[DT125 stuttering at high revs? (Sound clips)]

5 hours ago, slice said:

Err, thought I said that?

I do owe you some credit mate, cheers  

[DT125 stuttering at high revs? (Sound clips)]

I figured out what it was. It was the connector on the coil which I used as the feed for the tacho. The connector was loose so I just squashed it a bit and problem solved.

[DT125 stuttering at high revs? (Sound clips)]

2 hours ago, finnerz89 said:

Just sounded similar to mine when it had the rev limiter on. Where did you earth the cable behind the clocks? I'd double check it's all good. I'm also assuming you have an aftermarket rev counter then?

Sent from my E6553 using Tapatalk

I did have but got rid of it about a month ago. Actually I'll make sure to check the connectors on the coil because that's where I connected the tacho. I earthed the cable directly to the frame under the bolt for the radiator bracket.

[DT125 stuttering at high revs? (Sound clips)]

5 hours ago, finnerz89 said:

Is your bike derestricted? That's when the cdi starts to retard the powervalve to limit the power on restricted bikes

Sent from my E6553 using Tapatalk

No Iv'e derestricted it and im pretty sure thats not the problem. I remember what it felt like riding it restricted and this is differrent. It wants to rev more but it just cant whereas when it was restricted the bike felt like it was redlining at 7k rpm.

[DT125 stuttering at high revs? (Sound clips)]

10 hours ago, finnerz89 said:

What RPM does it start doing it? And what year is your bike?

Sent from my E6553 using Tapatalk

It starts at around 7k rpm and its a 2007 dt125x.

[DT125 stuttering at high revs? (Sound clips)]

1 hour ago, finnerz89 said:

How long has it been doing it? Have you put fresh fuel in it since?

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It started a few days after Christmas. I've gone through a few tanks worth of petrol since it started.

[DT125 stuttering at high revs? (Sound clips)]

15 minutes ago, Cynic said:

Plug colour?

Good spark?

Mileage?

How long has the top end been on?

Checked ALL the electrical connections for the ig, including the kill switch on the bars and the engine earth as well as the mag outputs.

Filter clean

Reeds in place and good condition

Exhaust tight

 

 

 

 

 

I can answer some of these now. The plug is a light brown colour, I think it's okay. As far as I know the spark is decent but I'll check properly soon. The bike has just broke 10k miles but it's only done at most 2000 miles since the top end was rebuilt. I checked the filter fairly recently and it was clean but I'll check that again. I'm also pretty sure the reeds and exhaust are okay but I'll make sure.

[DT125 stuttering at high revs? (Sound clips)]

Within the last couple of weeks my dt125 has started stuttering around when you reach the powerband. It also jerks forward  a bit while it stutters. I haven't changed anything on the bike recently so I don't know why this has stared happening. Just yesterday I took the carb off and cleaned it out as I thought the main jet might be getting blocked but that didn't solve the problem. I have also tried multiple spark plugs. Some things I have noticed: it doesn't do it nearly as bad if at all when the bike hasn't yet reached full temperature, so for the first minute after pulling away the bike feels so much better. I've got some sound clips where can hear the problem. Clip1  Clip2  Clip3. Anybody have any idea what the problem is? It's really annoying because you're unable to ride the bike at a decent speed as it wont rev past the point where it stutters.

Cheers

[dt125 running worse after new top end]

I was riding the bike again today and the starting issue is still there. The bike runs good but I can definitely hear a whistle or whine when I rev it up. I've tried the wd40 and still can't find anything though.

[dt125 running worse after new top end]

52 minutes ago, Cynic said:

I assume you were using the gas to see if the revs pick up by burning the gas that gets in?

That was the idea yeah.

I've just gone for ride since turning the powervalve the correct way up and it's so much better (it would be wouldn't it lol). I would say more power than before the rebuild. The popping seems to have gone but the starting issue is still there. Now I'm questioning if there is a leak, surely if there was it wouldn't run really well and there would be some other issues. I can't think what that sound may be though, definitely wasn't there before. I'll try wd40 though.

[dt125 running worse after new top end]

38 minutes ago, Cynic said:

Sounds like something interfering with the choke. 

Try giving the bike 4 or 5 kicks with the ig off before starting the bike.

Does it have a vacume fuel tap?

 

Hasn't got a kick start. Not sure about a vacuum fuel tap. I've just let the bike warm up and gave it a couple of revs. I can hear a fizzle sound when I rev it. It gets more noticeable the higher you rev it. I've tried going around the head, base, carb, intake, exhaust with a propane torch but I can't find a leak anywhere. I can say for a fact that the fizzle sound was not there before the rebuild.

[dt125 running worse after new top end]

42 minutes ago, Cynic said:

Depends. Not uncommon for air leaks not to show as the air is sucked in.

Does it start better when is warm?

Yes, it's just the first 30 seconds when the bike is cold that it will die if you let the revs drop below 3k.

[dt125 running worse after new top end]

2 hours ago, Cynic said:

Ok.

Step back and think.

Something is causing this and it isnt the pv. Once upon a time 125's were sold with the pv not having a controler. Never affected their starting.

I still feel there is some sort of leak. Either air, fuel or oil going or not going where it should.

Got good 2stroke feed? Good fuel supply?

If there was a leak at the head or base, would there be crap running out? because the head and base are clean. Also turns out my pv was upside down lol, just fixed that and the bike revs better, but it still had the starting issue so the bad things I listed in the first post aren't all caused by one problem. I'm going try and find a propane torch so I can test for air leaks.

2 Stroke feed is good, I bled it straight after "the accident". Pretty sure the fuel supply is good too.

[dt125 running worse after new top end]

2 hours ago, Cynic said:

This may sound daft but. Have you tried using your old plug? 

I haven't tried the old one but I've had 2 new plugs in it since the rebuild and neither changed the way it was running.

[dt125 running worse after new top end]

55 minutes ago, Airhead said:

yes indeed, something to check then, along with the pv orientation and the cables not too tight...that's all I can suggest

Will check all tomorrow, cheers

[dt125 running worse after new top end]

Just realised you were talking about the wire behind the speedo. My bike does have the wire coming from the speedo that has to be grounded to get better performance.

[dt125 running worse after new top end]

6 minutes ago, Airhead said:

Ahh right so with that one it's either right or a full 180 degrees out...didn't know about the punch mark indicator.

 

anyway...what about it turning the wrong way?

does your model have that wire that must be grounded out to perform properly?  well is it?

I've also just seen that, I'll check mine is the right way up tomorrow.

I'm not sure... How can I check?

 

[dt125 running worse after new top end]

25 minutes ago, Airhead said:

looking back at that old thread you linked I'd say the pv should rotate anti-clockwise with increasing engine speed, thus open up the port

 

BTW what shape is the end of the pv where the pulley attaches to it?

It's basically a rectangle, here's a pic I found...

[dt125 running worse after new top end]

28 minutes ago, Cynic said:

Nothing to do with the powervalve, air is getting in somewhere.

You need to check for air leaks, may only be small. Popping on deceleration is something a stroker  does when their is air going where it shouldn't.

Check your cylinder base, carb and reedblock joints, did you remove and clean (and profile slightly) the powervalve, you certainly SHOULD have. oe gaskets used? Could even be the plug not sealing properly.

The pv will have ZERO affect on the bike starting, no matter what position its in. If its healthy and set up right it should be possible for it to be started (carefully) by hand, I certainly can with my TDR250.

I totally removed the powervalve, disassembled it and cleaned it. I even replaced the o rings and oil seal. I used genuine yamaha base and head gaskets. I didn't touch the carb or intake at all during the rebuild. New plug installed properly as well. Any other suggestions where to check?

[dt125 running worse after new top end]

I recently did a top end rebuild on the bike but I'm not very happy with how it's running since the new top end, it's worse than before the rebuild. I'm not sure if my power valve is set up correctly, how can I check this and get it set up perfectly?

Ways the bike is different since new top end:

• It doesn't start as well. When you first start it you have to keep the revs above 3k for the first 30 seconds or so otherwise it will die straight away.
• There's not as much top end power, not sure if power valve issue or if the bike needs to be re-jetted. Is it common for 2t's to need jetting adjustments after top end rebuild?
• There is some popping in the low end when decelerating. non-existent before the rebuild.
• Bike revs very sluggish below 4-5k rpm. If it give it a really quick blip, I can blip and close the throttle and bike barely even reacts, you have to hold the throttle slightly and the revs picks up.
• Just doesn't seem to 'pull' as much as before. Acceleration is definitely worse.

What should I do from here, Is it worth taking it to get the carb properly set up? How can I check the pv, the gap/hole in the top of the pulley is already aligned with the hole behind it? I saw this thread, my pv rotates clockwise when I rev the bike, Is this wrong?

[I f**ked up, bike ran out of 2 stroke oil while I was riding.]

So I've rebuilt the top end and the bike works. However it's quite sluggish and doesn't rev as much as it would have with the same amount of throttle as before. How do I know if the power valve is set up properly? I've adjusted the cables so that the gap on the pulley lines up with the hole behind it. Does that mean the power valve is set up 100%? Or is it a matter of running the bike in and it will start to rev better? One other thing, I can now notice a slight rattle/tapping coming from the power valve, Is that normal?

EDIT- I've just seen this thread, my pv rotates clockwise when I rev the bike, Is this wrong?

[I f**ked up, bike ran out of 2 stroke oil while I was riding.]

Any idea what piston ring goes where? I have a thin one and a slightly thicker one. I know the expander ring goes under the bottom ring so I'm thinking the thinner ring goes on the bottom?

 

EDIT - Don't worry, just figured it out.

[I f**ked up, bike ran out of 2 stroke oil while I was riding.]

He shoots, He Scores...

 

I'm gonna order the parts and do it myself. I know a rebore place so I'll just drop the cylinder off to get rebored. I checked the small end bearing and there wasn't really any play, there was a bit of play coming from the crankshaft though. I'll order a new bearing just for the sake of it though. Thing is, I need the bike fairly soon but the 0.25mm o/s piston and rings aren't in stock at fowlers. Would it be terrible to rebore it to 0.50mm o/s just because they are in stock?

[I f**ked up, bike ran out of 2 stroke oil while I was riding.]

When you say 100 quid to sort it, do you mean the cost of just the parts or is that about what it would cost to get done at a garage? Is that including a rebore as well then?

[I f**ked up, bike ran out of 2 stroke oil while I was riding.]

I hate the fact that it might go at any point though, I use it to commute. Would replacing the piston, rings and bearing but leaving the cylinder make it any more dependable?