Stumble Off Idle

[x-Drag Racer]

The plugs were just replaced along with a pair valve mod and 4 degree advancer and full Muzzy exhaust. The old fuel in the carbs had a fuel stabilizer mixed with the fuel before the mods started. I hooked up an auxillary fuel tank to check the engine and lube the engine parts. When the bike warmed up it had a off idle stumble but the engine runs good after the revs are up. Any ideas what could cause this?

[riverszzr]

As is the case with nearly every mototrcycle sold in the USA, the off idle circuit gets really lean (for emmissions) so any amount of varnish or restriction gets them even leaner....Argueably a freer flowing air filter or exhuast could also produce similar results.

I found going down 1 size on the pilot air jet to work very well with the stock needles shimmed .030", then I set the idle mixture screw at 7/8 turn out (your bike and results can vary)~~but you need to start with carbs that are actually completely cleaned.

Drill the idle mixture screw cap and clean out the chips etc
Remove those screws ( spring, washer and o-ring)and clean the tips
Clean the passageway (multiple holes into the venturi on both sides of the throttle plate)~carb cleaner and compressed air is "ok", then if that is all you are doing (no change in pilot air jet etc)you can richen up the idle to your hearts desire and the off idle mixture some by having that idle mixture screw set further out than it was....if it was 2.25 turns out-reset it at 3 turns out
Best bet is always to use a gas anylizer, but for some general adjustment and to get "close enough" this should work...

[x-Drag Racer]

Thank you for your imput Riverszzr. I was kind of rough with the stick coils thinking one got damaged but when choke was pulled open the engine reved up with no miss. It looks like the carbs will have to be pulled. I know how to work on Holley carbs but don't know anything about these little buggers.

[rayzzr]

Take a digital camera and document everything you do step by step, remove all of the rubber bits, then use some decent carb cleaner like Berrymans B12 (get the can with the nozzle). Blow them dry with an air hose if you have one, then reassemble. If you forget how, remember you took 'notes' with the digital camera.

I have used this to do a lot of different jobs on my bikes, and it is really handy. I have done carb syncs, cleanings, valve checks - you name it, following that simple guideline of documenting what I was doing.

[x-Drag Racer]

Do the carbs have to be removed? This isn't clear in the instructions.

[jeffo8]

yes

[x-Drag Racer]

Originally Posted by jeffo8

yes

Thank Ye Jeffo8

[ZZRrocket]

Originally Posted by x-Drag Racer

Do the carbs have to be removed? This isn't clear in the instructions.

And just how do plan on completely cleaning the carbs without completely taking them apart?? Rayzzr's instructions look clear enough to me. If you spray carb cleaner on some of the rubber parts it will damage them. Then you just cost yourself a bunch of money replacing them.

Ray and I have ripped carbs out of my zzr in camp at night and re-jetted with four others holding flashlights. We didn't lose one part. We even did a carb sync in the dark. We've had the carbs out of my zzr at least two or three times and he's re-jetted his zzr I believe three times.

[x-Drag Racer]

Originally Posted by ZZRrocket

And just how do plan on completely cleaning the carbs without completely taking them apart?? Rayzzr's instructions look clear enough to me. If you spray carb cleaner on some of the rubber parts it will damage them. Then you just cost yourself a bunch of money replacing them.

Ray and I have ripped carbs out of my zzr in camp at night and re-jetted with four others holding flashlights. We didn't lose one part. We even did a carb sync in the dark. We've had the carbs out of my zzr at least two or three times and he's re-jetted his zzr I believe three times.

That says a lot for the advantages of modern fuel injection! The ZZR 600 is still a great bike!

[x-Drag Racer]

I installed the Dyno Jet Stage I kit and it really made a difference the way the bike runs now. It idles smoother and accelerates quite well but I would like to do some fine tuning with the needles spacers. As per instructions, the nedles c-clip is set on the third groove from the top and the stock spacer is used. The acceleration needs some minor tweaking low down but it might be the Muzzy full exhaust system and low revs that is causing it. I used the DJ124 on the inside and the DJ122 on the outside but a trip to the dyno is the only way for sure to tell if the fuel/air ratio is right.