lost 1/3 to 1/2 power (race bike)

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DanB
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lost 1/3 to 1/2 power (race bike)

Post by DanB »

At New Hampshire Motor SPeedway the other day the bike suddenly lost a fair amount of power on about my 2nd or 3rd practice lap. Just seems to bog. It starts and idles fine but as soon as any load is applied it immediately bogs down. Will run up the entire rev range with the same torque loss throughout.

I disconnected the fuel line going into the pump and it pours out totally freely with gas cap in place. Pump sounds normal I think: dit-dit-dit-dit--dit---dit----dit-----dit until bowls are filled which only takes a few seconds from totally empty.

It doesn't sound uneven like it's down one cylinder, but could be, or maybe down two?

Bike is totally stock other than having lights and sidestand stripped off for track duty.

Was thinking of just replacing the coils and needle valves but those parts add up quickly! Would like to figure out what's wrong rather than just replace parts at random. Any suggestions/ideas welcomed!
Thanks :)
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TomcatMJ
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Re: lost 1/3 to 1/2 power (race bike)

Post by TomcatMJ »

Sounds like the carbs are running to fat...did you check if the airfilter is (at least partially) clogged? Hanging/partially stucking choke possible? Perhaps check the Sparks also, maybe you can see there if it affects only special cylinders and posibly at least one of the sparks is defective.if two sparks are affected maybe a check of the sparkplugs and ignitioncoils would also be helpful..
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DanB
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Re: lost 1/3 to 1/2 power (race bike)

Post by DanB »

Air filter looks fine. Choke linkage and throttle linkage are OK. Will try to check resistance across coils and ignition wires this evening (hopefully). Will have a look at plugs, probably just replace them all in any case.

Probably remove carbs and inspect the needle valves and main jets. I guess the diaphragms too but not sure what to look for there...
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DanB
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Re: lost 1/3 to 1/2 power (race bike)

Post by DanB »

plugs all were light tan in color, though it seemed most were wet, at least one was dry... They were all in the .028" to .030" gap range, within spec.
Plug wires, and plug caps were all in spec resistance range, with the coils themselves a little higher than the max spec of 2.2 ohms at 2.4 and 2.8

Will dig into carbs tomorrow I guess...
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TomcatMJ
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Re: lost 1/3 to 1/2 power (race bike)

Post by TomcatMJ »

When you check the carbs, check also the air jets if some of them might be partially clogged and the swimmer-valves and valve-seats if there is one or mor worn-out...and bend the diaphragmas carefully in order to check for dents and cracks/splits/tears...
"The social dynamics of the net are a direct consequence of the fact that nobody has yet developed a Remote Strangulation Protocol." -- Larry Wall
Want Pics? Then have a look at my galleries...different topics: Bike and Car restauration, exhibitions, Trackdays (no, not me on the Track until now), carneval in cologne, other things.. ;)
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DanB
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Re: lost 1/3 to 1/2 power (race bike)

Post by DanB »

TomcatMJ wrote:When you check the carbs, check also the air jets if some of them might be partially clogged and the swimmer-valves and valve-seats if there is one or mor worn-out...and bend the diaphragmas carefully in order to check for dents and cracks/splits/tears...
Will do, thanks!
Also picking up an ignition tester to see if coils are operating OK despite being out of resistance spec. Will likely replace them anyway...
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DanB
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Re: lost 1/3 to 1/2 power (race bike)

Post by DanB »

Used a spark gap tester to confirm that coils/wires/caps were all OK. Removed carbs and whaddya know, whoever took them apart previously thought it a good idea to use either loctite or rtv, there was this rubbery reddish residue in a few places. Including one ~4mm diameter disk of the stuff LODGED IN THE SCREW SLOT OF THE #1 MAIN JET! Couldn't have been more perfectly placed! The symptoms fit this perfectly. Right off idle, everything is fine. As soon as load invokes the main jet circuits, #1 is AWOL. It *felt* like losing 1/3 to 1/2 power, but I guess it was only 1/4...

Looking forward to taking a test ride tomorrow. Looks like I'll make New Jersey Motorsport Park, Lightning track next weekend after all!
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Re: lost 1/3 to 1/2 power (race bike)

Post by Evilchicken0 »

Always good when you find the problem
I've seen this happen before when somebody used silicon to seal the float bowls - if you need some replacements got to Lite Tek http://litetek.co/
Don't read everything you believe
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