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Mid range acceleration issue
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Hi All,

 

i have recently bought a used 1993 TTR 250. Purple frame.
bike was abused, but engine was remarkably well maintained. no unwanted noises, etc.

my problem is that when im riding and through the revs, low end, runs perfectly, WOT, runns pretty well too. but in between, like with the throttle open about halfway. it runs like ****! no misfires and doesn't pull much until i rev almost to wot. i have checked the fuel lines, fuel filter, air filter cleaned and put back, snorkel on, snorkel off, changed the spark plug to a new NGK CR9E, removed the carby and cleaned, nothing seems to help. still the same issue. the main jet is  147. pilot jet is 50. was thinking that maybe the float level is too high, reduced it by about 2mm, still the same issue. the silencer does have a small leak from a weld, could that have anything to do with it? other than that, ive got no more ideas...



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Hello Romeshs and welcome to the forum.

Your problem is most certainly the accelerator pump at fault. My guess is that the nozzle is blocked but it may well be the O-rings or diaphragm perished. See here for info on this-

http://ttr250.activeboard.com/t53839715/rough-running-no-mid-range-power-bogs-down-in-top-problem-fi/

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

Enjoy!

Jarrah

 

 



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Hi,

first of all, thanks for the super quick reply, i forgot to mention that i checked the diaphragm, and cleaned the nozzle inlet and outlet with a piece of cut cable.. and put it together and the nozzle squirts gas into the carby when i accelerate with the carb in hand.. :(

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Oh, in that case I would suggest you are running slightly rich or extremely lean on the main jet. Hard to tell without a better explanation of the symptoms but I'd say rich. If the side holes in the main jet holder (AKA emulsion tube) are nice and clean and the main jet is not blocked, try raising the jet needle clip position two settings higher (towards the blunt end).

Questions-

Are there any other symptoms? (please explain all symptoms to the best of your ability).

What jets are currently installed?

What modifications have been done? (if any).

What is your elevation?

Jarrah

 



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I just started having the same problem. Except mine start to do it as the bike gets warm. It's even worse once it's hotter. Has a bit of a rough idle once hot too. I'm starting to wonder if my valves are too tight. Once hot, it's also harder to start. Do u have any of these symptoms?

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Hi.. Main jet is 147. In the first pic, the one below the emulsion tube, is that the main jet? If it is, I might have a problem bcoz mine looks different. Although I haven't taken it out of the tube, it has a head that u can remove with a wrench. Size 8 I think. Jet size itself is 147. Elevation is almost sea level. The emulsion tube, I did clean when I first took the carb out.

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About issues when warm, I don't have any. Runs the same as when cold. Bike does start up without using the choke, even when cold. Just a touch on the starter is enough to get it going.

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romeshs wrote:

About issues when warm, I don't have any. Runs the same as when cold. Bike does start up without using the choke, even when cold. Just a touch on the starter is enough to get it going.


 Sounds like its running rich If it's starting cold with no choke on.



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romeshs wrote:

About issues when warm, I don't have any. Runs the same as when cold. Bike does start up without using the choke, even when cold. Just a touch on the starter is enough to get it going.


 That confirms to me that you are running rich, refer to adjusting the needle as stated above.

Jarrah



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romeshs wrote:

Hi.. . In the first pic, the one below the emulsion tube, is that the main jet? If it is, I might have a problem bcoz mine looks different. Although I haven't taken it out of the tube, it has a head that u can remove with a wrench. Size 8 I think.


That is the pilot jet. It is an aftermarket 6 Sigma jet so not standard.

From memory the standard main jet requires a 6mm spanner and the nozzle (AKA emulsion tube) is 8mm.

Jarrah



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Terrence R wrote:

I just started having the same problem. Except mine start to do it as the bike gets warm. It's even worse once it's hotter. Has a bit of a rough idle once hot too. I'm starting to wonder if my valves are too tight. Once hot, it's also harder to start. Do u have any of these symptoms?


 Could be valves but from your description of the problem it is the pilot jet being too small. Especially if it gets hot enough to see a bright glowing red header pipe (even at night).

Are you still using the standard #50 with your mods? If so- no

Jarrah



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I have the 6 sigma 52.5 pj back in. It's running terrible. Just ordered a bunch of carb parts as I found a leak( looks like it might be coming from the accelerator pump area). A list of the new parts I ordered are as follows: diaphragm assembly, diaphragm cover, diaphragm o-rings, float bowl gasket, fuel/air screw set (pilot screw set), and a float bowl drain screw ( they call it an air screw set for some reason). Between the new parts and getting the valves checked out by my buddy, I'm hoping to solve the issues.



-- Edited by Terrence R on Wednesday 28th of May 2014 06:29:17 PM

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Thanks guys. Will drop the needle tomorrow and check if the issue goes away. One slot or two? Try with one first.. Thanks.


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Move the clip position up two settings towards the blunt end. This setting should be optimal and save you the trouble of pulling the carb apart again.

Jarrah



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I moved the clip up one position (it was one down from the top so I could only move it one further up) and there's a massive difference. Still sputters a bit at Mid throttle, but the amount of throttle movement during which it sputters is much much less. Thanks everyone. Should I go with a smaller main jet? From the 147 main I have on now? I almost never go off road, mainly on streets full of traffic.

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This was the position it was on before I moved it up. 



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Pic of the clip position. 



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Glad you are making progress romeshs thumbsup.gif

If you still can move the clip to the very last position (closest to the blunt end) I would do so and see if it solves it. However I would suggest to buy a #145 main jet (146 does not seem available) and try that.

The other thing you could do to lean it out a little would be to fit a larger snorkel, or remove the snorkel if you don't ride through deep water. An aftermarket air filter such as a Twin Air or GYT-R would also be advisable if you have not already got one.

Thanks for the update, it's good to seem people replying so we know whether it helped or not (even if only for others sake).

Jarrah



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Hi..
I did move it up to the very last position. The pic of the needle clip is before I moved it up. Will try the snorkel as well. Thanks for all the advice everyone.. Very very much appreciated..


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No problems romeshs

Here is the link to my snorkel mod thread- HERE

Enjoy!

Jarrah

 



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Hi guys.. Thanks for all the advice. My issue is resolved! After trying everything else, put on a smaller 142 main jet. And presto! Runs fine. No bogging in mid range acceleration. Thanks again.

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Thanks for the update!

For the record, your problem was not ''mid range throttle'', it was 1/3 throttle as the main jet does not start working until then.

Jarrah



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