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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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Old 23 Nov 2006
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More Carb-questions....

Still having problems with my 3AJ carb. The carb have been worked on by an earlier owner, and never worked well since.
I've checked the needle-clip position in 1st and 2nd carb, and they both are set on the third position (the middle position of five).
-Is this the right position? (only driving in the lowland max 50 m over sea-level)

Have been adjusting the pilot screw (referring to #16 on scheeme). The engine is idling nice. Have adjusted the secondary to open when a 6mm drill is placed under the primary.

Still my engine will die at about 3000 rpm.

-What is the pupose of the item #8 on scheeme, referred to as "Jet, Pilot" and how schould this be adjusted? I didn't touch that yet, but I think maybe someone have. Since I have to open the floatchamber to adjust thisone, I would like to do this only once.... .

I think the pilot screw is right adjusted since the engine is idling nice, but what do I know...

Anyone having advices?
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Old 24 Nov 2006
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carb problems

Number 8 It is the idle fuel jet. It is just screwed in snugly. make sure it is very clean. Check number 7 which is the main jet and can cause a high speed miss and check number 6 which is what I call a emulsifier tube. It should have very small holes in the sides. If these holes are plugged the engine will stumble with a very rich mixture.Then check to make sure you don't have a ignition problem.
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Old 26 Nov 2006
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Thank you Bill.
I did open the idle jet, and flushed with air in all directions.
The main jet main jet and the "emulsifier tube" looks nice. I now will make sure the timing of the 2nd is right before I put the carb back on the bike.
I'll leave the needles in the 3rd positions as I found them.

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Old 26 Nov 2006
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Speaking as an ex-mechanic - I've had lots of carbs come in that "weren't quite right and I've done everything" - and a full clean and reset to spec fixes them completely. Always!

Ideally you'd do a FULL clean with nasty chemicals to make sure the passages are really clean - air is NOT enough - and then set everything to exactly factory spec.

Along the way - check the floats are floating - not sinking. Metal ones are easy to tell, plastic ones harder, but they do soak up fuel and not float adequately high. Be SURE to set float level correctly, and replace float needles.

If the bike has lots of miles, replace the jet needles and needle jets. The jet needle is the one with the clip on it, and the needle jet is the one in the body that the needle goes through and wears out. Badly worn = excessively rich = dying at mid throttle.

Also be sure the air cleaner is really clean. NEW spark plugs, check the plug wires - if they're old, replace, and the caps.

If that doesn't do it toss it off a cliff...

Actually means there is something more basic the problem. Have you checked the compression?

Good luck,
Grant Johnson

Seek, and ye shall find.


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Old 27 Nov 2006
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Thanks Grant!

I'll try the cleaning with chemicals. I've not checked the compression and the spark plug wire/cap. I'll do that when I'm sure the carbs are OK.
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Old 27 Nov 2006
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Are you positive the carb is at fault?

I tried everything, to get a friends DR200 to rev, I was obsessed that it was carb/fuel supply related, even had the CDI and Stator checked out.

The problem turned out to be the sidestand switch.

May be worth checking.

Good luck, Phil
650 Transalp
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Old 15 Dec 2008
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Need Your Help On Similar Problem

Grant Johnson, I have a similar problem and am wondering if you can point me in the right direction.

My 94' XT 600E needs 8 to 10 tries to start/fire-up when cold. Am in the Philippines so no cold weather issues here. Starter cranks on every try though. If the battery doesn't run out of charge first and it finally starts and has warmed up, it will re-start easily after that and and runs great. It has just been overhauled by a trusted and experienced professional mechanic with all original and mostly internal engine yamaha parts, in addition to a new set of oem carb rubber joints on the front and rear of the carb and a new air filter.

However the cold start problem has the mechanic and myself (that can't contribute much by way of mechanical ability) at wits end.

The mechanic has followed the bike's shop manual recommendations on all suspected/possible areas that may be causing the problem such as: going through the whole electrical circuit, wiring & components, engine valve clearances/settings and had overhauled the carburetor after replacing the fuel enricher assembly and the main diaphragm due to malfunction and wear respectively, and resetting the carb as per the shop manual specs, like you had mentioned in your previous post. There is fuel in the carb when the choke is utilized. And the carb has been diasassembled more than several times after that to ensure that there is no gumming, dirt, blockages and etc, as the mechanic suspected that the carb could be one of primary causes of the problem. The air screw/idle adjustment and pilot jet settings were set as per the shop manual.

In addition, the rectifier was replaced because the battery wasn't being charged sufficiently and it now charges the battery properly. We had also disabled the kickstand switch .

However nothing done so far has resolved the cold starting problem.

At this point, the only possible cause of the problem the mechanic supects and has left to rule out is the TCI unit. Though this doesn't seem to make too much sense to me because there is a strong spark that jumps about a quarter of an inch when tested on cranking the engine during cold starts and the bike runs fine after it's warmed up.

Any assistance would really be appreciated.

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Old 15 Dec 2008
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Just a thought -change the spark plug .Very often a plug will look good when it sparks in the open air but will fail when under compression .
Another thing you could do is check the enricher is working properly ,after a few failed starts pull out the plug and check to see if it is wet with fuel .
If it's dry then try squirting some fuel into the carb mouth as you crank the engine ,the engine should fire with this very crude enricher .

If the engine starts OK when hot then the problem is most likely choke related or it could be a faulty battery or connections .Jump start the bike from a car battery to make sure that you have enough power to spin her over fast enough .

Good luck .
Blessed are the cracked, for they let in the light. - Spike Milligan
"When you come to a fork in the road ,take it ! When you come to a spoon in the road ,take that also ."
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Old 15 Dec 2008
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Carb problems

Check the diaphram on the secondry carb to make sure that it doesn't have any holes in it and its not perished, also make sure that it slides up and down nicely ( If you put your mouth over the carb opening where the air filter attaches to the second carb and blow the slide should lift up)
If this checks out, check the float needle valve (on the first carb, it controls the fuel in the float chamber) it has a rubber pointed tip on it. This can wear a lip around it as it stays in the same position for a long time,you have to look quite hard.
If removed and put back in a slightly different position it can cause it to splutter or hold back when it is revving hard as its not sealing properly ( check the gauze filter underneath this ,I think its held in place by a screw). its a long shot and i think the first is more likely but its worth a look if all else fails. vinegar is good for cleaning carb parts, leave them soaking in it for a day. GOOD LUCK
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Old 16 Dec 2008
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Firstly, thanks for the help orange & Dodger. Appreciate it.

I forgot to mention that the spark plug had been replaced to new and fresh fuel used after the overhaul. Will check the condition and operation of the secondary carb diaphragm as suggested if not yet done by the mechanic. Ditto on the float needle valve and gauze filter.

The enricher had been replaced after the overhaul, after noticing that the spark plug was dry after cranking the engine on cold starts. The passageway/tunnel (the right word for it doesn't come to mind) inside the carb for the choke had been cleaned and thereafter checked to ensure that fuel flows through it. So now fuel does reach the plug when the choke is on. Will ask the mechanic to test the new enricher installed as you suggest, to see if it isn't working properly. Battery is new and the mechanic has gone from rear to front on the bike checking all the wiring, grounds and etc. Whenever the battery runs out of charge from the cold starting attempts, the mechanic has utilized a car battery to continue the attempts till it fires up. Yet the cold starting problem continues.

The mechanic noticed just today that there is fuel seepage coming from the carb float bowl gasket. Though it still isn't clear if this was present immediately after the overhaul (though a new, supposedly oem rubber gasket was purchased from an authorized dealer and installed as part of the overhaul (which the mechanic on hindsight says seemed thinner than the original worn gasket), or, developed only after the repeated carb overhaul and cleaning done by the mechanic trying to fix the cold starting problem. Don't personally know if such seepage could cause the starting problem.

Will post results either way. Thanks again, and for any other advice from among the HUBB members.
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Old 16 Dec 2008
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Not sure if the XT600E has a fuel pump but if it does try bypassing the fuel pump and connecting direct from tank to carb.
You could just get a small tank with a long petrol pipe and hold the tank while you try starting your bike if it works you know you have a problem with fuel either taps or fuel pump.
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Old 16 Dec 2008
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No fuelpump
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Old 17 Dec 2008
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Hi again and thanks. But yes, no fuel pump on the 94' xt600e.

Still looking for suggestions/ advice.

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Old 24 Dec 2008
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Cold Starting Problem Fixed!

Grant JohnsonSpeaking as an ex-mechanic - I've had lots of carbs come in that "weren't quite right and I've done everything" - and a full clean and reset to spec fixes them completely. Always!

Ideally you'd do a FULL clean with nasty chemicals to make sure the passages are really clean - air is NOT enough - and then set everything to exactly factory spec.

Hi. The cold starting problem is finally fixed. Thanks to all for the advice and for pointing us in the right direction because yes, the carb was the problem. The advice quoted above from Grant Johnson long before I added to this thread was pretty much a good part of the solution.

Though the carb had repeatedly been dismantled & cleaned everytime using various techniques and materials in cleaning the carb after the engine overhaul, what did the trick was when the mechanic rechecked the very small passageways in the carb body he called "venturi holes" and recleaned them using (sounds a bit extreme) pressurized butane in a canister such as that for refilling personal cigarette lighters. And thereafter, his heating up the carb body (with extreme caution after removing any parts that could melt) and cleaning the carb body in and out with kerosene, while the carb body was still heated. Very carefully because overheating the carb body would result in reclogging the passageways or worse, a burned carb body.

The XT has been firing up on cold starts on the first attempt, for 5 consecutive days now. Thanks to all again.
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