jetting for VM38 on TT500 motor

[Marc.com]

Just doing a little TT500 tunning have horror flat spot off idle and theatening it with FCR carb if it doesn't change the error of its ways.

Anyone jetted VM for TT500 with 540cc and 10.5:1

[matcho mick]

+20 high comp TT,ran 2 38's
pilot    70  50
slide #2    #3
NJ     P8   Q2
N     6F39   6DP1
mj    370    280
confused?,(i was  ),

[crash n bern]

Have you tried leaning off the air screw or dropping the needle one notch? I'm assuming it's a bit rich in the pilot circle.  I'm not much of a carb tech head, but I have succesfully dialed in a few FCR's from scratch with seat of the pants tuning.

[Marc.com]

+20 high comp TT,ran 2 38's
pilot    70  50
slide #2    #3
NJ     P8   Q2
N     6F39   6DP1
mj    370    280
confused?,(i was  ),

Hi Mick,

looks like I will try 280 main and 3.5 slide with 50 pilot and see if that makes a difference .... or I will swap to Keihin

[bazza]

Mark try one change at a time. I had bottom end hesitation on Maicosport big bore XL motor,old guy said cut the shrowd (horse shoe shape) on top of needle jet.
I cut in half,so about3mm high, and never had a problem again.If desperate worth a try.
Get top end right with full noise plug chop,then do rest,one at a time

[Colin Jay]

Below is the jetting for the 38mm VM that I am running on my XT500C enduro / roadt trial bike. The engine is fitted with a 540cc 10:1 big bore piston, runs a Tighe 503 cam and a home made exhaust. Jetting was set on a dyno using a EGO sensor

Main jet - 190
Nedle - 6F9 (bottom groove)
Needle Jet - P 6
Slide - 2 (but could do with a 1.5)
Piolet jet - 25
Air Screw - 2 turns


My other hot engine, 500cc, 12:1 CR, Web 88A cam, open megaphone exhaust, runs the same jets except for the main jet is a 230, and Pilot 20.

CJ