Jetting Q: outside of the normal range.


Looking for suggestions. I have read all the jetting posts and I think most
of the jetting specifications are for off-road riding. Where you are on and
off the gas quite a bit. Most of the time off-road you are on the gas pretty
hard coming out of corners and climbing hills.
I am running my EC250SM on the street. With the exception of accelerating
away from a stop light. The bike spends a lot of time in cruise mode at between
1/8 and 1/4 throttle. With RPM's somehwere in 3,000-5,500 range.
My present jetting is/was a #7 slide. 45 pilot, 180 main and a LTR needle in
the second clip from the bottom. I put it there in an attempt to fatten up the
off idle mixture.
It ran pretty good, but would smoke quite a bit when accelerating from a stop
and when hard on the gas it seemed to lack any real snap. It felt too rich on top.
A couple of days ago. I moved the needle to the second clip from the top.
Thinking It might improve the smoking and restore some of the midrange hit.
It did reduce the smoking a fair amount, and the midrange power was a
slight improvement.
What got me concerned was when I was cruising along at about 60-65 mph,
(BTW, I am running 14/40 gearing), with the throttle open less that 1/4.
It felt like it started to bog down and loose power. I was afraid it was about
to seize. I gave it a hand full of throttle and it took off like it should. Only a few
miles from home. I slowed down and ran the motor at a lower rpm and lugged
the engine so I could give it more throttle and hopefully prevent a seizure.
Yesterday, I checked the plug. It is dry as a bone. With a very slight golden
color to the insulator. It looks to be on the lean side of perfect.
So I moved the needle to the middle groove and replaced the 180 main with
a 175 in hopes of clearing up the top end smoking and lethargic power
I have yet to run it like this.
Am I chasing my tail? Should I be looking at a different needle. One that
runs richer off the bottom? Replace the 45 pilot with a 48?
I am curious about your suggestions.
I may try my old stock needle, I think it was an N1EF, not sure though.
Thanks in advance for your input.
Jeff So. Cal.
I haven't seen anyone else mention running this combo but I have a 48 pilot (as sent with my LTR kit based on my riding style) and LTR needle (clip in the middle). Les recommended a 175 main but I run a 180, much more responsive. I do have the RBD head mod. My bike runs excellent. It only smokes when it's cold or when I ride with a group of faster riders (getting a little warmer and cleaning itself out at that point from previous cooler rides). I have a slight bit of spooge out the FMF TC spark arrestor. I run the Gnarly pipe.
I marked my throttle grip and I ride mainly 1/8 throttle to 1/4 throttle, probably 75/25%. Any more is pretty much 100% open but for short periods (hill climbs or catching up). Before the jetting change I was fouling plugs after long periods of downhills (cool-downs) then getting on the throttle.
I wonder if your "top-end smoking" is the excess oil burning out from not being run very hot? If you are sure you aren't sucking air through the ignition side crank seal or carb boot I would move up a size on the pilot jet. The real cure may be a needle with a little quicker taper but I'm not sure on how to advise which way to go.
I did run a 185 main for a while and it work (just) OK but I'm not sure that would help you while just cruising around.
Have you thought about calling Les? He's pretty good with this stuff and seems to love talking about it.

Good luck :)
I am no expert at all but if I was in your situation I would rip out the carb and clean everything and then check all screws ( idle etc are correct and then start again with the road tests, beginning on the rich side and then seesawing each way with jet sizes until you find what works for you somewhere in the middle.
This was what I did and it seemed to work
Cheers Mark
I'll get an ride impression update some time this week.
As a side note.. Being in So. Kalifornia. My riding is between
sea level and 500 ft most of the time. With a few trips to the
local hills to 3,500ft. Ride temps stay between 60F and 85F.
And I am running a BR8eg plug with the stock gap.
The bike has a Messico pipe with a FMF TC2 silencer. Recent
re-pack'd. LTR power valve cover.
This is a 1998 with a counter balanced motor and the Ducati
Picture for reference:

Over all the bike runs great, if a bit sluggish when you give it a hand full of throttle
at lower RPMs, It starts first kick and settles into a perfect idle within 30 sec.
I doubt the smoking is from a crank seal. It has not lost a drop of coolant for
more than 2 years. And it has never fouled a plug that I can remember,
So compared to other folks jetting problems. Mine sounds rather close.
Maybe I am just being paranoid, I tend to do that from time to time.
Thanks again, Jeff...... the worry wart.
I would recommend that you send the head to Ron at RB-Designs and have the squish dialed in - the compression is probably a bit low on your older motor as well. This will make the bike run cleaner and more efficiently in the given rpm range.

Also, if you have a bit of time on your bike - the nozzle (needle jet where the needle slides into) will be worn and the jetting will be be difficult and inconsistent. Ron machines up a replacement and can "refresh" it for you - I am not sure - but he only may do this as part of his "carb modification".

For your reference :

GasGas Riders Club
That's a great picture.
I'll bet you can dial in what you want with a different needle. You could try a non tiered needle. A CEK, or CEL needle from sudco works great in the low throttle openings. One thing to approach with caution is jetting by exhaust smoke. It is not a good indicator of rich or lean.
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Thank you, that is very cool.
Maybe you should have a "Bike of the week" or
"Bike of the month" photo on the main page.
It might inspire (some of us :D ) to get out and ride
more often.
Cheers, Jeff
Thank you, that is very cool.
Maybe you should have a "Bike of the week" or
"Bike of the month" photo on the main page.
It might inspire (some of us :D ) to get out and ride
more often.
Cheers, Jeff

Or copy what Cafehusky is doing with their intro. ;)