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Author Topic: throttle valve cutaways  (Read 2345 times)

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Doc

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throttle valve cutaways
« on: April 22, 2008, 08:46:26 pm »
okies this is a 2 fold question. First of all would anyone have kicking around a mikuni 26/28mm TM/RM carb 2.5 cutaway slide. Heavy chrome/brass type, O.D. 30mm and non cutaway side measures 48mm top to bottom. I'll gladly buy any decent item looking for a near new home.  :)

Now for the second part of zee question.

If I don't find a 2.5 and go with the 2.0 from the stock 26mm TM carb in the 28mm RM(M) carb what/where exactly will it richen? all over? up top? down low? I've never played with cutaways but I know for certain a 28mm with 2.5c/a works great...getting 1 in time mightn't happen hence I ask..clear as mud  ;)

I scored a really nice near new 28mm from an RM125M but it has no cap needle (same as TM anyway) throttle valve or spring. I ran Dodgee's new 28mm at coffs and it ran sweet as so I wanted flick the 26 and fit this baby before CD-5 and hopefully reap the same rewards ;)
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Offline Lozza

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Re: throttle valve cutaways
« Reply #1 on: April 22, 2008, 09:17:36 pm »
Might have, at idle/on idle circuit only.WTF is a cap needle??????
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Offline brent j

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Re: throttle valve cutaways
« Reply #2 on: April 22, 2008, 09:22:53 pm »
Doc the cutaway starts to work at idle, reaches maximum effect at about 1/8 throttle and tapers off by just above 1/4 throttle.

You can always file a 2 to a 2.5. I stand to be corrected but I understand the number relates to the cutaway amount in 16th of an inch graduations.
This works out pretty close as I've measured 7 different 36/38mm slides.

I used this same measurement to file my 36mm slides to #4 for my 500's.

HTH

Brent



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Offline Lozza

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Re: throttle valve cutaways
« Reply #3 on: April 22, 2008, 10:53:09 pm »
Spot on Brent comes from the old Pommy Amal measurements that Mikuni copied off all those years ago.
Doc I only have a 30mm with a 2.0 cutaway,the 2.5 cutaway I have is for the larger 32mm and is longer.
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Doc

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Re: throttle valve cutaways
« Reply #4 on: April 23, 2008, 01:16:02 am »
Thanks ppl..at a guess I may get away with a 2.0 on a 125 as it spends most of it's time above half throttle. Lozza the cap needle was a typo missing the comma between the words cap and needle ;) I'll give it a go and see..
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Mike

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Re: throttle valve cutaways
« Reply #5 on: April 23, 2008, 03:14:56 pm »
Hi Doc, do you know what main and pilot jet sizes were run in the 28mm at coffs?
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Offline GD66

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Re: throttle valve cutaways
« Reply #6 on: April 23, 2008, 06:50:02 pm »
 As you say Doc, if the cutaway is a problem, and you're rich way down low, you may be able to juggle out of it by only turning the mixture screw out one and a quarter turns, instead of one and a half. Normally, you wouldn't be down there much, but if CD5 is wet, then you may have to .... ;)
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Doc

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Re: throttle valve cutaways
« Reply #7 on: April 23, 2008, 10:38:06 pm »
Mike..the carb I used at coffs was std RM125M jetting, 180main and a 50 pilot. The only difference with the carb I have is I don't have the correct cutaway..bugger bugger bugger..close but not as identical as I'd liked.

GD..as you say a little jiggling maybe able to get it close and this was the answer I was hoping for..never swapped cutaways before to know the actual effect but a first time for everything..I'll give it a go  :)
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