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CR250r2003 run too rich

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Hi guys,

I know this question as been asked thousands times, but I need some help here.

I'm new to 2stroke world!

I just bought 2 months ago a cr250r 2003 and put it appart to clean everything, adding new tires, tubes, replate cylinder, new piston rings and gaskets, etc...

the bike start first kick.

I only rode it 2 times, (trail) the top end as around 2-3h on it.

 

I found the throttle at mid range boggy and won't clear out (seams too rich), I have some oil spooge at the end of my muffler too after a ride and near the exhaust manifold and joint in the middle, where there is the rubber. (it is normal??)

 

I repacked the muffler too with new fmf wool.

 

So I did a couple research here, read lots of thread, and decide to try myself to open my carburator and see what's inside (setting of the previous owner).

 

I have the manual so I looked at what is the stock setting recommanded. (found the carburator was setting stock, except for the air screw turns)

 

heres my current setting:

-32:1 fuel mix with Motul 800

-air screw 2x turns from fully close

-Slow Jet: 30

-Main Jet: 420

-Jet Needle: 6BHy38-73

-Needle clip position: 2nd from top

-Float height about 15.5mm (honda recommand 15mm) from the flat surface to the highest point of the float (carb maintain at around 45 degree to avoid any pressure)

 

So I know it's too rich because the engine won't clear out,

 

I do only trail riding, not always on the pipe, but in straight section, I tried opened it and still wont clear.

 

I read here to run the 410 main jet instead of the 420, so I ordered this morning the 410 from my local dealer, to begin with it.

 

The reed valve seams ok, when having in my hand and looking trough it, no light pass trough.

 

Well, before brining the bike to the dealer, I ask your help and advices here, will have the 410 Main Jet next week, but i'm not sure it's the right place to start, that's why I ask! maybe I missed something!

 

thanks for your time!!

 

cr.jpg

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Check the power valve operation (details in the manual) and cleanliness. Another possibility could be a bad wet side crank seal. Also, check the spark plug.

I don't think the jetting being that close to stock would cause it to not clear out at all.

Nice looking bike, super clean! 

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thanks for your answer!

the spark plug was new, when I remove it, it's dark and oily.

So I can adjust the powervalve? (will look in my manual).

for the bad crank seal, I assume i'ts a big thing to do, maybe i should bring the bike to the dealer?

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So you're probably gonna need a new plug for sure, but that's not the root cause.

The RC valve is adjustable and has a setup. In fact, if I remember correctly I think it is possible to get it completely wrong/backwards but I'm not positive on that. Been a while since I had my 02's. 

Judging by the work that you've already done, I would say that you could probably handle the crank seal. Look around on this site for info on doing it. Again, if I recall correctly it doesn't require any special tools or splitting of the cases to do it.

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thanks again!

When I did reinstall my cylinder, I looked in the manual for re-installing the RC valve the correct way with the two wires, is that setup that you are refering too?

will look in this forum for more info on the seal, I assume there is two seals, one on each side?

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Two things that help greatly for a trail / slower ridden 2T MX race bike:

 

- easily go 2 steps leaner on the pilot jet

- difficult as most think a 'racing' oil is better, rather a clean burning low flash point premix (Interceptor, Lucas etc.)

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try 410 and 37.5, needle 4 clip

then if it doesn't work you'll be on to something else?

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Lots of info thrown out here.. 

If you haven't purchased the S-7 and S-8 nozzles yet you'll absolutely need them. 

Between sea level and 5k elevation + there is a few things to change on my mikuni equiped 03 CR250. 

Summer time I always run the 30 pilot, S-7 nozzle and switch between the 38-73 and 38-74 needles and 380-420 mains. 

Winter I'll run the 32.5 pilot and S-8 nozzle with the same switch between needles and mains. The mikuni is a picky son of a gun but man does it let this engine scream when tuned right. 

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On 8/18/2017 at 2:49 PM, cadwarrior said:

wich part is that?

It is an internal oring in Keihin PWK carbs that can fail.  I think this bike actually came with the Mikuni TMX, so it would not be affected.

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14 minutes ago, turbo dan said:

It is an internal oring in Keihin PWK carbs that can fail.  I think this bike actually came with the Mikuni TMX, so it would not be affected.

yes, its a Mikuni

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On 22/08/2017 at 3:46 PM, WeekendRDR said:

If you haven't purchased the S-7 and S-8 nozzles yet you'll absolutely need them

those S7 & S8 nozzles are where the main jet screw in it?

I just try today the 410 main jet, and it run better, but still have a bit of hesitation, will have to try it in the trail for better test.

I noticed that the bike now idle faster with the 410. Should I reduce the idle by unscrewing the idle screw?

Edited by cadwarrior
refine my question
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The main jet only comes into effect above 3/4 throttle so increased idle speed isn't related.

It's rather the pilot jet and air screw settings that affect the idle / off-idle driveability.

 

Without doing any adjustments,

simply going from a hot / humid day to a cooler/dry day will make the engine run leaner and idle better & faster.

 

You set the air screw daily to compensate for ambiant conditions.

Adjust it to obtain the highest idle speed, you then re-adjust the idle screw for the proper idle rpm.

If outside of the air screw's adjustment range, you have to re-jet to a different size pilot jet.

 

Needle affects the 1/4 to 3/4 throttle range, best adjusted by 'feel' for best throttle response and acceleration.

Main jet from 3/4 to full throttle, slightly lean will give the best overev for short spurts (MX)

but will be too lean for sustained wide open throttle riding (open terrain, desert, dirt roads)

 

Edited by mlatour
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7 hours ago, mlatour said:

The main jet only comes into effect above 3/4 throttle so increased idle speed isn't related.

It's rather the pilot jet and air screw settings that affect the idle / off-idle driveability.

 

Without doing any adjustments,

simply going from a hot / humid day to a cooler/dry day will make the engine run leaner and idle better & faster.

 

You set the air screw daily to compensate for ambiant conditions.

Adjust it to obtain the highest idle speed, you then re-adjust the idle screw for the proper idle rpm.

If outside of the air screw's adjustment range, you have to re-jet to a different size pilot jet.

 

Needle affects the 1/4 to 3/4 throttle range, best adjusted by 'feel' for best throttle response and acceleration.

Main jet from 3/4 to full throttle, slightly lean will give the best overev for short spurts (MX)

but will be too lean for sustained wide open throttle riding (open terrain, desert, dirt roads)

 

verry usefull, thanks!, and yes, yesterday was a cooler day.

should i raised the needle clip to the first position?, now its stock at 2nd

 

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How is your air filter? If it's blubbery in the middle it could also mean there's not enough air for the increased amount of fuel. Make sure your filter is clean and not overly saturated with filter oil. Also it may sound simple but make sure there's no pieces of dirt or anything in your carb passageways, you have to use compressed air to clean them properly. Can't tell you how many of my friend's bikes I've "fixed" bc they thought they had cleaned the carb correctly.

I've had minor issues with my 01 CR250 and found the most effective remedy to be moving the clip between two positions (2 n 3 from the top) depending on the season... I have never needed to swap out any jets.

Keep is posted.

Sent from my SM-G930P using ThumperTalk mobile app

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1 hour ago, delawhere said:

How is your air filter? If it's blubbery in the middle it could also mean there's not enough air for the increased amount of fuel. Make sure your filter is clean and not overly saturated with filter oil. Also it may sound simple but make sure there's no pieces of dirt or anything in your carb passageways, you have to use compressed air to clean them properly. Can't tell you how many of my friend's bikes I've "fixed" bc they thought they had cleaned the carb correctly.

I've had minor issues with my 01 CR250 and found the most effective remedy to be moving the clip between two positions (2 n 3 from the top) depending on the season... I have never needed to swap out any jets.

Keep is posted.
 
Sent from my SM-G930P using ThumperTalk mobile app
 

My air filter is freshly cleaned and oiled equally on all the surface.  it's the air filter that came with the bike when I bought it, double layer foam... maybe I should order a brand new one.

the carburator is clean too from what I saw, but maybe compressed air inside can't hurt, had it in my hand recently to check what jetting I have in it, seamed clean. the airbox is like new too, pass many hours on cleaning every corner of the bike. I didn't play yet with the clip position of the needle, it's curently at the 2nd groove from the top.

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You are trail riding a motocross race bike

take into consideration that if not ridden hard enough it will load up even on a motocross track.

 

If everything mechanical checks out (reeds, float / fuel inlet needle & seat, crank seals)

 

As I suggested earlier, going 1-2 steps leaner than stock on pilot jet and needle settings,

setting the fuel/float level on the lower limit of the range and,

using a low flash point premix (not a 'racing' oil) would greatly help in low speed operation.

Install a new plug in the event your current one is fouled.

 

Use up your Canadian Tire points/money and go buy a litre of Lucas 2-stroke premix,

drain your tank and mix up a fresh batch of gas. 

If you don't like it, use up the rest of the Lucas in your garden equipment.

Edited by mlatour

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