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TTR90 Bogging and missing at 1/2 throttle

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My son's sock 2002 TTR90 has been running great since getting it used a couple of months ago. During last weeks riding the bike died. After restarting it starts and idles fine, but when you twist the throttle it boggs and no rpm increase. I pulled the plug and it's black as can be.

We've taken the bike out a dozen times with no issues so I know it's not a jetting issue.

The only thing I can think of is we filled up with 91 octane rather than the regular 87. Could that have caused it??

Any ideas would be greatly appreciated.

Thanks in advance.

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sounds like it's time to clean the carb!Just pull the carb,take it apart and blow compressed air through all the holes and jets!It's not too hard.

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do not put high octane fuel in a motor that does not need it. Contrary to popular opinion, high octane pump fuel DOES NOT increase performance. I don't care what you have ever heard, it does not. It will actually cause poorer performance. I could go into detail about it, but I won't unless you ask me to. Im not sure if that would have caused the black spark plug, but it sure looks as if it did. try going back to regular fuel and see how that works. If it was a carb problem you would more likely have a white spark plug, not black. Hope that helps some

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I run 91 to 93 octane in ours exclusively and it runs fine. I run that because that's what my 450 requires and I don't see a reason to carry seperate gas cans.

A good place to start would be with a good cleaning and adjusting of the carb.

Even though you say the plug is black, the stalling when you give it gas sounds like a clogged pilot jet. The black could be from being a little fat on the main from when it was running right.

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92 octane gas wont hurt the TTr90 a bit.

Your problem is a dirty carb. These little bikes are very sensitive to crud in the jets. Take the carb apart and soak it in carb cleaner overnight. Blow air thru everything and put it back together.

Sometimes even cleaner and air wont get the crud out of the jets. I had to use a small piece of wire to get the crud out of the pilot jet. I could see light thru it but there was still something in there. Varnish or something.

Clean the carb good and it will probably be fine. That and maybe check the valve adjustment. I had to adjust my 03 this year. It was loading up and running rich. Adjusted the valves and it runs much better.

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if ya'll really want to waste your money on buying high octane pump gas, then be my guest. It would be a lot cheaper to just buy a different gas can than to use more expensive gas. High octane fuel can cause your exhaust valves to get carbon build up and hinder exhaust flow. It will take time to do that, but if all you run is premium in your motor not designed for premium fuel, then you will most likely have problems down the road. If you just ABSOLTLY must run high octane fuel in yur bike because you have heard that it makes your bike faster, then I highly reccomend you bump your spark timing up a few degrees

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Dirty carb. Disassemble it and clean it good.(Mainly clean the jets) Higher grade of gas shouldn't hurt it.Put a new plug in and see how it runs :banghead:

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Dude 92 octane isnt exactly high octane. 108 is high octane. Any motor can run happily on 92 octane (unless it was built to run on race gas). Only reason I run 92 octane is my 3 other bikes require it. No sence having a seperate gas can just for the little ttr so it gets the same 92 octane as the rest of the bikes.

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Dude 92 octane isnt exactly high octane. 108 is high octane. Any motor can run happily on 92 octane (unless it was built to run on race gas). Only reason I run 92 octane is my 3 other bikes require it. No sence having a seperate gas can just for the little ttr so it gets the same 92 octane as the rest of the bikes.

Who was that directed to ? :banghead:

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Who was that directed to ? :banghead:

titoheadfaceman

I was going to say the same thing, but now I don't have to.

People that put higher octane in hoping for power gains in stock motors are going to be disappointed.

People that run it because they have other bikes that use it are lazy smart people in my opinion.🤣

It won't hurt it, but it won't help either.

But, if I put 87 octane in my YZ450 that's another story... :banghead:

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Dude 92 octane isnt exactly high octane. 108 is high octane. Any motor can run happily on 92 octane (unless it was built to run on race gas). Only reason I run 92 octane is my 3 other bikes require it. No sence having a seperate gas can just for the little ttr so it gets the same 92 octane as the rest of the bikes.

Ok, now you are trying to get into technicalities (i don't know how to spell that). In comparison to other types of fuel, yes, 92 pump fuel isn't all that high. BUT, it is a large jump from 87 octane in the way it burns. I am talking stricktly about PUMP fuel. Race fuel has other types of additives that makes it have totally different burn properties than pump fuel. As I have said numerous times...DO NOT PUT PREMIUM HIGH OCTANE PUMP FUEL IN A MOTOR THAT DOES NOT NEED IT. It's that simple. in a brief explanation, and I have argued to the bone about this to other people, premium PUMP fuel burns slower than regular unleaded. If you burn a slower fuel at the same spark advance as a quicker burning fuel, then you can possibly have fuel still burning at the time the exhaust valves are opening causing unburnt fuel to exit the cylinder and then result in excessive carbon build up on the exhaust valves. Like I said, if you just HAVE to run premium in a low compression motor, such as any stock ttr, then at least advance the spark.

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Bottom line is. Use w/e gas you want LOL. I'll use the cheapo stuff :banghead:. Running the 92 in your 90 is ok and really just a smart idea so you don't have to have the other gas tank.

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Tell you what.

I won't tell you what oil to run and you don't tell me what gas to run.

Deal? :banghead:

  • Haha 1

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Tell you what.

I won't tell you what oil to run and you don't tell me what gas to run.

Deal? :banghead:

That works. :banghead:🤣

My question to you ovrrdrive is.... Why do some bikes REQUIRE te higher grade gas?

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My understanding is it has to do with the degree of timing advance and/or compression they have. The YZ450 calls for 95 RON octane, which is somewhere around the 91 we have here in the states, in the manual. Higher octane gas just resists detonation, that's it. As you raise the compression or advance the timing you increase the engine's likelyhood of pre-detonation and need a higher octane level.

My knowledge of it is pretty basic. If you want a good explanation search the 250/450 forum. It comes up all the time over there.

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I run 91 to 93 octane in ours exclusively and it runs fine. I run that because that's what my 450 requires and I don't see a reason to carry seperate gas cans.

Same here. My lawnmowers even get premium :banghead: As far as wasting money, you're only talking about saving $1 per 5/gal can at most.

As far as running it in the bigger bikes, I find that it starts easier and idles better than lower octanes. As far as more power, I dunno. Kinda feels like it, but :banghead: . But if it only costs me that $1 to make me think i'm getting more power, that's way better than the hundreds of dollars it takes to fix up the engine for more power🤣

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Well thanks to all for the advice and help. It turned out the main jet was sitting in the float bowl when I took it off. I have the dealer clean the carb and tune when I bought it and for some reason the messed with the jets. I have a call in to talk about my $180 service bill.

Anyway I used the info on the TTR-90 upgrade (great work by the way) and installed a new main (tightened down) new pilot and a new FMF pipe.

Started right up and runs great.

As far as the "whole gas" debate goes . . . I guess I fall into the "smart lazy" catagory. I run 92 in my Expo, CRF230, TTR-125, TTR-90 and CRF70. Just easier that way. Fill the truck and the cans at the same time.

Thanks again everyone for the help. Great input.

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Same here. My lawnmowers even get premium :banghead: As far as wasting money, you're only talking about saving $1 per 5/gal can at most.

As far as running it in the bigger bikes, I find that it starts easier and idles better than lower octanes. As far as more power, I dunno. Kinda feels like it, but :banghead: . But if it only costs me that $1 to make me think i'm getting more power, that's way better than the hundreds of dollars it takes to fix up the engine for more power🤣

one of the reasons it starts easier and idles better is because it burns faster, regular that is. High octane fuel burns slower in low compression engines. and the only way an engine can develop any gain in horsepower is through the use of knock sensors and a computer, which motorcycles do not have. and any gain in that way is so small you would hardly notice it. the reason it does that is because a computer (im talking about cars here) can advance timing until knock, or detonation occurs. So you can run more aggressive timing advance with higher octane fuels. Running it with no change in timing or comression will do absolutly nothing power wise

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one of the reasons it starts easier and idles better is because it burns faster, regular that is. High octane fuel burns slower in low compression engines.

Read his post again... :banghead:

I find that it starts easier and idles better than lower octanes.

He said the high octane starts and runs better, not the low.

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