Vm29's jetting on a '77 1075

ok well ive replaced just about everything on my bike now, just broke-in wiseco 1075, new dyna ignition, and lots more. but the problem is and has been that when getting on full throttle it breaks up. im running 20 pilots and 122.5 mains and its better than it used to be with the 117's and if i flip the choke on and nail it it takes right off so i know it needs bigger mains. i was wondering however if you guys had any advice on how high to go? it has pod filters and a vance & hines drag pipe with a competition baffle. any advice will help im thinking 125's maybe?

Thanks, Brandon.

Im no expert by any means. But maybe raise the needle

I've got VM29's on my gpz750 motor
and am playing with 117, 120 and 122.5 main's.

At 1075 I'd sell the 29's to fund a
lot bigger set of carb's

Go to 130 and work your way down if it is too rich. 120s is the baseline setting for use on a 1000. Use the Mikuni VM tuning guide in the file base for specific info.
Sounds like you may have a different problem than jetting. Check for full voltage to the coils first.

How many turns out are you all running on the air screws? I am at 1 but read where some are down to 1/4.
Wayne

I had 130 mains on my 1075.

before you get too crazy with these carbs and start loosing your mind what is your altitude

kzz1king wrote: How many turns out are you all running on the air screws? I am at 1 but read where some are down to 1/4.
Wayne

Is this a street or strip bike. I'm running 29s with 17.5 pilots on a street bike with a stock 1015 engine. I get a good bit of lean popping at 1/8 throttle and below, at 1/2 to 3/4 turns out on the screws. 1/4 turn out didn't idle well.
In my way of thinking, the carbs are designed for 1 1/2 turns out on the air screws to emulsify the idle fuel mixture correctly, I'm thinking go up on the pilots until you are getting the proper volume of air moving through the idle circuits.

Not only will you have the proper A/F mixture at idle, you will have plenty of fuel flowing right off idle before the needle takes over. Am I not thinking about this the right way?

You need to keep in mind that the air screws on the 29s work a little different than they do on the other mikuni vm carbs. On the 29s the air screw has a hole in it near the end. So you should not need to turn them out as far as you would on the other carbs - I think a good starting point is about 1/4 turn from lightly seated.

Yeah, they are different that the air screws in the 28s.

I've gotten tired of thinking about this and went out and took the carbs(29s) off my bike. Gonna try some different pilot jets and see for my self how this will work out...building a carb stand now Anyone have a Colortune they want to sell???? :whistle: :lol:

FWIW, an it may not mean anything, I screwed the air screw all the way in and backed it out to 1 1/2 turns while watching the hole in the air screw through the idle air passage. At lightly seated position you could see the top edge of the hole, at half turn out, 1/3 of the hole was visible, 1 turn out, more of the hole, until at 1 1/2 turns out the hole was lined up in the idle air port. Maybe a coincident, I only got to do it on one of the carbs.

What throttle positions (or RPM)do these affect? Low to low midrange?
Wayne

gd4now wrote: You need to keep in mind that the air screws on the 29s work a little different than they do on the other mikuni vm carbs. On the 29s the air screw has a hole in it near the end. So you should not need to turn them out as far as you would on the other carbs - I think a good starting point is about 1/4 turn from lightly seated.

Idle, off idle to 1/4 throttle. Lots of variables to consider, circuits overlap a good bit.
Here is some good info to wrap your mind around:

www.iwt.com.au/mikunicarb.htm