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Old 11-18-2014, 05:28 PM   #1
ponyhorscroft OP
Joined: Mar 2008
Oddometer: 4
Yamaha XT225 jetting/carb issues - need help!

Hi There

I bought a non-running 1999 Yamaha XT225 as a project, here's what I've done and what symptoms the bike is showing:

Drained, cleaned and re-lined the fuel tank and installed new inline filter
  • Replaced battery
  • Replaced fuel petcock
  • Removed and cleaned the carb.
  • Replaced spark plug

The carb has no shims under the fuel needle, has a 130main jet and a 40 pilot jet, I removed the fuel screw plug and turned out the screw 3 turns (as recommended for this bike). I cleaned the whole carb with carb cleaner and compressed air, I removed and cleaned pilot and main jets, float needle valve and seat. Although everything was really gummed up it all came up nice and clean.

I installed the carb and put fresh gas in the tank and here's what i observed:
  • The bike started well on the choke and I was able to push the choke in fairly quickly as the revs peaked. off the choke the bike is a little hesitant like its choking a little but does not stall.
  • The header pipe started to glow cherry red (i'm not exaggerating and can attach a picture of this) after about 4 mins of idling.
  • I took the bike for a short ride and it ran great on the throttle but the revs stayed high after chocking/dropping the throttle (or pulling in the clutch) for a few seconds before returning to idle.
  • I removed the spark plug (assuming from the red hot pipe that it was running very lean) and it was white!
  • Small backfire/sputter when killing the engine

I know the bike is running lean (please correct me if this is wrong), but the carb is clean, all jets appear to be clear and are stock, the air box is unmodified, the fuel screw is turned out 3 turns and there did not seem to be any improvement with extra turns out. so why is it running so lean?

a couple more pieces of info: oil is probably about 3 yrs old! the only gas I had was fresh but 2/3rds premium (91 oct) and 1/3rd regular (87 oct). i know thumpers don't like premium but could this cause these symptoms alone?

The only things i can think to do are:
  • increase pilot jet size (42.5)
  • shim the fuel needle

BUT everything is stock so i'm concerned I may be missing something?

Any suggestions - anyone seen an XT225 header pipe glow red (in daylight)?

Thank you everyone
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Old 11-18-2014, 06:14 PM   #2
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Intake manifold is sucking air. Probably cracked.
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Old 11-18-2014, 08:49 PM   #3
ponyhorscroft OP
Joined: Mar 2008
Oddometer: 4
Originally Posted by Reposado1800 View Post
Intake manifold is sucking air. Probably cracked.
Thank you for your suggestion - can you elaborate? intake manifold? do you mean the rubber piece between the airbox and the carb?

if it is this, I checked ti thoroughly and I do not think it is sucking air.
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Old 11-19-2014, 11:49 AM   #4
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Joined: Mar 2009
Location: Denmark
Oddometer: 986
Whats the nonsense with premium...? Never heard that one before :)

Intake manifold is the rubber between the carb and engine.
2003 xt600e 150.000km
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Old 11-23-2014, 07:47 PM   #5
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Joined: Jul 2009
Location: Chandler, AZ
Oddometer: 4,994
I am also having some issues with my XT carb right now, but it's a bit different from yours. Mine starts and idles fine, does not overheat. But it cuts out at full throttle.

Do you know if the Z1 mod has been done? (cutting the baffle out of the exhaust) if so it will be a bit lean on midrange on up, but should still idle fine on a #40 (stock) pilot jet. If the exhaust is stock, a #130 main jet should work fine. I have a #132.5 in mine, and may either shim the needle or go to an even bigger jet.

If the pipe is glowing red (I've never seen that before, but I've heard about it) you are dangerously lean. And the size of the jets is not the problem. Nor is the position of the pilot screw. 3 turns is just about right. There are several other things that can cause it to run excessively lean. One is an air leak between the carb and the engine. An air leak between the carb and airbox can let dirt in, but it won't make any appreciable difference in the mixture. If you have a propane torch, start the engine, open the valve on the torch but DO NOT LIGHT IT. Hold the tip of the torch around between the carb and engine, all the way around. If there is an air leak, engine vacuum will suck in the propane, and the idle speed will go way up.

Another thing is a float level that is too high. It will cause a low fuel level in the float bowl.

Also check the black plastic coasting enrichener cover on the right side for cracks. That can cause all sorts of issues.

If you do not find an air leak, my next guess is that something in the carb is still plugged up. The emulsion tube (the long part that the main jet screws into the bottom of, and the needle goes down into the top of) has several tiny holes in it. Did you remove and clean that when you cleaned the carb?

The XT runs just fine on 87 octane. In fact, it runs better on 97 octane. It should run on premium as well, though maybe not as good. Premium does not burn fast enough, and can cause a loss of power. But it shouldn't cause the problems you are having. Overheating with an air cooled engine is a sure sign of running lean.
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Old Today, 10:51 AM   #6
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Location: Texas
Oddometer: 230
did you check the valve gaps?
2001 XT225, 1981 CT110, 2003 TTR125, 2009 CRF150F
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