Keihin PE32

Jays100

Jays100

Veteran Member
Joined
May 29, 2020
Total Posts
1,479
Total likes
1,005
Location
Enfield, CT USA
I finally figured it out. Take a never been in production nor has use history, and make it work on the 450. Check.
Must AHMRA legal, I.e. similar to a Mikuni VM series in that it’s a round slide design. I’ve received rules committee correspondence to that effect. Check. More on that later.
Must be tuneable. Check. More on that later.
Must fit under the side cover. Check.
Must fit the stock air filter boot. Check
Must be affordable. Check.
Must fit the intake manifold. Check.
Must have reasonable cost. Check.

Did I miss anything?
 
Note a 1/2” (13mm) spacer under the intake manifold. The spacing is ideal so the cable clears the crossover and the inlet bell fits the air filter boot. The inlet bell is 2mm larger than the 14H etc. carbs. The filters are sourced from Scrambler Cycle.
 
The development was crazy hard, there was a mix of bike issues as well as carb factory non-support. I had a backfire through the carb that I could t fix. Turns out I needed to adjust the valve clearances, both intakes were tight and the valves were being held open. Oopsie!

I used a O2 sensor which helped needle choice but the current draw drained the battery muchly so some of my data is questionable. Still, here I am with a workable solution to the high cost Mikuni kits.

My plan is to package a reasonable cost kit that can be raced in the mod production and up classes. Or used on the street. My bone stock 68 CL450 really likes them! The seat of the pants test is they’re a little bit more responsive, cleaner, at 1/8-1/4 throttle and 3/4-WFO throttle. Felt the same in the middle.

Gathering mileage numbers now.
 
I wrote to the AHMRA rules committee if this carburetor would be legal for racing. The response was positive.
 
Here’s what they said:

We reviewed the Keihn PE carbs and deemed them eligible for use under the rules that are already established for round slide carburetors.

The following is a listing, by class, of the various options: Sportsman 500 - CB450 legal with any size carb, CB500T illegal; Novice Production Heavyweight - CB500T legal, but only with original size, CV carb (Keihin PE = illegal); 500 Premier - CB450 legal with any size carb, CB500T illegal; Formula 500 - CB450 and CB500T must be "like design" to pre-72, any carb size allowed.
 
Nice work Jay! Now if only a left hand version was available for choke knob direction purposes, or is it? The better question is, just how available are these carbs? I've never seen one that I know of.
 
I have not seen a LH version and the options I could work out (for now anyway) was use the knobs, which is not difficult or overly inconvenient or a remote/cable which is available.

They are there if you know where to look.
 
Those carbs do have the cable actuated choke version, right?

IIRC they were used on some of the early-mid 80’s dirt bikes and a couple of ATV models - they were somewhat common around my era in the shop.

Pretty cool repurpose - are you planning on selling the kit as full carbs/spacers/jetting/needles or a separate kit with a “bring your own carb body” approach?
 
I've only ever seen small VMs around (mostly stock bikes), those look like an upsize version to me. Nice looking spacer, wouldn't notice if you didn't say to be honest, I imagine they'l look even better with the sync ports.
 
I did find a cable op kit but that only encompasses the plunger, spring and carb body adapter. I’ll have to add the split cable and handlebar lever. It’ll be an option. Truth to tell, it’s not hard to work the knobs by hand and it’s really only the right side. There is enough room to reach in there and the left one is outside, easy peasy.

The port size is 32mm and that’s the popular VM size - VM32 for the 450.

Yeah, I’d like to package a pre-jetted carb, manifold spacer (with synch ports) and cable dimensions (but not the actual cable). The reason is some folks have different bars than stock so one could tailor to the installation.

This carb, a PE32, has never been on a production bike but a PE28 has, so the manufacturer scaled up to a 32mm Venturi size and mixed/matched standard Keihin jets for this design. Non-existent factory manual or other support was one of my issues in tuning but, I’m taking care of all that going forward, with the kit. Just don’t be in a rush, I only have about 200 good running miles. Fine tuning so sea level up to 3000ft is a standard jet setting…unless you’re racing…
 
Here’s the very not exciting updated spacer showing a synch port.
Also, cable routing misses the hated crossover.
Finally, hidden behind the carb is the enrichener knob. Two fingers with plenty of room reaching around either side, a deft lift and it’s done, ready for a cold start.

IMG_3536.jpeg
 
The petcock on that tank seems to sit at an odd angle, or maybe it's just the angle of the picture.
 
An observation, I would prefer the fuel connection to be vertical, not angled for a cleaner installation.
 
Jays100 said:
Well, it is a CL from ‘68. They don’t hang perfectically vertical like the CB.
Click to expand...
I never noticed there was a difference, but then again I'm not sure how long it's been since I stood next to an actual CL450K1 either, guess I just never noticed.
 
Jays100 said:
This carb, a PE32, has never been on a production bike but a PE28 has, so the manufacturer scaled up to a 32mm Venturi size and mixed/matched standard Keihin jets for this design.
Click to expand...
I really enjoy threads like this that explore new solutions either for a specific purpose (AHMRA racing) or the eventuality that someone cannot find suitable replacements for worn out OEM components. The second motivation is more likely to hit home for me, but, in any case, this type of thread is really cool. As a part of following along, I was trying to find Keihin PE32 carbs, just out of curiosity. For example, I looked at Sudco and found PE20 through PE28 (increments of 2) and then a jump to PE38. I had read over the section above in bold too quickly — I guess you are working with Keihin (Hitachi Astemo) on this? If so, I'm surprised it is that easy to get them to do something like that, but I guess if there is money to be made through a kit then maybe they will work with you? I gather that the rest of the design is the same as the PE28?

I really like your spacer. You have given me motivation to look into the possibility of using a spacer on my CB360. I'm running Keihin 723A carburetors on mine and they don't match up with the OEM airboxes, so I have pod filters. I'm not sure that a spacer could help that situation, but I'm going to look into it!
 
Not revealing overmuch other than it has been a difficult project. Not having design support being foremost of the problems. Still, I’ve amassed a lot of data that I won’t be sharing back. That will aid tuning for custom applications though.

What is the C*360 port size? The 450 carbs may not be the best solution… there may be options. For instance, I like the KSR flat slide (well, ‘D’), they’re inexpensive and Jetting kits are available. But that’s just me.
 
Jays100 said:
What is the C*360 port size? The 450 carbs may not be the best solution… there may be options.
Click to expand...
I believe the CB360 port size is about 2mm smaller than that of the dohc CB450. I measure 34mm ID at the throat of the 360 carbs, as opposed to 36mm ID on the 450 carbs. The original carbs were shot and I had an extra set of the 723A carbs laying around, so I gave it a shot. It's probably not optimal, but has worked reasonably well. I mounted CB450 boots.
 
You must log in or register to reply here.
Back
Top Bottom