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1932 Plymouth
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Discussion Starter · #1 ·
Hi all new here. I introduced myself in a previous post. I really need some big brains to bounce my problem off of. I have a blown big block with 950 Quick fuel carbs. At first i had the lean backfire issue when stomping throttle on the line. I changed accelerator pump cams and solved that problem. I recently installed a two step and hooked up my trans brake. Now i have an intermittent backfire when i go to get up on the two step. I cant recreate the backfire EVER. It seems to only do it after I do a burnout pulling up to the line and then only sometimes. When it counts most GRRRRR:mad:. Any and all brain storming is appreciated.
 

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Backfire as in popping the blower pressure relief plate or afterfire popping in the exhaust? If it's popping the blower it would seem to indicate a lean condition assuming the engine is healthy and not worn out. When on the two step, the ignition is dropping cylinders to limit engine RPM, the cylinders are still seeing the required metered fuel through the carbs. Is the fuel pump up to the job of supplying the required amount of fuel? Electric fuel pump or engine driven fuel pump?

Keith
 

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1932 Plymouth
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Discussion Starter · #3 ·
Backfire as in popping the blower pressure relief plate or afterfire popping in the exhaust? If it's popping the blower it would seem to indicate a lean condition assuming the engine is healthy and not worn out. When on the two step, the ignition is dropping cylinders to limit engine RPM, the cylinders are still seeing the required metered fuel through the carbs. Is the fuel pump up to the job of supplying the required amount of fuel? Electric fuel pump or engine driven fuel pump?

Keith
Yes it's like a lean pop. Only sometimes. I may have it it figured out. Won't know until I can get back out to the track. 2 things the vent line for the tank had a loop that was holding gas so the tank couldn't breath. Take in air as fuel is pumped to the motor. And pvc hose fit real loose. After getting rid of loop and using tape to make hose fit better made one pass no problem. Hoping that was it🤞. I've been chasing lean problems for awhile now. Should be good there. Thank you for the reply. I will keep you posted.
 

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A loop in the fuel vent line is not uncommon as long as it isn't kinked and the end of the line isn't plugged. The pull of fuel from the tank will siphon the fuel back from inside the vent hose back into the tank.
 

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1932 Plymouth
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Discussion Starter · #5 ·
A loop in the fuel vent line is not uncommon as long as it isn't kinked and the end of the line isn't plugged. The pull of fuel from the tank will siphon the fuel back from inside the vent hose back into the tank.
I checked after a run and it was full. I started blowing out every time thought problem fixed. I'm hoping the vacuum leak was the final piece. If its not I'm open to suggestions. With it being intermittent I'm having a hard time tracking it down. I cant recreate it. Could it be my 6AL box doing random sparks at random times because of the 2 step?
 

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I would not run a pcv. This will be plumbed to the top of the blower / under the carb. You are pulling in acidic oil gasses that will also decrease your octane level. Try changing the squirters up 2 sizes to see how that works. If you are getting a backfire hitting the throttle, it's getting too much air and not enough fuel. Verify your timing as well. Are you launching off an idle or higher rpm with brake? If the throttle is partly open for higher rpm to launch, may not be getting the full fuel squirt causing a lean backfire.
 

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1932 Plymouth
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Discussion Starter · #7 ·
Hi Guys,
I'm still having the same backfire problem and wondering if I should go with bigger accelerator pumps? Any and all feed back is greatly appreciated. Ive included a video.
 

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1932 Plymouth
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Discussion Starter · #9 ·
Cold weather will require more fuel. Did you try bigger squirters? Lean backfire. Initial timing can be a factor too.
I did put bigger squirters still same. I’m thinking bigger accelerator pumps ? I put more timing in it last night. I’m locked out at 29 . Also turned up the idle so. I’ll know here in few if it works . I don’t have this problem when I just foot break it.
 

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1932 Plymouth
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Discussion Starter · #10 ·
I did put bigger squirters still same. I’m thinking bigger accelerator pumps ? I put more timing in it last night. I’m locked out at 29 . Also turned up the idle so. I’ll know here in few if it works . I don’t have this problem when I just foot break it.
Update the idle change seems to have helped along with the timing. Not only did I go 4 rounds i’m running in the 10s 🤙
 
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