Jump to content
Sign in to follow this  

carb problem, low rpm sputter yz250 02, please help

Recommended Posts

Hi everyone!

 

Hope someone can help me out here. I have a 2002 yz250 that won`t cruise in low rpm..  (Converted to sm so I want to be able to use it on the road without chasing the bike in the low rpm`s) The bike rides fine else, but at low rpm it is "ready to take off" if you understand. It does not bog. I think this problem is called "sputtering"? Its not any false air, I`ve changed all gaskets as the gearbox wouldnt live anymore.

 

The mods to bike are:

 

UNI Pod Foam Air Filter (I`ve fitted this because I have installed a battery in the airbox since it has lights and everything)

Fmf Fatty

PC 304 Factory Sound

 

The specs of the carb:

 

Pilot Jet: 48

Main Jet: 175

Needle: N3CW

Needle position: 3rd

Mixture screw: 1.5 turns out

 

All help is really appreciated because Im sick of taking the carb off and on, but I dont get rid of the sputter. I`ve tried to change needle clip up (2nd from top) and adjusting the mixture screw while I was driving (from 0.5 turn to 4) but that ended up with a bit better low rpm cruise but got a minor bog in the middle.

Share this post


Link to post
Share on other sites

What altitude and temp are you riding at? N3CW is a WAY rich needle. The stock needle (in the U.S.) is N3EJ position 2. If you have a book look at the "setting" section in the back and it will get you close. I assume you have already cleaned the carb including the power jet passsge?

Share this post


Link to post
Share on other sites

What altitude and temp are you riding at? N3CW is a WAY rich needle. The stock needle (in the U.S.) is N3EJ position 2. If you have a book look at the "setting" section in the back and it will get you close. I assume you have already cleaned the carb including the power jet passsge?

the altitude here is 140m/460 ft and the temperature is from 10 degrees celsius to 25-30 degrees max. The weather here in Norway isnt very stable :banghead: today it was 18C. The N3CW needle sat in the bike when I bought it. I`ve cleaned the carb several times to check if anything was stuck or something.. I dont have any manual or book but I`ve searched the internet but only got more confused about the carb settings.

Share this post


Link to post
Share on other sites

The best advice I can give you is buy the next leaner needle and 3 sizes up and down on the main and pilot. Google "Spanky's jetting guide" Changing the air filter and putting a battery in the air box is going to throw any normal recommendations out the window. I should have read your post better before I answered the first time.

Share this post


Link to post
Share on other sites

The best advice I can give you is buy the next leaner needle and 3 sizes up and down on the main and pilot. Google "Spanky's jetting guide" Changing the air filter and putting a battery in the air box is going to throw any normal recommendations out the window. I should have read your post better before I answered the first time.

yeah, I have to just order some jets for the main and pilot.. Yes, the pod air filter is a bit of a problem, but i dont have any other choice. It should be possible to make it run smooth anyway:) with the specs I have now the plug is a bit too wet and the exhaust paints my rear fender with oil, so its definitely not lean :ride:

Share this post


Link to post
Share on other sites

Some good advice already posted. My summary:

1. It's never totally going away. 48 pilot should be best for on the road cruising at under 1/8th throttle. Air screw important but will never fully resolve your goal/issue. Main jet irrelevant. Needle clip irrelevant. Needle shape matters and W works ok.

2. Leaner #8 slide!

3. New reeds. Dual stage.

4. Replace crank seals if any doubt.

5. Try smaller 40 power jet. I've not done this yet, but I'm hoping it clears up the burn in the use case you're trying to solve. If you do it then please let me know the result.

Edited by numroe

Share this post


Link to post
Share on other sites

Some good advice already posted. My summary:

1. It's never totally going away. 48 pilot should be best for on the road cruising at under 1/8th throttle. Air screw important but will never fully resolve your goal/issue. Main jet irrelevant. Needle clip irrelevant. Needle shape matters and W works ok.

2. Leaner #8 slide!

3. New reeds. Dual stage.

4. Replace crank seals if any doubt.

5. Try smaller 40 power jet. I've not done this yet, but I'm hoping it clears up the burn in the use case you're trying to solve. If you do it then please let me know the result.

 

I`ll check out the #8 slide! Do you have some recommandations for a cheap but reliable dual stage reed? I need to take out my reed and post a pic of it here. I didnt notice anything wrong when i had it out the last time..

 

I appreciate all input on this:)

Share this post


Link to post
Share on other sites

You're welcome.

 

JD make a #8 slide. You also need their cable holder, since the stock part kinks the cable. I think it was about $60 for the lot + post.

 

I have the Boyesen Power Reeds. Fiberglass petals. Dual stage.   Performs great for me. About $30. I'm overdue to check them out for wear, since they've done well over a 100 hrs now. I use a wide RPM range on my 295.

 

For $50 there is the Boyesen Pro Series Reeds, which are also dual stage, but a carbon fiber top petal to better match all engine RPMs.  If you want real crisp part throttle response, then the pro series reed looks very tempting.

 

How confident are you that your crank seals are good?

Share this post


Link to post
Share on other sites

Yes, I found it on their website after a quick search:)

 

Is the oem reeds in carbon? I have carbon in my bike i remember.. I think the fibreglass type is good enough for mye driving, nice price too!

 

Hmm, about the crank seals i`m not so sure, i splitted the motor a few months ago to change to gears in the transmission but didnt change the seals. I may have to change the gearbox to the wr400 gearbox beacuse the ratio is a bit tight.. So im thinking of replacing some more parts then.

Share this post


Link to post
Share on other sites

Those Pod filters are very tricky to jet for, a pod filter flows more air than a air box foam filter with a intake boot.

Usually you have to up your jetting- especially the main jet. In your case with the sputter you may have to increase your pilot.

Share this post


Link to post
Share on other sites

Do you have some recommandations for a cheap but reliable dual stage reed? I need to take out my reed and post a pic of it here. I didnt notice anything wrong when i had it out the last time..

You can also try a stock reed block assembly from ebay. I have 2 used sets for sale from a 2006 YZ250. Both are dual stage carbon/fiberglass.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...