still stumbling - aghhh!

[Black Sled]

I'm still trying to get the sled running good after rejetting back to stock mains.  The engine is cutting out, but only on the left side.  It is pretty rideable, but at any rpm, when you apply 2/3 or more throttle, the left bank will sputter and be down on power.  All the plugs on the left have a little frosting on the grounding strap - not so on the right bank.  I can find no vacuum leaks - all air connections to/from the carbs have been triple checked - even sprayed starter fluid everywhere, as suggested. 

I was running a fuel filter until just recently, so I am hard pressed to believe this is a fuel line obstruction.  Not sure how I'd check for that.

Any considered opinions would be more than appreciated.

[DFragn]

maybe check the needle diaphragms under the carb covers for pin holes or tears with a back light.
Be gentle they're somewhat fragile.

[Black Sled]

I have double checked the diaphrams and the slides.  Everything looks fine.

[Black Sled]

Examining the plugs from the left bank I noticed that #5 had a dark porcelan (sign of detonation) and the other 2 were white.  I pulled the main jet from that carb and cleaned it.  There was the smallest amount of crud in the jet - needed a magnifying glass to see it.   But it was enough to cause fuel starvation.  The bike is fast again.  I think the frosting was sediment from running Techron.

Lesson - soaking and blowing jets out is not good enough.  You have to physically ream them out with a paper clip.  Better yet, just replace with new rather than reusing jets. 

Also, if doing a Techron treatment, do it BEFORE replacing the spark plugs. 

[Patrick]

this right.. The bike is now running correctly??  Your right, if you remove the jets for cleaning they should something stuck thru them,,, a tag wire, drill bit, something that won't damage them and then some air.. You stated you had a problem with the left side,,but,, mentioned #5..

[Black Sled]

this right.. The bike is now running correctly??  Your right, if you remove the jets for cleaning they should something stuck thru them,,, a tag wire, drill bit, something that won't damage them and then some air.. You stated you had a problem with the left side,,but,, mentioned #5..

you got me there - it was #6.

[Robert]

The jets shouldn't be cleaned with a paper clip but next time try the little plastic tubes on the spray cans or something plastic. Flow through the jets can be easily disturbed by even the smallest of scratches so the jets being brass scratch easily and Techron doesn't leave usually anything but maybe a white film on what it cleans. Sometime crud that it cant clean will remain. I haven't seen all your posts so please excuse if I ask or go into things you've already covered. The one plug being black is not from preignition unless it looks like a black melted deposit, if its just dark then the carb is rich. I went back and found you have cobra pipes, Dyna ignition but you didn't say what air filter. Also since you cleaned the carbs and the bike is pulling harder I still think you may have a problem in them. There are the air jets or emulsion tubes in the carb that breakup the gas and allow it to flow into the jets easier and the holes in them is smaller than the idle or main jets. I would reinspect these to see if there may be a problem. Also by the sound of it the carbs were in pretty bad shape which means that the passage way in the carbs may be holding hidden dirt that needs to be removed. I have seen it clog the jets again or just never allow the engines to run well. You can check fuel flow to that bank of carbs by opening the drain screws in the bottom of the carbs and making sure the gas flows quickly out. Once you took out the larger jets did it make a difference in the plugs and running of the bike? With the smaller jets and a KN filter with aftermarket exhausts you may have to richen up the mixture even on the one bank. I would be tempted as a test to richen the needles and see if it makes the problem better. If it does then you know its a mixture issue. Two white and one black plug is not a good sign either, they really should be consistent across the board. I don't think that you have a problem in this area but I always like to check all the unknowns did you take a look at the cam timing to make sure its on and also that the valve adjustment is correct. You wouldn't be looking for small adjustments just to see if they were way over tight.

[Ricky-D]

I only am addressing the issue of the difference between the plugs (two are clean and one is dark).

I agree that all three should be similar in appearance and with the one dark plug I feel that a compression test is in order for that particular bank of cylinders.

A compression test will eliminate any possible causes of the difference due to the mechanics of the motor.

My feeling is that the most probable cause of the dark plug is a float problem causing a richness of the fuel mixture on that one cylinder.

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