I own a 1979 GS750E that's basically stock except for a Vance & Hines 4 into 1 pipe (the one sold by Dennis Kirk for all these old 70's Japanese muscle bikes)
She has K&N individual air filters, and Mikuni carburetors came off of a 1979 Kawasaki 750. I had them rebuilt, and I have had them professionally synced on a flow bench at a bike shop 6 years ago.
I recently changed the oil, I changed the plugs (yes I used the correct plugs with the correct gap) I cleaned the air filters, and I put a bottle of fuel injection cleaner in with a full tank of gas to give the carbs a good scrubbing. (I've always done this before without negative consequences)
I've owned this bike for 15 years, and she's dead reliable (never left me stranded, and she's always gotten me home)
All the things I've just mentioned I've done for years, and I've never had the reaction that I've gotten over the last few rides.
She starts, and idles fine - up through 1st, 2cnd, and 3rd gear - she's great. Once I hit 4th gear, and I'm between 50 and 70 miles per hour she starts to spit like she's either starved for fuel or air. Once I'm up in 5th gear above 80 miles per hour she smoothes out again.
She's never done this before and I'm really getting aggravated with her because she feels like she wants to cut off but doesn't. I give her gas, and she just bogs down until I get past 70 miles per hour - then she launches forward without the spitting.
I should mention that when I took her out of the shed after last winter and went through my spring regiment to get her ready for the summer, there was some type of obstruction with the carbs, and the fuel wasn't moving through the fuel tube into the carbs.
I had to take them off, and blow all the ports out with carb clean in order to get the fuel moving again.
I don't know if there's something restricting the fuel from getting into the carbs, or if the air/gas adjustments are all totally out of whack or if the plugs have prematurely fouled (which I severely doubt) or if the packing in the muffler is shot. I don't know what's wrong.
The last time she acted just like what I'm going through now was because of a vapor lock from fuel tank. I drilled a hole in the gas cap to relive the vapor lock, and she's been fine all these years………..up until now.
I'm at my wits end, and I know the solution is to just buy some new CR Keihin's - but I don't have $800.00 right now for new carbs.
Any and all advice would be greatly appreciated.
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