I am considering doing a Mikuni carb conversion on my 125 but have a few questions. It looks like a 28mm would be the best size but Sudco
doesn't list that anymore on their web site. Would a 26mm be a good
option or would that restrict the power too much? I am really after
better response in mid range and low end for trail riding than top
end performance and a 30mm seems like it may be too much. The engine
is stock. I have checked with the local cycle salvage and they want
as much for a used carb as a new one. Any thoughts would be
appreciated.
Thanks
Sam
Sam,
I may (will)cause an uproar with many poggers but get a Mikuni on your 6 days even if you go down to a 26mm it will run great. To me "Bing" is the sound the carb makes when it hits my trash can.
I have been told numerous times that the Bing makes more power. If you sacrifice ajustability and you are trackside watching your race go by where is the power?
I am running a 32mm on mine and when I switched bikes to test ride another riders bike with a stock Bing last weekend I will never go back. He took down the jet specs given to me by Donny Smith and will soon have a Mikuni on his bike.
Clean up the Bing, replace the needle jet( it gets worn oblong) and you are good to go.125cc races are won with the shift lever-piston port engines arnt really all that flexible anyhow. Hold it open, use the clutch and gearbox if you want to win!
Bent, you made me laugh... that is just about all that bings are good for anymore. I hear that there is a guy up this way that will bore them or and fix them but why. They wear too fast and they are hard to tune. Not to mention the jets are almost twice as much. I still have a bing on my 400 and it cost me a few postions and maybe even a win. I had to pull it apart and clean it up at the race. Not my idea of fun. As soon as I can it is going away and is going to be replaced with a mikuni. They are cheap to buy and work really well. I brought with me on Saturday my 250 that has a mikuni and with it raining and temps in the low 40's it started on the 2nd kick. what else do you need to know?
Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5
Do you have to do anything to adapt the Mikuni to the intake?
Tom,
Would you repeat what sound the Bing makes when it hits the Trash Can?[:o)] They do look nice on restorted bikes[8D].
Ron Carbaugh
Mikunis can be bought with a flange mount having slots on each side to allow the standard cylinder configuration to bolt right on. Look on ebay under the Mikuni listing. You should find one under $50. I paid $55 for my 32mm and it was in the box never having gas in it yet.
I did buy a flange 24mm for about $30 on ebay.
Keep your carb on a shelf as Ron indicates. If you ever sell your bike or decide to make a beauty out of it the value is far better with original equipment as with show cars.
Tomale, Glad to hear I got you with that one. Humor has always been a high priority around here because life is just too short. Based on your signature closing I have always liked.
Make it a great day guys,
Tom B
Tomale,
Based on your signature closing I have always liked, I think we share that priority.
I know that the Bing is problematic at least for me so that is why I am considering the change. I put a Lectron on a 1980 KTM years ago and it was a whole new bike after that. Thus the Mikuni consideration.I am not really racing the bike (yet) but who knows down the road. I mainly want clean running when it is off the pipe and may even teach a few newbies to ride on it. I'll definitely check out the possibilities you guys mentioned and thanks for that.
I'll let you know what I come up with.
Thanks
Sam
Bent, we do...life is too short not to include humor. I love a good pun. my wife and I will go round and round adding one pun upon another. It drives my kids nuts. which is half the fun.:D
I seem to have a collection of Bing carbs. Not sure were they all came from. Maybe we should establish a home for wayward Bings, Is your home safe from Disfuctional Bings? [:0]
Ron very true and that is why I took the stock intake and Carb on the 76 250 and put it away for safe keeping. I bought a intake on Gee-bay (Gee they want alot)and modified it to work on my bike. Do a search and find my post on what I did. For anyone interested. I guess I allowed my frustration with them from this weekend to get to me. It nearly cost me a day at the races. To be fair though, part of the trouble could be my fault. The tickler is kind of funky and it looks like part of the brass sleeve that seals out crud from getting in is missing. I should have been more careful about my prep and figured out a way to seal that up better. Still most of my hard starting can be attributed to the Bing. I had nothing but trouble with the 250 until I changed Carbs.
Dave on the 125's you should not have to make any modifications to make it work. you will need a intake boot to make the connection but that should be easy to deal with.
Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5
Greetings from Colorado, just a side note:
I have an article titled " Super Sachs Secrets " in it are instructions for 28mm Mikuni retrofit....It does work.
Can send if you send me a SASE:
Tom Brosius
Talk to you on the outside?
What are the challenges of converting a 74 175 to a mikuni? Anyone?
Tommy
Hi Sam
I have a 28mm Mikuni mounted on my 72 6 Day. It's fantastic!! Comes on quick and doesn't falter to the top end. I call it a clamp on. But I had a adaptor make local ($15) to fit into the Mikuni, of course you have to remove the original insert. I'm now looking for a 30mm to see how they work. Don't crop off the spiket!! I've seen that done. Try a Cycle salvage,usually the old Kawasaki's had the clamp on's.
Dake
72 6 Day
Thanks guys... DKWRACER I sent you an email..
Sam
Wow, granted bings are more expensive and more expensive to maintain.
Still, when working properly the tickle button make an easy starter-and you can run then leaner on the bottom due to this. They have also in my experience had more " punch" in the upper midrange. Maybe that is not a good thing but it make a 250 Katoom such fun to ride.
I put a mikuni on the Maico since it was missing a carb though and a new one for 149 is alot better than a used rebuilt one for over $300.
They have their own advantages but a a mikuni is a whole lot cheaper.
you might remember that like the Pentons they are found on-they gave lot more years of service than most others the first time around. One usually does not find a Penton that was not ridden into the ground for sale. This is a a testament to their durability. with the exception of Tom Green's case, most of these Bings have been used more than a mikuni you find in a salavge yard.
Tom B. the way you ride your 125 you can put a 38 on it. If only it were allowed in classic. James
7" and 4" travel? Hmm-that makes 11" Hey! I can live with that.
Tommy, Do yourself a favor and keep the bing on your 175. Put a new needle and jets in and it will work great. Very easy to tune. Like the above posts state, most of these bikes have had a long hard life. Your bike seems to be a low hours and shouldn't be worn out.
Dennis Jones
Quotequote:Originally posted by Dave Withrow
Do you have to do anything to adapt the Mikuni to the intake?
I was going to look for a piece of "Green Stripe" hose or something compatible with gas that is the right size and hose clamp it on to the engine. Unless someone knows the right combination to use...
I'll let you know what I come up with when everything gets here and I start working on it.
Sam
Sam,
Phil Schloss did this about 3 years ago for his sons 125 B engine Six-Day. here is what he had to do to make it work. THe bike ran well .
John D.
I purchased a 28 mm carburetor from my local dealer. He ordered it from Marshall, got it for about $85.00. Carburetor number is VM28SC-E0865.
The only changes I made were to change the pilot jet to 40, main jet to 160 and the needle to a 5F3. Needle is set at the first notch, or the richest position, (all the way UP). I'm sure there are a better needle and needle jet set ups, but this works great. The needle jet is a 169 N-8, which is standard on this carburetor. The air screw is out 1ΒΌ turns.
To mount it on a SixDay I did the following:
Cut the air boot on the air box side one ring making sure the diameter is the same. The boot is now shorter.
The diameter of the boot side of the carburetor is similar to that on a JackPiner with a Bing. Use the same rubber sleeve, clamp it together and the air box side is done.
On the engine side of the carburetor I shortened the spigot by sanding it on my stationary belt sander. Remove enough metal that the spigot on the carburetor fits close to the spigot on the intake of the cylinder. They are of similar diameter on most cylinders so a hose and clamps will take care of the engine side of the carburetor.
Now you will notice the carburetor has to lean about 15 degrees to clear the pipe. I ran mine like this for a year with no problems. Recently I did some "fine tuning" on the pipe to make room for the carburetor to stand straight up. This took no more than a torch and a hammer.
That's about it. Hope it works for you as well as it has for me.
SkipperClyde
Thanks John
I knew I had seen that post here somewhere but when I did a search I must have done something wrong.
Anyhow I would like to avoid cutting the spigot on the cylinder if at all possible but I will see how it all fits up when it gets here.
The jetting sounds pretty close to what I was figuring to start with so that will give me a good start.
Thanks for the info and the link...:D
Sam
Tom,
I blew my Six Day up in the last race in the fall of 2002. I had just finished a race on my Mint 400 and when I got on the Six Day, I held the throttle open at max revs for too long instead of risking a shift and the con rod bearings decided to give up. Due to all the other bikes having priority since then, I still haven't put it back together again but I have bought a 32mm Mikuni for it. Would you tell me the jetting info for your bike? With the non saddle time I am now faced with, I might finally get a chance to put it back together. I wonder if Doug would like to visit Missouri?
Thanks,
Teddy
Hi Teddy,
I was quite fortunate in that when Donny Smith had his 6 Days on ebay about a month ago, I noticed he stated that it had a 30mm Mikuni. In an email he was kind enough to send me his specs.
I went slightly richer to compensate for a 32mm flowing more cfm's.
No Doubt tuning will be needed for each bike...riding area...electrical system.
Main Jet.......170
Pilot Jet.......55
Needle Jet..159-N8
Jet Needle..5LF14..(I raced Arizona with a 6DP17)5LF14 was on order.
Good Luck with those ribs. Makes me wonder how your CFMs are flowing.
I just installed a 32 mm mikuni on my '73 125. I ordered the bing fiber bushing from Al Buehner then machined the inner diameter to accept the bushing then cut four slots with a hacksaw so I could clamp it on stock cylinder spigot with stock bing clamp. The air intake boot stretched enough to fit over the mikuni just fine. The stock cable worked just fine. As far as jetting goes, it came with a 200 main and a 35 pilot and at sea level seems to work amazingly well.
Don
Don,
Glad it works...your bike is really nice. I have a baby tank like yours coming for mine and hope to get it before Gaineville. The larger one is tough on the cubes during moto combat. Please e-mail me direct Don. Thanks,
Tom Benolkin
[email protected]
Sam,
I used radiator hose with a slight bend to adapt my mikuni. Check your local Yamaha shop for a used 28mm. I beleive either the Blasters or Warriors came with a 28mm. Also a Keihn will work very will. Bottom seam of exhaust pipe comes very close to top of carb. I have been using a 28 on my 72 125/6a. Easy start, smooth thru all ranges, even lugs very well without loading up(when racing with only 3 gears). Good Luck
Bob Brizzee
Right on to what Bob says,:)
Last year I took a boot into a Checker Auto store and asked if I could go behind the counter and see all the options they had hanging on the wall. You end up buying a hose that may be 20" long to cut out the 3 " you need. Ain't that the wasteful American way...GetRdun[:p]
Well my carb showed up today and it was pretty painless on the
installation part. I went with a new 26 because the cycle salvage
wanted as much as a new carb for a used. So instead of taking the chance on buying some elses problem I went that way. I had an old piece of fuel delivery hose laying around that I cut for an intake manifold hose and on the airbox side I needed to shim the diameter of the intake bell to meet the diameter of the air boot. I found a piece of radiator hose I had trimmed that fit perfectly and the intake boot between the carb and airbox is sealed in the same manner as with the Bing.
As delivered the Mikuni is very rich for this application but it runs and is a good starting place.
It came with a 190 mj 60 pj 182nj
I'll be off to the shop tomorrow to get a hand full of jets to start fiddling with it.
I'll let you know what I settle on when it is done..
Thanks for all the help and advise
As stated many times before the folks here are the best !
Sam
Installed a new 28mm Miknui on Christopher's '72 1256B this weekend. Marvolus, Wonderful, ... The bike takes 3-6 kicks cold and then only one tap when hot. Fall over, pick up and starts one tap. GREAT! Pulls clean top to bottom. Need to fine tune, a little rich on top and a little lean just off bottom. Will race this weekend at Evansville and report back how things turnout. Installation - 1-3/8" radiator hose, 2 hose clamps, stock throttle cable. So easy even I could do it. No interference with pipe, air booth sorta contorted but sealed - need to sort out better.
Jets: 180 main, 35 pilot, 5F21 needle, ?? needle jet. Plan on trying 160-170 main, 40-45 pilot.
Bing? I haven't given up and still run a 30mm on my race 5A. But, I'll be carefully evaluating how Christopher's rig runs.
Ernie P.
Chattanooga, TN
Ernie,
I have a 30mm Mikuni that works flaw less. I have a PVL so that helps it start, but less than 1/2 a kick when its warm.
My jetting is patterned after Donnie Smiths recomendations.
My only deviation has been a smaller pilot and up a little on the main jet (I haven't had a chance to really hold it open.)
Needle: 6d917 (middle clip position)
Needle jet: N8
Pilot jet: 50
Main jet: 180
RonW
RonW,
Tell me about the fit-up of the 30mm. How does it mount to the cylinder & air boot? Did you have to bend the pipe? The reason I went with 28mm is the smaller carb body ... but the 28s are getting harder to find. I do have a 30mm and 32mm Mik that I'd like to try if it isn't going to cause me to have to use a sledge hammer to get it to fit ;). 1/2 kick on the warm start is great! I'm sure the PVL helps but on Christopher's bike, all I did was change carb and presto-change-o, it starts like magic. Thanks for the jetting specs.
Ernie P.
Chattanooga, TN
Hi Ernie,
If you look close at the pics of my bike you can see a aluminum block that is welded to the cylinder and then bored out to 30mm.
It uses a Mikuni rubber manifold. It was that way when I bought the bike, but its a neat set up.
The rubber manifold is #VM-34-200.
Unless your going to bore the intake on your cylinder, I'd stay with the 28mm. The 28mm probably works better on a stock cylinder.
The stock boot fits the back of the carb, but I had to cut a ring off the large end and then use a hair dryer to stretch it back on the airbox.
RonW
I searched the POG on Mikuni jetting and results can be seen at link below.
http://pictures.aol.com/ap/singleImage.do?pid=c060XSuUTqrrxPgwkZuYlTOlDXjmtGxpl*y5v4xQp5Fd3Ig%3D
On Christopher's 6B with 28mm Mikuni, we went down to 165 main from 180 and we are now good to go.
Ernie P.
Chattanooga, TN
170 to 270 on the main jet. How is that possible?
Chuck,
72 125 Six Days
74 250 Hare Scrambles
74 250 Maico
73 250 Honda Elsinore
Chuck,
I just tabulated the results of the "search." It is intended to be an aid for someone jetting their carb to get in the "ballpark." There does seem to be a very wide spread of main jets on the 30mm. Donnie S and RonW use 170/180 in the 30mm, so that is what I would use as a starting point. There are just so many variables; state of engine tune, altitude, compression ratio, pipe ... use it as a guide.
Ernie P.
Chattanooga, TN