Carb Settings

Sylvester

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Jan 19, 2007
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Normandy, France
It would appear that my machine has recently been affected by witchcraft. All has been relatively hunky dory (in Airhead terms) and I have never had anything other than the normal issues, but now!!!!!!! So,I noted that the bike had recently started popping on the over-run. Normally it would be a silencer air leak but checked everything and found nowt. Then I noticed that one header is blue the other the normal straw colour. Both carbs set the same and balanced. Plug colour leaner on the blue (er) side. Cleaned and stripped the carbs and found the fuel level drastically (10mm) different in the float bowls but the float levels are the same when checked, both paralel when the fuel flow stops. The lower fuel float bowl level corresponds with the seemingly hotter side. For now I have adjusted the floats to compensate but still a bit of popping and still blue but much less. I've ordered new float valves to see if it makes a difference. Any ideas?
 
I thought about that but why should it need it all of a sudden? We have 70k of happy kms together but i have no idea why the carb bowl fuel levels are so different especially as the float levels look text book. I'll try the mixture screws later this week. Thanks for the reply Kenny
 
Valve clearances are spot bollock, Ive had the floats out for a shufty couldn't see/hear anything untoward. Ordered a shit load of carb spares as a precaution. I will probs overhaul both carbs this weekend as I can't remember the last time i did it but it must be 12 years ago. Damm how time flies. Anyhow compared with the amount of maintenance/spares/swearwords my KTM 950 needs to keep on the road its nothing. I have so much KTM stock I could qualify as a main dealer!!!!!
 
Check your diaphragms. This is what happened to more than one of my airheads over the last 30 years....
 
The Floats can become porous as they age so don’t float as much as they should :D
 
Hi Steptoe,
do you reckon that ethanol in fuel would maybe make the floats more porus ? Ethanol is a real bugger IMHO!
 
Swap the floats and see if the problem changes to the other side ? Am I just brilliant or what ?
 
I guess this would be a good use of those transparent float bowls, you'll see straight away whether the floats are floating correctly and if the true levels are right as opposed to the level you get by moving the flat manually with no bowl fitted.
 
Ethanol is rarely a problem, toulene, which is added to freshen up stale fuel , is.
Meths is almost ethanol, lacquer thinners can be toulene, so if you leave anything you are worried about in a jar of either you will soon tell if either is going to cause problems!

The only thing that matters when setting the floats is the resultant level in the bowl, so as a quick check scribe a line on the inside of the bowl 1/2" down from the top , and check that both sides are just a little below the line.
If you remove one bowl with the other in place very little drains out of the hose.

For tuning/ cleaning carbs best to find Mike Fishwicks article on Bing carbs, he shows circuits few others know about, which if blocked can have a major effect on the mixture in the most used throttle range.
 
So, I changed the floats, float valves all the O rings. Gave everything an ultra sonic clean. Put it all back together. The side that I thought the fuel level was low was actually correct and it was the other side that was too high! Both the same now and after a quick carb balance normal service has been resumed. Thanks for your help guys.
 


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