For all of you brave souls who think you have to have a faster 250/400, check out the Gem reed kit offered on ebay under "Penton"
Kip, I have bid on it. What kind of changes can I expect on a MC 5 250?
Rick Terry
Get ready to remortgage the house if you plan on buying that.
Invest a lttle more and have a block and carb spicot cnc machined new, design it around an already existing reed cage and pedals. I'd buy one or two.
Bob, Kip, I was thinking of mortgaging the Edsel to pick this up and use it as a model to have them remade. Of course, I want them to be available to use. Karl, if that is what you have in mind, be my guest, but I want to reserve two.
Glenn
What can I expect by adding a reed valve to my MC5 250
Thom Green,I own and ride a 76 250 MC5 MX which I bought new.
I have never used one as a stock 250 is fast enough for me. I have friends who swear by a reed for better power delivery and a few percent increase in HP.
For anyone interested, I have a GEM reed assembly for a 250, and would be quite happy to loan it as a pattern for anyone (Karl?) contemplating having them re-manufactured.
Mike
Yes,I already 3rd.mortgaged the house.If I get this damm Gem Reed,we will be offering copies-How Soon?? I don't know due to the fact that our other customers are keeping us running from MRP to JIT and back.If I don't land this baby,I will be looking for a unit to copy.
What I am wondering is, would the reed valve smooth out the power. It could be that I need to re jet my bike but it seems to be pipier than I remember. It runs kind of dirty on the low end and then comes on rather strong in the mid range. I am wondering if I need to lean out the pilot jet maybe one size. It is cooler and up here than when I lived in silcone valley and I have not changed anything.
Thom Green,I own and ride a 76 250 MC5 MX which I bought new.
Karl, Investment Casting........Correct?
Thom: Although the 250 Pentons were always a somewhat "pipey" motor, what you describe sounds more like the R.H. crank seal is a bit tired and letting in air;
Karl: If you want a GEM reed cage as a pattern, let me know. No need for the 3rd mortgage.
Mike
thom,
Just a thought, have you burned out the pipe lately?
You might just need to clean the carbon and oil build up out. you can use a torch or a wood fire in a barrel. we like the wood fire the best. it does a better job.
John
thanks mike and John,
Mike, I just replaced the RH crank seal a month or so ago. It should be ok.
John, I have never cleaned out the pipe. It is not as bad as it sounds. I bought the bike new, right.... well I rode 4-5 times and then a custom pipe was fitted, then I rode it 8-10 times and my life made a significant change..... that was 25 years ago and my bike has only been riden 4-5 times since then. I changed the R seal because I thought it was a good idea since I was planning on riding it regularly. A good cleaning of the pipe is probably in order. I have a fire pit in my back yard that should do the trick. If it was a seal wouldn't it lean the bike out?
the problem may be me, since I have only been on the bike once since I replaced that seal. And it has been a number of years since I rode the bike for more than a few minutes. boy have I missed my bike!
Again I say thanks.... I am finding that I did not really know that much about the bikes I have riden. riding a new bike is pretty easy, just keep up the regular maintance and your pretty much home free, A vintage bike well that is much different, you really need to know your stuff. And I have much to learn.
Thom Green,I own and ride a 76 250 MC5 MX which I bought new.
My son and I have a '76 MC5 250 we are prepping to race and are also very interested in the Gem reed kit. We realize that the price may be astronomical. Perhaps if we are reassurred that someone will offer a remake of this kit for a reasonable price ($250???)we can keep the bidding down and let everyone win. Is this likely? We have also considered the reed kit that Cycle Stop offers for the '73-'74 Elsinore. It might be possible to adapt this kit to the Penton.
The Elsinore kit is $229 and this seems reasonable to me. I know the bolt patterns are similar. I think the angle is wrong for the Penton, but perhaps an angled adapter plate would work. Of course, there's the question of how to properly modify the Penton piston. Anyone out there with the Gem istructions that would be willing to share this info? Should we fail to win
the GEM auction we will be looking into
the Cycle Stop kit as an alternative.
Although being racers we always are looking for an edge, in the spirit of sportsmanship I will gladly share any information we may
find in this regard with fellow POG members.
Jon Noyes
I rode for and worked in a shop in the early 70's that sold Maico's.We got in the GEM kits and I got a freebee so I could promote it's merit to the customer.I was not a good salesman for this product.I did not like the effect it had on the Maico.I put a lot of machine work and time in the project and in my opinion I ruined a good Mahle piston I couldn't afford.But the Maico 250 was a tractor to begin with.So maybe on a more pipey machine it would have merit.Frank
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.
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
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
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.
!!!YEAH FOR OUR SIDE!!!
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.
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
thanks rick,and everyone else. I will start looking.
Thom Green,I own and ride a 76 250 MC5 MX which I bought new.
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.
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
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
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.
Carl Cranke would NOT agree with putting this obstruction in the intake manifold! Pipey piston port power rules!!
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.