VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 34 master misfire under driving

My 34 master have started to misfire under driving. It almost dies, just stuttering and then a misfire out the exhaust so it is ringing in your ears. But then it is happy for maybe the rest of the trip or just 5 min. It is running like it should on idle but it struggles to get rpms and just stuttering and misfire if you try to rev it after start.

The car was fine when I parked it at the upholster after a 300km drive to get there. Picked it up after 4 weeks and then it started acting like this. Tried to clean the carb, but still the same. Ignition is all new and done 600 km, same with fuel lines, rebuild carb and fuel pump, tank cleaned and coated with sealer inside.

Maybe an exhaust valve is hanging up. I would do a compression test.

I would replace the condenser.

Make sure there are no loose connections in the electrical system. Good luck in your quest.

Could be that the Octane Selector and Vacuum Spark Time Control at the base of Distributor. Look at the Check Nut. Has it backed off due to vibration and changed your setting?

Also, I have had people "looking" and adjust that knob before I can say, "look, do not touch my car".


Have you, while motor is ruining and is normal on temperature, pulled out the choke. This may remove things from the carburetor. Then when the motor dies off push back in to normal. Let motor return to normal run. Do this several times. Then see if it cleared your trouble. This may remove water drops or dirt particles.

I have had new parts fail, too. Make sure your plugs are in the hole tight. Or look at the wires and make sure that one has not come out of the hole on the distributor cap.

I am sure you will find a simple thing as it is running. Good luck on it.

New things could fail, but evry single bit of ignition and electrical was new this year during the build 2018-2019. And nothing has come loose. Spark plugs are nice and tight.
If a valve is sticking it is never on idle, only while driving or reving, not sure how the comp test would be while engine is running? Never heard anyone do it while running.
Ignition is spot on when using timing light. The problem happen regardless of engine temp, rain etc. Could run fine for 3-4 hours or just give you [bleeped] and stuttering evry half min for a while.

The car have never liked choke, once you pull it it dies straight away. Never had the need for it either, cold start -4 celsius no problem without choke. But I will try the tip
, but the carb was in pieces and cleaned with compressed air and no change in the problem.

Try this first!

Carburetors go bad over decades; electrical components fail in the blink of an eye.

Carburetors, with few exceptions, have no "personality"; electrical components do.

Jon.

Would not a bad condenser be constant failure or would it come and go like it does?

These type of problems are often the toughest to find. If not found it will eventually cause the engine to not run at all and then you will be able to find the cause. Problem is that often happens in the middle of nowhere.

My first thought is points. If they stick or have a burned spot they can function as described. It is not common but does happen. Second, ignition switch or loose or broken wire in ignition system. Only fails occasionally at first but will get worse with time. Third is sticking valve, could be slightly bent?

Condensers can work/fail, especially new ones.

This is to what I was referring when I mentioned components with "personality".

Remember the old joke (different brand) - "Lucas Electric, inventor of the 3-position light switch - on, off, flicker"

Electrical components are susceptible to moisture, heat, vibration, and probably other issues as well.

Jon.

Okey, then I will order a new one, and get a spare set of ignition parts aswell and try. Wont be weather and salt free roads until May, so I got some time to swap the condenser.

Jon
I refer to "Lucas" as the prince of darkness.....will work properly during test but when needed fails to operate properly.
Tony

Know why the british drink warm beer? Lucas refrigerators. Hendo

It sounds like electrical. If the problem only happens after three to ten minutes into the running of your car; then with out a doubt it will be the coil. It has happened to me. The coil can freeze during the Winter when the temperature is below freezing. Then in the Spring or Summer when the car runs the coil will start to fail as it heats up. It will fail as the heat from the engine causes the coil to heat up also. You may test this by noticing the time when you start the car and when it starts to act funny. Let it cool all the way down and then note the time and run the car again until it messes up. My experience has been at three to five minutes...then it is the coil.

It can act funny right after start up or it can run for 3-4 hours. After it have been stuttering for 5-10sec and had a couple of misfire it can be gone for 1 min or 1 day regardless of engine or outside temp. But only when applying throttle on idle it is good

I have found that recently manufactured coils tend to overheat and internally short. It has happened 10+ times over the past number of years. High ambient temperatures, low engine speed and low vehicle speed are contributors. All I have to do is pour a little water on the coil to cool it down and all is good until the next time. I have learned not to lug the engine on hills to minimize occurrence.

Have you checked your oil level very carefully? If you see your oil level rise up slightly without adding oil....then the fuel pump is broken. If the fuel pump is broken the overflow of gasoline will go into the oil. This will cause the oil level to raise up on the dip stick. It may also be the cause of your problem of the car stop running then being normal.

Also, check the fine filter screen wire that is in the top of the sediment glass bowl that is near the fuel pump. Very fine small sand like particles can get trapped onto the screen and block fuel flow. I have cleaned out my glass sediment glass bowl and forgot to look at the screen wire in the top of the part where the glass bowl presses onto. I found it packed full of very small like sand particles.

If that area is clean and the oil is not rising up on the oil dip stick... I would look at the screen wire inside the carburetor. These are found behind the straight screwdriver slotted round disk plugs on the bottom of the carburetor. You will have to remove the carburetor to see them. I found that mine had partly plugged up with a very fine sand like particles. This caused my car not to run properly. I found this only after I had re-built the carburetor.

Perhaps one of these things is causing your problem. It will be worth looking at if you have not looked.

I concur with Terrill that his may be a good place to look if the electrical change does not help. I had the same problem with an older Italian car. It almost drove me crazy. I was lucky enough to find a mechanic (after several) that went from the fuel tank to the carburetor and cleaned the screens and it took care of the problem. And yes it was fine grains like sand in the screens
Good luck

Oil level has been stabile on half during the 600 km the car has done. Carb, fuel pump was rebuilt 600 km ago and cleaned after the problem started. Fuel tank was washed out and lined with sealer inside. And all piping new, so the fuel system is spotless, no dirt or anything when I cleaned the carb and pump after the problem started. And the problem was still there after the cleaning.
Just some thinking, centrifugal weights in the distributor, can they stick and make it like that? And when it missfire you get a nudge in the whole car and engine that breaks them free again?
The vacuum part is new does its job without sticking.

Been over the electrical system again, and nothing loose and no bad connection. Waiting for new spark plugs and condenser etc complete kit and try it.

I appreciate all inputs, ideas, tips and triks, I guess in the end it comes down to something small that I have overlooked :)

Hi there
I think I had a 1963 GMC with a 292 do almost exactly the same thing. Started and ran fine until it was out on the road. Then it would start missing and bog right down. Barely enough power to pull the truck. Once the truck was cold... same thing all over again. Finally found the problem.

One of the wires to the coil was mostly broken inside the insulation with maybe one strand of fine wire left holding. It worked until things warmed up and the wire got hot enough for the resistance to go up. Then the coil wouldn't saturate enough to fire the plugs with the increased cylinder pressure of an open throttle.
I found it by working my way along the wires, flexing them slightly until I came to a spot where the wire suddenly flexed very easily. In my case the break was just a couple inches back from the coil.

I suspect you may have a resistance issue somewhere as well. I was pretty sure I had an ignition problem due to the way it was working, but it still cost me some time and a coil, condenser, plugs, etc before I found it. Hope your problem is as easy to fix as mine was in the end... Good Luck!

A couple more thoughts:
You don't say what the upholsterer was working on, but check under the dash. They may have been rolling around in there and bumped some wiring under the dash.

Also, does your car still have the Electrolock armored cable? If it does, try running a hot wire straight to the coil and bypass it. If you have a "nearly broken" wire (as per my previous post) inside the Electrolock it's going to be pretty hard to diagnose any other way.

Best of luck
Ole

Okey, the upholstery guy did the whole interior so he could have bumped the wires. It does not have electro lock,but I am running half the original cable from the ignition switch. So it could be that bit. I thought I had replaced all wires,but when you mention it I have 30cm of the old one there.

If you have not inspected the centrifugal weights and springs in the distributor....you could have a weak or broken spring there. Also, this area needs some light oiling, but not enough to splash onto other electrical parts. These weights do effect the advancing of the spark as the car runs faster. This starts to come on at approximately 24 Miles Per Hour (American. Use different if in km..) With the engine not running... A quick check is to move the distributor cap by hand and watch it return to the normal. It should be quick to return as you have placed tension on the weight springs. But looking at them is the best. If it hangs or sticks or is slow to return you have a problem there.

Weights and springs was good. Swapped condenser, rotor and cap and stilk no change. But the edge of the rotor was black and all the points in the cap had 3-5mm with what looked like carbon dust hanging in strings down from them? Never seen that before. What could cause this? Resitance in cables or plugs? I am running coal/graphite cables and correct ac plugs from the fillingstation.