29RoadsterAU

1929 Chrysler Roadster backfires and dies under load.

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Hello from Australia.

First time on the forum, looking for some help with my father's pride and joy.

Recently his 1929 Chrysler with a Flathead 6 has become undrivable. Starts and idles just fine, he gets it going and into top gear just fine, but as soon as he comes to a hill, there's a backfire under throttle that ends up making the vehicle die and results in a tow home.

 

Thinks we've tried:

- Plugs cleaned and Gapped correctly.

- Distributor thouroughly cleaned and checked for wear.

- Points checked.

- Leads are good.

- Tried a spare Distributor and Coil with no difference.

- Carby dismantled and rebuilt, everything adjusted correctly.

 

Now everything I've mentioned was done by my father whom is by no means a mechanic, but very experienced, just not so with Pre-war stuff.

Anything not listed we've not tried.

 

He's talking stripping the motor to check the timing gear that he believes is the culprit, I'm not so sure.

 

Thank you all in advance, I'm hoping we can get to the bottom of this gremlin soon and get dad back in his pride and joy.

 

Cheers, Jarrod.

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One step at a time. Backfire is only caused by valves being stuck open, burnt, or from an ignition issue. Lean burn misfire from a vacuum lake can cause a similar symptom. Do a compression check before you take anything apart. Do not GUESS, diagnose the issue. Sounds like it’s running out of fuel, and misfiring from a lean condition and then stalls and dies. Don’t change anything. One thing at a time. Please give more detailed info.........Car was fine? New issue? Or newly rebuilt and never run right? 

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If I were you, I'd listen to Ed. He has A LOT of experience with pre-war cars.

If it starts and runs fine it is very unlikely that valve timing is the problem. You might have an ignition timing issue but you don't need to take the engine apart to find that.

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2 hours ago, edinmass said:

Sounds like it’s running out of fuel, and misfiring from a lean condition and then stalls and dies.

This is exactly what happened in my 48 Plymouth.  Took the tank out and found the pickup screen plugged so when you were drawing alot of fuel it would starve,  let off and the sediment would fall away from the pickup screen so it would then run until under a good load again.  Ironically it didn't have much junk in the fuel filter as it wasn't getting past the pickup screen. 

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I would certainly check in all the fuel places.  there could be several things such as auburnseeker had that could limit the amount of fuel getting to the carb .  What kind of fuel pump does this car have?

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Certainly sounds like fuel but just another thing that comes to mind maybe condenser ? 

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I have never seen a bad coil or condenser cause a backfire.

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Posted (edited)
2 hours ago, edinmass said:

I have never seen a bad coil or condenser cause a backfire.

 What Ed said ! 

 

The engine will quit under load as increased cylinder pressures of uphill load put more strain on the ignition system, but since the valves and fuel are still good, no back fire, just no spark. If anything, the ignition cutting out   might cause a muffler explosion in a hot exhaust system, but not a back fire.  (For those that don't know. technically, backfires are not out the back. They are back through the intake system. )

 

Valve guide(s) getting too tight under increased heat of load and sticking open, or fuel starvation under load. 

 

Had it happen with bronze intake valve guides and too little valve stem clearance. The cylinder head got hotter and expanded more with the uphill increased load. That slightly hourglassed the guides enough that some of the valve stems were binding and started to stick open. Reamed them  for a bit more clearance and it never happened again.

 

Some of the cars in the 1920's didn't have a screen on the end of the gas tank pickup tube - just an open ended tube. I've had a case of the gas tank rust scale temporarily cut off the fuel because fuel suction and gas sloshing stirring up the scale and it accumulated at the pickup tube, as mentioned above. But it never prevented the car from restarting and getting home on it's own because once the engine died, the scale would drop back to the bottom of the tank until the next round of fuel suction and sloshing motion stirred it back up to the pickup tube again. A bit stop and go, but never needed a tow.

 

Paul  

Edited by PFitz (see edit history)
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Had the pickup tube scale blocks happen to me also . Nothing small enough to get to filter . As auburnseeker and PFitz said .

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Are we trying to fix a "backfire" (lean fuel mixture firing back through the carb) or an "after fire" (rich fuel mixture firing in the exhaust {usually muffler} caused when the unburnt fuel ignites).

Many many people use backfire instead of after fire.

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58 minutes ago, Tinindian said:

Are we trying to fix a "backfire" (lean fuel mixture firing back through the carb) or an "after fire" (rich fuel mixture firing in the exhaust {usually muffler} caused when the unburnt fuel ignites).

Many many people use backfire instead of after fire.

Yep I guess when I suggested condenser I was assuming it could be either because I have only ever heard a few people say after fire. I know I should never assume anything as I remember my brother telling me years ago to assume is to make a ass of u and me 😁.

On the fuel pick up line being blocked a story that Dad told to me comes to mind about a new header they had that would run fine for while and then for no apparent reason stop. The dealership mechanics were puzzled they had tried all sorts of remedies then one old timer told them to clean the tank out and inside was a big moth that must have flown in while they were refueling one night, ever since Dad has been keen on refueling machinery at night 

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I would try an alternative fuel source, Hook up the boat tank, Every shop should have one.

 

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On ‎7‎/‎6‎/‎2019 at 3:36 PM, hchris said:

Are you running a vacuum tank ?

 

Questions like this need to be answered by the OP.  Waste of time if the OP does not respond.

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Hello to all, 

 

I sent him a PM and got a reply, and yes it was a fuel problem apparently the fuel pump is faulty, they have ordered a new one and now waiting delivery.

Here is the car in question with the proud owner.

 

IMG_2127.JPG

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