Mikuni Carburetor on a Penton /KTM 250

[johnacapp]

Has anyone had any success past or present installing a Mikuni Carburetor on a 74 Penton 250?

[Dale Sonnenschein]

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

[Rob Thatcher]

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.

[Mick Milakovic]

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

[skiracer]

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

[Mike Hufnagel]

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

[Big Mac]

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!

[Mick Milakovic]

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

[tomale]

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

[Dale Sonnenschein]

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

[Rob Thatcher]

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.

[Mick Milakovic]

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

[skiracer]

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

[Mike Hufnagel]

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

[Big Mac]

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!