Acceleration hitch

[SoCalCoupe]

Car is a '41 Coupe w/ 221 engine, helmet distributor, Skip Haney coil, Tubman condenser, stock fuel pump, and a Eddie Meyer intake w/ dual Stomberg 81s.


It was running really strong a couple of years ago but slowly degraded with less power and a pronounced stumble in acceleration. I was thinking timing so I re-timed it on the KR Wilson timing tool and that was a big improvement. No more stumble under normal acceleration.


But I still have a hitch under heavy acceleration. Not a stumble, but a single momentary hitch like the ignition momentarily cuts out. Of course it could be a fuel problem too.


Anyone else had symptoms like this they were able to fix? Rather than spend hours going through all the possibilities, it would be nice to cut to the chase.


There are several possibilities I can think of:
1. ignition switch contacts
2. low float level
3. water in fuel
4. need more timing advance above specification
5. low fuel pump flow


I had a year-old tank of gas in it back in March because the car was out of commission for a year with the rear end in pieces. The first time I drove it, it was fine, since then I've run the tank down to half full three times and topped it off with fresh gas.


I have an electric fuel pump I use for priming and a fuel pressure regulator with a gauge just before the carburetors. The easiest thing to do would be to check the fuel pressure at the outlet of the stock pump for the 1000n't time, it's always fine. I could then drive the car with the priming pump running to see if that makes a difference. That would point to or rule out the mechanical pump but I don't really think that's it. I was driving it around yesterday but just forgot to try this.


That still leaves four options.


Like I said, just looking for experience that would help me shorten this process.

[glennpm]

4. need more timing advance above specification

I would also check the vacuum advance. It may be exerting too much force and limiting advance.

[Flathead Fever]

Check to make sure the accelerator pumps are squirting. Two carbs squirting on a stock engine might cause a momentary hesitation. If you try to slowly accelerate and it's okay but if you accelerate suddenly and it hesitates then it might have accelerator pump problems, it's not squirting the extra fuel, or the two carbs are squirting too much fuel. It could be a million other things to, but I'd checked that out first. It takes a lot of fiddling around to get multiple carbs dialed in together.

I'm thinking that it's probably not the ignition system if the problem just momentarily happens then recovers. If you let cars with carburetors sit for any length of time (as I do) accelerator pumps can dry out and stop working or the floats needles and seats can stick closed or open. I know because I just fired up my '66 GT-350 for the first time in 10-years. It's going to need a carb overhaul. I had drained the fuel and replaced it. It cranked but wouldn't start. Blew in the carbs hose and it was plugged the needle and seat were stuck closed. I tapped it and it opened right up. I went for a ride, and I made it to the top of the street and ran out of gas; I had to get out and gently tap on the carb again to open it up and let fuel into the bowl. It fired right up and ran out of gas again when I got back to the house. Got out and tapped the carb again and it fired up, then it went back into hiding in the garage, probably for another ten-years. I have too many collector cars that just sit.

[SoCalCoupe]

Added a couple of notches of timing and backed off some more on the vacuum retard screw. Took a test drive and everything seemed awesome.... at first. As I got closer to home, started getting a couple of hitches in acceleration. Stopped on the way back to pick up some stuff. It ran terrible after that. Obviously fine when cold but runs like a dog when heat soaked. As I think about it, that's the way it was the last couple of times I drove it. Just wasn't paying as much attention.

The symptoms sound like the condenser and I'll look into that and hopefully eliminate it as the culprit. I replaced it with another but haven't taken a long drive with a heat soak yet to prove anything.

[tubman]

I believe you may have one if my condensers on your car. If so, and it has failed, I would like it back so we can conduct a post mortem. I have never had one fail before and would like to determine what happened. Of course, I would take care of any shipping expenses involved.

[SoCalCoupe]

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Originally Posted by tubman

I believe you may have one if my condensers on your car. If so, and it has failed, I would like it back so we can conduct a post mortem. I have never had one fail before and would like to determine what happened. Of course, I would take care of any shipping expenses involved.

That’s really generous of you, Tubman — I really appreciate that. For now, I swapped in another one of your condensers just to keep testing. It fired right up. I jumped the gun in my initial post before editing and haven't test things out properly yet.

It’s impressive you’ve never had one fail, and knowing that, I'd be surprised if mine was the first.

Hopefully someone spots something I’ve missed — I get these things wrong all the time.

If it does turn out to be the culprit, I’ll gladly send it back so you can take a look.

Checked all the connections too; everything’s tight.

[Phil Gillespie]

Originally Posted by SoCalCoupe

That’s really generous of you, Tubman — I really appreciate that. For now, I swapped in another one of your condensers just to keep testing. It fired right up. I jumped the gun in my initial post before editing and haven't test things out properly yet.

It’s impressive you’ve never had one fail, and knowing that, I'd be surprised if mine was the first.

Hopefully someone spots something I’ve missed — I get these things wrong all the time.

If it does turn out to be the culprit, I’ll gladly send it back so you can take a look.

Checked all the connections too; everything’s tight.

Hows the state of the coil. Break down when hot? Can happen.
Phil NZ

[hueyhoolihan]

thorough test samples with a laser temp gun when symptoms are present, should provide evidence of over heating if it's the root cause.

that's the process i am now involved in with my '41 with very similar symptoms.

[SoCalCoupe]

Originally Posted by Phil Gillespie

Hows the state of the coil. Break down when hot? Can happen.
Phil NZ

Well, I have the best coil and the best condenser (Skip Haney/Tubman) but to me the symptoms look like an ignition problem. I could be wrong though (wouldn't even be the first time this week.) It pretty clearly gets worse with heat soak. I did an AI search which said it sounded more like condenser than coil because in the machine's estimation, condensers fail slowly while coils fail all at once. So, I'll be starting with the condenser. If that's not the issue, I'll move to the coil. Not maligning these great guys at all, just trying to be logical. They've probably forgotten more about ignition than I'll ever know.


The car doesn't break down and it idles fine. Just under load.


I got tired of playing car since my post speculating about the condenser so I don't have any new information yet.

Originally Posted by hueyhoolihan

thorough test samples with a laser temp gun when symptoms are present, should provide evidence of over heating as the root cause. that's the process i am now involved in with my '41 with very similar symptoms.

That's a good place to look but I don't think overheating is my problem. I went through a lot of drive, stop, check the temp a couple of years ago and found my worst problem was the original(?) 1941 temperature sender. According to my temperature gun, I'm not overheating. Wouldn't hurt to check it again though.


BTW, that temperature gun is one of my favorite tools. Didn't cost much, works great and gives a lot of good information.


I also found a fuel line leak just before quitting time yesterday so I'm even less enthusiastic about playing car at the moment. I seriously doubt that leak has anything to do with my problem but is just yet another annoyance. I think some auto parts guy gave me vacuum hose rather than fuel hose a couple of years ago and the ethanol gas is rotting these things out one at a time. Long story I won't go into here but I have several separate short runs of rubber fuel hose. I'm going to make a mod to get rid of most them all at once next time I touch the car.

[Flathead Fever]

If the hesitation is just at one point and then it goes away above that hesitation spot, I still think it could be accelerator pump or pumps not squirting. With the engine not running, pull the air cleaners and look in the carbs and watch for the squirt of fuel when you move the linkage. As the engine switches from the idle circuit to the cruise circuit it will have a momentary hesitation if the accelerator pump does not provide that extra squirt of fuel. It mechanically squirts while the throttle is moving until the vacuum catches up and starts pulling fuel out of the main metering jets. It would idle fine, then hesitate fall on its face for a second or two when you step on the gas and then straighten out and run great once the main jets caught up with the rpm and opening of the throttle plates. It was big problem at work on carbs that sat around for a long time. The accelerator pump gasket would get hard and not pump the fuel when the pedal was pushed. Some of the pumps on carbs are adjustable by moving the accelerator pump linkage to a different hole in the linkage which makes it squirt more or less fuel. If your carbs are adjustable, try changing the linkage spots. Your two carbs might be injecting too much fuel. You have an accelerator pump designed to squirt enough fuel for an entire engine and when you put two carbs on it there might be too much accelerator pump fuel for it. One thing you can do is get the engine to where the misfire is and squirt some carb spray or propane into the engine and see if the misfire goes away. That's a good way to tell if it's a fuel problem or not. If you could post a video of it that would help a lot. Show the engine idling, then when it misfires and then if it will run okay above the misfire spot. It's hard determining if its fuel, ignition or an engine mechanical problem, it takes a little detective work.

[Lawrie]

One thing no one has mentioned, is oil inside the distributor, when ever I have a misfire in either my 33 or 34, the most often culprit, is oil on the rotor, and or the terminal plates, or the points,
From experience,oil on the rotor or terminal plates will drop a cylinder or two , oil on the points will drop the whole lot , mostly under acceleration from low speed in top gear like coming off a roundabout
I must also say my coil and condenser problems are well sorted, with skips coil and Tubman condenser.
Both are still 6v
Lawrie

[slowforty]

Dont forget the ignition resistor. I had intermittant issues with mine. Drove me nuts as it would not fail completely.

[Planojc]

Just a thought but check the connections on the back of the ignition switch.

[hueyhoolihan]

i just re-read my previous post and revised it. as i did not have any particular reason, and still don't, to think the root cause of your problem is necessarily overheating.

[SoCalCoupe]

Originally Posted by slowforty

Dont forget the ignition resistor. I had intermittant issues with mine. Drove me nuts as it would not fail completely.

Hmmm.... I'll check that; I have another. It's always a suspect.

Originally Posted by Planojc

Just a thought but check the connections on the back of the ignition switch.

Another good one. I've heard more than once that an ignition switch itself will give ignition problems. Hadn't quite figured out what to check though; this is a good start.




In hindsight, the issue points to ignition although with deference to Flathead Fever I haven't done the required testing to rule out an accelerator pump cause.


Given all the experience of the group with Tubman condensers and Skip Haney coils, I'll believe it only if I can prove it that one of those is at fault.


Had to work this week and haven't done anything except fix my fuel leak.

[Flathead Fever]

Something to think about is if you have the chokes hooked up. Sometime when you have a misfire you can make it go away by playing with the choke, it helps when you're trying to figure out if it's a fuel or an ignition problem by richening the mixture when driving. The other thing is I used to use the MAP gas that was made for setting A/F mixtures on smog carburetors. I don't think anybody uses that anymore, but we were required to use them when adjusting carbs during a smog check. I put an extension hose on the MAP gas can go from the inside of the car to the carbs. Then when I was driving it and it starts to misfire, I open up the valve on the can and give it some MAP gas or propane of whatever you have, and I see if the misfire went away. Rarely did I need to do that but every once in a while, I'd get one that kicked my butt trying to figure out what was wrong with it, fuel or ignition???

[SoCalCoupe]

I'm an idiot!


Changed the condenser with another Tubman condenser. Nothing.


Tried pulling out the choke when the engine stumbled. Nothing.


Playing with the plug wires at Cars and Coffee this morning. Found several loose connections. Went home and ran over the plugs with 300 sand paper and crimped the plug connectors with needle nose pliers.


Went to charge the battery and the ground strap on the battery came off in my hand! Cleaned the connection and wrenched it really tight. Duh!


A year ago everything was really, really tight. How did it all come loose?


Think I've got this thing fixed. Another test drive report next week.


So, Tubman condenser and Skip Haney coil, long live the gold standard!

[farmertom]

Originally Posted by Phil Gillespie

Hows the state of the coil. Break down when hot? Can happen.
Phil NZ

I'm having a acceleration hitch under heavy throttle myself on my '37 221 v8. wondering what acceptable temp of coil and condenser should be after a drive to complete warm up using temp gun? Tom.

[SoCalCoupe]

Originally Posted by SoCalCoupe

I'm an idiot!

Playing with the plug wires at Cars and Coffee this morning. Found several loose connections. Went home and ran over the plugs with 300 sand paper and crimped the plug connectors with needle nose pliers.

Went to charge the battery and the ground strap on the battery came off in my hand! Cleaned the connection and wrenched it really tight. Duh!

Think I've got this thing fixed. Another test drive report next week.

OK, car runs better now than it ever has in the four years I've owned it (including when I replaced the battery and hogged down the battery cables.) Idles and runs smoother and has more power. No hint of a stumble or hitch.


Did a test drive that included a heat soak. I think crimping the plug wire connectors and sanding the plug connections did it. Of course, tightening the battery cable didn't hurt.


If I ever find another plug wire again that doesn't have a death grip on it's plug, I'm all over it.

[tubman]

Try Rajah plug ends; they come in straight or 90 degrees versions. They have a very positive grip on both the plug and the wire. They're not Concours, but that doesn't bother me because they work so well. You can get them from The Brillman Company.