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Post Info TOPIC: TTR running rough at high Rpms


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TTR running rough at high Rpms
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I have been having trouble with my ttr since I bought it used. Thought it would be a simple carbeurtor cleaning, but that is not the case. Now I have done so much not sure where to go. Also let me say that I have just basic mechanic skills so I could have messed up on any of the following. 

 

symptoms:

-high speed bog. 

- engine kind if cuts out And then surges. 

- kind of like it has a governed that keeps it from getting to high of Rpms. But I feel it is only at 3/4 of its full Rpms. 

This is most noticeable at higher Rpms and really noticeable at higher speeds. 

 

Things I have tried

-brand new spark plug

-brand new uni high flow air filter

-removed snorkle

-removed spark arrestor this is a US model

-brand new carb *then rejjet to 140 and 52.5

-new spark plug

 

What I am looking at next 

-valves I have never done this so hoping to do other things before this

-I checked can chain but not sure I am doing it right. My symptoms are similar to what others have described when they skip a tooth. How tight should cam chain be?  Is my cam timing right?(see pic). This is on tdc and I check with screw driver in spark hole as well as with mark on fly wheel. 

-change oil and filter. Should be easy but dont think this would cause my symptoms that is why I have waited. 

- adjust fuel mix screw. Where can I find directions for this

- change throttle needle height up or down. 

 

So what's next?  I have done a lot of searching before I asked so that I would not ask a question that has been answered before.   Yes I have downloaded and printed service manual so feel free to reference it but I have found it skips some steps or is unclear at times. At least to me. It took for ever for me to confirm where tdc was. 

Thanks in advance. 



-- Edited by RHHogue on Thursday 16th of October 2014 02:52:26 AM

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if all you have done is ok .my next check would be the inlet manifold the piece between the carby and head 

the rubber comes away from the metal insert causing a vacum leak .

with the engine running try aplying a bit of presuure to the carby and see if the engine speed changes and or spray a bit of wd40 on it with it running if theres a leak the engine speed should change 

may not be the cause but worth checking 



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Sorry to hear you are still having problems.

Good suggestion from Les regarding the carb stub having possibly split biggrin

Also, have you checked your petrol tank cap is venting OK?

Does the TTR run better or worse with the airbox cover off?

Were the links that Jarrah gave you helpful at all? i.e.

http://ttr250.activeboard.com/t56226503/mid-rpm-range-bogs-down/

http://www.ttr250.com/Removing_carb/TTR_carb_removal.htm

http://ttr250.activeboard.com/t55374798/rebuilding-a-ttr250-teikei-y30p-carburettor/

http://ttr250.activeboard.com/t55887362/some-random-questions-from-a-new-owner/

Brian



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TTRfan wrote:

Sorry to hear you are still having problems.

Good suggestion from Les regarding the carb stub having possibly split biggrin

I will check this one tonight, should be pretty easy to try.  However I have visually inspected them and don't see any issue with both in and out of carb

Also, have you checked your petrol tank cap is venting OK?

I have not checked this.  I will see if I can figure it out tonight.  This could just be removed for testing, right?  The only purpose is to make sure fuel does not leak out and dirt does not get sucked in, but still allow air to come in and replace the space for the used fuel?

Does the TTR run better or worse with the airbox cover off?

It used to run better with airbox cover off.  That is what lead me to the bigger jets and removing the spark arrestor, adding high flow air filter, and removing the snorkel.  Last I check removing the airbox cover did not make any change to how the bike ran.  I will also try this again tonight to give better feed back on this suggestion.  

Were the links that Jarrah gave you helpful at all? i.e.

Yes they were.  Those links are what got me through cleaning the carb twice and checking everything, and then deciding to just spend the money for a carb that did not have float bowl post broken.  I am not sure the broken post had any bad affects on the bike, but I wanted to eliminate that as an issue, and at the same time eliminate the carb as an issue all together.  Because I have a brand new carb I now know it is not the issue, except for maybe some small adjustments.  

http://ttr250.activeboard.com/t56226503/mid-rpm-range-bogs-down/

http://www.ttr250.com/Removing_carb/TTR_carb_removal.htm

http://ttr250.activeboard.com/t55374798/rebuilding-a-ttr250-teikei-y30p-carburettor/

http://ttr250.activeboard.com/t55887362/some-random-questions-from-a-new-owner/

Brian


 Last night I got brave and checked my valves.  They were a little tight.  Some were in tolerance but at the very tight side.  One was too tight.  Exhaust.Left - .18(189 shim) Right - .18(184 shim) Intake L .10(205) r .08(200).  Of course I don't have the most confidence that I checked those correctly.  Because of the angle and me having straight gauges I could not feel real well when it was just barley dragging.  I am going to try and get some angled gauges today to double check myself.  Also going to get some shims to see if I can get the gaps closer to the looser end of the tolerances. Could valve gaps cause my problems? 

So for tonight:

- shim valves to high end of tolerances

- reassemble and hopefully get the timing correct.  

- Check to see if their are cracks in inlet hose between head and carb.

- Adjust fuel mixture screw.

- Check gas cap valve.

- Rerun bike to see if any changes were made, I will remove spark plug and take pics after this to see if that can help.

- Check to see how bike runs with airbox cover off, I will remove spark plug and take pics after this to see if that can help.

- I may try adjusting the thorttle needle height if I have time.

- Any other thoughts for tonight?  Already sounds like a lot to do, but any other quick thoughts on simple things to check.



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So tonight I got the valve shims in and now they are at the loose end of tolerances. 

Changed the oil and filter. 

Checked gas cap valve and it appears to be working fine.  I can put my mouth on it and blow air like it would blow into the gas tank. I also loosened and pretty much took gas cap off while riding and it did not fix problem. 

Sprayed starter fluid all around carb while bike was running. I could not hear a differance in idle sound. 

Ran bike with airbox cover off but it did not fix problem. 

fuel mixture screw is two turns out which is kind of right between the suggested values I have read. 

Attacjed are a couple of pictures of spark plug after tonight's run. Looks like it may be a little on the rich side?

whats next?

 



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first up well done on your work so far .

now im thinking jetting or a hidden carby issue .

if its a tad ritch running at constant throttle in the rev range where you have the problem and then roll off the throttle a bit and it should clear up for a second or two 

basicly creating a tempory lean situation . not easy to do but when you get the hang of it  you can check a few things this way .

im sure a few more sugestions are on the way 



-- Edited by ttboof on Thursday 16th of October 2014 10:10:11 AM

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Have you measured the float height?
Apologies if you've been through this already.
Really interested to see what you turn up. I have a similar issue on mine. I got it down to a bearable level but it's still not reliably happy on a constant open throttle in top gear. Has patches where it 'hunts' and 'bogs'.
I've started getting paranoid about the CDI or ethanol in the petrol messing the rubber on the float valve.
Mine also seems to be rich, but for no reason I can fathom.

ATB

Andy

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Just a reminder:

i BOUGHT A BRAND NEW CARB.  This should just about eliminate any carb issues.  I don't mind suggestions on carb issues but they will probably be the last thing I try (again).  I went through and check almost everything in the carb.  Cleaned it 3 times.  Then decided to just buy a brand new one that never had gas and never had been installed.  It is the cleanest thing on my bike right now.  

As for checking float bowl level, I have NOT.  But I am assuming(could be dangerous to assume) that the bowl is set correctly from the factory.  

I am going to replace spark plug cap, I actually already have a new one just did not install yet.

Then I am going to test the Ignition coil, and will replace if it seems bad.

Any other non carb suggestions?

As for the carb I will revisit it eventually.  May put the stock jets(brand new) back in.  

May change the throttle needle height.  This actually makes the most sense that it would affect my issue.  Since this is the part that will affect the top end of my RPMs.



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Faulty CDi - unlikely

Faulty igniter/sender on the stator - possibly

Faulty plug cap or ignition coil - possibly

Faulty spark plug breaking down when under max load - possibly

Fuel starvation when at full throttle from insufficient fuel flow caused by blocked tap or float valve filters - likely

Can't think of anything else at this stage...

Brian



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But you modified the carb to make it richer and in my (very limited) experience it already runs rich at stock settings (and by the looks of your plug you are indeed running rich). Maybe eliminate basic carb possibilities first, go back to the 137 main and try leaner needle settings. I was amazed how well my US '03 model ran when I finally got the right needle setting and clean jets (second position up (to the lean) works well with the 137, up to about 5000 ft.) -- just one clip setting difference and it was like the bike finally came alive. I tried a 140 and 145 main and ran boggy even up a notch (stock pipe).

I haven't noticed any real effect from the spark arrestor (if clean) or the air/fuel screw setting. Maybe a little difference with non-eth gas but not much.

Throttle cable/linkage? Governor screw on throttle linkage?

Squirrels in the pipe? Tried removing the pipe drain plug to blast em out?

Also, if you used to ride a dirt bike, the TTR likes the low end better than the high end, its taken me a while to get used to that. But that wouldn't explain your bike's symptoms.

Disclaimer: I'm a worse mechanic than you and don't know sheet.

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PlumasDude wrote:

But you modified the carb to make it richer and in my (very limited) experience it already runs rich at stock settings (and by the looks of your plug you are indeed running rich). Maybe eliminate basic carb possibilities first, go back to the 137 main and try leaner needle settings. I was amazed how well my US '03 model ran when I finally got the right needle setting and clean jets (second position up (to the lean) works well with the 137, up to about 5000 ft.) -- just one clip setting difference and it was like the bike finally came alive. I tried a 140 and 145 main and ran boggy even up a notch (stock pipe).

I haven't noticed any real effect from the spark arrestor (if clean) or the air/fuel screw setting. Maybe a little difference with non-eth gas but not much.

Throttle cable/linkage? Governor screw on throttle linkage?

Squirrels in the pipe? Tried removing the pipe drain plug to blast em out?

Also, if you used to ride a dirt bike, the TTR likes the low end better than the high end, its taken me a while to get used to that. But that wouldn't explain your bike's symptoms.

Disclaimer: I'm a worse mechanic than you and don't know sheet.


good idea i went up a size on the main and pilot jet ended up back to standard main runs spot on 



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As usual, Brian has given due consideration and come up with a good next choice for me.

I'm going to get an e-bay coil and a new plug cap. Having read through a few multibike threads about coil breakdown it seems that could be a likely fault. The symptoms do seem to match.

Once it gets here I'll do a few meter readings and try and remember to post back here. Fail or no.

Cheers.

Andy

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eager to read your posts with any improvements, mine too runs rough at around 7500 upwards ( I installed a tach )
Cheers

Henry

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Preliminary findings on the windings. Not results yet.

I got a £12 coil off e-bay. It was listed as for a KTM 450, or some such, but the same seller was listing identical coils for all kinds of models. Physically it was a perfect match. Electrically not so. I could find no listings for coils that had a chance of fitting that also had some electrical specs. Why would anyone want to know that when it's usually the only thing the service manual will tell you about the thing?

Primary on the pattern coil read 0.4 ohms, which is in the range from the manual 0.36 - 0.48.
Secondary on the pattern coil read 3.26 K-ohms, which is not within the manual's range of 5.44 - 7.36 K-ohms. So that's no good.

In comparison to the one on the bike, the first thing you notice is the 'quality'. The feel of the thing in your hand. Not as good as the stock one, which seems to be made by Mitsubishi going the logo on it and the CDI box. The pattern one doesn't weigh as much either, which I guess means less copper inside. No great surprise. It was £12.

The primary on the stock coil read 0.6 ohms which is just outside the range spec.
The secondary read 6.5 K-ohms, which is just about bang in the middle of the range.

So I'm thinking there is potentially a problem with the coil as the primary resistance is slightly too high, and this can only be magnified by the effect of the heat rising from the throbbing power cauldron that is the TTR's engine directly beneath it.

So I've ordered a new one from Fowlers. They will have to get it in but a nice bloke there thought it should be by the end of the week.
81 quid and change, delivered. I'll take some readings off it when I get it and post here.

One interesting, but annoying, thing I found doing this is that multimeters are not all the same. I have 3 and while they all gave broadly the same reading for the higher resistance, secondary coils, there was quite a lot of difference among the low resistance primary coil readings. I have included the most flattering ones here which were coincidentally from the most expensive meter. One of the others just about doubled the primary readings.

Did the pattern coil work on the TTR? Don't know. In my research I fused my brain into a big clump of 'Feck knows', but I did come away with a vague notion of backlash through the primary coil as the secondary produces the spark voltage, and this can damage upstream electronics like the CDI. I thought best steer clear of that scenario.

I also learnt that when a single core coil like ours is bolted to the frame, like ours, the bolts and the frame bracket assist the magnetic affect by closing a loop of metal around the coil. Hadn't thought of that.

Oh, and pick-up coil is reading 201 ohms so I guess it's good. (190 - 230 ohms.)


Andy

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Ok I went as far back to stock as I could.
With a brand new carb jetted at 137 and 50. Left the throttle needle at the middle setting. Reinstalled the exhaust spark arrestor and the air intake snorkel.
It is running much better. For other sreference. I now have stock jetting stock pipe with a high flow air filter. This is a us model and I am about 1000ftelevatuon.
It still has a little bog/ cut out at high Rpms. But I had to try hard to get it to show. I don't have a tach but it bogs/ stutters at higher Rpms than I would normally drive it. I only ran it up that high to try and get it to show symptoms.
I am going to leave it as is for now. Check the spark plug after the next long days ride and go from there. I also am going to make plans to get an after market exhaust so I can try and open it back up.
Any suggestions on an exhaust that is not too loud.

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