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Author Topic: tuning a new set of vm30s  (Read 1623 times)

Offline maddrill24

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tuning a new set of vm30s
« on: Sep 11, 2011, 15:28:13 »
i recently put some new mikuni vm30s on my cl 350. they deffinatly need some fine tuning . anyone with any info on where to set the air fuel screws at (atleast for a starting point) would be a great help

Offline teazer

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Re: tuning a new set of vm30s
« Reply #1 on: Sep 11, 2011, 17:52:09 »
Start at 1.5 turns out and work from there.  If they came pre-jetted, jets will need to be changed in all probability. Start there and see how many turns out it idles best at and then swap out the pilots if it's too many turns away from 1.5.

Offline maddrill24

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Re: tuning a new set of vm30s
« Reply #2 on: Sep 11, 2011, 18:12:30 »
alright sounds good thanks alot

Offline maddrill24

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Re: tuning a new set of vm30s
« Reply #3 on: Sep 11, 2011, 19:21:29 »
alright i started at 1.5 turns out but i cant seem to get it to idle down below 3k i turned the mixture screws in a half turn and i got it to idle down just a little bit >:(

Offline teazer

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Re: tuning a new set of vm30s
« Reply #4 on: Sep 11, 2011, 21:05:37 »
You want to start out with a little play in both cables and both crabs opening at exactly the same time.

Then screw in the throttle stop (idle speed) screws so they just touch the slides and then another 2 turns each.

Set the mixture (air) screws to 1.5 turns out and fire it up.  If idle is too slow, turn both idle speed (throttle stop) screws in another turn to a nice fast idle.

Adjust the air screws in and then out to find the fastest idle speed.

Then back the idle speed (throttle stop) screws back out 1/4 turn at a time on both until you have a nice even idle.

If the sweet spot on the air/mixture screw in much more than 2 turns out, the pilot jet is too large.  If it runs best at less than 1 turn the jets are too small.

Does that make more sense?

Offline maddrill24

  • Posts: 73
Re: tuning a new set of vm30s
« Reply #5 on: Sep 11, 2011, 21:30:48 »
yes this helps alot im going to try this soon and ill post results. thanks again for your time.

Offline maddrill24

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Re: tuning a new set of vm30s
« Reply #6 on: Sep 11, 2011, 22:00:59 »
well i tried what u said and it got the idle around 2k with mixture screws 2 1/4 turns out but now it backfires out of the exhaust and runs very un-even  and if u try to give it any throttle it just bogs the motor out this is turning into a nightmirror haha

Offline teazer

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Re: tuning a new set of vm30s
« Reply #7 on: Sep 11, 2011, 23:30:05 »
so far so good.  Now drop the idle slightly and tweak those air screws in or out and see how that changes things.  You should reach a point where the idle is fine but it won't necessarily move onto the cutaway which takes over from the slow jet from 1/8 to 1/4 throttle.  Those carbs often go from rich idle to chronically lean on the cutaway and back to rich on the needle.

Have you compared your jet settings with other people to be sure that you are in the ball park? 

If you could borrow an O2 wideband sensor and gauge you would be able to see the air:fuel ratio and from there it's easier to see which way to go next. 


Offline Nebr_Rex

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Re: tuning a new set of vm30s
« Reply #8 on: Sep 11, 2011, 23:30:11 »
Like Teazer said......
 
 
If the sweet spot on the air/mixture screw in much more than 2 turns out, the pilot jet is too large.  If it runs best at less than 1 turn the jets are too small.
 
What pilots and main jets do you have?
 
 
 
 
.

Offline maddrill24

  • Posts: 73
Re: tuning a new set of vm30s
« Reply #9 on: Sep 11, 2011, 23:54:07 »
i forgot to mention. when i was setting the starting point for the idle screws they werent identical. the left screw was about half way in and the right screw was almost bottomed out before it would move the slide. i took both screws out and they are the same length i even switched the screws around and still it is not right
 
and for the jet sizes i will get back to you on that and deff do some comparing to others. i ordered them from a sudco dealer and they were "supposedly" jetted for my 350.