Mikuni on Jackpiner

[imported_n/a]

Hi:

I'm rebuilding a '72 Jackpiner. It has a Mikuni on it which I want to keep for now. The rubber "adaptor" between the cylinder and the carb has split in half since the bike has been sitting for years. Is this a special adaptor or the stock Penton piece? If it is special, are they still available?

Thanks
Gary

 

[Chris Brown]

Your local auto parts store can sell you a foot of fuel-filler hose (green-stripe hose) of the correct diameter (or close) that works great for a carb manifold connector. And if you want to get trick, use the European style narrow clamps your KTM or Husky dealer should carry.
Chris

 

[imported_n/a]

After looking a little closer, it appears the stock manifold was used. The original stud holes were filled in and new ones drilled slightly outboard. Then some kind of rubber adaptor was used that had a flange on one end (to mate with the stock manifold) and a rubber tube on the other that slipped over the carb. The whole adaptor is only about 1" thick. I'm going to have some friends go thru the stock of old Yamaha parts to see if they can find anything similiar.

Thanks
Gary

 

[gooey]

I hate to butt into this when Im OBVIOUSLY a novice,,, but here's how I see it ....



if in fact the stock manifold was used, there would be no valid reason for re-locating the holes,,, BUT since it was done,, and now the bike is apart ... it might be a real good time to check with Al or Larry, or the POG members in general and try to un-do some kind of surgery that probably shouldnt have been done in the 1st place ...



 Might be a good time for a replacement cylinder, and intake manifold ...



 Hear me out please befor you say " I CANT AFFORD THAT "   cuz I'm the orginator of the shoestring budget,,, i know hoow it is ...



 piston-port timing is CRITICAL to the performance characteristics of a 2cycle engine ,,, these things are measured in thousnadths of an inch ... You can tailor, to a certain degree,, the power output and characteristics of a high performance  2 cycle engine by making minor alterations to this area ... thus the use of cylinder base gaskets,, or, more appropriately,, shims,,



 SO,, it would stand to reason that an incorrect or poorly modified part in this area would most likely alter performance,, and again,, more likely than not, in a negative fashion.



 The port work on your black KTM 175 motor is pretty radical,, and really IS the mystique of this esxtremely powerful engine .... probably the most powerful engine in its class ... so I seriously doubt you would want to alter that ....



 Furthermore,, if I remember right,,, port timing can be SO far off ( agian,, we are dealing in thousandths) that you can "trick" the engine into thinking it is in a very lean conditioon,,, and we all know the disaster that spells,, and, with pistons for these thngs becoming harder and harder to find, and increasingly expensive,, maybe its a "pay me now or pay me later" thing ....





last, but not least,, I have done some experimenting,, and Chris had the ultimate working example, in my opinion ( DAMN Chris,, I really did LOVE your 'Piner) that a Mikuni,, at least up to 34mm will readily work on the stock manifold



 SO,, to sum this up,,, I would suggest trying to find a reasonable price on a good used cylinder, and manifold combo and run that Mikuni ... i think you and your bike would be MUCH happier



 Any input from you penton Guru's that know LOTS more about this thanI,, the flunky   Am I on the right track or just full of poop  



 good luck !

1973 Jackpiner 175,          my  "real" name is Mark McGrew, my friends call me Gooey,, Please,, call me Gooey!

[Chris Brown]

Sounds like the manifold on an old IT175 that sits in my garage that I built for a friend. The dealer wanted $50 to replace a cracked one.
You might see if Larry Perkins has a stock steel manifold that came on the KTM motor. The carb then connects with a factory rubber or fuel-hose coupler and clamps. A lot of the older bikes are setup this way and it makes them easy to service.
If you use green-stripe fuel hose you can just replace it when it gets fatigued. The green stripe means it's fuel proof; don't get the kind with the wire reinforcement in it, just the plain one. It's a little hard to find and about $12/ft. You can make several out of a chunk of it.

Speaking of cheaper substitutes, I buy small pieces of neoprene sheeting and then cut out my own rubber washers with a hole-saw and a forstner style drill bit. About a third the cost of the little washers the parts dealers sell. And you can make them the size, thickness, and hardness you need.

Also, although not completely to original, I like to replace fastners that show with stainless steel. A good industrial supply will have all the correct metric sizes and styles. Allen drive pan-heads can be polished to look like chrome. Very nice for number plates, side covers, etc. For a few bucks it gives the bike a like-new overall look on a restoration.


Edit: Funny, Gooey's post came at the same time I sent mine.
I think he's on the right track, although nothing radical may have been done to the cylinder casting. It may just have had a modified manifold connector adapted. However, we both agree to put it back to stock. Anyone else???

When I was a kid, one of the neighborhood tuner gurus machined a reed valve manifold for my Sachs motor. Once we got the jetting setup right it would really scream. It made an Elsinore eater out of it. Now all bikes come with reed valve intakes.



Edited by - chris brown on 01/30/2001  11:54:21 PM

[gooey]

the Gates green stripe stuff is real popular in truck shops .... I work in one ... usually the truck guys will cut a few inches off an save some $$$ for you ... the car guys dont use as much and are probably less willing

1973 Jackpiner 175,          my  "real" name is Mark McGrew, my friends call me Gooey,, Please,, call me Gooey!

[kurt k]

My '77 Jackpine has a 34mm Mikuni set up like you guys are talking about and appears to be fine.  Starts and runs good on my bike stand anyway.  I'll let you guys know when the weather gets better. Thanks again Gooey for the pipe!  Got to get this thing outside before I get too much of this 100 octane / golden spectro mix!

 

[ktmkirk]

quote:I will be recieving a 72 piner this week that i will be working on.  It is coming with a mikuni on it and i prefer to put back the Bing Carb.  Does anybody have a Bing that will fit?  Should I keep the mikuni on it?  The bike will need some work before it will run so I may wait until i get it, get the bike running with what it has on it and then try putting a Bing back on it. I'm just looking to get the bike back to original condition....any thoughts would be appreciated....Kirk Sessions
Hi:

I'm rebuilding a '72 Jackpiner. It has a Mikuni on it which I want to keep for now. The rubber "adaptor" between the cylinder and the carb has split in half since the bike has been sitting for years. Is this a special adaptor or the stock Penton piece? If it is special, are they still available?

Thanks
Gary

 

Edited by - ktmkirk on 01/31/2001  07:33:32 AM

[penton117]

Hi Guys,

I just went through a similar carb hassle, so here are some random thoughts: The original carb I believe had a clamp mount, like the 125cc motor, which slipped over the snout of the bolted on manifold. ( which I believe was aluminum, not steel)Finding a replacement carb is easy, but finding one with this clamp mount is not so easy. Most folks use the radiator hose kinda retrofit. It works OK but most 2 stroke tuners will tell you that for optimum performance you must keep the intake tract as short as possible. That kind of retrofit moves the carb back at least an additional 1 inch from stock, and also makes mounting the rock-hard air boot almost impossible. (Of course if we wanted optimum performance we probably wouldn't all be riding 30 year-old motorcycles) On your bike it sounds like the intake was swiped from a Yamaha. Lots of them used a rectangular, 4 bolt mount with a female end for the Mikuni to slip into. Here's a thought: The RD350 motor had a reed valve block mounted into the rubber manifold. If you already have the right bolt pattern you are 1/2 way to having a reed conversion setup. Wouldn't that be slick?
Last thought: Huskys use a real heavy duty rubber mount that fits perfect for those snout-to-snout conversions.

Don

 

[imported_n/a]

After some research, it appears that the adaptor I have is a Mikuni part that is still available. I've ordered one and will report back if it is the correct part.