"D" motor blues

[rick823n]

Can any "D" motor owners help me jet a mikuni properly for this motor. My "B" motor settings dont seem to work. Do these two motors have very different jettings, or should I be looking for some other reason for a loaded up condition? Thanks for any help. Rick Nicholson

[tomale]

Rick, A couple quick questions. where did the carb come from,did you take it apart to make sure it was clean and that the float does not stick or that the main jet did not fall out or any other jets for that matter.  What does the air cleaner and the pipe look like? I hope that you are not offended, The back ground wil help to figure out what is really going on. I would imagine if the porting is similar and the pipe pretty close to the same. the jetting should be close. The jetting could be very different if the the Pipe on the B has a race pipe and the pipe on the D is a pipe made for the street. A street pipe is going to be much more restrictive and will not allow the motor to breath the way that it could if it had a pipe that has a unrestricted muffler. Steet pipes are often more concerned with noise than raw horse power. I am no expert on the little bikes but the princples are the same. In fact the jetting on a big bike can be off a couple sizes and run pretty well but that is not true of a little bike. The need to be spot on to run well. Hope this helps:)

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5

[rick823n]

Thom, I've checked what you have mentioned. The bike has a newer mikuni, I've torn it apart   and cleaned it. Air cleaner is clean( I've also tried it with air cleaner off). Has a race pipe, though I have not checked the silencer to see if it is clogged or broken internally. I guess I still havent checked the carb choke system. Do you think a "B" motor jetting setup should at least be in the ball park for a "D" motor? As far as being offended, I have, as have others, left a shop rag in the carb before, and my best mechanic friend routinely askes me, when I ask him for help, "What did you worked on last." Thanks for the ideas. Rick Nicholson

[tomale]

Rick, I would think that it would be in the ball park... I was hoping that some of the other guys would weigh in. There are several guys that come to mind that are much better at this stuff than I and should have more say than what I have already given. Keep checking. At the very least you are getting to know the bike.... a good thing:)
I have done my fair share of "what was I thinking" I put something together only to find it does not work and when I pull it apart I find that I had turned a part up side down or left something out...or worse!
Last year my buddy Terry and I were working on a bike. It did not turn over very well and finally did not turn over at all, Off come the top end...The problem.... A very dead mouse under the piston and on top of the crank. I freaked out when I realized what was in my hand..when I went to clean it out.. [:0][:0] I never moved so fast in all my life and it seemed that nothing was strong enough to get my hands clean.....[V]It still gives me the shivers

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
78' 400 MC5

[Doug Wilford]

If you are talking Pentons the "B" and "D" jetting is very close.   I would for sure make sure the muggler isn't partially plugged.

[rob w]

Doug,

I'm not familiar with the muggler, where is that located?

Bob

[firstturn]

Rob W,
  It is at the end of the plumbing or part that holds the pinion steady while you are polishing the bearing that fits in the ocular bar.  I thought you knew better.[:0]

Ron Carbaugh

[Doug Wilford]

That is what happens when the chrome bearings in the muffler can't juggle.    If they get to carboned up they cease to juggle and become part of the muggler.    Even first turn knew that!

[firstturn]

Yes I knew that.[]

Ron Carbaugh

[rob w]

Gentlemen of infinite wisdom,

 Okay, now that you mention it. I believe that happened to one of my bikes once. If I remember right, I think they said is was either one of those muggler problems, or it could have been a short in my wheelbase.
 
Bob

[john durrill]

Rick,
 Your Pipe and if the D cylinder you have has the exhaust port mod would contribute greatly to loading up problems. THE CHANGE IN THE EXHAUST PORT WOULD MAKE THE sachs power band almost like a road racer. sorry for the caps. typeing one handed has its draw backs chuckle chuckle !!!
john d.

[rick823n]

Thanks,everyone. Seems as though the choke circuit was not going all the way off. The jetting is getting closer, and I will avoid any major port changes. Just trying for a good running "D" motor, I cant wait!  Rick Nicholson

[john durrill]

Rick,
 Its the change where the port meets the pipe that would give you the most trouble. the lip where the port changes from rectangular to round in the modification. the lip control's when the wave in the pipe is reflected back. that should give you much higher rpm power and you should loose the bottom end the stock B cylinder had. Its all a trade off when you go for max power.
 John D.