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

Paul C · Veteran Member

wont idle without some choke

TTRfan · Super Guru

Almost certainly a blocked pilot jet Paul. Most common problem with bikes that have been laid up.

See here for its location.

Brian

-- Edited by TTRfan on Friday 4th of January 2013 06:51:54 PM

Paul C · Veteran Member

Thanks Brian. I had already read that, it was a good guide. This time I'll get the spares first then give it another go. At least it's a pretty easy job getting the carb off.

BTW the clutch bracket was perfect, thanks.

Paul C · Veteran Member

Well, it's been a busy winter, but not with the TTR.

I have rebuilt the carb. Stripped. Bits all left in the ultrasonic cleaner for a while. New diaphragm thingy and teeny O rings. New air mixture screw. New float bowl gasket. All sparkly clean. Refitted it yesterday and it runs much better, but still not right. Runs cleanly but it just won't tick over at a sensible rate. Idle screw has the spring almost compressed fully.

Looks like another close look needed. Upside is that I doubt that anyone is much faster at removing or replacing the carb!

I was even sad enough to track down some tube videos to check out the tickover speed.

-- Edited by Paul C on Tuesday 19th of March 2013 06:14:59 PM

MarkH · Member

Well unfortunately I can't help with your idle issue, but just wanted to say that I too am a TTR and Guzzi LM1 owner! Can't be many of us out there.

good luck with the idle issue and keep us posted

Paul C · Veteran Member

Just an update really.

After many many many rebuilds, cleans, soaks, blasts etc. The problem remained. As a last resort I pulled some fine copper wire out of some electrical cable and used it to "floss" every jet, hole, tube etc I could get to. Then gave same things a good air blast... It works! Clearly some little critter was in there which soaking, ultrasonics and compressed air woud not remove.

Just need an MoT now!

Ronridesbikes · Member

Hey guys, I'm in the same position. I cannot get this bike to idle.

I aquired a 2003 TTR 250 from a family member who left the bike in his back yard for several years.

I have removed the carb, replaced the float bowl and fuel mixture screw O-rings.

I have clean it with carb cleaner and air.

As you can see from the photo, I broke the float pin post which I hear is a common occurrence on these Models. I looked at some of the suggested repairs and came up with a different idea.

I cannot find a place that will Ultrasound or soak the carb. I live in Norther California and I don't think there is anybody that does this due to environmental laws.

My issues is the bike will not idle without the choke on. It runs very well from 1/4 throttle and up.

Each time I remove the carb (at least a dozen times now)the pilot jet(50) is clean.

The air mixture screw (set at 3.5 to start) has no effect unless you turn it completely in - bike dies.

Any ideas??

TTRfan · Super Guru

Hi Ron and welcome to the forum!

Excellent repair to the carb post. Did you make up the piece yourself and what was it made from please? If you can make up a few more to send over to me I would be delighted wink

Regarding your idling problem, it has to be in the pilot jet circuit somewhere. If not the jet then there has to be a blockage in the galleries leading from it.

Brian

nelly · Senior Member

can I jump in here quickly, where do I find the pilot circuit galleries please, I probably need to check them out
thanks

Ronridesbikes · Member

It's a common thumb screw. I filed the winged sides from it. The drill and tap were $5 as a set.

Be careful with the tap. The aluminum casting is so soft it gums up the tap threads quickly. 1/2 turn in, 1/4 turn out and remove it to clear the treads every 2 turns. Go Slow.

I center punched the top of the post and pre-drilled with a smaller bit to be sure I stayed in the middle of the post. Make sure you drill straight down, Check it from two sides as you drill. Again, go slow. Don't drill too deep. Measure the post and put a piece of tape on the drill to set the depth.

Don't worry about tapping all the way down. Put tape on tape as well. Let the thumb screw cut the last few threads so it sets tight. But go slow. If you feel it binding, pull out and use the tap a little more.

You'll have to put the screw in once to mark where to drill the float hinge pin hole. Remove the thumb screw to drill the float hinge pin hole. Center punch that too. The drill likes to move around on the chrome finish.

File the thumb screw wings to within 1/16 of an inch all around the hole so the float bowl will clear and the float it self can pivot the full radius it normally would.

Note - depending on the length of the thumb screw, you may have to cut it down. Make sure you put a nut on it before you cut it so you can clean the threads up before you mount it in the carb.

I found someone to Ultrasonic/Hot tank the carb body. I hope this works.

TTRfan · Super Guru

Brilliantly detailed and clear instructions Ron - thank you very much - thumb screws on order! biggrin

I can tell you are going to be a very useful new member wink

Brian

ttboof · Super Guru

Brilliant in its simplicity a great tip

Ronridesbikes · Member

Thanks for the kind comments guys. I don't know how much help I can provide, I can't get this bike to idle.

I have now had the carb ultrasonic hot tanked. The shop owner stated that there was some residue left in the tank and that he checked all passages and they were clear. I reassemble the carb and installed it.

Although the bike will not idle, at least the idle mixture screw has an affect. At 2 turns out the bike will idle with the choke 1/2 off. This is an improvement as the bike would only run with full choke prior to the ultrasonic bath.

I'm not sure where to go from here.

Even though I'm fairly sure it does not have an affect on the idle, I have not set the float height. If someone knows the static measurement, please provide the details. I do not have the glass tube to check the level on the bike.

I do have a question about the item in the picture. What does this part have to do with the idle? You will notice one of the passages is connected to the idle air mixture screw and the idle jet. I have not replaced the "o"ring gasket that you see. When I place the plate over the gasket and tighten the screws, you can feel the "O"ring being pressed.

Anybody know what this is and if it has an affect on idle?

Thanks.

mossproof · Super Guru

Out of interest, what jets are you running, and what airbox/exhaust mods have been done? If it won't idle without choke, I think it's running lean, which is either not enough fuel or too much air. Is the inlet manifold stub sound (rubber still bonded properly to the metal)?
Bit of a head scratcher!
Good luck,
Simon.

Ronridesbikes · Member

Idle jet is #50. The bike runs good from 1/4 throttle and up so the main jet is good. #147 I think
No modes to the intake or exhaust.
Intake intake manifold is supple and flexable. No cracks or failed bonding.

Correct me if I'm wrong but, most chokes block air to enrich the fuel mixture for starting. It appears this carb, opens a passage for more fuel and the air mixture screw at the base lets you adjust how much air needed to achieve idle.

With the choke 3/4 on (at a high idle), I can get the bike to rev enough to ride it. Keeping the bike reving.

As i said before, the bike does respond a little to the air mixture screw now that i hot tanked it. But the air mixture screw does not have enough of an effect to get the bike to idle down and still not die.

I think the air is coming from the item I pictured above. I'm not sure what it is or how it works with the choke. I'm going to buy a new o-ring for it and see if that helps.

Any help on what it is would be greatly appreciated.

TTRfan · Super Guru

Hmmm - I know you say the pilot jet is clean but your symptoms point in that direction. Did you "floss" it with some copper wire as Paul mentioned in an earlier post?

I really can't think what else it could be if you have done this and the carb stub is intact confuse

Brian

Ronridesbikes · Member

I have done all of the above. Bike will not idle. This carb is a POS. If I thought I could buy a Mikuni for it I would. I've looked into it and there is no direct fitment offered.

Not sure what I'm going to do....

TTRVN · Veteran Member

Man you have too little fuel for the pilot, since the main jet is fine. Maybe change the pilot jet to a bigger size? Try a 52.5 or 55.

ttboof · Super Guru

I went one size on the pilot kept the main standard

the carby is a good bit of kit when everthings ok

66T · Veteran Member

May I suggest you check the intake manifold? The rubber comes apart from the aluminium casting, allowing unmetered air into the engine. Can be catastrophic in muddy/dusty conditions.

Alternatively. the rubber can perish. Even a small crack can stuff up low-speed running, and even lean the engine out too much at higher throttle settings.

-- Edited by 66T on Wednesday 11th of May 2016 04:44:56 AM

masterbill · Veteran Member

Hello,

I've been following this thread and the other ones about idle problems etc.

I have a genuine Yamaha service manual for the TTR250L(C) - that's what's on the front page . What I didn't realise is it's an American manual.

The carb specs listed are as follows.

ID mark 5GF100

Main jet 137

pilot Jet 52

Jet needle 5C9C-3/5

Pilot screw 1-1 1/2 turns out

Float height 26.5 - 27.5 mm (1.04 -1.08 in)

Fuel level 7.5 - 9.5 mm ( 0.30 -0.37 in )

Below the float chamber mating surface .

engine idle speed 1,250 - 1,350 r/min.

Cheers Bill

Ronridesbikes · Member

Replacing the intake manifold O-ring solved the idle problem. It starts and idles good. But now the bike stalls when i first crack the throttle open. I tried increasing the idle screw (not the air mixture screw). once the screw starts opening the throttle, the bike dies. That's how sensitive the carb is to opening the throttle.

Some have stated this is the accelerator pump. I can't believe this is the issue because the throttle is hardly moved before the bike dies.

When I had the idle issue and the bike would run with partial choke, the bike ran great from 1/4 throttle and up.

Any ideas??

PlumasDude · Senior Member

Buy a new pilot jet. Otherwise impossible to be sure its clean.

masterbill · Veteran Member

Hello,
I've followed this threads and others about the pilot jet etc. My own bike has always started but never really easily. I've never had a 4 stroke single before - had plenty of 2 and 4cylinder bikes over the years and they have always started easily. A press on the button and away they go, sometimes with choke if needed.

The TTR had to have several attempts to get it going and once it was warmed up a bit it was ok , but again it wasn't brilliant at starting.
Recently I had a rebore and I replaced the carb as mine had been modified.

The pilot in both carbs was a 48 and to get it to tick over it was about 4 turns out - but that wasn't the real problem I was having .

It pulled ok etc but when you came to slow down the revs would rise and sometimes it would stall. Ok, people are talking about 50 and 52 pilots. Tried a 50 ,about 3 turns out - but still outside the 1 to 2 that it should.

Did some looking on tinternet and because the adjustment is on the inlet side of the carb, turning it out makes the mixture richer.

Right then 48 = 4 turns. 50 = 3 turns 52 = 2 turns ?

I got a 52.5 from Allens and I also got a 55. Tried the 52.5 and 55 but I still had the same problem with the running and the starting.

So changing the pilot hasn't really altered anything.

So think outside the box, I've come to a dead end with the pilot, I've cleaned it out, blown it , several new jets !

The only other thing I can alter is the needle clip - move it 1 down to make it richer set 55 pilot on 1 1/2 turns out.

Press the button starts straight away , blip the throttle revs a treat no problem. Ticks over perfectly .

Try it on the road - lovely, Hot , cold crack open the throttle no problem at all . It just works .

Have you tried the needle ? because it appears to me that the bike runs weak at bottom end .

Cheers Bill