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Carb issues on my '74
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↓ dn ʎɐʍ sıɥʇ ↓
 
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Carb issues on my '74 - October 14, 2008, 06:52 PM

I've been having some idling issues with my '74 yamaha tx500.

The bike revs through the rpm band rather well (even when riding) but if I let it idle it almost always dies within a few seconds once it's warm. I've adjusted the idle screw but when I get it set high enough to keep it from dieing (1.5k-2k) the revs will climb if I blip the throttle (I imagine this is because the throttle plates are being held open.

I've rebuilt the carbs and the jets all seemed clean (I can see straight through them). The floats are right around spec too.

Any ideas? Anyone want to earn some cash stopping by sometime and helping me figure this out (someone with good carb experience)?


-Ryan
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October 14, 2008, 07:06 PM

Probably the air/fuel screws (depends on the bike) need tweaking or maybe the pilot jets are too rich and it's loading up. And you may have an air leak too. Check the spark plugs after it dies.


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↓ dn ʎɐʍ sıɥʇ ↓
 
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October 14, 2008, 07:12 PM

Thanks for the reply!

The carbs are completely stock but I can't confirm the air/fuel screws haven't been touched.
The only other adjustment for fuel is the needle that is on the slide but again I don't think it has ever been changed.

I've done numerous tests on both manifolds (the spray test with brake cleaner) and found no affects.

With the choke off I have to ease on the throttle or it will bog and die. Choke on and the throttle works like normal.

The bike just turned over 700 miles.


-Ryan
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October 14, 2008, 07:22 PM

What happens when
- you restrict the intake?
- you remove the air filter?


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↓ dn ʎɐʍ sıɥʇ ↓
 
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October 14, 2008, 07:36 PM

With the intake removed the bike wont rev passed 6k. I'll have to see how it reacts to restricting the intake tomorrow.


-Ryan
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October 14, 2008, 07:40 PM

Quote:
Originally Posted by Dark View Post
With the intake removed the bike wont rev passed 6k. I'll have to see how it reacts to restricting the intake tomorrow.
But how does it idle without it?


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↓ dn ʎɐʍ sıɥʇ ↓
 
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October 14, 2008, 07:52 PM

without the intake it was idling pretty well but I recall the revs jumping slightly when I put my finger the in the carb inlet.


-Ryan
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October 14, 2008, 09:29 PM

i have carb issues on my old bikes too. I need them professionally worked on. I hate carbs, they never work for me.
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October 15, 2008, 06:41 AM

I have yet to hear one good review on the Keihin carbs.

This was my first 'adventure' in to carbs, they aren't bad but I definitely do not prefer them.


-Ryan
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↓ dn ʎɐʍ sıɥʇ ↓
 
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October 15, 2008, 07:30 PM

I'm going to have the carbs off tomorrow to replace the float bowl gaskets, anything I should check/try in the process?

I'll try the idle without the box again.


-Ryan
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