Author Topic: PWK carbs  (Read 666 times)

Online chaterlea25

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Re: PWK carbs
« Reply #15 on: 06.08. 2020 22:00 »
Hi All,
Apologies to Berger, I have not had a chance to go through the Mikuni tuning book to assess the settings he gave for his A7.
Mikuni's seem popular in USA, so I went to Britbike forum and looked for topics on them. there are quite a few!!!

http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=599048&page=1

RD,
How far away from the "standard" (as supplied) VM34 settings have you changed?
Image attached (pilfered from Britbike)

John



John
1961 Super Rocket
1963 RGS (ongoing)

Online berger

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Re: PWK carbs
« Reply #16 on: 06.08. 2020 22:27 »
that's fine john thanks for the link. i  had a quick read and will never be any wiser on how to get the mik working properly so i'm with rd fella now------ fed up with it , my needle is a 5f21 and the jet is fixed and I can't even see a number on it.??? as for the carb the sticker has worn off and I can't find a model number, I am guessing it is a vm round slide with a lever choke and is 28 mm bore. it will be sold hopefully--- even at a great loss. the amal has got the bike back to first kick every time-- hot or cold *woo*

Online RDfella

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Re: PWK carbs
« Reply #17 on: 06.08. 2020 23:04 »
Hi John.
Obviously there is no 'standard' setting for a carb - it depends on the engine it's fitted to and mine's unique. I tended to aim for Yamaha XT specs as the cyl heads I'm using are SR, but then my bore / stroke ratio is way different.
Anyway, I researched what others who fitted 34mm VM's to XT's had done, and I referred to those specs earlier. My out-of-the-box specs were close, but not exact. Indeed, even people with similar bikes use differing combinations.
Mine came with 15 pilot, needle jet P6, needle 6F9, main 175, air 2, slide2.
Changed pilot to 35, now 30. Changed main to 230 and changed slide to 2.7. Tried needle up, down and inbetween. It's presently OK idle to 1/4 throttle (needle down), but with needle up won't take half throttle - just bangs and farts. With needle down, it will rev higher, but really rough, hence my analysis that the larger pilot has enriched the needle circuit (remember all jets work together on these carbs). As I said, at £30 to change a jet in two carbs, I could spend thousands and still not get it right. Take the needles for example. Presuming the attachment comes out, you can see not only are there single and twin tapers, the needles in fact don't really have a taper - they have 6 different diameters along their length. Take 6F9 (mine) and compare with the supposedly richer 6DH4. But is it? The HD64 is richer at stages 5 and 6, but leaner at stage 2 and 3. How the hell can anyone get to grips with that mess? How many needles does an Amal have?
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online metalflake11

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Re: PWK carbs
« Reply #18 on: 02.10. 2020 02:22 »
that's fine john thanks for the link. i  had a quick read and will never be any wiser on how to get the mik working properly so i'm with rd fella now------ fed up with it , my needle is a 5f21 and the jet is fixed and I can't even see a number on it.??? as for the carb the sticker has worn off and I can't find a model number, I am guessing it is a vm round slide with a lever choke and is 28 mm bore. it will be sold hopefully--- even at a great loss. the amal has got the bike back to first kick every time-- hot or cold *woo*

Out of interest, what were you trying to achieve by putting a Mikuni on Berger?

Just a thought, is yours the same as S.R.M. sell for A10's? If it is, they might tell you the jetting etc they have fitted to theirs?

They kept trying to get me to put one on, but how can you improve on a bike that starts first kick unless I cock up, and pulls like a train all the way up to my bottle going?

I can understand if you're racing or have raced and have gaining that extra few percent in your blood, but most of us aren't like that.
England N.W
1960 A10
England

Online KiwiGF

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Re: PWK carbs
« Reply #19 on: 02.10. 2020 09:55 »
A mate fitted twin Wassell concentric lookalikes to his a65, half the price of amals apparently. They work well and give over 70mpg. Ive not tried them myself but will next time.
New Zealand

1956 A10 Golden Flash (1st finished project)
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Online berger

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Re: PWK carbs
« Reply #20 on: 02.10. 2020 11:41 »
metalflake11 , I wasn't trying to achieve anything exciting but I was fed up of playing with two leaky and well abused 60 year old carbs and had stories in my head about how good mikunis are. one came up for sale " jetted for a BSA shooting star engine" so muggings me bought it only to find out it didn't do what it said on the tin. starting hot or cold was pot luck. so I played with it using a few jets and gave up. since fitting the new pattern amal there are no problems

Offline rocker21

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Re: PWK carbs
« Reply #21 on: 14.12. 2020 13:29 »
I have a 26 mm JRC on my A7ss, runs a treat, no problems at all, even put one one my Ariel Fieldmaster to replace the so called refurbished monoblock , runs well, very simple to set up as well. great if you want a road bike that works, maybe not so good for shows.
had to make my own cable but thats not a problem .
bought my carbs from www.brillbikeparts.co.uk