Anybody have the magic Mikuni jetting specs for a Bershire? After threatening to do this for 3 years, I will be able to bring my six day to Harpers next weekend. I have a 100cc jug, head and piston, but have no clue for carb setup. Need to beat the Hodakas again. HELP. Mike Lenz will be there with his 100cc Piner engined Bershire. Maybe I could just leave the 125 jug on it and put a 100cc label on it with a red tank???? Oh Teddy, that's not right!!!!!!!
Teddy
I checked that the Bing setup is the same for both engines, maybe the Mikuni will also be the same.
Teddy
Can you give the 125 specs and let us know how they work ? I want to put a Mikuni on my K100GS Hercules for the ISDTR this year.
Dwight
Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.
Dwight-How's the back/neck?Hope your procedure went well!I have a Mikuni on my Mettco 125 6 days.If you want the specs. for it i can give you those.The porting doesn't look super wild so it would probably get you in the ballpark.
Ric
ric emmal
Ric,
Yes, please do. The specs I have for the Mikuni 6 days is for a higher tweaked engine. 230 main, 2.5 slide, 6F5 needle, 35 pilot, P5 jet. This was for a 32MM carb. I am going with a 30mm.
Teddy
The highly tweaked engine was one that JP Morgen loaned me until he got mine redone.
Teddy,I'll make myself a note,but rattle my cage if i don't post it by tommorrow nite-lots going on right now-don't let me forget-ok?!!!
Ric
ric emmal
Teddy, You would be better off going with a 26mm for the 100cc. Or a 28mm which has the same body size. The 30mm is the same size as a 32mm and will be harder to fit. A 30mm is a pretty big carb on a 100cc piston port engine. A Hodaka 100 only uses a 24mm. The Penton 100 used 27 and 28mm carbs. Zundapp 125s only used a 26mm or a 27mm.
Just a thought.
Dwight
Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.
Quotequote:Originally posted by sixdazed
Dwight-How's the back/neck?Hope your procedure went well!I have a Mikuni on my Mettco 125 6 days.If you want the specs. for it i can give you those.The porting doesn't look super wild so it would probably get you in the ballpark.
Ric
ric emmal
Neck is getting better. I am walking about 3 miles a day now. No real pain. Still some numbness in my fingers but I hope that will go away with time.
I would love to get your specs. I will be using a 28mm carb.
Dwight
Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.
Quotequote:Originally posted by Dwight Rudder
Can you give the 125 specs and let us know how they work ? I want to put a Mikuni on my K100GS Hercules for the ISDTR this year.
Dwight
Dwight, I thought you were going to ride your Jackpiner? I'm with you, I think a 26 or 28mm is about right for a bike that is going to be used for cross country.
Brian
'72 Six Day (on loan from Ernie P.)
I was going to ride the "Piner" but the neck surgery kept me from riding the Hercules K100GS that I was building for Teddy's ISDTVQ so we decided to ride them at the ISDTR. The Jackpiner is a hell of a fast bike. It would be like cheating. LOL. So I'm going to ride a 100 just to give Paul a chance. LOL. ( Like Danik needs a chance, I just want to ride a 100. )
Cher'o,
Dwight
Dwight Rudder
7 time ISDT / E medalist
8 time National Enduro Class Champion.
I know all conventional wisdom says that a 26mm or 28mm will work better on a 100cc engine than a 30mm. However, I have put a 30mm Mikuni on my bike for a number of reasons. 1. You have to go up a size if replacing a Bing with a Mikuni, the Mikunis do not breath as well as a Bing, so if 28mm was the right size Bing, use a 30mm Mikuni. 2. I don't have a 28mm Mikuni. 3. The 100cc conversion is only for this weekend National 100cc Motocross (not CC) race at Harpers in Missouri, I will be putting the 125cc jug, head, and piston back next week and I don't want to have to redo the carb adapters, just stay with the same carb.
I put it together Saturday and with a 49mm piston, P5 jet, 6F5 needle in middle groove, 2.5 slide, 30 pilot and 230 main, it was so lean that the revs took forever to back down and it didn't pull very well. I changed the pilot to 35 and the revs came down quicker, felt good but couldn't get it to rev as high as I though a 100cc engine should. Then I finally cleaned the filthy air cleaner, and it was too lean again. Put in a 40mm pilot and now the bottom was good, idle air screw out to 1.5 turns, comes off the bottom well, but didn't seem snappy enough in the mid range and the top was still MIA. I lowered the needle one groove and now the mid range pulled nicely. I did a spark reading after running flat out for a while and it was showing lean. Put in a 240 main and the top was better, then put in a 250 main and it improved again. However, it still doesn't rev as high as I would like. It may be the pipe, or maybe I should have done some Carl Cranke grinding on the exhaust port. It is a stock cylinder.
The inlet port on this cylinder is 32.8mm OD and 26mm ID. I ground and smoothed out the first 1/2" of the inlet to 30mm ID feathered to the 26mm going in. I wrapped a strip of 1/8" thick flat stock rubber around the inlet port to make it's OD closer to 40mm, the OD of the carb outlet and used a piece of 1.5" ID rubber radiator hose to connect the carb to the inlet. Heating the air box boot with a hair drier, you can stretch it to fit over the Mikuni inlet horn. I cut the Mikuni inlet horn off until it was only about 3/8" long. The air boot doesn't look too tortured, you can see the inlet of the carb easily with the air cleaner out, so there is a good direct path for the air to follow.
I can't wait 'til Saturday to see how it stacks up against the other 100s. I just wish it had more power, maybe I could slip a turbo charger on it and no one would notice???
Teddy
A 28mm Mikuni is the way to go if you can find one. Sudco for example does not stock the 28mm small body any longer. I have heard of a snowmobile varient that can be reworked slightly to function correctly on a motorcycle.
Teddy,Dwight,-I've gotten close enough to almost get to the Mettco stuff(it was BURIED!)-Taking a break for chow and will dig out the mikuni and open it up.It's set up for sea level,mild temps(Nor Cal.)
Ric
OK --I Found It-appears to be a larger body 30 or maybe even 32mm-how do you tell?The guy i got it from very nicely put it in a zip lok bag but forgot to drain out the old gas so slide is stuck and bowl stubborn coming off,soaking in penetrating oil now.I'll take it to work with me and dip it tomorrow.i don''t expect to be able to read jets tonite(the dreaded brown carb cheese!)but if i can i'll post what i find.Later.Ric
Ric,
Measure the discharge ID with calipers or even a measuring tape. 30mm = 1.18", 32mm = 1.26". At least it won't smell like Limburger (sp?) cheeze.
I put a 32mm Mikuni on JP's engine that he loaned me and I wanted a little more bottom end, but then, that may have been because he modified the inlet side of the cylinder and piston so much to optimize the top end (he is a MXer) that it didn't have much bottom left. I got the hole shot in the Walnut CC last year with it against MUCH bigger bikes. Kinda like the Lillian Swamp Team guys at the ISDT Qualifier last month.
I can't wait to get the 100cc jug off the engine next week to see how the 30mm carb does with the 125cc jug.
Teddy
I run a 30mm Mikuni on my 125 GS jug and it just sings...the best thing I did for the engine. You won't be disappointed.
Teddy,It's a large bodied 28mm (early style) and here's what i can read(with lighted magnifying glass!)5dp7 needle 2nd notch,O4 nozzle also has 190 stamped down towards the main on the nozzle(needle jet)as far as main and pilot go it's a guess as the numbers aren't really legible so it KINDA looks like a 210 main and a 35 pilot but i can't be sure and that's for sure!Hope this helps a little-looks like i'll be guessing a bit when i first get this together.I have other carbs to look at yet(i know i have at least 1 more mukuni for a 125)and i'll let you know how that comes out.
Ric
ric emmal
New VM round slide Mikunis and old ones from the 70s are different internally so the jetting is not likely to be the same. It might get you into the ballpark, but be very careful on the first run that its not too lean.
Brian
'72 Six Day (on loan from Ernie P.)
Mine is a new 30mm Mikuni and it sounds like the jetting is really different. It runs fairly well with the 40 pilot, 250 main, P5 jet, 6F5 needle on second hole from top. Thanks for your help. I'll know Saturday how competitive it is against the Hodacrackers.
Teddy
Don't know if this will help any, but I remembered jotting down some stuff on Mikuni setups a while back.
This is what member Lindeman wrote to Rick/calif in '03.
"The 28 makes great mid-range power and enhances this riding style.We all know smooth is fast!It also works much better for Hare Scrambles type riding.Anyway here is what works on my stk.125 with 28mm mikuni. Sea Level-165 main,60 Pilot,2.5 Slide,5EI4 Needle 2nd from top,Air screw 2 out.B8HS plug.In Denver area where I live 5500ft.I run a 155 Main,50 Pilot,Needle top.Good Luck!Dave"
Now on my own 125 with the mikuni,my carb has these specs:
main-130, pilot-30, slide-1.0, needle-5d5 on the bottom slot(raised all the way up). It has 427 over 60 stamped on the side, with 34 on the spigot mount side. Spigot od is 34mm and id is 27mm. This is also at sea-level, or below, here in the lowcountry.
Please take in mind that this was on the bike when I got it in '73, and I haven't run it except in the yard since Doug rebuilt it.:(
Man, I got to get my priorities straight.[8]
Robert Manucy
72 Berkshire
72 Six Day
82 Honda cr250r
04 BMW K 1200 GT