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Speedmoto VM30 Kit

OldPainless

OldPainless

Forum Newbie
Alright, need some bigger brains than mine to work on this. I recently bought a VM30 carb kit from Speedmoto to replace the damaged carbs that were on this 82 GS450 when I bought it. They actually work great - once the engine is warmed up.

Thats the issue, however. The enricher circuit appears to be way too rich and kils the engine in about 3 seconds of starting. It almost wont run at all without holding the throttle for 30-40 seconds to get it warmed up enough to run without the choke/enricher.

I read somewhere (think it was crazypj at HondaTwins) that you could drill/tap the enricher circuit and install a smaller sized jet. Does anyone have any info on doing something like this?
 
First get hold of the Mikuni Carburettor Super Tuning Manual. There are some good exploded views in there.
It looks like the starter circuit fuel jet is in the bottom of the float bowl - and may not be easy to access.
But the air side is alongside the starter plunger and may be worth a look.
If you can't fit a smaller fuel jet, lean it off by going bigger on the air inlet.
 
VM30 sounds tremendously oversized for a stock GS450 IMO. I think I saw the kit you must have with a google search, I'm wondering how the two carbs are held in sync?
 
Split cable keeps them in sync. They do sound majorly oversized but they seem to run fine - except for the enricher circuit.
 
Not a carb guru, but why tremendously oversized? It came with 34CV's & aren't they appx. equal to VM 28's? Are VM 30's tremendously larger than VM 28's?
 
While I can appreciate that there is poor support for 450 carb rebuilding, I still can't help but think that simply rebuilding a stock set is the easiest way to make sure your bike runs properly. Aftermarket carbs are a crap shoot, NOT turn key. So if you have to F around to get them to run right, how is that better than fixing the BS34's?
 
Might be true. Was missing the airbox, etc. How well do the stock carbs respond to K&N pods? Still have the stockers and don't object to going back. I came from the metal-puck Honda CV carbs that were impossible to correctly tune to pods so I assumed these would be similar.
 
I agree with Nessism, seems like getting the stock setup to work would be much easier. They're floating all around Ebay for $30-50 it looks like. Certainly cheaper than $350+ for this "racy" VM30 setup IMO.
 
Havent been able to find any stock airbox units for a 450t that would have cost less after buying all the missing bits. I'm under the impression the airboxes mount differently between models?
 
You're probably right, I had taken just a quick look and I should know better, after hunting around for Yamaha XS500 airboxes and carb boots with almost annual changes made by the factory. I would explore some other options like the GS salvage facebook group and calling around some motorcycle junkyards (a dying breed!).
 
Firstly, VM30's are not too big for this motor. I've run bigger on race 450's. Secondly, once set up they will carburate better than the OE CV carbs.
If the only problem is the starting circuit as seems to be the case, it's worth spending a little time sorting it.
 
OldPainless said:
Might be true. Was missing the airbox, etc. How well do the stock carbs respond to K&N pods? Still have the stockers and don't object to going back. I came from the metal-puck Honda CV carbs that were impossible to correctly tune to pods so I assumed these would be similar.
Click to expand...

The stock CV carbs run horribly with K&N pods, the diaphragms in the OEM CV carbs need smooth laminar air flow into the carbs to get a good reliable vacuum signal. It works after some fidling around, and some people say they run fine...I don't believe them at all. I have had pods on a stock GS450E and although the sound was fun, it never ran as good as with the stock airbox.

VM30's with pods should work but maybe you should have it tested on a dyno and get a proper A/F ratio reading and a re-jet.
 
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