Vintage Dirt Bike Q & A

My Elsinore is a stock restoration and stock rebuild on the engine with the stock Kiehin carb. My first time out was at the vintage races. The track was sea level and the weather was cool, maybe 60 degrees. The bike ran ok but with a little mid-throttle break-up. The plug was a little wet. I took it home, bought jets, and replaced the 185 main, which is stock setting, to 180 and keep the needle clip at 2nd position from top. Last weeks race weather was hot, 80-85 degrees at sea level. The bike ran like crap at mid-range. So bad I pulled at before I melted the engine. The plug looked good put a little on the lean side. I drop the needle clip 1 position and ran worse. I then replaced the main with a 190 and still ran crappy. I loaded the bike in the truck and didn't run my last moto.
The only thing I can think of now is maybe an electrical problem and not a jetting problem. Maybe a bad ground? I'm busy untill next week, but when I get back to the Elsinore, what else should I check?
As always your opinions means the most to me.
Thanks again,

Rick

Since the up and down main jet changes didn't help, and you suspect a lean condition, I would perform
a leak down test. An intake, ignition side crank seal or center case seal air leak will all cause a lean
condition that won't necessarilly be evident at idle but will be evident as RPM builds increasing vacuum.
I would also check to make sure the timing is not too advanced.

If on the other hand, the engine idles and is strong at WOT, you may have a problem with the needle jet
as in the wrong needle or a damaged needle. The needle controls from slow jet to main (about 1/8 to 3/4).
Check to make sure the correct number is installed, stock is 28A. Also, make sure the needle is seated
correctly and the spring clip is installed.

Good luck with it.

dogger

_________________
1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

IMHO, you are running rich (not lean) and as your settings were actually moving in the right direction to lean the bike out for the higher temperature, I too suspect a worn needle, worn needle jet or an optional needle. The bottom line is sea level and 85F is spot on for So Cal and I ran very similar settings to you just fine. The ignitions on these bikes are very reliable and binary. If there is a problem with the ignition it won't run. Also a leak-down test is a nice idea for peace of mind, but any kind of air leak will make it race or hunt when idling.

...so if you can find Honda part # 16012-430-000 I would get it. It's a new needle (28A), clip, needle jet etc. Or you can go to http://www.sudco.com and get Keihin parts direct. Your carb is a 36mm round slide PE. The needle jet is part # 021-792 (Honda part # 16164-KA5-0041).

...or you could put all this behind you and spring for a new 36mm round-slide Mikuni. I put the specs in the CR Reference section.

...check your float height while you're at it - 19mm.

_________________
Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF