Discussion in 'Airheads' started by Uncle Pollo, Oct 2, 2012.

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2. ### Kt-88I like everything.

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Maybe they mean 2.5 slides? I'm not clear on the needle jet size there, either.

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There are 26 needle jets in the 159 series and they increase in size by some arcane formula I don't understand but can regurgitate. The letters increase by 0.050mm, so O-2 is 0.050 larger inside diameter than N-2. The digits are increments of 0.005mm, so N-3 is 0.005mm larger inside diameter than N-2.

The arcane point I don't know enough about is the lack of uniformity between the letter series: 5ea N, 6ea O, P, Q, 4ea R. So the diameter makes a bigger jump between sizes at the lean and rich ends than it does in the middle ranges. Haven't found an explanation for that yet.
4. ### chasbmwLong timer

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It seems to me to be strange that people have been fitting Mikunis to airheads for at least 20 years and there is no consensus on what the jetting should be.

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I believe the whole point of this thread is to build a knowledge base for that exact reason.

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There are so many combinations .... Better to have as many as possible
7. ### DeutschMarkLong Way Round Here

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Different engine combinations, altitude, etc. Even Bings, which compensate for altitude, were jetted differently over the years.

I'd venture to guess most combinations here aren't 100% optimal, including my own, unless a wideband and dyno were used.

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Agreed, dyno results and wide band plus idle sniffers would really flesh out the discussion. All the same, we're talking carbs so humidity, air temp and altitude are always going to interfere with perfect results.
9. ### chasbmwLong timer

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There should really be baseline jetting, that you could adjust for altitude silencers etc .

Not having baseline info, persuaded me to fit dells about 7 years ago and it seems that things have not got better since.
10. ### blaine.haleLong timer

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Well my Mikuni's are on the way.
I'll be sure to post results.
11. ### Kt-88I like everything.

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I'm loving mine more and more.

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13. ### BeemerboffLong timer

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The 2928 / 123 adapters fit a 40 mm stub , and have a 28 mm center section in the bore, so they can be ground out to match 32/34 mm Mikunis to the inlet stubs on the head.

They also set the carb back a little, and depending on your set up with either Bings or Mikuni's this can sometimes work a little better too.

Wont cost much to try.

I also have around a dozen settings for Mikunis, but as I don't know the state of the bikes they were developed for I don't see much point in detailing them.

The cables are easy to alter too - the adjuster that screws into the top of Bings screws straight into the Mikunis, and the ferrule that fits into it unscrews from the end of the cable. So you can remove the ferrule, cut back a little off the outer sheath , replace it then replace the nipple with one to suit the Miks. I added a second adjuster up at the throttle end too, to make it easier to adjust the cables.

Amal used to have separate four and two stroke needle jets, difference being small bleeder holes in the jets. They now supply and recommend the bleeder jets for both four and two strokes, and one guy has picked up on this for the Mikunis too.
14. ### blaine.haleLong timer

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Definitely ordering a set of those today. It looks like the measurement for 32mm mikuni is 2.25" ID x 2" but I'll be on a 34mm mikuni. Any idea if that tube will still work and stretch or if I need something ever so slightly larger?
15. ### supershaftbecause I can

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I get them at the local hardware store.
16. ### hardwaregrrlignore list

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Hey Blaine, keep in mind to not crush the oem elbows when tightening down the clamps. I did it, and then added a metal ring that I have no idea where I got, inside the elbow to kept it from crushing. Just like the elbow into the airbox has one. Well, maybe not on the R90??
17. ### supershaftbecause I can

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+1
18. ### bgoodsoilDare to be Stupid

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2 1/4" ID fit my 35mm keihins perfectly. You can get silicone intake elbows that are very hard to crush in any color as long as it's glossy. Oughta look a bit better than my radiator hoses.

From the website:

Crap! I've completely ignored sticker tuning! No wonder Jenna's so much faster than me. I bet I'd pass her on the straight-aways if I get one of those 'Jon Stewart for President' stickers.
19. ### ontic…

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I just checked thorugh my emails and those are the ones I got (#RS225X20X25)
Page 105 of the Sudco catalogue lists the dimensions of the VM series carbs- VM32 and VM34 have the same ODs on the the in and out spigots (58mm and 40mm).
They fit the spigot on my VM34's very well- a nice tight fit before hose clamping- I didn't have time to properly hook them up to the elbows before I left Australia last year but from what I could tell it seemed like it was going to be fine (as it worked well for elite-less).
20. ### ontic…

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in elite-less's thread I linked to he said he had trouble finding an exact fit with local hardware store plumbing supplies and this was the case for me too.

These fit well and are good quality rubber and finish.

here is one of elite-less's images-
38mm carbs so a wider fit to carby but you get the picture.

On a classic black bike, personally I like the black rubber rather than the glossy coloured silicon.