A forum for owners of Yamaha TTR250 trail and enduro bikes!

TTRfan · Super Guru

Carburettor - pictorial guide to stripping and checking a carb

RodYorkttr · Senior Member

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!

TTRfan · Super Guru

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

Yep - green arrow is pilot jet

Indigo · Member

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,

tom13 · Senior Member

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

ttr steve · Super Guru

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.

Indigo · Member

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

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

miltos · Member

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.

TTRfan · Super Guru

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

miltos · Member

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?

TTRfan · Super Guru

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!

miltos · Member

Here you are.

Look at the cooper wire.

JOHNYBOY · Super Guru

whats that for

TTRfan · Super Guru

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?

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?

miltos · Member

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.

miltos · Member

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

TTRfan · Super Guru

Wow! What made you think of doing that?

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

ttr steve · Super Guru

Brilliant, appreciate your effort

miltos · Member

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)

Cubber · Super Guru

Let's not be negative about these pictures!

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

Not bad, eh?

Martyn

ttr steve · Super Guru

Cool I say, bloody cool smile smile smile

miltos · Member

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

TTRfan · Super Guru

I have just made a small change to the carb removal web page to remind owners to use or drain the fuel before removing the carb else it gets real messy!

Brian