Well, with the help of a couple of mid atlantic trial riding friends, I think I found the answer for replacing a Bing carb -- and not having to modify a Mikuni carb for fitment on Penton/KTM (Montesa, Bultaco, SWM, Can-Am, etc...).
I was asked to bring my 77 Penton 250 GS6 to our local riding area yesterday, so that that we could install a 30mm OKO K-101 carb to see how it would run. Of course I was little skeptical, but I figured nothing ventured, nothing gained.
My motor was built by Gary Ellis (great motor!!!), and the bike was equipped with a rebuilt 36mm Bing carb. Despite some previous jetting changes, during the last run a few weeks ago, the bike was still running rich down low, but was OK from mid range to top end. The loading up I was experiencing, made it slightly difficult to navigate tight single track sections (particularly steep inclines) unless I kept the revs up, and fanned the clutch.
Well, yesterday we installed the new OKO carb on a cold motor. It had a 48 pilot and I believe a 155 Main jet. Bike started on the second kick, and then settled into a nice idle. The motor sounded noticeably crisper than it did when it was running with the Bing installed.
I let it warm up, and then did some 1/8th of mile passes. No more hesitation, or loading up! Next, I took it to the woods, and lo and behold the bike ran terrific on the single track. I could lug it around -- almost trials like. No more problem with going up tight single track inclines. The transition from low to mid range to top-end was way better than I would've ever imagined.
In the end we surmised that it was a little lean. Unfortunately we only had a 55 pilot us, so next weekend we're going to install a 50 or 52 pilot at our next weekend ride.
But what was perhaps the highlight of this experience was the ease of installation. Since the carb is so much smaller than any carb I've ever seen, installation was a breeze. Now, it's very easy to access and tune. The rear bell of the carb was actually only slightly smaller than the Bing. So when I got home last night I installed 1.5 to 1 inch rubber plumbing coupling into the airboot and simply reinstalled the OKO carb with no problems -- great fitment, no leaks.
Needless to say, I'm happy with this purchase, and even happier that I ride with guys who have great knowledge of the OKO carb. Later this week, I'll post some pictures of what it looks like installed on my bike and show pics of my rear carb bell/airboot spacer modification. I'm also going to purchase a whirlpull throttle body, as the stock cable was too long.
In the meantime, if any of you are interested please take a look at this link and contact Roger. He is very helpful and knowledgeable about the OKO carb, and definitely goes the extra mile in helping you with set-up.
http://www.mid-atlantictrials.com/OKO.html
Hope this will help those you whom have struggled with the Bing/Mikuni/Lectron carb dilemma like I have for so many years.
Cheers,
JC Hubbard
Remember that this is a flat slide carb and is not "VINTAGE" legal, in any AHRMA event. Same with a Lectron. I wish the Lectron was legal as I run one on my modern Husqvarna and love it. This carb is legal for any Historic class and up (1975 and newer).
"D" slide carbs like that are not legal in any AHRMA class, not just Vintage.
Brian
Yep -- Brian and Dwight, I am aware of those facts. I sure wish it was legal. Fortunately, this is not one of the bikes that I race in AHRMA events. It's a bike I like to trail ride with my vintage bud's and ride at local "fun/charity" events.
John
Did Lectron carb's become available in 74" ? I seem to remember seeing a write ups starting in 74 or 75.. It is scary how much I do not remember, now where did I put my keys?
JC, it sound to me that the reason that your bike was loading up with the Bing is because the Needle jet and jet needle are worn. If the gaskets have not been replaced in a while, do that.. including the O ring on the Head. That should make a big difference. I was told by Bing international to replace them both each year..
Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74' 1/2 440 maico
70' 400 maico (project)
72' cr125 Husky (project)
93' RMx 250 suzuki
Honda TL 125
2004 Suzuki DL1000
Remember that this is a flat slide carb and is not "VINTAGE" legal, in any AHRMA event. Same with a Lectron. I wish the Lectron was legal as I run one on my modern Husqvarna and love it. This carb is legal for any Historic class and up (1975 and newer).
"D" slide carbs like that are not legal in any AHRMA class, not just Vintage.
Brian
Yep -- Brian and Dwight, I am aware of those facts. I sure wish it was legal. Fortunately, this is not one of the bikes that I race in AHRMA events. It's a bike I like to trail ride with my vintage bud's and ride at local "fun/charity" events.
John
Did Lectron carb's become available in 74" ? I seem to remember seeing a write ups starting in 74 or 75.. It is scary how much I do not remember, now where did I put my keys?
JC, it sound to me that the reason that your bike was loading up with the Bing is because the Needle jet and jet needle are worn. If the gaskets have not been replaced in a while, do that.. including the O ring on the Head. That should make a big difference. I was told by Bing international to replace them both each year..
Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74' 1/2 440 maico
70' 400 maico (project)
72' cr125 Husky (project)
93' RMx 250 suzuki
Honda TL 125
2004 Suzuki DL1000