Topic: 4-1 exhaust question.

[mrbonilla]

hey guys i have a 1976f currently straight pipe 4-1 exhaust (no baffles), and a k&N airbox filter, so my question is do you guys think i would need to reject carbs? they are stock right now 40 slow, 105 main, or you guys think raising the needle would work?
Thank you in advance.

[70CB750]

You may need to raise the needle but the engine is not overly sensitive to exhaust restrictions.

One needle notch is approximatelly 1.5 in jet numbers. If you get to the end of the needle, go next size but as I said, with open exhaust and stock airbox you should be fine.

[PeWe]

Try 115 main jet first and test.  (Max 120)

[JWExperience]

I have a 76k with 4-1 and kn in stock box and run a 120 main and 42 pilot. 40 pilot would be fine but I wanted it a little rich and my plugs have been good for a few thousand miles with nice tan color


Sent from my iPhone using Tapatalk

[Don R]

 I liked the 110's in a stock one with a 1" through glass pack baffle.

[mrbonilla]

thank you guys, i'm going to start with the needle first, and see how that works out. will keep you updated, i had to buy new air boots because i found out they were leaking. so once that is taking care of will go to the needle.

[Don R]

105's are a smog/economy jet, according to hondaman's book they make the engine run hot.

[PeWe]

Why change the tricky one first? Remove throttles need resync and will take time. Main jet change 1/2 hour.
If you have bad responce in the needle area after main jet change, OK check that the carb boots are OK before taking carbs apart for needle adjustment.

I changed needle 1 step richer (from 3 to 4) AFTER upgrade with 836, ported head and cam.
My K6 with 4-1 only and std airbox, main jet only, from 105 to 115.

[mrbonilla]

Awesome, thanks for input..

[PeWe]

I forgot:
If first time it will take longer time to change jets. Find correct tool  (short screwdriver) to remove main jet or entire needle jet which can be easier (8mm). Be careful when removing the needle jet when carbs are on. Easy to think backwards and tighten instead of loosen. I use 8mm, 1/4 socket wrench with setting for loosen that I double check before. Not possible to do wrong then and strip threads in carb body

[mrbonilla]

hey guys so i went ahead and replaced air boots, not vacuum leaks anymore:) thought tho that this will fix my low rpm's issue, when i accelerate is fine but when i left of full throttle, and drive it partial throttle bike bogs a little, could this be a slow jet issue since i'm straight pipe.