sosomechanic
Member
- Jan 8, 2001
- 24
- 0
I thought this might be of interest to some of you other off road riders. I made a divider plate ( similar to the RB designs one, on the reed side of the throttle slide) to see if it would clean up some slightly raspy low end jetting below 1/8 throttle that hadn't responded to pilot jet and air screw fiddling and also hoping it might bump up the low end torque. My first test with the divider plate a couple of weeks ago showed that in my particular application ( '03 RM 250 with low/mid porting and head mods and a 19 ounce flywheel weight) it made the jetting WAY rich for both the pilot and needle. I went as lean as I could with a spare 40 pilot ( stock is 50, most people recommend a 48) and needle clip moved to full lean with stock needle. This was still so rich it would barely pull itself and would have fouled a plug promptly.
I removed the plate, ordered a 35 pilot ( the leanest available from Keihin for the PWK carb) and while waiting for the pilot a V-force reed setup I'd ordered from **** came in.
The V- Force definitely lowered the RPM range where the midrange surge of torque came in and perhaps made the low end a bit more responsive, but not impressively improved there. The neat thing is that after reinstalling the divider plate in combination with the V-Force setup the bike pulled very cleanly with the stock needle ( still full lean on clip position) and the new 35 pilot. Using the stock reed cage and the 40 pilot it was still hopelessly rich even with the airscrew out 3 turns or more so. After initial tuning the airscrew was set to 1.5 turns out with the 35 pilot and low end and mid range is remarkably clean and crisp even if you lug it down to near idle speed. More tuning will likely go in a bit more on the air screw and richer on the needle clip.
The divider plate and V-Force combo made a VERY noticeable difference in the low end torque on my particular bike. At low RPM levels where the engine was sluggish and didn't have enough torque for inclines it is now WAY more responsive and torquey. Night and day difference below 1/4 throttle. Not a bid deal for motocross racers but if you ride in slow, slick and loose stuff off road this was a major improvement. Really big improvement on terrain where lugging at low RPM's in a higher gear is a big plus for traction because it will pull the taller gear much more smoothly now. Feels like it bumped the useable torque output range at very low throttle openings ( 1/8 and below) down by at least 1000 RPM's, probably more. The engine has to be lugged very far down now ( pretty much purposefully) to get below the responsive and useable low end torque in the first three gears.
Anyhow, I don't claim this would work on any two stroke. I've spent numerous hours the last few weeks trying to dial in the low end on my bike and it made a BIG improvement in low end , very low throttle opening torque and response on my bike.
Later,Michael.
I removed the plate, ordered a 35 pilot ( the leanest available from Keihin for the PWK carb) and while waiting for the pilot a V-force reed setup I'd ordered from **** came in.
The V- Force definitely lowered the RPM range where the midrange surge of torque came in and perhaps made the low end a bit more responsive, but not impressively improved there. The neat thing is that after reinstalling the divider plate in combination with the V-Force setup the bike pulled very cleanly with the stock needle ( still full lean on clip position) and the new 35 pilot. Using the stock reed cage and the 40 pilot it was still hopelessly rich even with the airscrew out 3 turns or more so. After initial tuning the airscrew was set to 1.5 turns out with the 35 pilot and low end and mid range is remarkably clean and crisp even if you lug it down to near idle speed. More tuning will likely go in a bit more on the air screw and richer on the needle clip.
The divider plate and V-Force combo made a VERY noticeable difference in the low end torque on my particular bike. At low RPM levels where the engine was sluggish and didn't have enough torque for inclines it is now WAY more responsive and torquey. Night and day difference below 1/4 throttle. Not a bid deal for motocross racers but if you ride in slow, slick and loose stuff off road this was a major improvement. Really big improvement on terrain where lugging at low RPM's in a higher gear is a big plus for traction because it will pull the taller gear much more smoothly now. Feels like it bumped the useable torque output range at very low throttle openings ( 1/8 and below) down by at least 1000 RPM's, probably more. The engine has to be lugged very far down now ( pretty much purposefully) to get below the responsive and useable low end torque in the first three gears.
Anyhow, I don't claim this would work on any two stroke. I've spent numerous hours the last few weeks trying to dial in the low end on my bike and it made a BIG improvement in low end , very low throttle opening torque and response on my bike.
Later,Michael.
