cross over pipes

seattle##gs · 2026-06-20T19:55:08-0600

I have a MK2A with cross overs and the mufflers are reduced at the tips to 1".
This is affecting carburetion bit. I'm jetting a VM34. I started with the usual #3 slide 40 pilot 6DH3 needle P-0 needle jet needle clip on 4th position counting down from the top and 240 main. It runs great, starts and idles beautifully (TriSpark) but not perfect. I tried a 37.5 pilot and it was a very noticeable improvement in acceleration. Now, the difference between 37.5 and 40 is a micro adjustment and I was surprised to see such a big gain. I am curious if anyone else has used the mufflers with the 1" restriction at the tip and is the crossover has need different jetting.

Carl H · 2026-06-21T08:27:18-0600

seattle##gs said:
I have a MK2A with cross overs and the mufflers are reduced at the tips to 1".
This is affecting carburetion bit. I'm jetting a VM34. I started with the usual #3 slide 40 pilot 6DH3 needle P-0 needle jet needle clip on 4th position counting down from the top and 240 main. It runs great, starts and idles beautifully (TriSpark) but not perfect. I tried a 37.5 pilot and it was a very noticeable improvement in acceleration. Now, the difference between 37.5 and 40 is a micro adjustment and I was surprised to see such a big gain. I am curious if anyone else has used the mufflers with the 1" restriction at the tip and is the crossover has need different jetting.

at least the Mikuni carbs give you many choices and sizes of jets, But with Amals I altered parts to get 1/2 size step increases, And You need to blue print them first, to assure the parts are the same dimension wise. For instant modifying a #3 slide to make it a #3-1/4, etc.

seattle##gs · 2026-06-21T09:34:42-0600

Many times I've wanted a half size change in a slide. I have a small box of mikuni slides that I need to cut for #3 cutaway. I have a mill and an angle vise so it's possible.
Later that same day I raised the clip to lean it a bit and had more good results. I'm happy but curious as to why leaning it is necessary. The only difference is the crossover pipes and the 1" reduction at the tip of the muffler.

L.A.B. · 2026-06-21T10:02:57-0600

seattle##gs said:
I have a MK2A with cross overs and the mufflers are reduced at the tips to 1".

I assume somebody has fitted fitted the Mk2 reduced outlet peashooters to a Mk2A then as that would have had black caps (and black plastic airbox) airbox presumably not fitted?

cross over pipes

seattle##gs

Carl H

seattle##gs

L.A.B.

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