GT250 Jetting

[EvanB]

I bought a 74 GT250 a couple weeks ago that I have been working on getting running. The airbox I got with it was supposed to be the stock one but the spacing on the carb boots is too close together and it won't fit. I am thinking about getting some UNI pod filters to replace the airbox. How much should I go up on the jetting?

[H2RICK]

What's the altitude where you run the bike ?? Average temps ?? Average relative humidity ?? Is the bike totally stock other than the missing airbox ?? What condition is the engine in ?? Compression ??
Ignition timing checked lately ?? Are you a lead-wrist ?? Or a mild-mannered Clark Kent type ??

All these questions need to be answered before I'D venture an opinion on jet sizes. Ventilated pistons are soooooo depressing......

[EvanB]

Altitude is about 800 ft above sea level on average, temps of 60-90deg F, humidity is average I suppose, not to high or low (Ohio).

Engine has around 17k miles on it, not sure if it has ever been rebuilt. I haven't checked the compression yet. I will be doing the ignition timing soon. I tend to be a lead-wrist when I only have 30hp at my disposal.

[krwalsh]

I forget what I have in mine, but it has K&N pod filters. I just checked my last Sudco order, and I have pilots from 27.5 to 32.5, and mains from 122.5 to 127.5. That was an order to complete my kit so I had every one in a range. IIRC I have 120 mains and 25 pilots in there right now. I am sea level, and it was exceedingly rich last I ran. My advise is to get a full kit of jets, and start with something very, very fat. It is easier to take the carbs off, pull the jets, and do it again, than it is to pull the motor, pull the jugs, replace the pistons, and hope you got every last bit of metal out of the crankcase.

[EvanB]

Also, what style of jets do the VM carbs on these take?

[krwalsh]

They are the hex style.

[EvanB]

The small or large hex style from Sudco?

Thanks for all the help by the way.

[krwalsh]

I thought it was small hex, but I'm not sure. My 127.5 Main Jet was part number: 004-191

So, cross-reference that in the Sudco catalog and you should be able to figure it out.

[EvanB]

That part number shows up as the large round type.

[krwalsh]

Yep, that makes sense. I seem to remember now that they are round, with a screwdriver blade cut in the bottom.