Will Start w/ choke but dies w/out

Tesla73 · Post by **Tesla73** » Sun Jan 11, 2009 10:30 pm

ok....My wife and I have a 96 YZF600 and a 97 YZF750. The wife's 600 sat for a month between rides, she broke her foot. But ran 3 weeks ago after her foot healed. My 750 was ridden for short rides every two to three weeks since May last year. When we recently went to start the bikes, the batteries were bead. Replaced the batteries and Wa La, they started like normal when cold with full choke. But instead of warming up like normal they stayed idle around 2500 to 3000K with the choke. Instead of warming up to 4-4500K. And as soon as you removed the choke they would stall. If I gave either any throttle they would die. Or if they picked up I would have to keep high revs to be able to ride. But as sson as you let off the throttle ...dead again. We emptied the tanks and put fresh 93 octane fuel in, but the same thing. Fuel is getting in to the carbs. Checked for sparks and no fouled plugs. I was told by friends that the cabs sound to need to be pulled cleaned and rebuilt. What are your thoughts? And if this is so what all would I need? The 600 has 18000 miles and the 750 20000 miles on them. Adjusting the idle makes no difference. after removing the air box, from above things look clean, but maybe something deeper inside I need to look at. Fuel milage has been good too, around 45 miles per gallon on both bikes. I would rather not pay a dealer to repair this if I can do the work myself. Any help would be greatly appreciated.

ExupElvis · Post by **ExupElvis** » Mon Jan 12, 2009 2:48 am

The choke valves themselves might be causing you grief here Tesla.
They are a simple slide valve (spool type) with an O-ring on the valve body, a rubber cap that also seals, and a flat seal (I think) that shuts them off when closed.
You should be able to find an exact illustration for your carbs in Yamaha's online parts manuals. (Source your parts anywhere, - I don't pay Yamaha prices if I don't have to - but at least you'll have a good idea of what your looking for).
Air leaks past any of those seals will lean the mixture out and cause poor running.
To check - get at the choke cable - make sure it's returning as it should, you'll want to remove the fuel tank most likely so you can see the actuator slide that moves the choke valves.
If the cable looks free enough the next suspect is the choke valve bar (actuator slide) itself.
You don't have to teardown the carbs or even take them off the bike to check that stuff.
Chances are if both bikes were working fine a short while ago, and now neither one does you've got something simple a bit out of whack.
Weather is often a factor with those kind of symptoms, High humidity and oxidation can accelerate the failure of a marginal seal.
Bad fuel could be a trouble spot too.
Did you fuel both bikes at the same spot last time they where ridden?
Maybe it's time to replace the fuel filters even though the tank fuel is new. A splash of watered down fuel is sometimes enough to clog up an aging filter quite badly.
You'll have to look around a bit to find the failure, I hope some of that helps out.

gane · Post by **gane** » Mon Jan 12, 2009 4:03 am

Tesla,poor response,failing to run off idle w/out choke is usally plugged pilot jet/s/circuit. unfortunatly, access/cleaning means r&r carbs.... the pilot jet orifice's are miniscule, and often plug after sitting after as little over a month. luck G

kiwi60 · Post by **kiwi60** » Mon Jan 12, 2009 4:18 am

Tesla,poor response,failing to run off idle w/out choke is usally plugged pilot jet/s/circuit. unfortunatly, access/cleaning means r&r carbs.... the pilot jet orifice's are miniscule, and often plug after sitting after as little over a month. luck G

Yep, with you there Gane, I aways run the FZR carbs dry if it's not going to be used for a few weeks (or months as the case may be), and never have any problems with blocked drillings.

Tesla73 · Post by **Tesla73** » Mon Jan 12, 2009 5:19 pm

Thanks Gang....I will look into it this week if work allows.

Tesla73 · Post by **Tesla73** » Mon Feb 02, 2009 12:48 am

OK. Pulled the carbs off and found a lot of build up on both sides. But I was unsure about pulling the needles. If I remove the float bowls and clean the jets will I need to recalibrate the float bowls and reset any mixture screws ? If I only remove the bowls and jets these should be able to stay the same ? And what is best used for cleaning the carbs ? I have pressurized air for the small holes. And should I consider replacing any parts while pulling the carbs apart ? Sorry for all the questions, but this is my first time working on motorcycle carbs. I have rebuilt three carbs for cars with nothing more than a basic rebuild kit and taking my time. I appreciate all you help. Any sites to assist would be great too.

NMEXPAT · Post by **NMEXPAT** » Mon Feb 09, 2009 1:00 pm

I had the problem. In fact, I just posted my solution to it. while working on my carbs, I noticed two of my "choke plungers", the same valves "EXUPELVIS" is talking about, were cracked. They would let in extra air. I also cleaned my carbs. I highly suspect the cracked rubber was causing the problem. I cleaned my carbs, but they weren't very dirty.

Check the little rubber choke valves. It is easy once you have the choke rail bar removed.

ExupElvis · Post by **ExupElvis** » Fri Feb 13, 2009 3:42 pm

NMEXPAT wrote:Check the little rubber choke valves. It is easy once you have the choke rail bar removed.

Glad it worked for you NMEX, 15 year old machines are going to have problems like that.

Tesla73 · Post by **Tesla73** » Sat Feb 14, 2009 1:43 pm

Well, finally got them out again and cleaned everything, so I thought. After starting them up, the 600 runs a little ruff, but Stays idle and only has a little bit of a chug feeling while riding steady. getting on the gas it pulls nicely.

As fo the 750, it now runs but after taking the choke off from warming her up, she does not want to drop below 3K. If I put it in gear and let off the clutch a bit it drops, but idles a little rough. Any throttle causes the 3 to 5 K revs. Guess I need to pull the carbs and check those choke plungers. I figured, if they were working why would I need to clean them...I will have to see next weekend if that works.

Friends down from out of state this weekend, so no time to work on them That sucks. I want to ride so much. I had to ride my buddies Kawi just to get a fix.

Thanks for the assistance again.

Tesla73 · Post by **Tesla73** » Wed Mar 18, 2009 4:56 pm

OK. Pulled the carbs apart again. Found a little build up in the Idle Screw passages. And when pulling the choke plungers I found that number one had a split rubber seal. I ordered it Saturday and I should be able to replace it this weekend as long as it comes in by friday. I want to get this 4 - 5 K Idle to go away so I can ride and not worry about slowing the idle with engine breaking to stop at a light. I reset the Idle screws to 2 1/2 turns and once this plunger is replaced, I will make any other adjustments.

Then I can start on painting the bike. Thinking of Duplicolor or Kylon Fusion with clear coat. I don't have $800 for the paint job right now.

ZoltanP · Post by **ZoltanP** » Sat Feb 27, 2010 4:23 am

so i presume this did the trick? just curious after all this time. ...

Tesla73 · Post by **Tesla73** » Sun Feb 28, 2010 10:14 am

This did a big reduction...I also had to replaced the rubber collars between the Intake and Carbs. This helped reduce the occurance more. But I have the bikes in now to have the carbs re-cleaned, fully adjusted (fuel level, Idle screw, etc), and synced. I could not find any other issues. So hopefully Back to like new running condition in the next week.

ZoltanP · Post by **ZoltanP** » Mon Mar 01, 2010 3:39 am

ok, let us know? ta.

Tesla73 · Post by **Tesla73** » Sat Mar 06, 2010 9:25 pm

Hell yeah !!! Had the carbs pulled apart, cleaned and fully calibrated. Found one drain and jet bad. Replaced the spark plugs and started right up. A final adjustment and they run like new !

My wife and I had a blast riding them home....god I missed them. I was just missing small issues and the sync tool to make sure they were right. Now I have to see what price I will be looking at for a Black paint job for the wifes 600 and a pearl white for my 750.

ZoltanP · Post by **ZoltanP** » Sat Mar 06, 2010 10:08 pm

good stuff. it's always good to see what the end solution was and i wish people would always post solutions as these postings are often read a year or more later by people having similar problems.
thanks mate.

Post by **jjs777** » Fri Aug 27, 2010 6:53 pm

well...after talking to exupelvis this is likley the same issue I have

I havent ridden for a really long time...mostly due to both my 90 and 95 sat for about a month...then when I went to ride they wouldnt idel worth a darn.
Pulled carbs off both...cleaned etc (using wifes diabetic needles to clean tiny jets...blew air etc)
swapped carbs between bikes...nothing worked
maybe it was gas...so I emptied - refilled etc...nada
they would start but not idle...
So I'm looking for someone around my area to go over the carbs.
As for the 'other' 90...well...I'll be trying to throw my recently built motor into it and see what happens.
I just wont do it till I get carbs gone over.

EXUP Worldwide

Will Start w/ choke but dies w/out

Will Start w/ choke but dies w/out

Carbs

cleaning carbs

Carbs

Choke Plungers

Fixed ???

My babys are back home !!!!!