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CV carb mainjet style question

  • Thread starter Thread starter tirebiter
  • Start date Start date
T

tirebiter

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1) Can someone give me advis me as to the mainjet style on CV carbs ? I have a 1980 GS850LT with stock carbs as far as I can tell. From what I can decipher afetr reading numerous websites, they use the "small round" head style mainjets. If I'm wrong I hope somebody can chime in and straighten me out.

I'm hoping to place an order for at least a couple of sizes this coming week and do not want to have to remove the carbs and float bowls to look at them before ordering. I'm using the bike a lot to get around with and do not want to spend that much time working on it to find out. Not if I can get away wthout it.

Who knew Mikuni has several different mainjets styles ? I surely did not when I had the carbs off or I would have taken note of which style is in there. I do know the mainjet in there now is a stock size 115 - at least the one carb I looked inside of.

2) Another item I am wondering about is do the other styles of main jet physically fit into the same place ? Large round, hex small, large ? Do I absolutely have to use the stock style mainjets without rethreading, "squeaking in" for the last thread or otherwise complicating the job ?

3) Are the "equivalent" jets I've seen advertised on various websites really equivalent ? Do they work and act the same as Mikuni brand name jets ? Are they actually equivalent regardless of the difference in numbering/labelling and nomencalture ?

This is in search of making a decent running bike (in this newbie owner's opinion anyway) into a better running bike that has a non-stock 4 into 1 exhaust system ... and who knows what else is done to it that is not factory bone stock.
 
LARGE HEAD ?!! OK like the new HSR carbs use ?
 
Last edited:
No idea what the HSR carbs use, but the BS-series carbs on your bike need the large-head style main jets.

Depending on how "free-flowing" (loud) your pipe is, you might need to add 2-5 sizes. That would be 120 to 127.5.

You still running the stock airbox? If so, great. If not, add another 4-6 sizes for that.

.
 
large head like all the Gs's used for 30 years.
not familiar with the HSR carb.
same jets as the RS series flat slides.
 
ok thanks blowerbike this helps a lot. I just HATE ordering obviously wrong parts.

As always Steve I am very greatful for your input. I retained the stock airbox even though I had to make my own filter element "cage", being the cheapskate that I am. It's possible it is a little more restrictive than a stock cage. I usually a take very conservative approach to rejetting but I respect your knowledge, Steve. I'll get a few sets starting at 120, skipping the 117.5 and going one size larger each. The exhaust seems very quiet until the engine gets on the cam.

This last pilot screw adustment - was 3 now 4 turns out gave me more power and less bad at full throttle. Pulling the choke out made it better at full throttle, too. But then there was the surge during throttle roll off. Not too far off, I think.

Wish I knew somebody local who's been down this road before and already has a good selection to test before buying but ... hey, I can dream can't I ?
 
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