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Occasional carb backfire

Old 01-26-2007, 04:21 PM
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Occasional carb backfire

So I've got the stock air filter back in now cause the bike was running all screwy with the K&N.... Only mod motor-wise is the slipons right now. Occasionally, esp when its cold out, the bike will make a thunk/tap noise and drop 200 rpms and back to a normal steady idle, sounds like a carb backfire. Any ideas what could be causing this? Carbs out of adjustment maybe? Plugs have been done, dont know if the carbs have ever been adjusted or resynched, bike *did* sit for a while (only 11k miles and a 98 model).

Thanks guys....I'm debating playing with the carbs myself but I haven't done much work with carburetors before, I'm an EFI tuning guy more than anything...
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Old 01-26-2007, 09:24 PM
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Sync the carbs and adjust your mixture screws to 2 turns out. That should cure the problem. While you're in there, do the stumble after braking mod as shown on my site.
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Old 01-26-2007, 09:53 PM
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Unhappy

same thing happens to my 98 always when I go to rev hear a pop and spit kinda thing , then goes right back to normal rpm's?have k&n and dynojeted w/tbr pipes. but other than that the power is great is this somethin i should worry about?
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Old 01-27-2007, 03:09 PM
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Well, if it bothers you, fix it. It's a combination lean condition and possible out of sync carbs, as I said. It doesn't take that long to fix. Dealer could probably do it for $100.
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Old 01-27-2007, 03:47 PM
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Appreciate the info.....checked your site out Greg, I'm really debating buying that Twinmax thing and doing the tweaking myself, seeing as I plan to have the hawk for the long haul... I've just never worked on carburetors before, but it seems simple enough....
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Old 01-27-2007, 07:53 PM
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Originally Posted by SuperHawkins View Post
Appreciate the info.....checked your site out Greg, I'm really debating buying that Twinmax thing and doing the tweaking myself, seeing as I plan to have the hawk for the long haul... I've just never worked on carburetors before, but it seems simple enough....
Always does, til ya get in there, that is when I say @%$^%$$% why didn't I just let the pro's do it.....
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Old 01-28-2007, 02:31 AM
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Wink

agreed!
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Old 01-28-2007, 07:45 AM
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Hi! I'm quite new with tinkering around with my bike, just want to ask about the carb adjustments. When you say two turns out, is one turn 180degrees or 360 degrees? Thanks!!
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Old 01-28-2007, 08:51 AM
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Same thing was happening to my 2001. I changed the spark plugs and decided to disable the P.A.I.R. valves when I found one of the reeds had broken allowing hot exuast to enter the air box. No good. Went to the Honda dealership bought a new reed valve and have not heard a hic-up since!
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Old 01-28-2007, 09:04 AM
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the pair system serves two purposes; to clean up the exhaust emissions and to pervent (lessen?) the backfires on trailing throttle.
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Old 01-28-2007, 10:36 AM
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Originally Posted by BIRDOPREY View Post
the pair system serves two purposes; to clean up the exhaust emissions and to pervent (lessen?) the backfires on trailing throttle.
This is true, but a broken reed in a p.a.i.r. valve serves as a window for hot exhaust to enter the airbox constantly, and that can't be a good thing It's worth takeing a look at and while your down ther you can disable the pair valves which make the bike sound a little more pleasant and supposedly run cooler. You can find insrtuctions at Greg's Honda literbikes online.
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Old 01-28-2007, 12:58 PM
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my brand new 05 VTR did this from the day I picked it up.

It's a huge V-twin. Sometimes they backfire.
It isn't easy to make a big V-twin idle.

rob
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Old 01-28-2007, 03:40 PM
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Roisman, 2 full turns, as in 720 degrees.

Birdoprey, with anything other than stock exhaust you will have an increase in popping on decel. Not really a backfire, just the unburnt fuel combusting in the pipes. That's why most disable PAIR, cuz it's annoying, though some think it sounds cool.
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Old 01-28-2007, 04:27 PM
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As long as I know the exhaust pops are PAIR, it's all good. As for the carb backfires, I'm due for a tune and rejet as it is....so maybe I'll just get the twinmax, sync the carbs myself, and throw the K+N back in and take it to have the rejet done.

By the way in that K+N kit, it has these little rubber cap-offs that cover these two inlets, I thought they may have had something to do with a type of EGR system (I'm a car guy okay).....would those be the PAIR inlets?
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Old 01-28-2007, 07:33 PM
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Hawkrider, good to know. now I just have to convince the wife that I have to get slip-ons before they stop making them. you know, the bikes out of production and all...better jump to it...soon. what? yes dear, coming.
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Old 01-28-2007, 08:42 PM
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Originally Posted by SuperHawkins View Post
As long as I know the exhaust pops are PAIR, it's all good. As for the carb backfires, I'm due for a tune and rejet as it is....so maybe I'll just get the twinmax, sync the carbs myself, and throw the K+N back in and take it to have the rejet done.

By the way in that K+N kit, it has these little rubber cap-offs that cover these two inlets, I thought they may have had something to do with a type of EGR system (I'm a car guy okay).....would those be the PAIR inlets?
From memory, I think they run to the carb diaphragms.
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Old 01-28-2007, 08:47 PM
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Originally Posted by shayne View Post
From memory, I think they run to the carb diaphragms.
I should rephrase then....why are they capped off on the K+N?
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Old 01-28-2007, 09:13 PM
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The standard filter has them built in as well somehow I think, so the end result is the same. The K&N just does it with separate caps.

There is no airflow into the engine via these inlets. They just allow the diaphragms to operate.
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Old 01-29-2007, 04:54 AM
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Thanks Greg!!
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