GEM Reed Kit

[tomale]

Hi everyone, I have been giving all of this alot of thought. And I was thinking about the differences between bing and mikuni carbs. If a mikuni will smooth out the power on a 125 would it not do the same for a 250?
I would be willing to lose just a little on top to gain some on the botton- middle. And the thought accured to me that I would not have to modify the piston, which is something I do not want to do, I want to try to keep it pretty much stock. Because at some point I want to restore it. So for me what ever I do, I want to do so with out ruining what I already have. One of the things I like about my bike is that the ride to maintance ratio is very low, compared to other bikes. Like maicos which are great bikes but I remember spending alot of time and money to keep GP 400 up and race ready.

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[Cathump]

Thom, I have a Mikuni on my 250, and it does help with bottom end, and I really can't tell much difference on the top. I first put a 38mm on it, but the body on that carb was too long and hit the case. The next one I tried was a 34mm, which fit just fine. What I have now is a 34mm bored to 35.7mm, and I think it is working out just fine. I did have to go to Lowe's and get an intake boot.

My main reasoning behind the swaps is the Mikuni jets are very available around my home, but I would have to order Bing jets.

As far as the GEM reeds, I was bidding on them, but unlike others on here, I WILL NOT bid against another forum member.

Rick Terry

[deek]

How was the reed set up on a 125?? I just picked the bike up yesterday, and there it was (reed valve), looked like it was welded on though.. Still need to get it running though.

Dale



 

[[email protected]]

Mikuni conversions are realitively simple and my experience has always been positive.Find a used 36mm VM Mikuni and I have a pretty good starting spot on jetting that works well on my other 2 stroke singles,(Bultaco's)Yo won't have to spend a whole pile of money and I think you will be happy.Especially when it comes to starting.

 

[rob w]

!!!YEAH FOR OUR SIDE!!!

 

[tomale]

Hi Fb,
I am liken this idea. what does a vm come off of(what bike)? and what will i need for jets? What about the intake manifold, does it need to be changed or can I use the stock one?

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[Cathump]

Thom, the VM is the old style, spigot mount, round slide. Just about any Jap bike came with them, with the exception of Honda, of course. I used the carbs off my Yamaha's for experimenting, and bought the final one from Pro-Flo.

As far as jetting, mine were already jetted for the Yamaha's, and I would have to actually look to see what final jetting I have now, but the jets that are stock, plus 3 sizes richer and leaner would be a good start.

You can find these carbs on E-bay a lot.



Rick Terry

[tomale]

thanks rick,and everyone else. I will start looking.

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[[email protected]]

Pretty much everything stated as above the manifold will take some "engingeering" but the appropriate rubber hose will work.Actually they seem to be one of the few things on ebay that represent good value for money.I buy every reasonably priced (30 to 40 dollars) 36 mm I can find.Pro flo is cheap on new ones but I have yet to not have to change their jetting.Sudco offers a book from Mikuni for about ten bucks that takes most of the mystery out of jetting these old carbs.It's money well spent.They list a setup for every size that is a good starting point on jetting.

 

[Cathump]

Another good resourse for jetting is on Eric Gorr's website. http://www.eric-gorr.com/techarticles/carbtuning.html

I also have yet to find a carb that is spot on when I install it.

Rick Terry

[john durrill]

Getting the right needle , needle jet combo is the hard part. if you can find someone that has a working cab to get your starting specs for thats a big Jump. If the specs have a 2 or a .5 air jet be very carefull.
 The air jet on a vm is used to fine tune the needle. .5 and 2 are the limits at both ends. if the specs have a 3.0 slide the same thing. the main and pilot jets are not expensive and we can ususaly get them right. its the part throttle setting that can be hard to come up with. And thats where one would generaly sieze an engine. when you roll off wide open at the end of a straight or run a part throttle setting for some time.
Like when you get out on a good jeep trail.
 i have had a carb with the needle jet off so far that it was impossible to jet the main.
 Mikuni's are very good carbs . just need the right jetting info on one. the lectron will do the same thing , maybe better but they are expinsive and the the needles are $29 each. you need someone to help you their with which needle to get to make it worth it.
 we just put a 32 mm Lectron on my sons piner and it took about 20 mins to get close. that was because we had already done one lectron on my bike and had Al Buehners help with his needle info to work with.
 He has been runnng a Lectron for years on his Piner. he did that to make it a better trail bike with its power delivery.
 the Mikuni is cheaper i think even if you have to buy a lot of parts to get it working right. the lectron is much easier to tune.
 Al has some of the older Lectrons fitted with the new gas type float bowls . you might try him if to choose to go that way instead of the Mikuni.
John & Peter



 

[tomale]

Thanks for all the great help, It sounds like quite a bit of trouble but worth the effort. I will give al a call when I can set aside a few minutes.
Happy trails to all.

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.

[Mike Lenz]

Carl Cranke would NOT agree with putting this obstruction in the intake manifold! Pipey piston port power rules!!

 

[tomale]

I guess I've been spoiled by riding and racing a Maico 400  "the original dial a power"

Thom Green,I own and ride a 76 250 MC5 MX which I bought new.