down on power

reggiegasket · Post by **reggiegasket** » 24 Apr 2005, 16:43

I have a standard Mk3 which is running very well - starts, idles and goes okay - but is a bit weedy, especially at the top end. There's nothing obviously wrong. Just wondering where the problem might be. I'm thinking compression, electrics, reeds? The power valve is moving. I have a new plug. I'm tempted to do a top end rebuild, but maybe there's a simple solution. Any ideas?

CRMR · Post by **CRMR** » 25 Apr 2005, 20:33

yes ,, front and rear sprockets ,, Standard 14 and 42 will get you 100+ mph
If there different then the bikes geared for other types of riding style..

reggiegasket · Post by **reggiegasket** » 26 Apr 2005, 21:17

Thanks for the feedback. When I say lacks top end, I mean top end power. It's just not picking up properly up there. Am having to start a process of checking everything. Have done power valve and plug. Next is oil pump and exhaust. Then carb & electrics. Just wondering if there's a common problem with CRMs that results in poor top end.

BALLISTIX · Post by **BALLISTIX** » 26 Apr 2005, 23:26

What do you mean by 'not picking up at the top end' ? does it bog down, as in opening the throttle and not alot happens?

Andy

Rufus Ruffcut · Post by **Rufus Ruffcut** » 27 Apr 2005, 20:21

Hi Guys,

All this talk about 100mph from a 250? Is this for real?
I'm about to order new chain and sprockets and have just checked what's fitted (13/ 45) and it seems fine for green laning but over geared at the top end on the road (it's as quick in 5th as it is in 6th) and only pulls about 120kmh which I think is about 70mph.

So is my bike tired, duff or am I just expecting too much from the poor old gal?

Stay safe

Rufus

Post by **baldy 67** » 27 Apr 2005, 21:47

Hi Rufus,
You are reading the speeds correctly. I often travel at 100MPH+ and have had no problems (except for an unmarked pan european police bike) the only draw back is that after an hour or so your arms begin to ache as you are constantly in the wind.

I have also fitted 21 inch full road tyres which are excellent in the corners / wet

Regards
Baldy 67

Rufus Ruffcut · Post by **Rufus Ruffcut** » 29 Apr 2005, 13:48

Hi Baldy,

OK so now I'm perplexed!

Have ordered new C&S from leisure trail who recommended 13/45 gearing for the Mk3 for green laning. I have to agree with them cos in the dirt 1st is just about usable with 2nd and 3rd providing excellent,drive, torque and acceleration, but out on the road she feels overgeared / flat at the top end!

I assumed that this was normal for a 250 trail bike!

So this weekend it's pull it apart time, but she starts easily, has a clean airfilter doesn't smoke but just seems a little lifeless at the top end.

I'll check the power valve adjustment and change the plug etc, but cananyone recommend anything else?

Thanks in advance (keep the admin happy

) for any info'.

Regards

Rufus

reggiegasket · Post by **reggiegasket** » 29 Apr 2005, 14:46

Hey Rufus, glad to have you in this topic

Seems like we may have similar problems i.e. a bike that is not very powerful at the top end of the rev range. My bike pull well low down (in the rev range), picks up okay in the power band, but doesn't pull well as the revs rise. It doesn't bog down or misfire, it just doesn't pull hard. I've checked a few things and now feel it may be the carb or exhaust. Maybe the engine needs more fuel / air or can't get rid of the gases fast enough. The only other idea is low compression or poor spark / timing. Will keep you posted....

Thanks for the feeback.

Rufus Ruffcut · Post by **Rufus Ruffcut** » 02 May 2005, 20:30

Hi Reggie,

Had a good check over mine at the weekend, power valve adjustment is fine, new plug, cleaned the carb and filter and it's still the same.

Personally it's so sweet up to 120 and I only use it for green laning I'm not going to worry, if it ran rough then I'd persue it but it doesn't and I can't believe it'd go much quicker so believe I'm worrying about nothing!

Thanks for all the info

Regards

Rufus

reggiegasket · Post by **reggiegasket** » 10 May 2005, 06:55

Yes, I did the same and have reached the same conclusion. Off road the bike is perfect and I don't want to loose that low down power by focussing on top end power. I love the way the bike really digs in at low revs on a steep climb. At some point I'll check the piston and cylinder, as it's an easy job, and probably put some new rings in. I've gone to 13/49 gearing which has also made the bike more fun to ride on back roads.

Paul P · Post by **Paul P** » 11 May 2005, 15:01

I have 13/49 on my mk3 only ride it in the dirt and I can tell you that it will do exactly 123kph in top gear no more no less but boy does it get there quick I reakon this is fast enough on a gravel road , from memory when it still had the the standard gearing 14/42 it certainly would have got to 160kph/100mph but as I never really ride it on the road I never tested out the top speed with the original gearing but I do remember it didn't pull in 5th and 6th like it does now it's much more like a motocrosser

nelly · Post by **nelly** » 16 May 2005, 18:50

hi every1, i had the same problem with my mark 1.
when i first got it, it would do about 95-100 mph on standard gearing but after a year it start toppin 80ish. it didnt bother me at first because it ticked over fine and started in 2 kicks.

but about a couple of months ago i started feeling a tiny vibration from the engine, it wasnt too much to worry about because it was very small but after a couple of weeks it was getting worse. i actually thought it was the balance shaft bearing.
so the time came to rebuild the old girl. anyway while going through the motions of removing the lump, i removed the exhaust and thought i'd have a quick peek up the exhaust, and behold!!!!!!!!! the dreaded sight of carbon down the side of the piston (blow-past).

now i have the lump removed from the frame and have removed the top-end to find that the blow-past marks are all the way round the piston but are at their most extreme around the thrust faces (over half way down the piston) . THAT WOULD EXPLAIN THE LOSS OF POWER.

p.s it wasnt the balance shaft bearing that had gone it was the big-eng bearing on its way out, so it looks like a new crank, piston-rebore and bearing throughout( better safe than sorry).

down on power

down on power

100 +

speed