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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Lost Power
Post Info TOPIC: Lost Power
Fladdem


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Lost Power
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Hi everyone, another problem again.

After my spirited riding at the MX track last month, the bike doesn't feel the same. At about half throttle, she develops a splutter which leads me to think about fuelling issues again. But I also noticed that the compression seems quite low, I can near enough hold my finger over the plug hole while cranking the engine. I rebuilt the top end about 8,000 KM's ago with a 2mm overbore. I however didn't do the valve seals while I was in there so I'm wondering if it could be those leaking? I can't hear the piston rattling, so don't think it's rings but I will need to get a proper compression tester.

I also, after the most recent carb issues rejetted, immediately afterwards, the bike pulled so well, better than ever before, which is why I don't want it to be fuelling issues again. Again, recently I had my first attempt at re-packing a silencer, a DG-O, when I was done, there was no difference to volume, but it does now pop a bit on the over-run. Could I have re-packed differently and caused it to run poorer?

Thanks, Adam.



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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)
TTRfan


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Blown head gasket = low compression and poor performance as does any damage to a valve/valve seat



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comeragh


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Its bike cruelty to put a ttr around a mx track not to mind the embarassment of being passed by kids on 80 cc 2strokes .

Your bike should be confiscated and rehomed .



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Fladdem


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comeragh wrote:

Its bike cruelty to put a ttr around a mx track not to mind the embarassment of being passed by kids on 80 cc 2strokes .

Your bike should be confiscated and rehomed .

Hey, you shut your face! biggrin We did alright, a standard one would struggle to keep up a bit more... I even gained on a CRF150! I'm going to view an EXC 300 this weekend to fulfil that side of things, I'll keep the TTR though, got an LDT coming up, hopefully, won't be doing that on a KTM!

Blown head gasket is a good call, the bike does have an oil leak from around the head. I have ruined what used to be a cracking machine about 18 months ago. If I'm going to tear into the engine again, is there anything you would suggest me grabbing for it, i.e. piston rings, valve seals, valve shims, etc. I want to get everything I'll need for the job then just do it over a weekend, ready for work again on the following Monday. I don't think it is valve related, because there is no smoke from the exhaust. It's an unusual problem, for instance on the way home, I didn't really notice the problem but other times it seems to be a bit spluttery and seems to need more throttle to get up to speed. Which makes me think it's a fuelling issue. I'm not sure anymore.



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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)
ttboof


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Sounds a bit odd but fix it up and do it again . I had mine out doing grass track MX  took a bit off effort but I got passed an 8yrold on a ktm 50 .made my day 

Actually the ttr has a long list of places it shouldn't have been both off road and on but fronts up for more and always makes me smile 

 

IMAG0492.jpg



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TTRfan


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Taking your TTR on an MX track?!
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I am sure it's a wind up but, just in case, you can see from the thread below which side of the fence I come down on wink

See here

Brian



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PlumasDude


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RE: Lost Power
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The TracToR on the track? I thought we all bought these things in our dotages to stay on the ground and avoid injury.

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Fladdem


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Steady on, I'm only twenty... I bought mine to get learning before flying and injuring myself, but I fell in love. Here's my attempt at keeping up: http://ttr250.activeboard.com/t58452752/daventry-mx-track/ In fact, Brian, I saw your thread and saw that the bike could deal with it OK, which is why I went to play on mine.

Is there any test I can do that will definitely point me towards the engine? Apart from grabbing a carb of another bike to eliminate that? Should I try putting the standard exhaust back on and see what happens?



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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)
PlumasDude


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Well I'm glad to know someone is tearing it up out there. That shot coming off the jump is pretty cool.

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TTRfan


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Fladdem wrote:

Is there any test I can do that will definitely point me towards the engine? Apart from grabbing a carb of another bike to eliminate that? Should I try putting the standard exhaust back on and see what happens?

On a newly rebuilt engine you should have loads of compression.

The fact that yours is low on compression leads me to suspect that the other symptoms might be related to something like a blown or leaking head gasket. This could also allow air to be sucked into the engine on the induction stroke causing what might otherwise seem like fuelling issues.

If you put a small amount of oil down through the spark plug hole and turn it over, does the compression greatly improve? If so, then there may be a problem with a ring or rings. If it doesn't improve the compression then its probably a head gasket or, less likely, a valve not seating properly.

Was your air filter clean, properly oiled and sitting properly such that no dirt could get past it? It can get incredibly dusty on an MX track and, in extreme, if dust gets through to the combustion chamber a bit of grit may have lodged itself on a valve or valve seat stopping it from sitting properly. A valve clearance check would rule this out.

Brian



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Fladdem


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TTRfan wrote:
Fladdem wrote:

Is there any test I can do that will definitely point me towards the engine? Apart from grabbing a carb of another bike to eliminate that? Should I try putting the standard exhaust back on and see what happens?

On a newly rebuilt engine you should have loads of compression.

The fact that yours is low on compression leads me to suspect that the other symptoms might be related to something like a blown or leaking head gasket. This could also allow air to be sucked into the engine on the induction stroke causing what might otherwise seem like fuelling issues.

If you put a small amount of oil down through the spark plug hole and turn it over, does the compression greatly improve? If so, then there may be a problem with a ring or rings. If it doesn't improve the compression then its probably a head gasket or, less likely, a valve not seating properly.

Was your air filter clean, properly oiled and sitting properly such that no dirt could get past it? It can get incredibly dusty on an MX track and, in extreme, if dust gets through to the combustion chamber a bit of grit may have lodged itself on a valve or valve seat stopping it from sitting properly. A valve clearance check would rule this out.

Brian

 
My air filter was cleaned and oiled before going to the track, as far as I am aware it was seated correctly. It seemed to work well as it was covered in dust and dirt. I noticed it going back to work after the bank holiday on Tuesday, so my thoughts went to the air filter being blocked with dust, so I cleaned the filter, re-oiled it and re-applied the grease around the seating nub thing after cleaning the box out. No improvement, no difference at all really. I checked the valves, they are all at the upper end of within spec, so I may get some shims to bring them closer to where they should be.

I am thinking that it could be the head gasket now. Especially as oil has been oozing out for ages. Perhaps the hardship of the track was the final straw and it gave way completely?



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Adam. 1993 Open Enduro: 14/48 Gearing, Uncorked, Twin-Air Filter, Snorkel Removed, 263cc Piston, Ported and Polished Head, Shorty Header, DG-O Silencer(Loudener!), 140 Mikuni Main, Standard Pilot, Bottom Needle Clip (Still A Touch Lean)
TTRfan


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Fladdem wrote:


I am thinking that it could be the head gasket now. Especially as oil has been oozing out for ages. Perhaps the hardship of the track was the final straw and it gave way completely?

That's where I am pushing you to look but try my checks first wink 



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