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post #1 of 11 (permalink) Old 05-13-2012, 10:33 PM Thread Starter
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Question carb adjustment?

not sure if this is a carb problem, but lets find out:

i think my bike is running too rich. it back-fires anytime i let off the gas. it back-fires alot coasting down a hill in town. does that mean i need to adjust my carbs so it gets less gas and more air? if so, how do i do this?
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post #2 of 11 (permalink) Old 05-14-2012, 01:06 AM
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the back firing is fairly normal for our bike on decel. Coastering and adjusting the air/fuel screws to 2 1/2 turns out helps a lot with it, though after such I still get a little backfiring on decel.

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post #3 of 11 (permalink) Old 05-14-2012, 01:44 AM
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Quote:
Originally Posted by Ndr View Post
the back firing is fairly normal for our bike on decel. Coastering and adjusting the air/fuel screws to 2 1/2 turns out helps a lot with it, though after such I still get a little backfiring on decel.
X2 ,he is right ,the trick here is to make sure you have no exhaust leaks as well and minimizing popping on decel is really about all you can do,pretty hard to eliminate completely on these bikes.
If you don't want to coaster you can stick some marbles in the AIR hoses going to the reed valves,whick brings me to another question .

Would removing the vacuum line that goes to the air valve and plugging it ,keep the valve from opening and thereby not letting fresh air into the exhaust?Might be an easy way to block off the hoses ,just not sending an air signal to the valve to open under high vacuum situations,ie:decel.
Who wants to try it first? I am curious if it would work.




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post #4 of 11 (permalink) Old 05-14-2012, 03:49 AM
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Quote:
Originally Posted by denny6006 View Post
Would removing the vacuum line that goes to the air valve and plugging it ,keep the valve from opening and thereby not letting fresh air into the exhaust?Might be an easy way to block off the hoses ,just not sending an air signal to the valve to open under high vacuum situations,ie:decel.
Who wants to try it first? I am curious if it would work.
I've read a post somewhere on here where someone did something like that. From what I understood from the post, they left the original reed valves in place but removed all the hoses and put a vacuum plug on the valves (same as we put on the right vacuum port of the carb when coastering)
As i understand it, this would be the same as coastering, without spending the money on the blank plates. pretty much just spending $5 on vacuume caps rather then $30 on the coaster. The downside however, would be that the vacuume caps are prone to wear out. (although not likely for quite awhile)

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Last edited by Ndr; 05-14-2012 at 04:01 AM.
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post #5 of 11 (permalink) Old 05-15-2012, 10:18 PM Thread Starter
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well that brings me to 2 questions:

1) where are the "air/fuel screws" and what do they look like?

2) what is this "coastering" you're speaking of? sounds interesting
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post #6 of 11 (permalink) Old 05-17-2012, 09:49 AM
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post #7 of 11 (permalink) Old 05-28-2012, 08:46 PM Thread Starter
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so i got my air/fuel mixture screws to 2.5 turns out, and it runs worse now than before. the throttle response sucks, and it idles down really slow. i assume this means i have bigger problems, but what the culprit is is the question at hand now. is it dirty and need cleaned by a pro or is something potentially broke?

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post #8 of 11 (permalink) Old 05-29-2012, 11:28 AM
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Well first I'd set the airscrews back to where they were and see if it gets better.

Backfiring is usually do to a lean mixture..(but not always)

When say "backfire" do you mean a short run of popping sounds are do you mean one big bang?

You need to check for - air leaks in the carb boots, your air filters and associated hoses, and your gas for contamination.

Popping is normal on this bike, so not sure what your problem here is.... But turning the air screws out should NOT make things worse.

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post #9 of 11 (permalink) Old 05-29-2012, 09:13 PM Thread Starter
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tried again today. on cold engine, everything seemed just fine at 2 turns out. after it warmed up, the throttle response went back to sucking a$$. slow rev, slow wind down. put the air/fuel screws back to where they were (about 4 turns out) and no change (except having to adjust the idle screw).

the backfiring has actually gone away for the most part (as of yesterday when the problem started).

when i say "backfire", i mean popping sounds just in the exhaust. not too annoying really, just don't wanna get people pissed off when i coast down hills in town. i'm told this is normal, and there are ways of making it better (i'll take care of that later, one problem at a time lol)

gas looks fine. ran tank down really low then re-filled it. how do i test for air leaks in the boots, air filters, and hoses?

- 1998 Vulcan 750
- Black with red
- MCCT conversion
- Pick up coil mod
- Stereo with 3.5 inch speakers
- Sylvania ridiculously bright headlight
- Westco maintenance free battery
- Vance & Hines slash cut pipes
- Custom turn signal bracket
- Arrowhead universal turn signals (rear only)
- Kuryakyn longhorn offset highway pegs
- Suzuki Savage 650 rear shocks (2 inches shorter)
- Lowered front 1.5 inches
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post #10 of 11 (permalink) Old 05-30-2012, 12:06 AM
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4 turns out is a heck of a lot with a stock air intake setup.

Check your air filters. Are they dirty, or deteriorating?

You can check for leaks with something that emits smoke, like incense. If you notice the smoke get drawn into a boot, etc, then you know you have an air leak.

The pilot jet(s) could be clogged. You could leave some SeaFoam in your carbs for a few days.

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