Author Topic: Engine backfire through carb  (Read 143 times)

Offline MWilley

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Engine backfire through carb
« on: July 01, 2019, 08:44:46 am »
Looking for some help! My son and I are new this year to Legends. Bought a used car and everything was great for 3 races. 2 races ago at the end of a run the motor sputtered and backfired through the #3 carb destroying the air filter. Checked valves, tightened carb clamps, changed plugs and wires. The motor sounds great in the pits but when it is on the track and hot there is a ?fluttering? sound down the straightaways and the backfire keeps happening. This last race we borrowed a new set of carbs and it sounded great for about 10 laps and then backfired again and the ? fluttering? came back.
Any thoughts or ideas before I pull the motor to have the top end rebuilt??
It?s a sealed 1250, red ignition.
Thanks



Offline MWilley

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Re: Engine backfire through carb
« Reply #1 on: July 01, 2019, 11:10:04 pm »
Sooo I found the problem!! Did a compression test and with the carbs off and had air pumping out of the intake on cylinder #3. Yeah at only 60lbs I can see why we sounded like a steam engine!! Lol Yankin the motor and sending it up to Vegas for a top end rebuild. Thanks for all of your help. Lol

Offline justfreaky

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Re: Engine backfire through carb
« Reply #2 on: July 02, 2019, 01:51:54 am »
Thank you for the update. Sorry that I had no answers for you.
Best of luck to you!

Steve
Better to be hated for who you are, Than to be loved for who you are not.


Offline MWilley

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Re: Engine backfire through carb
« Reply #3 on: July 03, 2019, 09:02:04 am »
Thanks Steve. Yeah I hope this helps anyone else with this issue. After talking to the guys in Vegas the motor is going back east to ULSCI for a full rebuild and the carbs are going to Hank Scott. Any suggestions on proper break in once I them back?
Thanks

Offline Legends57x

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Re: Engine backfire through carb
« Reply #4 on: July 03, 2019, 11:05:48 am »
The USLC engine shop will normally supply you with easy to follow list of instructions for proper break-in with the proper engine oil after rebuild.

Good luck!
Mark Ritger
INEX Legends #1x

Offline Tom Cole

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Re: Engine backfire through carb
« Reply #5 on: July 04, 2019, 01:20:02 pm »
FYI, the valve seats on these engines often get beat into the head which closes up your valve lash.  The problem you are describing is a symptom of this.
 It robs you of compression and if it is on an intake valve, you can lose port pressure...essentially pushing air the wrong way into the intake.  Both kill power and RPM.  You change the little pucks in the top of the spring caps to set the lash, but there is a minimum thickness on these pucks before they become a liability themselves.  Once you are at that point, the engine will have to go back to the builder for valve work because that part is under the seals.

Offline MWilley

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Re: Engine backfire through carb
« Reply #6 on: July 07, 2019, 08:33:10 pm »
Thanks for the info guys, I did change the puck on that intake before the race to get it back to .006 after noticing it was down to .003. It didn?t seem to make a difference and after a couple of practices we noticed it sounded like it was only running on 3 cylinders and the #3 cylinder header was about 100 degrees cooler than the rest. The new carbs brought the car to life a 1 practice and about 10 of the race.  I think we had a combination of things goin on.
My son still ran his fastest yet on 3 cylinders..LOL
This is our first experience having to send a motor out to get fixed. It?s all boxed and ready to go. I?ll keep guys updated when get everything back and get to running again.
Thanks


Offline MWilley

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Re: Engine backfire through carb
« Reply #7 on: Yesterday at 11:08:50 pm »
Ok, got the carbs rebuilt from RRC. Had the wrong jets,springs and was told that the butterflies were closing back to 3/4 open when fully open. I had checked to make sure the throttle pedal stopped when the carbs fully opened when I bought it...I should have looked at the butterflies. Engine is back at USLCI should here something soon.

 

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