Intake air leak - carburetor - intake - pics

T

tirebiter

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When I read Blompod's "Not Idling?" thread it reminded me about something I found when I checked the intake to carb fit my bikes. That might not be his problem tho.

Here's something I found on all my kits. If you assemble the intake and the carb just the way they come, the carb can't fit all of the way onto the intake tube. There's a pretty good sized leak at the bottoms of the grooves in the carb flange. Each kit's a little different but on the one in the pics the tube can only go into the carb .420" before it hits the weld on the tube. The grooves are .500" long which leaves .080" of the groove uncovered. The clamp on the outside doesn't cover the grooves either but that doesn't really matter because air will leak down the grooves anyway if the carb doesn't slip on at least past the ends of the grooves. Air leaks on the intake are not good. :devilish:

On the bike I ride I smoothed the weld all the way to the bend and also ground a little off the end of the carb flange. That way I could slip the tube in until it bottomed out. Maybe I'm a little fussy but I thought I'd bring it up in case someone else is fussy too. ;)

Here's some pics of the measurements I just took off a fresh kit.



Carb
 


jonylevers

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Aug 16, 2008
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spot on tirebiter !! have done the same on my engine though i still have issues with flooding at present-may have to equip motor with 70cc sports carb though at 110mm it may be awkward to fit.
 

Bronzebird

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Aug 7, 2008
Messages
86
Have you checked out the float valve or float level?

spot on tirebiter !! have done the same on my engine though i still have issues with flooding at present-may have to equip motor with 70cc sports carb though at 110mm it may be awkward to fit.
I have found a small pieces of debris on the valve seat or on the float valve. Or any bind in smooth operation. Float level is checked next.
 

Bronzebird

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Joined
Aug 7, 2008
Messages
86
I have an o-ring at base for snug seal.

When I read Blompod's "Not Idling?" thread it reminded me about something I found when I checked the intake to carb fit my bikes. That might not be his problem tho.

Here's something I found on all my kits. If you assemble the intake and the carb just the way they come, the carb can't fit all of the way onto the intake tube. There's a pretty good sized leak at the bottoms of the grooves in the carb flange. Each kit's a little different but on the one in the pics the tube can only go into the carb .420" before it hits the weld on the tube. The grooves are .500" long which leaves .080" of the groove uncovered. The clamp on the outside doesn't cover the grooves either but that doesn't really matter because air will leak down the grooves anyway if the carb doesn't slip on at least past the ends of the grooves. Air leaks on the intake are not good. :devilish:

On the bike I ride I smoothed the weld all the way to the bend and also ground a little off the end of the carb flange. That way I could slip the tube in until it bottomed out. Maybe I'm a little fussy but I thought I'd bring it up in case someone else is fussy too. ;)

Here's some pics of the measurements I just took off a fresh kit.



Carb
Great idea to clean parts and check fit.
 

jonylevers

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Joined
Aug 16, 2008
Messages
7
g'day bronzebird - i must have striped the carb down 5 times now believing the same ,have set float 2mm above jet, i even made up a gasket for the fuel primer base ! its annoying as motor has just been run in,have ordered another carbi from Zbox after reading a few posts.
have moved E clip on needle 1 down and 1 up from factory settings though to no avail it seems no matter what i do the results are the same-bike starts-runs ok 4 a bit then power starts to die with throttle open fully !! fuel can be seen on chain guard,now using NGK B6HS plug problem is still the same !
 
Joined
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Messages
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I have found a small pieces of debris on the valve seat or on the float valve. Or any bind in smooth operation. Float level is checked next.

I would suggest a good inline fuel filter if you dont have one already. And the other is the oring seal. I even use that on the Mikuni carb I installed, that way you really dont have to mess with RTV as the end of the manifold seats against the oring for the seal....

http://www.motoredbikes.com/showthread.php?t=4976&highlight=oring
 
Last edited:

Bronzebird

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Joined
Aug 7, 2008
Messages
86
I would suggest a good inline fuel filter if you dont have one already. And the other is the oring seal. I even use that on the Mikuni carb I installed, that way you really dont have to mess with RTV as the end of the manifold seats against the oring for the seal....

http://www.motoredbikes.com/showthread.php?t=4976&highlight=oring
Inline fuel filter, rinsed fuel tank, debris must have fallen into carb tube during shipping or installation. Thats when I noticed the poor seal at clamp to intake manifold. 9/16th O-ring fitted nicely onto carb with a touch of high temp "ultra black" RTV. Also used RTV on exhaust gasket as it leaked on next ride which is number seven under my belt. Head gasket is starting to seat very nicely and minimum retourq finally.
 

jonylevers

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Aug 16, 2008
Messages
7
got it !! have also sealed where the cable enters carbi as another potential air leak won't know till tomorrow if its a winner!!
 

ra42mario

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Jun 17, 2009
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So has ANYBODY found at where to seal all these air leaks on this carb? I've had my bike for three weeks and will still not idle. I can put the clutch in and rev the bike to keep it running and spray starting fluid on the carb and it chokes it out, so its sucking it in. So far I've choked it by spraying on the carb intake tube and the throttle cable hole.

I put two oil drain plug gaskets RTV'd together in the intake tube to seal up the carb, it has helped and when I spray the starter fluid there it doesn't choke up, but it still won't idle. There are more air leaks somewhere.

Who sells the best carb? I'm just about sick of this one I got on here. The bike is losing power and the no idle is annoying. Next carb I get I"m just going to JB Weld the intake tube to the carb so it never leaks.
 

Hawaii_Ed

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Joined
Mar 9, 2009
Messages
698
JB weld will work :) How old is your engine? Could also by a base gasket leak. Throttle cable should not be much of an issue. Does adjusting your idle screw change idle at all? Can also tighten up the throttle cable to hold it open more, but that is not ideal. Also check your fuel flow, I have had two with petcock problems. Take the intank filter out and see if it helps.
 
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