Vintage Dirt Bike Q & A

I have a 1974 MT250. I just rebuilt the engine because the original piston was burnt so bad by the previous owner that it broke and fell into the bottom end. I put in a new con rod, crank bearings, 1st over piston and rings,seals, gaskets and etc. I bought everything from http://www.re-mx.com. He told me the stock rod was unavailable and lot of people use a rod that is slightly longer than stock. He provides a thick base gasket to compensate for the extra length. Anyway, I got it all back together it has good compression, spark and clearly gets enough gas. I was having problems dialing in the carb so I temporarily disconnected the oil injector and I'm running 40-1 pre mix. I have the carb dialed in now and the plug has a perfect light brown color.

Now the reason for the post. The bike is fouling plugs if I'm not over revving it all the time and cost out like the timing is off but I checked and it's not.
Can somebody tell me what the stock squish would be (distance between the piston and head at top dead center)?
Also, where do I buy carb rebuild its for these bikes?
What was the stop main jet size?

I think the stock piston-to-squish-band clearance is probably close to the MR175's, which is about .070" / 1.8mm. At this distance obviously there's very little squish effect. My MR's currently at .024" / .6mm.

The stock main jet was 122. For the stock carb, the Keyster 58-0009 kit is pretty good:

http://store.dixieinternational.com/ind ... t_id=11598

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks for the info. It appears that RE-MX gave me some bad info relating towards the con rod and thick base gasket. My initial measurement of squish is .3 inch with the thick gasket and new rod. I'm starting to think he gave me the wrong rod or doesn't know as much as he thinks he does. I am going to measure more accurately and make adjustments.

Remx sold me my rod for my mt250 build and I am very happy with it. It should come with a shim plate that goes under the cylinder to put it at the right height for the taller rod. Now I had a very nice port job done on my cylinder after the rod was installed so I dont know what it would be like in a stock mt. Here a some pics of my fugly mt250, I still have a lot of work to do on it including fixing the hack job my friend did on the frame. http://s201.photobucket.com/user/wooshe ... t=3&page=1

Sorry I made a mistake, I got my rod kit from this site http://www.badbrush.com/we_race.htm Sadly it dosnt look like they have them anymore. I hope you get yours worked out.

Woosh,


Yeah, I have the spacer installed. Do you remember what part number your con rod is? Mine is a Wiseco WPR124. Says it for CR/ATC/TRX250. Have you run your engine yet? Looks like you put a lot of work into it. Also are you Washington? I'm in Seattle, I saw the plate on your bike is Washington plate.

might want to look at the heat range on the spark plug.it should have a NGK B8ES spark plug in it.

I have found on my personal MT250 it does not foul the B8ES plug that easily.I ran a equivalent Champion N3 plug and it usually fouled that plug.also make sure you are not running it for too short a period,this practice also will foul plugs much more frequently.

Woosh,your bike tooks pretty trick to me with the 1973-74 CR250 top end with a reed valve on it.looks very trick!

I noticed the Radial head on it,who made that one?

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(2) 1968 DT1 1970 RT1M,1970 DT1C 1971 RT1B Enduro 1974 MT250 1974 DT250A (2) 1975 DT400B 1974 DT100,1978 DT175
1975 CR250M1 1979 CR250R 1979 Kawasaki KZ400H1 Jesus is Lord!!

Sorry Seattle I dont remember the part number anymore but I found this for you viewtopic.php?f=21&t=1739
I live in maple valley which is about 45 mins south of seattle. I have run the engine for about an hour but not a whole lot. I have had to take it apart a few times as well. Thanks Dave Its got some nice stuff on it but it looks like a beater but it just means I can drop it and not worry to much. The reed valve and porting were done by Rich Gagnon and thats a dg sand cast head. I had one of the other dg heads too the sunburst but didnt like the looks as much as the one thats in it so I sold it. I still need to work the jetting out before I can really run it but I am working on my 76 xl340 right now, this is next though.

Thanks Woosh.
Looks like I have the right rod and spacer kit based on that thread. I measured the squish again and came up with this.





I think it is in spec although maybe a little more than needed. Are you running the oil injector on yours? Have you ever heard of the VME Bonehead ride? It's a dual sport vintage motorcycle ride. Anyway its next month if you have a runner I recommend it, it's an absolute blast.

Here's a pic of my bike too