Backfiring through carb
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Novice
Joined: Oct 2013
Posts: 16
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From: Indiana
Backfiring through carb
Well, now that we've been formally introduced, I already need a little help from the Evo clan!
The 87 Softail had been sitting for nearly a decade. So I rebuilt the carb, and it starts and runs fairly well, with 2 exceptions. The big one being, at low rpm, it backfires through the carb. I first notice it when it's warming up with the enricher pulled out. When it's idling low, and almost about to die, I'll give it a little blip of the throttle and hear it suck air, then POP! I've also noticed it when shifting gears (especially when going slow up an incline). I'm assuming it's running a little lean, but I'm not sure what my steps should be for troubleshooting it.
My second issue is, once it's warm up, it doesn't return to lower rpm quickly. If I roll the throttle a bit, then let go, it's slow to return to idle. It's only running a single throttle cable, so I thought it may be friction in the housing, but I don't really notice it until it's warmed up enough to run without the enricher pulled.
Any suggestions will be greatly appreciated! Thanks in advance!
(A couple details I should have included. It's a Mikuni carb, and I did not change the jets. I only see one vacuum hose that runs from the back of the carb, to something behind the horn. The vacuum hose is a pretty loose fit.)
The 87 Softail had been sitting for nearly a decade. So I rebuilt the carb, and it starts and runs fairly well, with 2 exceptions. The big one being, at low rpm, it backfires through the carb. I first notice it when it's warming up with the enricher pulled out. When it's idling low, and almost about to die, I'll give it a little blip of the throttle and hear it suck air, then POP! I've also noticed it when shifting gears (especially when going slow up an incline). I'm assuming it's running a little lean, but I'm not sure what my steps should be for troubleshooting it.
My second issue is, once it's warm up, it doesn't return to lower rpm quickly. If I roll the throttle a bit, then let go, it's slow to return to idle. It's only running a single throttle cable, so I thought it may be friction in the housing, but I don't really notice it until it's warmed up enough to run without the enricher pulled.
Any suggestions will be greatly appreciated! Thanks in advance!
(A couple details I should have included. It's a Mikuni carb, and I did not change the jets. I only see one vacuum hose that runs from the back of the carb, to something behind the horn. The vacuum hose is a pretty loose fit.)
Last edited by theundeadelvis; Oct 19, 2013 at 06:56 PM. Reason: Added some info
Elite HDF Member
Joined: Oct 2005
Posts: 3,872
Likes: 83
From: Canton, Michigan
More likely the hose for the VOES. His 87 probably has the manual fuel petcock.
In addition to the carb seal, I would also check the manifold seals for leaks.
In addition to the carb seal, I would also check the manifold seals for leaks.
Seasoned HDF Member
Joined: Sep 2010
Posts: 10,237
Likes: 799
From: Indiana
I don't think I ever said this to you, but, WHY YOU !@#$%&**&*(&($*%#$^%!@#$!@%$&$&^&@#!$$~@!^@$%&^*() ^*((%$%^!#$
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Novice
Joined: Oct 2013
Posts: 16
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From: Indiana
Thanks to both of you! I'll probably just replace that seal and eliminate it from the equation. I looked up a pic of the voes, and that's definitely what it goes to.
What's the best way to check the intake? Can I just spray some carb cleaner around them and see if it gets sucked in?
What's the best way to check the intake? Can I just spray some carb cleaner around them and see if it gets sucked in?
Seasoned HDF Member
Joined: Sep 2010
Posts: 10,237
Likes: 799
From: Indiana
That would be........
and 
SIR.............
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Road Master
Joined: Apr 2009
Posts: 1,123
Likes: 43
From: NJ
spray the carb cleaner on them while it's idling, if the idle changes then they are leaking, usually it idles faster with carb cleaner and leaking seals...
Ds
Ds
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Elite HDF Member
Joined: Oct 2005
Posts: 3,872
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From: Canton, Michigan
On a bike that's sat for ten years, more than likely things have dried up.
Trust me, I've been sitting for the last decade, and... Well... You know....
Traildog: I figured you were a diet soda sorta guy...
Trust me, I've been sitting for the last decade, and... Well... You know....
Traildog: I figured you were a diet soda sorta guy...