Keihin PWK 30 Carb

[Weldangrind]

Sorry, Jerry and Dan. I failed to explain that I'd be looking for a spigot mount that matches my current flange mount. I'd really like to maintain the current orientation with a flat slide like Jerry's. I'd also really like to find an angled spigot mount that has a nipple for a vacuum hose; a vacuum gauge might be really useful for tuning.


Jerry, it's a Lifan GY5 from the mid-2000's; it was one of the more prominent bikes on the forum back in the day. You can read about it here: http://www.chinariders.net/showthread.php?t=12512 It's fun for me to re-live the thread from five years ago.
Jerry, where did you end up putting the pilot mixture screw with the 38?

[Weldangrind]

To answer your question with pics Jerry, here she is:

[JerryHawk250]

Originally Posted by Weldangrind

Jerry, where did you end up putting the pilot mixture screw with the 38?

I started at 1 1/2 turns out. I may have turned it in 1/8 to 1/4 of a turn.

[Megadan]

Originally Posted by Cravin01

Well I cant seem to be able to decide if this is worth my while, I read that a 4 stroke doesn't need a power jet but it never said it wouldn't give a improvement if used.

As always Dan threw in some valuable info about the carb and I will not be decking my head but I could polish the exhaust port myself, so I thought maybe I should look at the Keihin PWK28 ...But I'm not positive going to a power jet and a slide valve will give the desired improvement over the butterfly valve in the PZ30.

Opinions please!

You can use a power jet carb on a 4 stroke. The idea behind a power jet is a little different from a pumper style carb in how they operate. Pumpers shoot a little fuel in right when the throttle opens to help eliminate throttle response delays, giving them an almost instant throttle response, but otherwise use the traditional jetting methods.

A power jet only adds extra fuel at wide open throttle conditions. It was originally developed for 2 stroke race bikes to try and give the best of both worlds, the extra power and higher rpm capability of a leaner main jet, but with the extra fuel needed at high rpm and high load conditions where a lean main jet can cause potential harm.

On a 4 stroke application, the same basic ideas can apply. It would allow for leaner jetting for part throttle operation, but then contribute the extra fuel needed for WOT to help prevent melting a hole in the piston or other such lean fueling issues. The benefit is not as great on a 4 stroke, but still there. In Jerry's case, if he disabled the power jet on his carb. he would likely need to up the main jet one size to compensate.

You could actually add a power jet to a pumper carb if you were really feeling froggy, but that would be a total pain in the ass to tune lol.

As far as the half round flat slide on his PWK 30 and the round slide on your PZ30. The Flat slides main advantage is that they have a higher intake velocity across the jets and less turbulence. This means they tend to be much more responsive vs. a typical round slide. The exception of this is adding an Under Flow Optimizer. The Mikuni VM30 (genuine carb) that I bought for my ported head has a UFO fitted to it. Now I just have no bike to install it on.

As far as porting your head. Do it. If you see how restricted the exhaust port is with your own eyes, you would understand that even without decking the head to raise compression there would be a definite power gain from the port work. You won't suddenly be pulling power wheelies, but the motor will pull much stronger in the higher revs, where it usually starts to feel a bit flat.

[JerryHawk250]

Originally Posted by Megadan

You can use a power jet carb on a 4 stroke. The idea behind a power jet is a little different from a pumper style carb in how they operate. Pumpers shoot a little fuel in right when the throttle opens to help eliminate throttle response delays, giving them an almost instant throttle response, but otherwise use the traditional jetting methods.

A power jet only adds extra fuel at wide open throttle conditions. It was originally developed for 2 stroke race bikes to try and give the best of both worlds, the extra power and higher rpm capability of a leaner main jet, but with the extra fuel needed at high rpm and high load conditions where a lean main jet can cause potential harm.

On a 4 stroke application, the same basic ideas can apply. It would allow for leaner jetting for part throttle operation, but then contribute the extra fuel needed for WOT to help prevent melting a hole in the piston or other such lean fueling issues. The benefit is not as great on a 4 stroke, but still there. In Jerry's case, if he disabled the power jet on his carb. he would likely need to up the main jet one size to compensate.

You could actually add a power jet to a pumper carb if you were really feeling froggy, but that would be a total pain in the ass to tune lol.

As far as the half round flat slide on his PWK 30 and the round slide on your PZ30. The Flat slides main advantage is that they have a higher intake velocity across the jets and less turbulence. This means they tend to be much more responsive vs. a typical round slide. The exception of this is adding an Under Flow Optimizer. The Mikuni VM30 (genuine carb) that I bought for my ported head has a UFO fitted to it. Now I just have no bike to install it on.

As far as porting your head. Do it. If you see how restricted the exhaust port is with your own eyes, you would understand that even without decking the head to raise compression there would be a definite power gain from the port work. You won't suddenly be pulling power wheelies, but the motor will pull much stronger in the higher revs, where it usually starts to feel a bit flat.

Thanks Dan for explaining that. I knew you could explain this better than I can. lol I can should how something works but not so good at explaining. Glad we got you around. lol

[JerryHawk250]

Originally Posted by Megadan

Yep, same result on my part. If you want a spigot mount carb, you are covered. Flange mount, not so much. I swear at one time I saw some 30mm flange mounts, but now I can't find them.

Dan, Do you think rotating the CRF intake 180 degrees would work? I'm at work so checking would be later today. Besides I would have to pull off the carb a try it. You have your head and intake were you could try it.

[JerryHawk250]

Weld, the BI0160-B might be it. https://www.biiee.com/motorcycle-par...ipe-p-345.html

[Megadan]

I dont think it would work due to the bolt pattern being off of center

[JerryHawk250]

Originally Posted by Megadan

I dont think it would work due to the bolt pattern being off of center

I never really noticed that. Oh well, and the search goes on. lol

[Weldangrind]

Maybe I'll just play with the new pumper carb I have en route for now. When I tear into it, I'll see if I can make a CRF intake work.

[JerryHawk250]

So today I got out and got some ride time in. I'm really impressed with the performance of this carburetor over the stock pz30. Performance throughout all throttle positions is so smooth. I found the biggest improvement is in the lower end power. I got out on the highway and just cracked it back. I found it was falling off in 4th and 5th if I went past 3/4 throttle. No problems 1st through 3rd. Was still getting 74mph. So I turned around and back to the house to swap out to a 125 main. Went out and made another run on the highway. Now it runs perfect through all gears. It got a little windy but still manage to get to 77mph. I think it will get 80 or close to it. Just too fast and windy for the knobbies. here's a few pictures comparing the pz30 to the pwk30. The pwk30 is no where as restrictive as the pz30. Plus jets swap is so much quicker and easier
Loosen the clamp and the carburetor comes right out. No fighting nuts with open end wrenches.

[Weldangrind]

After I've done some testing with my new Keihin pumper, I might try a carb like yours. I can see it being a real improvement on my quad.

[Megadan]

I think the data I can extrapolate from your testing and riding is that, with a ported head, the PZ30/VM26 becomes the restriction in the system. I am sure a stock Hawk would also respond well to a true 30mm carb as well, but a 125 main jet with the power valve also supplying fuel is really good evidence of that increased top end flow.

[JerryHawk250]

Just got back from a 150+ mile ride. Started off a cool pleasant ride. About halfway I stopped and took a break and ate. The ride back was not so pleasant. Only 94 degrees with a heat index of 103. Too damn hot. Yes Dan, with the ported head and new carb definitely makes a difference. only thing that wasn't flowing was the air. Nice and thick humid air. Lol the HAWK is parked for a little while. May take a ride after the sun goes down.

[JerryHawk250]

In case anyone was wondering were I was riding for 150+ miles. Riding the twisties through the Louisiana swamps. Ran across two alligators and one big racoon. And lots of snakes.