Been awhile

[audijunky]

Hello All, I hven't posted in sometime, I am still livin, bought a 05 zrx1200 and the ol 11 got put on the back burner. Started tinkering again with it again. As you have heard 100 times ( from myself and others) I am having low RPM issues( below 5k), stumblin and grumblin, back firing on deceleration. pulled the carbs, adjusted all floats to exactly 26.5 mm, set needles to 3 slots from the top, and the rest of the mods are in the signature. SO rode it for a couple minutes, idling good, revs with no load good and smooth. stumbles below 5k with load. checked plugs for color, #1 perfect chocolate color, #2 rich sooty black, #4 rich sooty black, and #3 lean. Carbs were all set the same. had a sync done under 200 miles ago. not sure where I got the mix screws set at but they were all set the same, except for #2 which I had turned in because I had to drill out a broken mix screw tip, which enlarged the hole. Any Ideas why my plugs are so off?
thanks

PS gonna be my drag bike and I am looking to blow through turbocharge w/carbs. did some searching here and elsewhere. I know, I know much cheaper and easier to get a modern sportbike, but it is just not the same as doing it yourself on an old beast. Any help in this area would be greatly appreciated as well

[tarzan]

I would guess that #3 has a plugged idle circuit.The other three being rich may be the needle being up too high.
I would put some seafoam in the tank and let it run for a few minutes to get the seafoam in the carbs.Then let it sit for a day or two.Then ride that tank out.
Then eavaluate.
Rick

[Cobia]

I had similar a problem

Audi,
I had a similar problem with my XJ, except that the stumble was between 1.5k and 2.5k rpm's. Have you cleaned your pilot jets yet? They live under your main jets. You need to take out the diaphram/slide needles first, then unscrew the mains and with a dowel of appropriate size tap the pilots out into the throat of the carbs. The mains screw into the top of the pilots.
Be careful when putting them back in, there's a notch at the top of the pilots that corresponds to a pin at the top of the tunnel they fit in.

Good luck, I hope this solves your issue. I actually replaced mine with larger ones and that solved my issue.

[audijunky]

thanks guys, I will take another look at the cleanliness, however I have had these suckers apart and cleaned more times than I can remember. And Cobia it sounds like you are describing the brass tube with holes in it (cant remember exactly what its called) the needle slides into. from my understanding the pilot jet is under the screw in the tower next to the main jet??

[audijunky]

Emulsion tubes, thats what they're called

[Cobia]

You're right, they are called emulsion tubes. Although in the yamaha manuals they are called main nozzles. And those are the ones that I'm talking about. Most ppl don't know they are there and don't clean them.
I did go up a couple of sizes on my pilots on the XJ to cure my symptoms, which were similar to yours except in a narrower rpm range.

[thewiz]

Also called ...

it sounds like you are describing the brass tube with holes in it (cant remember exactly what its called) the needle slides into

Needle jets as well ... just to confound things some

Audi ... If you haven't already done so, I would run a pick up coil wire test too ... eliminate the ignition first cuz it sounds like you've been through the carbs pretty well.

[audijunky]

Is that the one were you solder bigger wire to the leads under the left hand side cover (timing plate area) if so, than that has been done, and was actually done backwars so I had to swithc around my spark plug caps (4-1) and 2-3) . and the problems remained the same.

[audijunky]

I actually think my 4-2 straight header has something to do with it, I realy am looking for suggestions on why the plug colors are so different. gonna pull the carbs again and go through with a fine tooth comb.

[cywelchjr]

Don't just adjust by number of turns out on the idle mixture screws. Adjust each one for highest idle, then back in just a shade, they may not be at the starting point, and they likely will NOT be all the same. Remember that the idle circuit handles up to about 3.5k and affects mixture at all settings, so make SURE it's right before anything else is adjusted.

[thewiz]

Have you tested ...

The primary and secondary ignition coil wiring yet? Original coils and wires? You are also 5 sizes up on the main jet and one up on the pilots .... Unless it is an exhaust that I'm unfamiliar with, a 4/2, even without the baffles, isn't really a header per se .... so the only performance engine mod I can identify is the PODS ... so I'm naturally doubtful that all that extra jetting is really helping... could turn out that it is hurting.

Mikuni, as well as others I'm sure, all say that a straight pipe is hard if not impossible to tune for the street. So you maybe oughta' decide if you wanna' tune it for the track or street. If you're thinking 'street'....we are both probably thinking that some baffleing and hence additional back pressure would be helpful in tuning it. The backfiring is most likely comming from your lean cyl.

[petejw]

Hey Audi,
Good to see you back around.
With regards to the bike have you checked your valve clearances?
I had 3 intakes closed, once they were opened up (gapped correctly), solved all my low end problems and had perfect colour plugs, something i never had before,
also like you say, the 4 -2 open headers will give you troubles, might be worth while trying it with a cpl of mufflers on it.

[XJOK2PLAY]

I am still having low RPM issues( below 5k), stumblin and grumblin, back firing on deceleration.

Hi, Audi, and welcome back to the forum.

Just for clearification, when you say backfiring on decel, is it actual backfiring (explosions), or is more like popping on decel?

I had the popping on decel start in on mine recently, and discovered a major difference when just the idle speed was raised. if my idle was around 850-900, it would pop... very annoying. When I raised it to 1100-1200, it was cured. Noticed it causes a much slower drop in rpm... like when pulling up to a stop light. Tach holds around 2000 longer, then drops... eliminates the pop.
JAT

[audijunky]

thanks for all the replies guys, didn't see them over the weekend so I wasn't able to apply any yet. What I ddi do was swap out all my diaphrams and needles from a spare set of carbs I had purchased. WHen I original bought the bike and started cleaning the carbs I had used fine grit sand paper to clean the original needles, thought I had damaged them or altered them. So I swapped out , I noticed the numbers were different on the other ones,they were a few mm's longer. anyway raised the clips on those to the 4th position down and installed. Now it really runs bad even in the top end, low end felt a little better though, when winding it out it feels lean still (flat).??? Gonna have to do the tune by ear I guess for the idle mix screws. gonna put the old needles back in too so atleast I can have the top end. And I am trying to get this bike on the strip. Gonna make it my track bike. Got an 05 ZRX1200 for the street, twisties, Thanks for the advice, looking foeward to getting this monster right

[audijunky]

Hey Audi,
Good to see you back around.
With regards to the bike have you checked your valve clearances?
I had 3 intakes closed, once they were opened up (gapped correctly), solved all my low end problems and had perfect colour plugs, something i never had before,
also like you say, the 4 -2 open headers will give you troubles, might be worth while trying it with a cpl of mufflers on it.

I have done a valve adjustment under 200 miles ago, thanks for the thoughts though