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Ttr 90 help!!!!!

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I have a 2004 TTR 90ES. I have been pulling my hair out over this thing for quite some time. I have a lot of experience being a part time motorcycle mechanic. My question is...the bike runs great except when I have it at full throttle the bike pulls well from the bottom end all the way until it starts getting into the high rpm and it falls on its face popping and sputtering. If I let off to around 3/4 throttle it picks up are revs right up through the RPM range. I have checked and cleaned everything. I have seen a lot of posts on this and it is always something obvious that I have already checked. Compresion is at 140 but when I did a leakdown it wasn't good at all. I had air coming out of the carb and exhaust. And yes it was at TDC on the compression stroke and I could wiggle both rocker arms. I know this indicates leaking valves but when I took the motor apart and sprayed inside the valve chambers with carb cleaner nothing leaked by the valve seats. I have tryed a leaner jet and it ran worse. I ran it hard at WOT and did a plug test and it was black indicating a rich condition. PLEASE HELP. I am starting to the think that these carbs are junk.

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Hopefully the TT member SMACARONI will chime in on this one. He should sooner or later. He's got a bunch of experience with these little bikes. He may like them a little too much.

Anyway you are in that bad place we all get into once in a while. Since you are a mechanic and I only play one on TV, you have more hands on experience then I, so I won't give you all of the easy stuff to check and maintain. I had this problem with a TTR 125 a couple of months ago and wasnt getting enough air into my tank through the breather hose at the cap. I know its a long shot but just one of those things where I couldn't see the most obvious thing right off the bat. Don't be frustrated young grasshopper you know it will be resolved with patience.

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I heard my name somewhere...

One problem, I only fool around with the kiddie smokers. I can take a PW80 apart in my sleep. Still working on the putting it back together part though. When I master that I'm gonna save loads of time!

Hmm... compression is 140, that's good. Craps out at WOT but is good till 3/4ths? First place I'd check is float height too low, since you mention closing the throttle momentarily (allowing the bowl to refill) resolves the problem.

Next restriction in exhaust or intake, when was the last time you cleaned the air filter? Does the 90 have a restriction plate in the exhaust? I don't think so, but pull the pipe off the head and look for any type of crap. Granted, this is unlikely with a four-stroke, but anything is possible.

Make sure your electrical connections are good and clean. This is more of a long-shot, but it's not a bad idea to check everything since it's possible there's enough resistance to impede high current flow.

Now that you're sure the electrical stuff is the way it's supposed to be, I'd check the timing. It's entirely possible that it's running a little retarded which on most bikes would show up near the top end since the newer CDIs cut out some advance near the top of the RPM band.

Oh, and just to be certain we're talking about the same thing, you did try a leaner main jet, since a pilot jet has almost no effect on 3/4+ throttle. Right?

If none of these suggestions work, I'd look for assistance in the Pee-Wee/Mini forum under special interest. There's way more knowledgeable people there than I.

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I heard my name somewhere...

One problem, I only fool around with the kiddie smokers. I can take a PW80 apart in my sleep. Still working on the putting it back together part though. When I master that I'm gonna save loads of time!

Hmm... compression is 140, that's good. Craps out at WOT but is good till 3/4ths? First place I'd check is float height too low, since you mention closing the throttle momentarily (allowing the bowl to refill) resolves the problem.

Next restriction in exhaust or intake, when was the last time you cleaned the air filter? Does the 90 have a restriction plate in the exhaust? I don't think so, but pull the pipe off the head and look for any type of crap. Granted, this is unlikely with a four-stroke, but anything is possible.

Make sure your electrical connections are good and clean. This is more of a long-shot, but it's not a bad idea to check everything since it's possible there's enough resistance to impede high current flow.

Now that you're sure the electrical stuff is the way it's supposed to be, I'd check the timing. It's entirely possible that it's running a little retarded which on most bikes would show up near the top end since the newer CDIs cut out some advance near the top of the RPM band.

Oh, and just to be certain we're talking about the same thing, you did try a leaner main jet, since a pilot jet has almost no effect on 3/4+ throttle. Right?

If none of these suggestions work, I'd look for assistance in the Pee-Wee/Mini forum under special interest. There's way more knowledgeable people there than I.

Float height spot on. I went through the carb and checked everything. Air filter is good. I even ran the bike with intake boot off...no change, ran the bike with the choke on...no change (to the top end problem). I read on another forum that someone had the same problem with a ttr125 and it turned out to be a loose connection to the coil and the spark wasnt powerful enough to ignite the bike under load but when you take the tire off of the ground and peg it, it runs good. I bumped the pilot up to a 15 since I couldn't dial in the throttle response with the 12.5. Now with a 15 the low end response is spot on. Yes i did try a leaner main "80" and the plug was still black and it didn't run any better. I am really starting to think it is not generating a good enough spark under load and it is "eight stroking". I haven't checked the timing but why would it scream at 3/4 throttle with out a problem? Valve clearences are good and I fail to see how a 90 couldn't keep up the fuel flow under full throttle to drop the fuel level enough in the bowl to have a problem but anything is possible. :thumbsup:

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What I did last night:

Checked all connections

Put my meter on the coil, magneto, pick up coil, lightup coil and all were perfect so I am ruling out electrical. It seems that a lot of people are posting the same problem so I hope someone knows of a fix.

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Go with the bigger main jet. I would guess you are not running in the lean condition long enough to change the color of the plug. 90 is the stock main jet and I run a 95 in both of my ttr's and they run perfect.

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I cleaned to plug and ran the 80 and it still turned black. I wonder if something is wrong with the starter circuit. Maybe some fuel is leaking by the pluger and dumping into the carb. It did always fire right up in the winter without the choke even on. It does function normal when you open it (rpm inceases so I think the o-ring is sealing good but maybe the bottom of the plunger isn't closing the circuit. When I had the intake boot off the carb was spraying out fuel once it started popping, which is normal if the bike isn't firing correctly. Maybe I'll look into that next.

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When I had the intake boot off the carb was spraying out fuel once it started popping, which is normal if the bike isn't firing correctly. Maybe I'll look into that next.

and oh by the way this is what made me first drop a size on the main thinking it was to fat.

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Float height spot on. I went through the carb and checked everything. Air filter is good. I even ran the bike with intake boot off...no change, ran the bike with the choke on...no change (to the top end problem). I read on another forum that someone had the same problem with a ttr125 and it turned out to be a loose connection to the coil and the spark wasnt powerful enough to ignite the bike under load but when you take the tire off of the ground and peg it, it runs good. I bumped the pilot up to a 15 since I couldn't dial in the throttle response with the 12.5. Now with a 15 the low end response is spot on. Yes i did try a leaner main "80" and the plug was still black and it didn't run any better. I am really starting to think it is not generating a good enough spark under load and it is "eight stroking". I haven't checked the timing but why would it scream at 3/4 throttle with out a problem? Valve clearences are good and I fail to see how a 90 couldn't keep up the fuel flow under full throttle to drop the fuel level enough in the bowl to have a problem but anything is possible. :banghead:

Shot in the dark being this post is so old. I find myself in the same position as apparently many other ttr90 owners. I have increased both pilot and main jets, now up to 15 and 95 respectively. Still have that sputtering at 3/4 to WOT. It does seem to smooth out once rpm's are higher. I have no idea how to check float height but I have heard that is seldom the issue with these. Any direction would be appreciated. Carb has been thoroughly cleaned, jets are new along with petcock. Perhaps Smacaroni is still around to comment as well. Thanks.

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Posted (edited)

Reviving from the dead....Having a similar problem. Anyone figure this out...?

Edited by TTr90E

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TTr90E, hey! I did get mine figured out. Now the problem with that is that is has been a while now since I did. Best I remember though it was a jetting issue. I went up in jet size, thoroughly cleaned and now definitely only use 100% gas. I would only order jet kits from manufacturer and not just online. I had one kit I bought and something was weird with one of the jets not fitting. If the problem is in that upper range you may only need to go up on main jet size. You need to confirm but I believe the pilot is for early throttle stages and the main for the rest, again confirm. Ours is running strong and since running 100% have had no carb issues. 

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Thanks a ton for the reply! Mine acts a lot like the others here in this thread. Going to dig for a 95 main jet and see what happens. Using a 90 now.

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