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Discussion Starter · #1 · (Edited)
The bikes history - ZX-7R P7 bought by the original owner in April 2003, he rode it for 93 miles then it was left untouched until I bought it April 2012.

It wasn't in the best condition, inside the tank was rusted up bad, one inner fork leg was pitted, fork seals had gone, petrol tap shot, corrosion inside the carbs with the needles almost eaten through and some other minor items needed to be sorted.

Well, its all done now and she looks like a brand new bike:smile

My query is this, the carbs were cleaned in an unltrasonic bath and new parts fitted where needed including Factory Pro emulsion tubes and main jets. The guy who did the carb rebuild and set up turned the pilot screws out 2 1/4 turns. The bike runs well except just off idle and up to about 2000 rpm. To try and solve this I turned the pilot screws back to 2 turns but after doing this she would only run on three cylinders, number 4 wouldn't fire up. I thought this must be coincidence and thought it's possibly a plug issue but when I changed the plugs around No 4 still wouldn't fire up. I turned the pilot screw on No 4 out to 2 1/4 turns and all 4 fired up but still lumpy. Well, after a bit of fettling with all the pilot screws to get the best idle she's now set up with carbs one to three 2 turns and four is 2 1/2 turns and it's the best off idle she's ever run...what's all that about?

Has anyone experienced this or can anyone explain why?
 

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The pilot screws control your idle mixture only. Just off idle is your pilot jets which have really tiny passages through them. I would suggest putting everything back at where they started and pull the number four pilot jet and clean it again. If you go on factory pro's website you can find a tuning guide which will explain everything
 

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+1

Sounds like you're troubleshooting properly. I'd assume that there's still fuel gumbo in the pilot air passage or that some of the pilot air screw components may have slipped off during installation and are now jammed in on #4. A lot of people work on their carbs on a work bench where the pilot air screw geometry is perpendicular to gravity. It's important to note that the pilot air screw's washer & O-ring can slip off when installed horizontally in this way. It's best to pick the carbs up and insert the pilot air screw from underneath, to facilitate proper fit.


I just did this work for a riding buddy <write-up here>. Several O-rings and washers were pinched inside. And while we had the pilot air screws and jets out, we blasted their passages using a regular carb cleaner aerosol, butting the nozzle top's red 6 inch tube into each port for a good blast and observing that each carbs' port plumbing would shoot an equal amount of cleaner through it. (Awkward sentence, I know). Shoot into: pilot air screw hosing, pilot jet housing, and the carb's air jet inlet (at the mouth of the carb).


Lastly, on the pilot jets themselves, you'll want all it's orifices to be clear, no exceptions. So those holes at the top need to be clear as well.

 

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Discussion Starter · #4 ·
The pilot screws control your idle mixture only. Just off idle is your pilot jets which have really tiny passages through them. I would suggest putting everything back at where they started and pull the number four pilot jet and clean it again. If you go on factory pro's website you can find a tuning guide which will explain everything
Okay Thanks - but adjusting those pilot screws definately helped the bikes running through to about 1800-2000 rpm. When in traffic and the engine running real hot it was almost unridable, now it's much better. Pehaps something shifted while I was fettling with them?

Is it easier to remove the carbs to change the pilot jets or is it easier to drop the float bowls.
 

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Discussion Starter · #5 ·
+1

Sounds like you're troubleshooting properly. I'd assume that there's still fuel gumbo in the pilot air passage or that some of the pilot air screw components may have slipped off during installation and are now jammed in on #4. A lot of people work on their carbs on a work bench where the pilot air screw geometry is perpendicular to gravity. It's important to note that the pilot air screw's washer & O-ring can slip off when installed horizontally in this way. It's best to pick the carbs up and insert the pilot air screw from underneath, to facilitate proper fit.


I just did this work for a riding buddy <write-up here>. Several O-rings and washers were pinched inside. And while we had the pilot air screws and jets out, we blasted their passages using a regular carb cleaner aerosol, butting the nozzle top's red 6 inch tube into each port for a good blast and observing that each carbs' port plumbing would shoot an equal amount of cleaner through it. (Awkward sentence, I know). Shoot into: pilot air screw hosing, pilot jet housing, and the carb's air jet inlet (at the mouth of the carb).


Lastly, on the pilot jets themselves, you'll want all it's orifices to be clear, no exceptions. So those holes at the top need to be clear as well.

After I cleaned the carbs in the ultrasonic bath I blew all the orifices with 100 psi unoiled air, but unlike your way with the fluid, I couldn't see what was coming out the other end. Thanks for the tip:smile

The pilot jets are the cleaned up originals, so they could be the problem.
 

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when your done cleaning you should also do a carb sync. you would be surprised what unbalanced carbs can cause in terms of fuel mixture.
 
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