Question: LTR Jetting an MC High comp head

[Ryno]

All,

One of my 1st post on here and have a little question with a big story behind it. Last week I installed an MC head on my 06 EC250 and was previously running LTR needle and this jetting. 42pilot, LTR needle in middle position, 185 main. 30deg-90deg at sea level. New England terrain.

I had the chance to run a higher compression head from an 06MC and was told to bump the pilot up to 45 and run the main at 185. I had very good luck with the LTR needle and stuck with that needle. The person I got the head from did not use the LTR needle and was using the stock needle. 50/50 Sunoco race fuel was necessary.

Anyways, the bike flat out ripped and I could not believe the pull from the bottom into the midrange. We just had our 1st harescramble in Maine this Sunday, 20degrees and dry air with plenty of frozen ground and ruts. My bike ran great for the 1st 5 laps of a 6mile loop and about 1/2 way through the 5th lap it started making some knocking noises, almost like a rattling crank bearing. Well I was doing pretty well in the A250class so I kept running it. The knock would get worse as I chugged the motor so I kept it in the RPMs a little more. Well the last lap it died in a corner and wouldn't start. Sounded almost like it ran out of gas I sat there for a couple of minutes bummed but then looked and plenty of gas. Kicked, kicked ,kicked, choked it and it fired up and the knock was gone for bit and then came back near the finish. Finished the race but discovered I was pretty much out of coolant. I think I was just running hot and boiling the fluid out over the course of the race, the terrain wasn't that bad with a quite a bit of speed and I've never boiled my bike out of fluid in the summer.

Was the LTR needle too lean off of the pilot and making the bike run hot? The bike is torn down and the lower ring was siezed and the head 0-rings were rock hard from being so hot. Cylinder is within spec and everything else is checking out OK. Thank goodness for TORCO- 12miles with no coolant!!!! I'm looking for root cause??? Any suggestions?
Les, do you have any experience running your needle in the MC250?

 

[bobr]

your post explains you changed the head. I'd guess you drained the coolant? i think this is where your problem was. you might have had an air bubble in the coolant line preventing proper flow. be sure to check this next time and bleed any air out of the system when you change coolant or remove the head. the Korns have been running that head since the start. check with them on what jetting they use for the cold weather. did you read your plug? was it light?

 

[GMP]

Ryno,

Assuming there was no coolant leak from a pinched head o-ring, loose hose, etc.

I've seen so many variables with these bikes its almost impossible to give a hard recommendation as far as jetting. The kit is good but only a starting point. I had two 250s, same setup, that liked completely different jetting, even a different slide. '03 ending up way richer that my '00, even with the same CDI. The numbers don't sound lean at all but obviously you were at some point. Only you know where your right hand was most of the time. Start over rich and work down. Also, there have been 3 different LTR needles since '00. The original was too lean in my '03. Call Les if your in doubt. If you like the power with the MC head have RBD fix the squish and retain the compression.

I've had these apart and refilled more than a few times and never saw an issue with trapped air in the system, like on some KTMs. Its wide open, straight up and down and fills easy. Every time I filled mine, started it, and rechecked, it never needed any more added.

Regardless what my next bike is, I'm going to run the EVANS NPG-R coolant. It won't boil until 375 F. In your case the motor might still have gotten a little hot but the coolant would stay in the system and do its job. You can rock crawl a big 4-stroke without worry using this stuff.

 

[Ryno]

Well, so far no smoking gun. Going for a test tomorrow with the needle one clip richer with the stock head. Still about the same temp 20deg and should continue into this weeks enduro on Sunday. Still need to check out the MC head to make sure it's not warped. I know I was riding the bike in the meat of the needle on down to the pilot a quite a bit and it may have just been running a bit lean/hot. I also meant to top off the radiator fluid before the race and forgot so maybe it was slightly low causing it compound the overheating issue. Whats the deal with the RB head, why would I want to reshape the MC head?
Thanks for the input guys!

 

[GMP]

Because the squish clearance is too big on the stock head. Once its matched to the piston at approx 1mm, compression is then set as desired. You can have either head modified to the same spec. Good cheap mod, for any bike.

Another thought: Is the Sunoco fuel oxegenated, as around here it comes from a pump right next to the regular stuff? Pump gas has a lot of ethanol now, so if you add all these factors up including cold it could be lean.

 

[Ryno]

I'm not sure about the Sunuco fuel, I got it from the guy that gave me the head. They have been running the stuff all year and mixing 50/50. I know for a fact where I get my fuel normally and the stuff I mixed with the Sunoco said it contains ethynol. Is there any fuel stations who don't use ethynol? I haven't been able to find one locally. But haven't had any issues before it got so cold, I think I was just running on the border of lean using the LTR needle in the same position as I was in the summer. I really should have known better!!! Live and learn as they say!

 

[jefgil123]

Another candidate for an overflow bottle.....That Main Jet is pretty big. But I'm running a 182 with the -0 needle. Did you have any indication of pinging? What compression reading do you get with the MC head? Over 200 psi may be a little high.

Do like GMP says and hook the Radiators together with a crossover line without the GG expansion tank. Then run the Radiator overflow hose to the lower side of the GG expansion tank fitting and use it as an overflow tank. Run a little line off the other side of the GG expansion tank straight up a few inches , then 180 bend down for overflow.

 

[Ryno]

Overflow bottle, do tell. Not sure if that would have helped completly but still interesting. What the heck is the tank behind the headlight for then. I also went up to a 1.4 cap instead of 1.2.

 

[GMP]

That tank is just an expansion tank, not an overflow as on a Yamaha WR, street bike, or a car. It operates at full system pressure. If the cap burps the coolant is still lost on the ground. IMO its just another thing to fail. On the ECs it is constantly rubbed by the wires, I could see the wear marks. I scrap it and just run a crossover line in front of the fuel tank, the way my '00 XC250 came. I also ran a 1.4 bar cap, LTR impeller(my OEM was plastic), with no problems EVER.

Just run the EVANS coolant, problem solved.