PWK help

[jfarrar30]

im trying to get a PWK 21 and 24 to work on our 50. currently has the PE 20 but puts out way better power and response with the larger carbs specially the 24. problem is if you stab the throttle from an idle on both carbs it will bog and die or bog then take off. will not do it just off idle and takes off like a raped ape. does not bog at all with the PE. i have adjusted mains and needles to no end thinkg its dumping to much fuel cannot get it out. not the clutch definetly carb. what other adjustment do the PWK's have? or should i scrap the idea? the power difference is huge and how quick it revs to

[nordic quad]

What size are the pilots your working with?

Stein A

[mmsoup]

Pilot

[jfarrar30]

i think the 24 has a 50 or 52 in it but after a little research i see alot of guys in the 40 42 range.i am out 2 3/4 turns on the airscrew so it can afford to come down just didnt think the piot would do that. its a 2011 50 motor w/ minor porting , koso intake with snyder rev pipe and runs best with the 24 if i can get the bog out of it. will mess with it more next weekend when im back in town and hopefully have his new axle

[fomospede]

whats the stall rpm?
stock cvt?
roller weights #S
try a lower weight
a little slower shift may bring the revs up smoother?
itsa 50 you cant have it all :blah:

[nordic quad]

We have newer gone higher than 40 on the pilot with 21 and 24mm PWK carb both on our 100cc and the Polini 70 and 1-1,5 turns out on the air screw.But of course humidity,temp and altitude also comes to play.


Stein A

[familyof5]

Do you want to sell the PE20? I am looking for one.

[EthansDad]

Carb selection for the 50s will come down to what type of motor you built (torque or rpm). Are you trying to get massive low- mid power or all top/high rpms? Telling us what cylinder/ pipe will help.

In my experience, the smaller carbs like the 20mm give good low- mid and good high rpms too. A 16 or 19mm is excellent down low, no top, and a 21-24mm has very poor low-mid and excellent top.

I run a 20mm on our mod 50, but know I can get more rpms out of a 21mm. The problem is the low mid sucks so much on the 21mm, it result in slower lap times.

That low rpm bog you get on the larger carbs is because they are larger and letting to much flow in at low rpms. If you can find a way to tune that out, let us all know.

[Team-Ty]

Here a link of our 50cc last year with a 24mm carb on it. You just need to know how to tune your bike. Every bike is different so listening to people (some) will get you close but you need to just play.

http://www.youtube.com/watch?v=XiY8lcMwrnk&feature=youtube_gdata_player

[EthansDad]

checked the video out and this sounds to me like what an over sized carb sounds like. when he starts, the rpms are flat for a split second, then it spools up and rips. that lower end flat spot is what I've been unable to tune out on a 24mm carb for a 50cc. if the rider can keep it pinned all the time, then they might never hit the flat spot, but on a tight track, or if the clutch is fading, the bike will tend to get "stuck" in that flat spot and not come out.

on ours, when clutch engages, the rpms climb straight up with no flat spot. I think what we'd see if we put our two bikes in a drag run (yours 24mm, mine 20mm) is our bike would take yours in 0-125ft drags, but yours would take ours in 0-200ft drags. its really a trade off in how you want to set up the bike. I also think the smaller carbs are more forgiving to jetting misses. If we're off on our 20mm, it will still run OK, but if your pilot is off on the 24mm, the flat spot will get bigger in a hurry.

[Team-Ty]

yes it is a very small window but when its on its on and the bike rips. You have to keep the engagement of the clutches high inorder to use a big carb, but we run TT alot and the big carb really shows on the straights.

[EthansDad]

for TT racing, that makes sense. I could see how the larger carb would give the top end you need for that style of racing. I think in mx its mostly short range accel bursts that get good lap times.

curious, how high did you go on the stall? I was experimenting with one setup and took the stall over 10k. it got great drag times, but turned out my rider did not like it on the track, slower lap times.

[hanker]

Originally posted by Team-Ty
yes it is a very small window but when its on its on and the bike rips. You have to keep the engagement of the clutches high inorder to use a big carb, but we run TT alot and the big carb really shows on the straights.

This quad dose run great^^^^^^^^and it is super fast! :)

[hanker]

Shawn, here is video from last year at Pine Lake. Ty is on the far left hand side.http://www.youtube.com/watch?v=5GlVM8rBv60

[Team-Ty]

yeah its our video we took I was going to post it but the music is wack LOL. Thats why I didn't

[Team-Ty]

I am not going to get into exact details on how I tuned his bike but the clutch hit in around 6.5k and I am really fat on the pilot jet. Reason for the big pilot jet is when the throttle cracks open it has the fuel there to use other wise the flat spot is really big if not impossible to take off with out feathering the throttle. If you understand how a carb works it will make sense. Reason for the great throttle response of the little carbs is the velocity of the air passing over the venturi, with a big carb the velocity isn't there in the beginning and the motor starves at first.

Also when tunning remember the velocity thing sometimes even though the bike might seem lean going to a smaller jet will pull more fuel in hint hint.

[wrhracing]

Usually the larger the carb the further the stall needs to go up, to some extent. Often a slightly lighter roller weight can mask the boggishness of a larger carb.
Another way to approach it would be to take your 20mm that worksgreat and make it larger a little at a time. A divider in the intake of the carb helps. Oval Bored 20mm round slides work pretty cool. Small at the bottom and larger at the top.
Maybe put the larger carb on that works the best and try advancing the timing .2 or .4 mm and see if your bottom end response improves.
If you are running a race fuel try cutting it with up to 50% pump gas in all this heat and humidity. That may put the pop back into the engine. After all race gas burns slower than the pump gas.
When it is hot outside there is a lot less oxygen per "gulp" of air your engine takes in. When it is colder there is more oxygen . So a setup that doesnt worknow may work great in the winter.