Carb backfire?
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Mountain Pass
Joined: Jan 2018
Posts: 102
Likes: 1
From: Sonoma County, CA
Carb backfire?
So, I've searched the web and this forum and found a few good places to start...but thought I'd try to get some more specific advice on here.
My 351c has been back firing through the carb recently. Did just get a rebuild kit for the Autolite 2100 so it may have something to do with that. I've seen sticky exhaust valve or faulty accelerator pump or timing? Have it set at 10 btdc...it was running kinda rough at 6 so I stepped it up and it runs strong. Just replaced valve cover gaskets and checked the valves...all seem sturdy and set right.
Thing is it only backfires when I punch the throttle. If I ease into it, no problem...but when I hammer on the pedal it pops a few times then carries on.
So...any suggestions?
Would the A/F ratio play a part? Maybe float level?
Any input would help! Thanks!
My 351c has been back firing through the carb recently. Did just get a rebuild kit for the Autolite 2100 so it may have something to do with that. I've seen sticky exhaust valve or faulty accelerator pump or timing? Have it set at 10 btdc...it was running kinda rough at 6 so I stepped it up and it runs strong. Just replaced valve cover gaskets and checked the valves...all seem sturdy and set right.
Thing is it only backfires when I punch the throttle. If I ease into it, no problem...but when I hammer on the pedal it pops a few times then carries on.
So...any suggestions?
Would the A/F ratio play a part? Maybe float level?
Any input would help! Thanks!
Posting Guru
Joined: Jan 2011
Posts: 1,670
Likes: 8
Accelerator pump. With the engine OFF and the ignition key OFF, pull the air filter off, look down into the carb and pump the throttle. You should see a STRONG shot of fuel pumping down into the carb.
If you do not, your pump is most likely bad.
Need a rebuild kit...
If you do not, your pump is most likely bad.
Need a rebuild kit...
Thread Starter
|
Mountain Pass
Joined: Jan 2018
Posts: 102
Likes: 1
From: Sonoma County, CA
Accelerator pump. With the engine OFF and the ignition key OFF, pull the air filter off, look down into the carb and pump the throttle. You should see a STRONG shot of fuel pumping down into the carb.
If you do not, your pump is most likely bad.
Need a rebuild kit...
If you do not, your pump is most likely bad.
Need a rebuild kit...
Logistics Pro
Joined: May 2015
Posts: 4,463
Likes: 954
From: Tri Cities, TN
2100D
So, I've searched the web and this forum and found a few good places to start...but thought I'd try to get some more specific advice on here.
My 351c has been back firing through the carb recently. Did just get a rebuild kit for the Autolite 2100 so it may have something to do with that. I've seen sticky exhaust valve or faulty accelerator pump or timing? Have it set at 10 btdc...it was running kinda rough at 6 so I stepped it up and it runs strong. Just replaced valve cover gaskets and checked the valves...all seem sturdy and set right.
Thing is it only backfires when I punch the throttle. If I ease into it, no problem...but when I hammer on the pedal it pops a few times then carries on.
So...any suggestions?
Would the A/F ratio play a part? Maybe float level?
Any input would help! Thanks!
My 351c has been back firing through the carb recently. Did just get a rebuild kit for the Autolite 2100 so it may have something to do with that. I've seen sticky exhaust valve or faulty accelerator pump or timing? Have it set at 10 btdc...it was running kinda rough at 6 so I stepped it up and it runs strong. Just replaced valve cover gaskets and checked the valves...all seem sturdy and set right.
Thing is it only backfires when I punch the throttle. If I ease into it, no problem...but when I hammer on the pedal it pops a few times then carries on.
So...any suggestions?
Would the A/F ratio play a part? Maybe float level?
Any input would help! Thanks!
Thread Starter
|
Mountain Pass
Joined: Jan 2018
Posts: 102
Likes: 1
From: Sonoma County, CA
Thanks for that shop manual description, need to get me one of those! I will cut the end of the valve off. So, 20 to 25 degrees at 15" of vacuum? As far as the power valve...is there a way to test it or what are the symptoms for a failing one?
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Logistics Pro
Joined: May 2015
Posts: 4,463
Likes: 954
From: Tri Cities, TN
Yes, with the vacuum advance hooked up and working you should see about 20 to 25 degrees of advance at idle. If the power valve fails it will cause a very rich condition. The easiest way to tell if it has gone bad is to start the engine let it warm up. Then turn the idle mixture screws in until they gently seat, keeping track of how many turns you move them so you can put them back, if the engine continues to run the power valve has likely gone bad.
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Thread Starter
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Mountain Pass
Joined: Jan 2018
Posts: 102
Likes: 1
From: Sonoma County, CA
Yes, with the vacuum advance hooked up and working you should see about 20 to 25 degrees of advance at idle. If the power valve fails it will cause a very rich condition. The easiest way to tell if it has gone bad is to start the engine let it warm up. Then turn the idle mixture screws in until they gently seat, keeping track of how many turns you move them so you can put them back, if the engine continues to run the power valve has likely gone bad.
Thread Starter
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Mountain Pass
Joined: Jan 2018
Posts: 102
Likes: 1
From: Sonoma County, CA
OK, took the carb off today and cut the umbrella valve...also reset the float to the correct level. Still backfires when punching the throttle, though slightly less it seems. Haven't hooked up the vacuum gauge yet or checked the power valve...but will tomorrow. Would the faulty power valve be the cause of backfires...or would it just cause the rich condition?
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