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Post Info TOPIC: Carburettor - pictorial guide to stripping and checking a carb


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Carburettor - pictorial guide to stripping and checking a carb
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See http://ttr250.com/Carb/TTR250_carburettor_strip_and_rebuild_guide.htm

There is advice on taking out the carb here http://www.ttr250.com/Removing_carb/TTR_carb_removal.htm

Also, there are a couple of tutorial videos showing removal and replacement of the carb here https://youtu.be/0k1EG1LuPBc and here https://youtu.be/Nlhl9aD9wHI

Totally TTRs sell a superb carb repair kit here which might be useful to have before you start work if you think replacement parts and gaskets will be needed.

These are all the tools you will need for a basic strip:
Carb strip 005.jpg

An aerosol can of carb cleaner would be handy to have but beware, carb cleaner, along with clutch and brake fluid, can damage most rubber, and some plastic components. Only use it on metal parts of the carb such as the jets.

Start off by removing the two screws and taking out the diaphragm and check it isn't damaged. If needing replacement because the rubber part has hardened or torn then the part number is 4GY-14940-00-00 or buy here.

It makes sense to replace the two little O rings (part number 5Y1-14397-00-00 or buy here) when re-assembling.

Carb strip 006.jpg

The pic below shows the carb stripped as far as you need to go if just cleaning jets. My advice is NOT to take the float assembly off without very good reason as you risk breaking the support post arrowed in red. The retaining pin is usually very tight no

Pink arrow is airscrew, green arrow is pilot jet, blue arrow is main jet and its supporting emulsifier tube.

Bigger photo of airscrew below with it's O ring and spring:

Pilot_screw_new.jpg

Take out the airscrew and clean it up. If the O ring is perished/damaged/worn then replace it so that you don't get an unwanted air leak!

The pilot jet needs special attention as its hole is tiny and easily blocks. Spray it through with carb cleaner but, most importantly, ream it with a piece of soft copper wire to make sure any old petrol deposit or debris is cleaned out. Blocked or partially blocked pilot jets are the biggest cause of poor slow running on a TTR250.

The emulsifier and main jet rarely suffer from blockages so just clean them with carb cleaner and blow them out with compressed air if available.

Most carb leaks seem to occur because the float bowl gasket (part number 4GY-14384-00-00 - or buy here) - gets flattened over time. For the amount of hassle involved in putting everything back together only to find a leak, I advise putting a new one in if it looks "flat!!

Carb strip 007.jpg

 

Make sure you don't lose the little brass check valve arrowed in red below. It has been known for them to fly across the garage (never to be seen again) when blowing out the float bowl with the airline disbelief

Carb strip 008.jpg 

Not much more to add really other than to pop it all back together and wind the airscrew out 2 to 2.5 turns* before putting the carb back on the bike wink

*The manual says 1.5 turns and this may suit your bike but I have found that the more open settings work better.

 



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I wish I had read about the "flying" brass check valve!!!- thats 40mins I will never get back- I take it the green arrow is the pilot jet?
excellent write up Brian- thank you!

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Thank you for the compliment Rod!

Sorry to hear you suffered from flying check valve syndrome - not good to be searching around the floor with your back no  

Yep - green arrow is pilot jet



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Hi all;

Some weeks after I got my blue TTR 250 I can finally give her a bit of attention.

Reviewing and cleaning the carb, I´ve lost the brass flying check valve. What´s it´s function ¿

(in fact I thought it was a positioner to align carb´s bowl with main body when fitting carb.... (but it´s seems she has another job !!)

Is it possible to perform nice without it¿

Thanks / best regards,

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Google translator
Brian is right when he writes - DO NOT take off the float assembly without a very good reason - I broke it and I couldn't fix it even according to the instructions

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Googled this response

The check valves are what makes your fuel pump work. If you understand how the fuel pump works on your carbs you will realize that a bad check valve means yourcarb isn't pumping at its normal flow rate. I've had motors run lean and hot due to a bad check valve. Replace your check valves and rebuild your carbs.



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Cheers, Steve.
One is flying home. Cheers, Indigo !



-- Edited by Indigo on Wednesday 4th of September 2019 09:22:47 PM

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Hi everybody,

First post to the forum.

Is there any solution for the missing choke rubber end?

Moreover, I am considering if I should fit an O ring at the top of the main nozzle.

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Hi Miltos and welcome to the forum!

The choke O ring is a square section if I recall correctly so not an easy one to match.

One owner found a solution using silicone sheeting - se https://ttr250.activeboard.com/t52237312/freeing-off-a-jammed-choke/

I do recollect  mention of fitting an O ring on the nozzle (Jarrah maybe?) but have never done it myself on any of the carbs I have rebuilt.  Has anyone else?

What is the problem that you think it might solve?

Brian



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What is the problem that you think it might solve?

I don't have a specific problem.

The brief story of my bike, is that after 2 days in my possession, it had a problem with the starter motor. Having removed all the parts needed to dismantle the starter motor I thought it would be a good idea to check the carburetor, which did not work well enough.

So, I cleaned the carb and now I am reassembling it. (The problem is the luck of free time, so by the way, excuse me for the delayed response).

An O ring would not allow any petrol to pass through the thread.

PS. I have found two passages at the carb that I have not seen to that guide, any other guide, or to the service manual. Would you like me to upload two photos, that you could add to the guide if you think they would be helpful?



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miltos wrote:

PS. I have found two passages at the carb that I have not seen to that guide, any other guide, or to the service manual. Would you like me to upload two photos, that you could add to the guide if you think they would be helpful?


Yes please!



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Here you are.

Look at the cooper wire.



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whats that for

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You are very observant Miltos! Really interesting questions wink

First photo. I had not seen the passage you have shown here. I can only think that it is for pressure relief such that if the throttle is opened very quickly, it allows surplus fuel to bleed off through this hole rather than damage the diaphragm.  Do you think my explanation is plausible and, if not, what other function do you think it might perform?

1.jpg

 

Second photo. I knew this one existed but had not thought before as to what function it performed. Again, do you think my explanation is plausible and, if not, what other function do you think it might perform?

1_2.jpg



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I am newbie at carbs. This is the first time I am involved with.

I intend to make a schematic diagram with the carb function, like the one here greywolf.ru/index.php

Meanwhile, about the hole at the accelerator pump circuit, it is probably used to suck some air (and petrol vapors), and not only fuel at the accelerator pump chamber. This way, the over pressure protection is guaranteed (the air acts as an expansion vessel)

The hole at the choke circuit seems to be used to supply air (and petrol vapors), in order to limit the amount of petrol being sucked at the low pressure side.

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I had an idea to try x-rays at the carb.
I think that is at least interesting

(I had the float seat fitted)

 

 

 

 

 

 



-- Edited by miltos on Tuesday 3rd of March 2020 08:29:42 PM



-- Edited by miltos on Tuesday 3rd of March 2020 08:38:23 PM

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Wow! What made you think of doing that?

You must either work in a hospital or airport security Miltos biggrin



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Brilliant, appreciate your effort



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TTRfan wrote:

Wow! What made you think of doing that?


I thought I might could have a more clear understanding of some passages that way.

I was aiming mainly at the connection of the pilot screw passage to the pilot nozzle and the second small hole beside the one under pilot jet, but I had no success.

Only first part of the passage from the pilot screw to the nozzle can be seen (better at the second attachment)

 



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Let's not be negative about these pictures!

Here's positive proof that they can be looked at differently:-   

 

1a.JPG

3a.JPG

5a.JPG

Not bad, eh?

Martyn



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Cool I say, bloody cool smilesmilesmile



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That's "inverted". I can do it through the x-ray displaying soft, but you did it better!

-----I updated the images with better resolution----

 



-- Edited by miltos on Tuesday 3rd of March 2020 08:40:54 PM

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