BannedCR500Riders.com

What is the best Carburetor for the CR500?

I’m interested in your experiences with carbs for the CR500. My OEM carb starts easy, but has a "4 cycle spot” from 1/8-1/4 throttle and then a big hit when it goes into 2 cycle above 1/4 throttle. It’s very difficult to tune out during the summer heat. Not a problem on the motocross track, but in the tight trails it’s a handful.

I see the Service Honda bikes use a Keihin 39.5mm carb, but I can’t find a listing for a 39.5 in the Keihin catalog.
I did find a listing for a Keihin 39mm PWK and its very reasonably priced.

Some folks are telling me to run the Keihin 38mm Air Striker as it’s easier to tune for a wide range of conditions. I rode a CR250 with an Air Striker and the throttle control was awesome, but I'm concerned it's too small for a 500.

I'll reply but I'm no expert just what I understand from the sites:
stock PJ38, I still run it but I run mainly dunes, I have no complaints but then again I am just in an ignorant bliss.

39.5 PKW, this is the carb that seems to be the best all around, Eric Gore claims it adds 3 HP to the top end and everyone that runs them here seems to have good things to say especially regarding running on the low part of the throttle like to mention.

38 PKW AS, same size as the PJ, it does have some obstructions in it but I would think anything you loos on the top would not be noticeable with the exception of a drag race.

You can read up on the new carbs and the pulse systems, I think the jury is still out on them.

Lectron, if you want wide open only, I hear that is about all they are good for but maybe with the right tuner they could be made to work?

I have a 39.5 PWK waiting to go on my bike but so far I'm too satisfied with the PJ to make the change, I feel like now I have something very reliable, making a change like that could cause me to melt my engine. or I'm just too lazy

well this could take some typing

Keihin Carbs
-On the flow bench a pj, pwk, pwk AirStriker all flow the same CFM WFO.
-The divorced choke-pilot circuit makes the PWK series respond crisper and meter more accurately at low slide position compared to PJ Carb.
-The Airstriker carbs with their intimidating vanes in the bell will flow more velocity with less turbulence than other Keihins, so more accurate pilot jet metering because of the stronger vacuum signal.
-PWK series are known for excellent starting

Mikuni TM
-Looks good
-pain in the nuts to tune

SmartCarb
-Billet 38 I ran was decent, adjuster moved on its own but updates from APT were available.
-Very clean running on the engine, even smells different
-fitment was a bit queer, clamping flange was a worrysome seal
-Cast 38's are requiring primer bulbs for 500 applications

Pulse Induction modified PWK AirStriker
-reversion of the intake charge is captured for less multiplying of fuel map
-tuning is extremely simple and forgiving to rich conditions
-Low end response and power is increased dramatically
-starting is extremely better
-read more here to understand it http://www.bannedcr500riders.com/board/ ... 963#144963

Easy... the 39mm PWK

Where do you purchase a 39.5mm Keihin as they are not listed in the Keihin catalog?
Could the Keihin 39.5mm and the 39mm PWK be the same carb?

Yup....

Are the slides different? Is the slide that comes with the 39mm PWK the one to use?

Hey, I'm about to do a rebuild on my cr500. Going to order a new cylinder, piston and reeds. Just ordered the fmf fatty and a powercore 2 witch should be here by tomorrow. At the moment I run the stock PJ carb but I have to rebuild the top on it and buy new jets. The engine is a 1997. Question now is would it be better to order a pwk carb?

Carb parts warehouse has new pwk39,5 on ebay for 209$. Will the pwk fit like the pj carb or do I have to modify something? I mostly ride mx on pretty sandy tracks. Will the pwk be a better choise for me?

I went with a Keihin 38mm PWK Air Striker. If you are only interested in peak HP, then the original PJ works fine. The problem with the PJ is it is impossible to tune out the off idle lull/dead spot. If you want seamless throttle control without the sudden hit, then the Air Striker is the way to go. It really smooth's out the power band, yet retains the top end power.

If you do some research on carbs for the CRF250 and YZ250 you will find the Air Striker is the best carb out there. It is the last carb redesign since they switched to injection. The PWK air striker has several engineering updates to improve air flow as well as venturi signal to the jets. The 38mm PWK Air Striker is a direct replacement for the OEM Keihin PJ that came on the CR500R.

Correct, and it flows more velocity at low rom with the same cfm wfo. It can be bought as an oem 2000 cr250 carb for 180-190$

So the pwk 38 airstriker should be a better choice then. They're pretty cheap over there if you can get them for 180-190$. About 309€ here when I checked quickly wich should be around 390$ Maybe cheaper to order from the us.

What about the pulse injection system you have Roostius. Just checked out your youtube account. The bike seems to run much nicer with that. Something you have made yourself? Is it running with the pwk 38as carb?

You should also look at the JD Jetting complete carb kit. He sells a new Keihin 38mm PWK Air Striker pre-jetted with spare jets and needles for $245. Pretty good deal. If you purchase a new Air Striker and it comes with the wrong slide, jet, and/or needle, you will spend more than $245 getting it all together.

I run JD jetting on my suzuki and it works great. But now I'm really curious about the pulse injection. I need new cylinder, piston, reeds and a carb anyway

dont try metering a bike with a mix of JD or genuine jets, they are no where near the same

No, but the JD jetted pwk is probably a good setup. More interested in the pulse injection though

Roostius_Maximus wrote:dont try metering a bike with a mix of JD or genuine jets, they are no where near the same

The JD kit I got for my YZ250 came with Genuine Keihin jets. Only the needles were not.

Anyone running the 40.5 mm pwk?

MojoScojo wrote:

Roostius_Maximus wrote:dont try metering a bike with a mix of JD or genuine jets, they are no where near the same

The JD kit I got for my YZ250 came with Genuine Keihin jets. Only the needles were not.

Thanks Scott, They must have changed from the ones I'd received before.