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Low Power with any incline in 5th/6th #146025 09/17/19 02:57 AM
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NewRiderXT Offline OP
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I have a 96 XT225 (assuming the engine matches the VIN) that is having trouble with maintaining speed on the highway when there is any kind of incline. I'm 6' 200lbs and on flat ground I can get to 55mph in 5th and just barely hit 60 in 6th with WOT. Down hill will let me get to just over 65. Once I hit an incline, it doesn't even have to be that significant, I can barely maitain 45-50 depending on how steep/long the incline is. I have nothing to compare it to, but it seems to pull well through 4th, up to ~45mph.

I'm hoping to get some ideas of what else I can check besides the compression. I don't have a compression tester yet, but I think that is my leading hypothesis of what could be wrong. When I try to bumpstart it in first I just skid tire even on asphault, so that means compression is not terrible, right?

Is there anything else I should be checking?

I have just checked the valve clearances, exhaust was good, but the intake was tight. I did ensure I was on the TDC stroke and not BDC. I do have some wiggle in the rocker arms, I think I read that there should be no lateral movement allowed...

I have the stock 15/45 sprockets. Tires are aired up and not super aggressive. Kenda270 front and Shinko244 4.10 rear. Wheel bearing seem good.

Cobra exhaust with Uni Air Filter. I've had the same problems with and without the airbox snorkel.

Unfourtunatley I'm running a China knockoff carb at the moment, but I do have the original carb but the pilot jet is rounded out and stuck in that one and it had other various stripped screws. I think it is salvagable, but needs serious work. The China carb has a different thread pitch so I had to get China Jets, tried both a 130 and 125 with similar results, and a 135 was way to rich (surging with Throttle). Genuine Mikuni 42.5. Air screw is 2.5 turns, but I still have a tough time starting, so I'm pretty sure the air screw need further adjusting, but once started, I have smooth throttle response.

Besides possible compression issues, is there anything else that I should be looking at?

Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146028 09/17/19 12:00 PM
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peejman Offline
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Checking the compression is the first thing that comes to mind. A local auto parts store likely has a compression tester in their "loan-a-tool" inventory. Top speed should be closer to 70-75 mph with a healthy engine.

The carb slide is vacuum operated, so it's possible there's a leak or its got the wrong spring and isn't opening up like it should. With the bike warm and it neutral, does a healthy whack of the throttle cause the engine to zing up to high rpm fairly quickly? Does it idle normally (some hunting is normal) without being abnormally high occasionally?

Bump starts usually work better in 2nd gear than 1st. A trick is to stand on the pegs and then crash your butt down on the seat as you release the clutch. It helps keep the tire from sliding, but be prepared should it suddenly come alive with all that weight on the back.


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.
Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146029 09/17/19 02:45 PM
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Muniac Offline
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As for compression the shop manual states:

Standard 171 PSI
Minimum 128 PSI
Maximum 185 PSI

This is after the engine warms up for several minutes.


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Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146031 09/17/19 06:37 PM
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Paul49 Offline
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What does the plug look like after a run? Sooty? Is it using any oil?


1958 Ariel 650 FH, 2014 Tiger Sport1050, 1995 XT225 Serow, Tiger 800 XRx.
Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146035 09/18/19 12:06 AM
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NewRiderXT Offline OP
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Luckily my brother in-law does have a compression tester, so I'll be trying to get that checked out this weekend. Thank you Muniac for the specs!

So the spark plug looks decent, I had been running the 130 jet until recently, and it was kind of partially tan on one half and more white'ish on the other half of the electrode insulation and the first 5 or 6 threads are a bit sooty. I haven't actually done a plug chop yet to confirm those results though.

As for oil, its hard to say definitely since I have some oil leak when warmed up from the shifter seal and the stator cover gasket. Its not crazy bad, so I havne't gotten to fixing it yet. But I don't really see any blue smoke from the exhaust at all.

For the carb I literally bought a brand new knockoff carb, so build up's shouldn't be an issue. It does pull decently hard and revs out (granted I don't have a calibrated ear for where redline is, but its defitnely reving up there good even 1-4 and at like 55 in 5th (on level ground or any down hill, uphill is another story and I can just barely maintain like 45-50, it just kind of fades off). Hard to say if the rev'd out at 4th is the same as 4th, but I think it not quick as high RPM. The knockoff carb does add some uncertainty to the equation, but the OEM one I have needs some love (and that pesky pilot jet extracted before I can attempt to use it again).

Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146038 09/18/19 03:34 PM
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Muniac Offline
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Keep in mind it's a 223cc engine. I think 18 HP at its best.

I've done a few jet extractions here in my shop on XT carbs. It's a very delicate operation to say the least. Usually a couple of hours to complete. As for screw thread extractions, some go well others not so.

I have a reworking solder station that has a hot air tip. Very handy for heating localized areas. Good luck!


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Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146042 09/18/19 04:55 PM
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peejman Offline
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The plug sounds fine. You could try 1 size up or down and see what it gets you, but the compression check will tell the tale. If compression is good, I'd suspect the carb or possibly the cam.


This shall pass, be still and know.
2006 XT225, UNI filter, ProTaper bars, MSR handguards, SS front brake line, Shinko 241's.
Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146056 09/19/19 08:00 AM
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Paul49 Offline
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Originally Posted By: NewRiderXT

Cobra exhaust with Uni Air Filter. I've had the same problems with and without the airbox snorkel.


I fitted a K&N filter to my previous xt225, never got it jetted right before it was stolen. Wouldn't get above 50mph, did 70mph easy with the oe filter. Mebbe Yamaha knew what they were doing eh.


1958 Ariel 650 FH, 2014 Tiger Sport1050, 1995 XT225 Serow, Tiger 800 XRx.
Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146059 09/19/19 06:05 PM
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NewRiderXT Offline OP
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Still have yet to check the compression, but rode the bike into work this morning, a cold 39F ride, and it seemed like the the power fade was slightly less. The relatively minor grade that I struggled to maintain 50-55 I was able to keep it up to 55-60.

Not sure what that means in terms of the issue, but colder air = more dense, could I still be running too rich despite what my plug looks like??

To the air filter comment, the previous filter was all crumbly so it got trashed, so I don't have an easy way to test that theory. The uni is the same style of filter though, the foam didn't look all that different from the OEM, not like the K&N does.

Re: Low Power with any incline in 5th/6th [Re: NewRiderXT] #146060 09/19/19 06:18 PM
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Paul49 Offline
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If you can hit 60 up a slight grade, not a lot wrong with it.

Mine gets up to 50 ok then takes its time.


1958 Ariel 650 FH, 2014 Tiger Sport1050, 1995 XT225 Serow, Tiger 800 XRx.
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