters, engine shakes and when driven will only get up to 10-15mph.

I noticed when the timing light is on and the engine is reved up, the light will start to fade out and the RPM guage will drop to 0, then up to 1900 for a brief moment and back down to zero...so I'm guessing my problem is spark or lack there of when accelerating so we pulled the distributor, dissasembled, cleaned, replaced and retuned it but with the same results. I even tried a different cap/rotor/points/coil/condensor etc. with no luck...each cylinder has the same effect, the spark appears to weaken and dissapear upon acceleration.

Any other ideas?

Did you check the spring tension on the points? If it is weak then the points can "bounce".

Another thought is a bad ground or other electrical connection. Apparently as the speed increases the voltage or current decreases to the ignition system. A increase in resistance in a connection can cause it. V=IR

How old is the fuel??

hoppy

spring tension to the points is fine - ground is good but I will double check all areas of electrical system this week...

gas is fresh, fuel system has been completely replaced over the last month or so as a result of this problem so I've ruled out fuel...

You didn't indicate it but did you try switching out the carb with a known good one?

After a review of your posts over the past several months, I believe your problem is in the carburetor.

A while back you posted "My 52 Styleline was parked for a few months then had the carb rebuilt, fuel pump replaced, lines cleaned, plugs, wires, cap and rotor changed etc. (routine maintenance up to date)" and that it ran well before being parked. The natural conclusion is that something changed (or you changed) that caused the problem. The recent checks and replacement of the ignition system have failed to change the situation. That takes us back to the carburetor or fuel pump. I vote carburetor. I have had to rebuild carburetors that were "rebuilt" by national advertising rebuilders because they were not as good as their charges to the customer would indicate.

No, I have yet to locate a known working 1bbl carb...There are a few on eBay in less than desireable condition but I'm holding out for something local to pop up...I'm still thinking electrical with the weak spark at each cylinder on acceleration. I'm going to get back into it tomorrow while the weather is warm. Too many projects going at the same time :)

Maybe MrMack has an extra that he could loan you. He is only ~100 miles from Austin and understands "Rochester" better than I do.

Have you tried by passing the ignition switch by running a jumper wire direct from the battery to the coil? It would be nice to try another carburetor so you could narrow it down to either fuel delivery or ignition circuit. I know you have tried a lot of different parts but it is possible to have 2 parts that are both defective, that will really mess with you!

There lies the problem with replacing several parts at one time ..... which one is the culprit?????

I've been unable to mess with the car in recent weeks but I tried bypassing the ignition switch and running a wire from the battery to the coil but get the same results, no difference at all. I'm fairly certain it's not fuel related due to the spark weakening on acceleration, the tach drops to zero the harder you accelerate and the spark plug tester installed between the plug and wire eventually dims to nothing...When it's idling or on a light acceleration (very light) it gets good spark, the light is bright, and the rpm's are good...I went ahead and bought a new cap/rotor/plugs/coil just to be on the safe side and completely rule all of that out. The distributor has been pulled, cleaned, and reinstalled, points re-gapped, dwell set.... I'm going out on a limb now and bought a new horn relay knowing that alot of the circuitry passes through there. Could the firewall mounted voltage regulator be an issue? Everything is original and remains 6volt.

Hmmm, If you have done all of that including a hot wire from the battery to the coil I doubt that the relay or regulator are going to make any difference. You should have by passed them when you ran the hot wire to the coil. The only thing left on the ignition that I can think of is something going on inside the distributor such as a broken wire from the coil to the distributor or something changing the points gap when you accelerate. I am starting to think the guys maybe right about the carburetor being the problem.

Ok, here's the latest discovery...I used a multimeter and confirmed everything is within spec EXCEPT when testing the ground wire that runs from the coil to the side of the distributor. The coil shows approx. 3 volts when testing the ground wire noted AND it drops to 0 when accelerating! The wire is new so I narrowed it down to the bolt that runs through the distributor. It has two insulators on either side where the bolt runs through, somewhere in there appears to be my problem. If I test the coil but bypass the wire going from the coil to the distributor and just use the ground from the battery I get 6+ volts. Unfortunately, I did all of this right before coming to work so I will have to wait until tomorrow to do some more testing. The ground from the battery to the block is fine, cable is new, no rust or paint in the way on the block...Also, if I remember correctly, the coil was mounted upside down on my engine years ago when original. I have it mounted right side up, that shouldn't make any difference right? Thanks again for all of the help here.

I am thinking out loud here! Since the volt meter measures the potential difference between two locations and current is only flowing when the points (ignition switch) are closed, the voltage measured should drop as the engine speed increases. To put it another way, in a given time period the points are effectively in the closed position more. So what you found is normal.?

Guess I need to go to the shop and test this to see if I know what I think I may know.

Whether the coil is right side up or not only makes a difference if water is dripping on it. Hooking up the wires correctly can make a big difference.

If I am thinking right, the only time that wire is grounded is when the points are closed and you should not get any voltage reading when the points are open. If you get voltage with the points open you must have a short in the insulators that the bolt goes through. I am not sure as I don't recall ever testing that way. If you unhook the - wire from the coil and have the points open you can test from a ground to the distributer wire with an ohm meter and you should not get a reading.

The factory mounting of the ignition coil is with the high voltage coil/dist wire at the BOTTOM side of the coil.