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Motorcycle Repair/mikuni carb on a gsxr 1100 1990


QUESTION: Hey I syncronized my carburetors and cleaned them no vacuum leaks at all. I have a new fuel petcock and running k&N air filters and yoshimura exaust. On start up when the bike is cold when I give it alot of throttle I will get hesitation and backfiring when RPM are trying to rise. Also the bike is in neutral. Althought when the bike warms I have no symtoms of backfiring at all and everything is normal. I will try to turn my pilot jet out 1/4 of a turn and see if that will solve it. The motorcycle smell rich when cold but when it warms up exaust smell is normal. When its cold outside my idle has to be ajusted to bring it up to normal idle then when the bike warms up I have to turn it down or else the idle will be to high. This is a problem when cold. I have not been able to pull the spark plugs to see how each cylinder is running but will attemt it this weekend I have to grind my spark plug so it will fit in the well.

ANSWER: This all sounds so familiar. I would purchase a (Gunson Colortune Tool. 14mm)
This tool lets you see the color of combustion in the cylinders.
It goes in your sparkplug hole and you connect your sparkplug wire. Put the bike on its center stand and put a fan blowing on the engine as it may get warm.
Start the engine and raise the Idel screw to get the engine running at 2000 RPM's.
Then you adjust your Pilot Jet Screw to get the right color of combustion.
Your looking for a bluish white color not yellow. I f search this tool it will explain how to use it.
The weird thing is that an engine can be tuned to the ambient temperture.
Meaning you can tune it to cold weather and to hot weather.
As when its hot outside the engine dosent need such a rich fuel mixture.
I laearned mine after time. In the colder weather I would open the Pilot Jets Screws 1/4 turn out and when it was hot I would turn them back in and then Colortune the engine again.
It sounds like your using the wrong plugs or your threads are messed up. I think I would use a thread chaser to clean them up before you have real problems.
The popping sound is a sign of a lean fuel mixture.
My 1983 XV920MK ran exactly as you described. I would just start it with a little choke.
I would let it run 5 or 10 minutes to let it warm up before I woiuld ride it.
If not I would get the same hesitation and popping as in most cold engines..

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QUESTION: Well your definetly right about the temperature thing,I noticed that too. The threads I will check this weekend. I will turn the pilot screw out 1/4 of a turn out clean the spark plugs then check them again in a week to see how they are burning. The spark plugs are the exact match and threads are great. I dont have that tool so I was wondering will this method work too?

The (Gunson Colortune Tool) can be found on Ebay.
I have 3 of them. I do Carburetor Rebuilds and sales.
I think the tool is a MUST. It takes the guesswork out of getting the perfect
fuel mixture. I have 60 sets of Virago carburetors in Stock.
I can let you use 1 as I do alot of my Customers.
Its a $60.00 Deposit to my PayPal accout. + $500 for Shipping.
I Refund the $60.00 when I get the tool Retuned to me.
Once in a while on Ebay you can get 1 for under $60.00 but not often.
Visit my website. I have more contact info there...
Phone Numbers and email Address...Joe

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william joseph stack


I specialize in Virago carburetors. Internal parts sizes, Needle and jet sizes for each and every year and model. Hitachi and Mikuni. I also can give tech support and Tech Support for carburetor problems and issues. Carburetor tuning and syncronization. Carbburetor rejetting and dynojet installations for engine modifications. I know every needle and jet size for every Virago made. I have done over50 Virago carb Salesand Rebuilds in 2012. I have over 50 sets ofVirago carbs in stockright now. I Build, Ride and Breath Virago. I have both the 1983 Midnight Virago's. The XV750MK and the XV920MK. 1 of my 1981 XV750H is is Premier Cycles, Billy Joel's Bike Museum.... I am an Honest and Fair man. I am also a Finicky Perfectionist withmy carb work. Ihave all the obsolete hardto find carb parts. I have new diaphragms, new floats, I have the float level setting down to an art. I have fabricated transparent bowls for both version 1 and version 2 carburetors.


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