I've trying to get my choke set properly. 70 RR 440 six barrell. When I start it up cold. I set the choke & get a small backfire thru the carb when i start it. Is the choke set to tight or is it open too much ??
Backfire thru carb
- Thread starter clazar
- Start date
Rusty knuckles
Well-Known Member
Generally speaking I use the guideline that popping through the carb is lean condition. So fatter jets or more choke.
R413
Well-Known Member
Are you pumping the gas while cranking the engine? That will make it pop quicker than anything.
First pump the gas to set the choke and squirt fuel down the intake. Then remove you foot from the pedal and turn the key to start it.
First pump the gas to set the choke and squirt fuel down the intake. Then remove you foot from the pedal and turn the key to start it.
I pump the gas to set the choke & start the car. It does a little backfire & starts.
it's closing all but 3/16".
topside
Well-Known Member
Where's the timing set ? Every Mopar I've owned liked more initial timing, though not more than 36 total (mechanical).
And the "bigger" the cam, the more initial they liked. Dead stock, 10-12 degrees initial wakes 'em up.
And the "bigger" the cam, the more initial they liked. Dead stock, 10-12 degrees initial wakes 'em up.
Stock cam. 36 total all in, 10 initial. I believe it's choke & fast idle start up setting.
If I’m not mistaken, that engine has a divorced choke and a vacuum pull off to pull the choke to position as soon as the engine fires. The pull off may be pulling the choke open a little too far, leaning out the mixture. You may need to bend the connecting rod a bit so it doesn’t pull it quite as far open.
However, if it’s backfiring as soon the engine first cranks this probably isn’t an issue as vacuum would not have developed yet to operate it. In that case the choke valve might need to be closed a little more when the choke/fast idle is first set as noted above.
Kind of surprising it would need much choke to start in this summer weather though. I have the chokes on my garaged cars set pretty lean to avoid overly rich start up. Does it fire immediately when starting it cold or does it take a lot of cranking? Todays fuel evaporates out of these old vented carbs really quickly anymore and for that reason I usually prime my carburetors before trying to start them. If it’s only been a couple days since driving one, sometimes I’ve tried to crank them and pump the gas between cranking to get it to start. Sometimes it will not quite get primed sufficiently from cranking and will cough or even get a small backfire due to the lean condition. Holleys are easy to prime with a squirt bottle through the bowl vent. I look down the throat and I quit priming as soon as I see fuel drip on the blades. Pump the gas twice, hesitate a couple seconds and hit the key and it will fire right up and run clean & smooth.
However, if it’s backfiring as soon the engine first cranks this probably isn’t an issue as vacuum would not have developed yet to operate it. In that case the choke valve might need to be closed a little more when the choke/fast idle is first set as noted above.
Kind of surprising it would need much choke to start in this summer weather though. I have the chokes on my garaged cars set pretty lean to avoid overly rich start up. Does it fire immediately when starting it cold or does it take a lot of cranking? Todays fuel evaporates out of these old vented carbs really quickly anymore and for that reason I usually prime my carburetors before trying to start them. If it’s only been a couple days since driving one, sometimes I’ve tried to crank them and pump the gas between cranking to get it to start. Sometimes it will not quite get primed sufficiently from cranking and will cough or even get a small backfire due to the lean condition. Holleys are easy to prime with a squirt bottle through the bowl vent. I look down the throat and I quit priming as soon as I see fuel drip on the blades. Pump the gas twice, hesitate a couple seconds and hit the key and it will fire right up and run clean & smooth.
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