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 Mikuni jetting.
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Larry Perkins
Advanced Member

USA
2111 Posts

Posted - 11/13/2017 :  8:16:42 PM  Show Profile  Reply with Quote
They bore straight through to make entire opening more mm.

Larry P
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Richard Toghill
Senior Member

United Kingdom
30 Posts

Posted - 11/14/2017 :  3:13:48 PM  Show Profile  Reply with Quote
400 main jet? You must be running on methanol! This thing will start from cold with no choke at all. I have gone as small as 22.5 on the pilot and it STILL goofs up.I am rapidly appproaching resolving the issue with a bale of straw and a zippo lighter as it seams impossible to get some ballpark settings to work from.
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Larry Perkins
Advanced Member

USA
2111 Posts

Posted - 11/14/2017 :  3:33:39 PM  Show Profile  Reply with Quote
Just put a Bing on it like it came with with a good slide and a NEW needlejet and use the tickler to start and it will be fine and will flow more gas per mm than a Mikuni. The only trouble people have with the Bing is when they have a worn slide or a worn needlejet. Make sure those are in tiptop shape and you will pull no more hair. Don't look at theneedlejet put a new one in and make sure slide has no smileyface.

Larry P
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Dale Fisher
Advanced Member

USA
1532 Posts

Posted - 11/14/2017 :  4:45:29 PM  Show Profile  Reply with Quote
This is the first article I could find with reference to standard Carb specs for a 250 Harescrambler. There is a wealth of information in the publications that were so painstakingly scanned.

http://www.pentonusa.org/publications/keepingtrack/No.%2015%20%20June-July%201974.pdf

When all else fails contact Chicago Jerry or Gary Ellis....


Dale Fisher
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Edited by - Dale Fisher on 11/14/2017 4:47:08 PM
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Richard Toghill
Senior Member

United Kingdom
30 Posts

Posted - 11/14/2017 :  5:16:56 PM  Show Profile  Reply with Quote
Unfortunately I purchased the bike as a box if bits and there was no carb with it. I would have lut a bing back on it if I could have found one. The price of a new 36 bing would make your teeth bleed, hence the mikuni.
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skiracer
Advanced Member

USA
955 Posts

Posted - 11/14/2017 :  7:11:29 PM  Show Profile  Reply with Quote
So Larry, where did you get the 35.5mm slide to fit the new bore?

quote:
Originally posted by Larry Perkins

My reed valve 250 motor uses a 34mm Mikuni bored to 35.5mm so the airboot and body would fit.

Larry P



1976 MC 5 Original Owner
1976 Penton 175 XC
1985 20' Hi Point trailer
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Larry Perkins
Advanced Member

USA
2111 Posts

Posted - 11/14/2017 :  8:33:51 PM  Show Profile  Reply with Quote
I guess I am not explaining well but will try again. When a carb is bored the throat is bored from intake side to aircleaner side. The orofice the slide runs in does not change so the same size slide is used. Most all Mikuni slides for bigger bikes is the same size slide in diameter. There are different cutaways on slides that change the running characteristics but the size is the same. It is a bigger opening from front to rear that flows more air which flows more gas. Hope that explained it.

Larry P

Edited by - Larry Perkins on 11/14/2017 8:37:24 PM
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Richard Toghill
Senior Member

United Kingdom
30 Posts

Posted - 11/15/2017 :  06:45:59 AM  Show Profile  Reply with Quote
Sorry to rain on your parade but mikuni slides are most definitely not all the same size. A 34mm carb is physically smaller than a 36mm so the slide is smaller - trust me. Going back to the original question, can any of you guys tell me what you have INSIDE your miks. Pilot jet, main jet, needle, needle jet and slide
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skiracer
Advanced Member

USA
955 Posts

Posted - 11/15/2017 :  07:50:15 AM  Show Profile  Reply with Quote
Thanks Larry! Being of Polish decent sometimes I need a bit more detail than others!

quote:
Originally posted by Larry Perkins

I guess I am not explaining well but will try again. When a carb is bored the throat is bored from intake side to aircleaner side. The orofice the slide runs in does not change so the same size slide is used. Most all Mikuni slides for bigger bikes is the same size slide in diameter. There are different cutaways on slides that change the running characteristics but the size is the same. It is a bigger opening from front to rear that flows more air which flows more gas. Hope that explained it.

Larry P



1976 MC 5 Original Owner
1976 Penton 175 XC
1985 20' Hi Point trailer
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Dale Fisher
Advanced Member

USA
1532 Posts

Posted - 11/15/2017 :  08:30:20 AM  Show Profile  Reply with Quote
Have you tried the search function? Here is one of many on the subject

http://www.pentonusa.org/forum/topic.asp?TOPIC_ID=14244&whichpage=1&SearchTerms=mikuni%2Cjetting

Dale Fisher
Penton Owners Group - President/Memberships
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Mudlark Registry
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