Hello everyone! I bought my 96' ttr250 about a year ago. One of the first things i noticed was that the motorcycle was burning oil as i could see smoke coming out of the exhaust, mostly on higher revs. For that matter, i replaced the piston rings, valves and valve seals and since then my motorcycle stopped burning oil. Also, the reading on my compression tester was about 172psi and given that the manual says that 174 is the standard pressure i was quite happy. Even though everything seems fine on paper, my motorcycle feels underpowered and has also quite high fuel consumption of ~5.5l/100km, on normal street use, but for some reason i always assumed it was a carb issue. A couple of days ago i gave my ttr to a mechanic, who has revitalized quite a few ttr250s, and he told me that the bike indeed feels underpowered. He proposed that the engine should be opened, and most likely we would have to widen the bore size of the cylinder and fit a new wider piston.
My main question is whether or not a compression reading gives you the whole picture of engine health after all, or there are other important aspects too that are not so straight forward. Finally, I was thinking whether by putting new piston rings on i managed to seal the piston a bit better to the cylinder, good enough so that when i measure compression the readings are fine, but in practice the actual power is not there because cylinder or piston are a bit worn out. I would really like to hear your thoughts, thanks!
Before assuming its an engine issue, I would make sure the drivetrain is good. This includes checking for a slipping clutch while in gear. Check the wheel bearings and brakes as well.
Hey, thanks for answering. Initially i thought too that clucth may be slipping so i replaced it a month ago but nothing changed. I can try changing sprockets and bearings but how can that make a difference?
Not saying that sprockets need changing. Just saying to check for excessive resistance and that front and rear wheels roll easily. Raise the bike off of the wheels to check. Check for anything that could possibly rob your engine power. A restricted exhaust or incorrectly jetted carb could also be suspect.
It doesn't make sense to tear down an engine with good compression and does not consume oil unless something is binding in the bottom end like the main bearing.
I'm with Jeff here - good compression and no oil burning would suggest the piston/rings and valves are in good enough condition. All they do is stop the explosion from being wasted in blowby, which they appear to be doing.
Apart from checking the rest of the bike for drag - binding brakes, seized chain, check for blocked air intake system and exhaust system (collapsed baffles for example). Also look for a healthy spark, GOOD FRESH fuel, check the cam timing (and maybe check the flywheel key has not sheared and altered the position of the flywheel)
If I have calculated correctly, 5.5L/100km translates to 52mpg (UK), which does seem a bit poor. I know it is unusual for a TTR to run rich (they normally run lean from blocked carbs!) maybe your jetting needs checking? What sort of state is the spark plug in after a ride?
Yesterday i tried to check the things that Jeff kindly pointed out. All front, rear sprockets and chain appeared to be fine, although i dont have a tone of experience of what they should look like if they are not . While the bike was on the stand i checked for drag in both wheels. The rear could spin almost freely, there was just a tiny spot where pads disk touched once in every spin. The front wheel was not as free as the rear one but it seemed acceptable to me. I took off the front pads completely and went for a small ride just to check out if that small amount of drag affected bikes performance. I noticed 3-4kmh increase in performance on my second gear, which i often use as a reference point. When i got home i check on the internet what the acceptable drag on a front tyre looks like and it was much heavier than what i had, so i dont think that was the problem.
I have changed quite a few spark plugs, and the latest was installed 2 months ago. I checked again the color of the plug is a nice brown, which if i am not mistaken indicates that the mixture is good. Also cam timing is correct and fuel is always fresh and of good quality. Air filter is also new, clean and well oiled.
I have not check the exhaust system neither the flywheel key yet but i probably should :) .
I doesn't make much sense to me either why the bike behaves like that. Fuel consumption is poor and i can seem to pass 105kmh without the bike wanting to die. I would to completely change carb just to check the difference, but thats another story
What is your gearing?
I geared mine up, in preparation for some interstate touring. It wouldn't pull 6th. It's been re-geared.
Mine is thirsty. It uses more fuel than the DR650s I'm sometimes riding with. Because it's got a pumper carb & is always WOT while I'm trying to sit on 100km/h with them. And I always have to go back to 5th if it looks like a hill.
You know what? It's a 22 year old 250 single. It's a great bike, just not a KTM, which means it will wear out rather than just break. It's a good touring bike, just not a BMW, but I don't have to spend $30+k on it.
I'd try and find another 4 stroke 250, of similar vintage, and compare it to that, then start wondering if the performance is poor.
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In the Riverina.
'73 RD250, '80 XS1100, '81 RD373LC, '96 Tiger 900/sidecar, '02 TTR250, and another XS11 - this time a chain drive Period 5 race bike that may be ready to race eventually.
. While the bike was on the stand i checked for drag in both wheels. The rear could spin almost freely, there was just a tiny spot where pads disk touched once in every spin. The front wheel was not as free as the rear one but it seemed acceptable to me. I took off the front pads completely and went for a small ride just to check out if that small amount of drag affected bikes performance. I noticed 3-4kmh increase in performance on my second gear, which i often use as a reference point. When i got home i check on the internet what the acceptable drag on a front tyre looks like and it was much heavier than what i had, so i dont think that was the problem.
