Never ending VM30 enricher problem

Hi guys.

I've had my CB400N scrambler running on VM30's for about 3 years now and everything about the carbs is awesome. Great throttle response, smooth idle, NO off idle hesitation, pulls much harder through the low, mid and top end than the standard CV carbs (which never ran well on pods anyway). I dialed them in myself and have made a few tweaks over the years to get them exactly spot on.

However, there's one thing that no matter what I try, I cannot get to work and it's the damn enricher/starting circuit! With the enrichers off, the bike won't start when cold but starts instantly when warmed up. Never had a bike start so quickly, the engine literally rotates about once.

So naturally, when cold I need the enrichers. Flick them on. Press the starter and it starts instantly and revs up to around 3000rpm or so (no tacho so just a guess). However, after about 5 seconds the revs will start to drop and the engine will stall as if it's way too rich. If I flick them off before it stalls, the bike will idle for a few seconds then stall because obviously is hasn't warmed up yet and still needs a little richness but the level provided by the enrichers is far far too high! So I get stuck in a cycle of enrichers on, start bike, enrichers off, wait for stall, enrichers on, start bike, enrichers off, wait for stall... This goes on for about 5 cycles until the bike can finally hold idle without needing the enrichers.

I can compensate by richening the idle circuit with larger jets and winding in the air screw which negates the need to use the enrichers but then the bike is way too rich once warmed up and I get the dreaded off idle stumble.

Surely I'm not the only one with VM's who has this problem. I need a way to lessen their effect. They're off/on and have no middle ground. Holding them open 3/4 or 1/2 or 1/4 etc. doesn't help either, it still stalls out.

Here's a picture of my ride. Love it to bits, but 3 years down the track and I still haven't solved this issue.

when "setup" how many turns out is your air screw

You have an enrichener so bike does run way too rich when it's operating.
It's like having a second mini carb built into main carb
The enrichener jet is massive compared to what you probably need (as it was designed for a 1970's two stroke motor) but as it's (usually) pressed into float bowl you can't change it. It should be possible to drill out jet, tap hole and fit replacement jet several sizes smaller.
Trying to 'play' with the plunger only blocks the air side so motor gets even more fuel,

Thanks crazypj. That would explain perfectly why me trying to regulate the levers had no effect whatsoever. I guess I'll have to give the drill/tap/jet thing a go because as the carbs work now the bike is insanely frustrating to start! I mean it always starts, but it's such a bitch of a routine and I'd never be able to sell the bike the way it is now.

there is a balance you need to strike on the pilot fuel air screw vs enrichener

the engine should start easily when cold then drift up to bout 3k rpm then as it warms it will slowly choke

itself down and if you leave it long enough it will flood out

how many turns out on your air screw are you ?

Your statement about no off idle hesitation makes me think the pilot jets are way too big.
If you open to full throttle suddenly you should actually be pretty close to stalling out as air speed is real low compared to flow and can't get fuel delivery through jets.
The primary choke from two stroke fitted stock will help but it will over deliver fuel at higher rpm.
Personally I gave up on VM's and 'fixed' stock carbs on CB350, CB360 and DOHCCB450's

the number of turns out on the air screw will instantly tell you if you are really even close on the pilot

this is not a complicated procedure

Yep. I use the three turn rule... Over three too small under 1.5 too big and visa versa for fuel screwed ️


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that is close

i use 1 and 2 and run most of my kits at 1.5 turns and a little rich at idle not enough to foul a plug

but you can smell it

it help prevent off idle bogging and stalling after longer idle periods