VB with VH top end - much bigger jets ?

[john.nash]

Now that I have put the right cam in, then by VB/VH hybrid pulls over 30mph.
HOWEVER, with the standard carb (on OEM jet sizes) then it requires about a 1/2 to 2/3rds closed air slide to stop spitting back and stuttering at wide open throttle. It doesn't have an air filter.

To me this appears to be down to the main jet not being big enough ?
Yes the capacity is now about 540-ish cc with the VB bottom end (and compression plate) so I'd expect to go up a few sizes of main jet ..... however this seems way, way out from stuff I've done before. The carb doesn't appear to be sucking in air through it's joint, it has a steady tick over and responds to the mixture screw (usually they won't if the slide is worn and letting in air).

Being tight, I don't want to buy tens of jets.
I am at 200 now, what would be a ballpark size to get it rough so I can fine tune ? 220 ? 250 ? 300 ?

[Dave.Barkshire]

I would have thought that 200 was ok. The slide cutaway might be an issue. It all depends on what amount of throttle opening you're having the problems.

[john.nash]

wide open throttle.
It's fine on idle, just off idle and everything else.
Crack it wide open and it requires the air slide to get it to run.

I've had cutaway issues on the enfield's amal. Coming off and onto idle - that would spit like good un'. Went to the next richer cutaway and it was sorted.

[dave.pitt]

Hi John

I'm with Dave on this. I would have thought 200 was maximum. My KH is a 150, VB should be 160 but I run it on 150.

[keith.hodgenia]

It's often said that the solution to a lot of carb problems can be found within the ignition system. My NH used to spit back at low revs, I invested in a new carb, it ran much better but still spat back at low revs. I borrowed a different mag and the problem went away.

[admin]

I would say this too.
However, your man Merv rebuilt this mag 4 months back and the bike ran fine with it as a pure VB600.

I do take your point though.
I have a 220 and a 240 main jet, in my hand. If I am right, then any one of them should improve matters.
Otherwise I am looking elsewhere.

Of course, it could be my old carburettor (in which case I buy another nw concentric - I am not paying hundreds for an original repro)

[john.nash]

Update:

A 240 main jet cures all the issues, air slide not needed, no more spitting back.
Seems excessive, but we'll see how we go.
I'll do some plug chops at speed.