Carb boots and exhaust gaskets - SuperHawk Forum


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Old 11-01-2017, 05:28 PM   #1
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Carb boots and exhaust gaskets

My bike ran fine until I let it sit too long. So I cleaned the carbs, did the PAIR valve flip, TPS, and carb sync. I now have a backfire out of the exhaust. The bike runs mostly fine....except for the embarrassing pops out the back end.

I believe I am chasing a lean issue with my bike. I have replaced the carb boots but when I test spray for leaks with carb cleaner the RPM's jump. I am wondering if there is such at thing as tightening the boot clamps too much? Should the clamp be tightened until both ends are touching or is there a gap?

Onto the exhaust gasket, I noticed if I spray carb cleaning where the pipe meets the head I get a slight jump in RPM as well. However, if I do a smoke test around the area, I don't see the smoke being moved by an exhaust leak. Do you think this is a problem?
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Old 11-01-2017, 07:25 PM   #2
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I honestly don't think you could over tighten those clamps. I probably shouldn't say that. Where there's a will, there's a way. Are you sure the carbs are down in them the whole way?
And the exhaust thing, smoke should be disturbed with a leak. Is it possible the spray is finding it's way to your intake issue?
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Old 11-01-2017, 08:25 PM   #3
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Quote:
Originally Posted by sdhawkrider View Post
My bike ran fine until I let it sit too long. So I cleaned the carbs, did the PAIR valve flip, TPS, and carb sync. I now have a backfire out of the exhaust. The bike runs mostly fine....except for the embarrassing pops out the back end.

I believe I am chasing a lean issue with my bike. I have replaced the carb boots but when I test spray for leaks with carb cleaner the RPM's jump. I am wondering if there is such at thing as tightening the boot clamps too much? Should the clamp be tightened until both ends are touching or is there a gap?

Onto the exhaust gasket, I noticed if I spray carb cleaning where the pipe meets the head I get a slight jump in RPM as well. However, if I do a smoke test around the area, I don't see the smoke being moved by an exhaust leak. Do you think this is a problem?
Is it backfiring at idle? Under acceleration steady cruise or deceleration?
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Old 11-02-2017, 11:33 AM   #4
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Is it backfiring at idle? Under acceleration steady cruise or deceleration?
It backfires at low rpm cruising speeds and deceleration. Somewhere in the 3000 to 4000 RPM range. It will pull fine on acceleration and doesn't backfire at all.
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Old 11-02-2017, 11:39 AM   #5
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I honestly don't think you could over tighten those clamps. I probably shouldn't say that. Where there's a will, there's a way. Are you sure the carbs are down in them the whole way?
And the exhaust thing, smoke should be disturbed with a leak. Is it possible the spray is finding it's way to your intake issue?
I thought the same thing with the clamps but I have snapped one and distorted another. Both were replaced with new ones. That's what got me thinking that maybe if they are too tight, they distort and don't seal properly. The carbs are sunk in place properly.

With the exhaust issue, I am thinking you might be onto something. When I spray it, it obviously vaporizes and maybe those vapors are working their way my intake issue.
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Old 11-02-2017, 03:22 PM   #6
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Too tight? The torque listed in the service manual is .7lbft. So yeah maybe it was too tight when the band was distorted and broke.
Also sounds like you have an exhaust leak at the head (maybe). The joint nuts that hold the exhaust are ones that you really don't want to f' u. Snap a stud and the crying will begin They are only 9lbft.
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Old 11-06-2017, 08:22 PM   #7
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It backfires at low rpm cruising speeds and deceleration. Somewhere in the 3000 to 4000 RPM range. It will pull fine on acceleration and doesn't backfire at all.
Where are your mixture screws set at? What size slow speed jets?
The way you describe it it sounds almost as if you have air leaking in through your pair valves.
But lean on the slow speed circuit can cause it also.
I would suggest recheck your carb settings, and the pair valve mod . If you have an intake leaking usually you have erratic and not very smooth idle, and you blip the throttle it will tend to hang a bit before returning back to idle.
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Old 11-07-2017, 01:09 PM   #8
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Where are your mixture screws set at? What size slow speed jets?
The way you describe it it sounds almost as if you have air leaking in through your pair valves.
But lean on the slow speed circuit can cause it also.
I would suggest recheck your carb settings, and the pair valve mod . If you have an intake leaking usually you have erratic and not very smooth idle, and you blip the throttle it will tend to hang a bit before returning back to idle.
​​​​​
It's an air leak for sure. Mixture is at 2.5 turns out. If I go richer, it pops more. The hotter the bike, the more the pops. The idle does seem to be erratic. I have to adjust the idle screw almost every time I start the bike and I do get a hang in the RPMs when the throttle is blipped.

On the PAIR, I added a vac line to the PAIR Valve nipple and blocked it off. I also blocked off the vac line from the carb that use to connect to the PAIR Valve. I assume that was the correct thing to do? I do wonder if all my vac lines are hooked up correctly. My bike is a California model so it has a extra Pulse Air System. So does the PAIR get hooked up from the Carb, and the secondary system get hooked up from the port on the front cyclinder used for carb syncing?

Since my last post, I have replaced the front boot.... again. Still the RPM's bump when test spraying carb fluid at them. Still getting the pops. They get worse as the bike warms up. I am so frustrated and so close to trying to seal the carbs up with liquid gasket. I think I might give up and take it to a shop.
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Old 11-08-2017, 09:19 PM   #9
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Originally Posted by sdhawkrider View Post
It's an air leak for sure. Mixture is at 2.5 turns out. If I go richer, it pops more. The hotter the bike, the more the pops. The idle does seem to be erratic. I have to adjust the idle screw almost every time I start the bike and I do get a hang in the RPMs when the throttle is blipped.

On the PAIR, I added a vac line to the PAIR Valve nipple and blocked it off. I also blocked off the vac line from the carb that use to connect to the PAIR Valve. I assume that was the correct thing to do? I do wonder if all my vac lines are hooked up correctly. My bike is a California model so it has a extra Pulse Air System. So does the PAIR get hooked up from the Carb, and the secondary system get hooked up from the port on the front cyclinder used for carb syncing?

Since my last post, I have replaced the front boot.... again. Still the RPM's bump when test spraying carb fluid at them. Still getting the pops. They get worse as the bike warms up. I am so frustrated and so close to trying to seal the carbs up with liquid gasket. I think I might give up and take it to a shop.
Unplug the two pulse lines from the valves and block them off. Also to eliminate as much as possible pull the air injection hoses coming from the valve cover fittings and block them off with bolts wooden dowels or what ever have same size.
Then I would try using a can of wd40 with the long straw to track the leaks instead of carb cleaner.
That stuff is so high flash it would be hard to pinpoint if it's maybe leaking around the throttle shafts in carb bodies. It will also easily find its way through any possible opening in airbox to engine. Not the best choice for tracking vacuum leaks for sure.
Have you had a set of vacuum gauges on it to check synchronization? If they are far enough out of whack it can show all the symptoms of a bad vacuum leak as you've described.
A cylinder that is leaking air will have a very unsteady needle reading on the gauge as well.
I'm wondering if maybe there is something else going on besides an air leak. My intake boots were the original 1997 vintage with 50000 miles on them and though hard as a brick they didn't leak air.
This is why I suggest using wd40 to check, and checking the sync.

Last edited by rktdoc; 11-08-2017 at 09:23 PM.
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Old 11-13-2017, 11:07 AM   #10
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Unplug the two pulse lines from the valves and block them off. Also to eliminate as much as possible pull the air injection hoses coming from the valve cover fittings and block them off with bolts wooden dowels or what ever have same size.
Then I would try using a can of wd40 with the long straw to track the leaks instead of carb cleaner.
That stuff is so high flash it would be hard to pinpoint if it's maybe leaking around the throttle shafts in carb bodies. It will also easily find its way through any possible opening in airbox to engine. Not the best choice for tracking vacuum leaks for sure.
Have you had a set of vacuum gauges on it to check synchronization? If they are far enough out of whack it can show all the symptoms of a bad vacuum leak as you've described.
A cylinder that is leaking air will have a very unsteady needle reading on the gauge as well.
I'm wondering if maybe there is something else going on besides an air leak. My intake boots were the original 1997 vintage with 50000 miles on them and though hard as a brick they didn't leak air.
This is why I suggest using wd40 to check, and checking the sync.
Well I tried this route and sort of failed. With everything plugged, capped, and closed, I could barely get the bike to run well enough to test things. It would only run with the choke out. I used the choke to get the bike as close to idle speed as possible and tested. Using WD40, it seems that the carb boots were ok. Next step was another carb syncing. Done. Since the bike wasn't wanting to run with everything plugged, I decide to reverse everything and take it back to stock. Reversed the PAIR so they function. Weird thing was the front PAIR reed was full of oil. Well, reversed everything and the bike started running better. At this point, I am hoping the bike can run well enough to ride it to a shop. I put the air box back on, so the bike is back to "original". Fire it up, and it runs and idles fine.

My obsevations.... I did notice some Vac lines were cracking at the end. I snipped the lines and they seemed to fit snugger. The other thing is that it just doesn't like to run without the the air box. It just get too lean with the it removed. Does anyone else have this issue?

I still need to test ride it to see where I am at with the back firing.
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Old 11-13-2017, 04:40 PM   #11
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I have not run mine without the air box, but IIRC it has been posted that the engine will just run with the enrichment **** pulled out. That fits what your experiencing.
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