Mc 250 performance

[widebear]

Did a complete rebuild this winter including raising the transfers and exhaust with gskts and matching the cases and jug, left the head alone. The new setup required raising the needle clip by one and going up to a 170 main from a 168. Still very torquey and manageable at lower throttle openinings with a big gain in the mid range and absolutely schreiks on top. On Wed night did a 91k or 56 mile @ race speed loop, 12 k of that cruising road on return leg. Got back four hours later with only a couple of onz of fuel left in the tank. all in all very happy with the outcome.

 

[AZRickD]

How much more gasket (and/or total height) did you need to match up with the ports? What was the starting point?

 

[widebear]

The mc cylinder was fairly close I added only one green gskt to the original factory setting of two gskts in order to have the top of the piston completly expose the exhaust port at b.d.c. I did not concern myself to much that the transfers where still not completly open @ bdc but focused more on matching the cases to the cylinder by gently blending the two, same with the exhast spigot and port. At this point I have had to go up two main jets to provide the required additional fueling.The guy who did the crank for me did a really good job as the engine has very little vibration at all speeds. Perf wise did a couple of second gear to top speed roll on comparisons with my friend Brad who rides a tight 04 cr -250 and weighs about 40 lbs less, pretty much neck to neck.

 

[GG27]

I have been meaning to send my rider's report on my EC 250 engine's rebuild for some time now.........

I have done about 20 hrs on my new piston and cylinder port matching. We kept the original EC head with a 3mm base gasket, getting a 1.65mm squish measurement . The main job was to match the transfer ports and exhaust spigot, as widebear has described.

Results are that the bike has a very linear power delivery, excellent throttle response with a DDK@middle clip and 42 pilot and 180 main. Absolutely no spooge and really economical on fuel (three to four hours in mixed conditions)!.

What really amazes me with the bike is the power delivery coming out of corners, I can pin it and all the power goes down without excessive wheelspin.
Also I can keep it in one gear higher and just use the clutch to get her in the happy zone. Climbs up hills in an easy third where before I had her in a pinned second!

I ride with a friend who rides a RMZ450 and we go about the same on the straights till we get into the tighter stuff where I just disappear. Also swapped with a friend's new EC 300 Racing version and was not impressed with the engine, just no overrev and about the same power in the bottom end. My friend was really impressed with the 250's power, he wouldn't come off the bike. Overall I am really pleased now.

Next time I change my piston, I will raise the cylinder by .8mm and shave the head about .5mm, although I have good overrev power as is now, I just can't imagine how much more pleasure this engine can give out.