Has anyone had any success past or present installing a Mikuni Carburetor on a 74 Penton 250?
I have one on my 75 250. I had to shorten the carb front and back. And fit the airboot to the back. I used a cut down fernco plumbing fitting for the back of the carb. It's not easy but I got it done. I haven't ridden it yet,I was starting to mess with the jetting and Mr winter came along. Once Mr Spring shows up I'll finish up.
I bought a new mikuni on ebay.
74 puch 175 SD
73 Husky 360 WR/RT
76 Husky WR360
75 Penton 250
10 ktm 250xc
02 bmw r1150r
Jerry at Carb Parts Warehouse in Cleveland hooked me up with everything I needed. I used radiator hose on the inlet and he supplied a cool machined aluminum step down ring for the airboot side. I did trim down my airboot but have seen it done without trimming. The kit had jets, cable, carb, adapter and throttle, way too easy one stop shopping.
I've got a 34mm Mik on my harescrambler. Had to cut about 1/2-3/4" off the intake manifold. The 34 fits better than the 36, didn't have to cut the air box boot, but it's tight fit. Bike starts and runs great.
Mick
I have a 36mm on my 76 250 MC5. Yes, it is a bit of work to make it fit, but well worth it. The bike starts easier, and had much better response from the bottom up. I wish I had done it years ago!
1976 MC 5 Original Owner
1976 Hercules 250 GS
1982 Suzuki PE 175
2002 KTM 200 EXC
1976 Penton 175 GS
Have a GEM reed on mine running a 36mm(bored to 36.5mm) Didn't have to machine the carb, just had to grind the case down a bit and the jet access bolt down to fit. It's still close. Had to make a flange from carb to ait box. Cant remeber what I used for the boot.
'12 Husaberg TE300
74 Yamaha TY 250
84 Yam IT200
75 Jackpiner w/ 250 eng.
82 KTM GS250II (import)
82 KTM 495 (2)
98 KTM 300mxc
04 KTM 125 SX
00 KTM Duke 2/rd. racer
06 KTM 950 Adv.
08 Suzuki DR70Z
Search MIKUNI and you'll finds scores of posts on this topics. Seems the best solution for size and fit is to use a 34mm Mikuni with its bit smaller body, and have it bored to 36mm, then adapt both ends... not a lot of cost for carb + bore, about the same as a new Bing slide alone.
One of the big joys of old mx bike tinkering and racing is the very low cost to play and bike value staying strong on re-sell. Making the old stuff work as it should without new bling or extra $'s makes me happy, so I've stuck with reasonably good Bings and made them good starters and tuned well by using a fresh needles and new needle jets, low-wear used slides and bigger pilot jets (usually) for easier starts.
However, fighting to get any bike to start and poor carb performance is a big kill-joy and nothing but frustration--so IMHO spend the money on a new Mikuni carb and good electronic ignition, if you can afford it!
I agree with Mac on the 34 being best fit for the available area between intake and air box. However, my 250 starts easy and runs very strong staying with the stock 34 bore. It took some jetting and gearing changes, but the bike runs stronger and faster than I'll ever make it go! Also agree with Mac on the money issue: I'm always telling friends and young people how affordable (by comparison) vintage bikes are to modern.
Mick
I think Mac is remembering my bike. That's what I did, I installed a 34 mikuni bored out to a 36. It works great. If you check some of my old posts you will find what I did and how I jetted it.
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
I have one on my 75 250. I had to shorten the carb front and back. And fit the airboot to the back. I used a cut down fernco plumbing fitting for the back of the carb. It's not easy but I got it done. I haven't ridden it yet,I was starting to mess with the jetting and Mr winter came along. Once Mr Spring shows up I'll finish up.
I bought a new mikuni on ebay.
74 puch 175 SD
73 Husky 360 WR/RT
76 Husky WR360
75 Penton 250
10 ktm 250xc
02 bmw r1150r
Jerry at Carb Parts Warehouse in Cleveland hooked me up with everything I needed. I used radiator hose on the inlet and he supplied a cool machined aluminum step down ring for the airboot side. I did trim down my airboot but have seen it done without trimming. The kit had jets, cable, carb, adapter and throttle, way too easy one stop shopping.
I've got a 34mm Mik on my harescrambler. Had to cut about 1/2-3/4" off the intake manifold. The 34 fits better than the 36, didn't have to cut the air box boot, but it's tight fit. Bike starts and runs great.
Mick
I have a 36mm on my 76 250 MC5. Yes, it is a bit of work to make it fit, but well worth it. The bike starts easier, and had much better response from the bottom up. I wish I had done it years ago!
1976 MC 5 Original Owner
1976 Hercules 250 GS
1982 Suzuki PE 175
2002 KTM 200 EXC
1976 Penton 175 GS
Have a GEM reed on mine running a 36mm(bored to 36.5mm) Didn't have to machine the carb, just had to grind the case down a bit and the jet access bolt down to fit. It's still close. Had to make a flange from carb to ait box. Cant remeber what I used for the boot.
'12 Husaberg TE300
74 Yamaha TY 250
84 Yam IT200
75 Jackpiner w/ 250 eng.
82 KTM GS250II (import)
82 KTM 495 (2)
98 KTM 300mxc
04 KTM 125 SX
00 KTM Duke 2/rd. racer
06 KTM 950 Adv.
08 Suzuki DR70Z
Search MIKUNI and you'll finds scores of posts on this topics. Seems the best solution for size and fit is to use a 34mm Mikuni with its bit smaller body, and have it bored to 36mm, then adapt both ends... not a lot of cost for carb + bore, about the same as a new Bing slide alone.
One of the big joys of old mx bike tinkering and racing is the very low cost to play and bike value staying strong on re-sell. Making the old stuff work as it should without new bling or extra $'s makes me happy, so I've stuck with reasonably good Bings and made them good starters and tuned well by using a fresh needles and new needle jets, low-wear used slides and bigger pilot jets (usually) for easier starts.
However, fighting to get any bike to start and poor carb performance is a big kill-joy and nothing but frustration--so IMHO spend the money on a new Mikuni carb and good electronic ignition, if you can afford it!
I agree with Mac on the 34 being best fit for the available area between intake and air box. However, my 250 starts easy and runs very strong staying with the stock 34 bore. It took some jetting and gearing changes, but the bike runs stronger and faster than I'll ever make it go! Also agree with Mac on the money issue: I'm always telling friends and young people how affordable (by comparison) vintage bikes are to modern.
Mick
I think Mac is remembering my bike. That's what I did, I installed a 34 mikuni bored out to a 36. It works great. If you check some of my old posts you will find what I did and how I jetted it.
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
I went with the 36mm only because I already had 2 of them. Had to drop down to a leaner slide though.
'12 Husaberg TE300
74 Yamaha TY 250
84 Yam IT200
75 Jackpiner w/ 250 eng.
82 KTM GS250II (import)
82 KTM 495 (2)
98 KTM 300mxc
04 KTM 125 SX
00 KTM Duke 2/rd. racer
06 KTM 950 Adv.
08 Suzuki DR70Z
To all,
I am responding to an earlier post of mine about putting a Mikuni Carburetor on my 250 Penton.
I want to be prepared and dialed in for the OVBSAOC reliability ride at the end of May!
I am hoping that I can call on the collective experiences of the group for help? I am planning on going with a 34 mm, I am looking for photos and more information on jetting, intake manifold connections and what sounds to be the toughest/biggest issue back of Carburetor to air box!!!
I have contacted Jerry at Carb Parts warehouse and was told that he has a complete set up with some kind of aluminum piece for the air boot but he would not send a picture. I am not sure but I feel my current air boot will not be able to be used with a Mikuni? Can anyone enlighten me on these issues?
(Please send pictures?)
John, I think you will have to get the carb first and see what needs to be done to make it fit. I put a 36mm and there was some work involved to fit it. A 34mm may not be as hard to fit. The air boot may be close to fitting. It's a process that you just have to go a piece at a time. Maybe someone else here did a 34mm and can help out.
74 puch 175 SD
73 Husky 360 WR/RT
76 Husky WR360
10 ktm 250xc
02 bmw r1150r
Thanks Dale,
I understand all that, I have an inquiry to CPW about their set up just looking to minimize the learning curve.
I want to ride more and wrench less (my goal)
John, I didn't have to do anything to my air box or boot for the 34, but it's a struggle for sure. In cold weather I have to soak the boot in hot water to get it soft, in warm weather I can do it as-is. My boot is an original, hard-as-nails boot; someday I'd like to get a soft re-pop. I did cut the intake manifold 3/4" to help in clearance. Hope this helps,
Mick
Mick,
Thanks
Is there any way you could share with me your jet specifications your running so I have a starting point?
I have an old posting where you state 210 main & 40 pilot and 1 turn out on airscrew is this what you are still using?
What needle groove are you on?
I am assuming everything else is stock Mikuni VM 34-168?
My air boot is a new one from Al B. it seems to be almost vinyl "very stiff", Honestly it doesn't fit the bing very well it so tight length wise that it appears almost folded upon itself if that makes any sense.
I know the back of Carb. to air box connection is going be challenging!
On those stiff air box/carb boots, warm them up with a hair dryer to get them soft and then hit them with some Armorall right away and work it in with your hands. May take repeated applications but should help.
Type at you later,
Dan McEntee
John, those are my settings. haven't touched them in two years and going strong, needle in the middle clip.
Mick