Today's troubleshooting question...

Okay. I got the bike running, but it still bogs down after a while. Plugs are sooty. While I don't see anything coming out of the pipes, if I hold my hand near the exhaust, I get black sooty specks on my hand. Two questions:

1) Although I blew out the air filter with my air compressor, I am assuming that these two symptoms indicate that rather than a fuel problem, I'm dealing with an air problem. Correct?

2)If so, what's the next step? I don't think I have cracked intake plugs (or whatever they're called coming from the air box or from the carbs to the engine), but that's all I've checked.

 

Sooty plugs would indicate a rich mixture. Either mixture screw settings, mis-adjusted floats, leaking float valves or restrickted air flow.

You blew out the air filter, but how dirty is it?

Maybe time for the colortune.
Check the float levels.
Get a new air filter, or run without the air filter(not recommended)in a clean enviroment. and see if it makes a difference.
Good luck

 

I'll chip in on what Rich just threw at you. Get a new airfilter, if nothing else you have a spare you will use in due time. I would not run without one as even a brand new filter provides restriction to flow that the carburetors have been engineered (jetted) to deal with. But Rich is right on the nose so let's hear what you find when you apply the list of suggestions to your bike.

 

While we're at it, here's another REALLY dumb question I came up with as I was getting ready to check the float levels yet again..

There's a clear plastic type hose running from the tank to the carbs, the vacuum hose thingy. Can you guys tell me anywhere else on the bike that a clear hose would be located, because I swear this other hose I just found came off the bike the first time I took it apart...

 

Shouldn't be using clear hoses on vacuum lines. They are not tough enough to withstand the vacuum. They will suck in on themselves and restrict airflow.

Unless PO has used clear hoses on the fuel lines then normally the only other place you will find a clear hose is on the battery breather.

 

Hmmm...perhaps we have the problem here. I'll take care of that.

 

Well, I'm just about at the end of my rope here. No matter what I try, it still starts and runs on choke, but refuses to run when I take the choke off. I'm about this far from just parting the damn thing out on eBay...

 

All i can say is "the carbs need doin"

 

The choke is an enrichment circuit so it works by adding fuel to enrich the mixture. If you are checking your plugs with the choke on then all you will get are sooty plugs.
If it runs with the choke on then it needs more fuel to keep running. That would mean lean carbs due to mixture screws, float level too low, inline fuel filter clogged, vacuum line restricted and not allowing fuel to flow from the petcock, sediment in the tank or carb bowls restricting fuel passages, or just plain dirty carbs.
Best thing to do at this point is a colortune.

 

Have you at least 'drained' the carb bowls there is a small phillip[s headed screw on the bowl bottoms put there for the purpose. All are reasonably easily accesible . they are intended to be Oftem this will drain out the worst of the accumulated crud deposited there. BUT if you find evidence of stuff coming out then it would be clever to remove the carb assembly and clean out the float bowls carefully. The carbs are bolted to gether as a unit, so no adjustments are lost while doing this.

 

Oh, yeah. I've taken these carbs apart several times. The one thing I can guarantee are that the carbs are clean. I should probably recheck my float levels again, and I admit I haven't done a thing with the mixture screws. The float levels are more likely, as the bike ran well at one time. I can't help but think the problem is something I did. (Oops...there I go "assuming" again! )

 

One more addition: After I try and fail to get the bike to run without the choke, if I check by pulling that drain screw out a ways (actually mine's a hex bolt), there is definitely gas in the bowl. I just don't see fuel to the carbs as the problem.

 

If you didn't pull out the mixture screws when you cleaned the carbs, the carbs are not clean.
Pull them again and completely dissasemble them.
Pull all the jets, including the emulsion tube the needle slides down into.
Pull the mixture screws, there are springs, tiny washers, and tiny o-rings on them, so be careful.
If you plan on soaking the carb bodies, dissasemble the throttle shafts and pull them, as the throttle shaft seals will be destroyed in the soak.
If you are not soaking them, let the carb cleaner soak in all the passages before blowing them out with compressed air. I prefer to repeat this process several times.

Carbs are too finicky to do a half job on, it's easiest to get it done right the first time.

Nachoman

 

You'll have to dive-in to those carbs again. Check the slim brass extension tubes ... (Siphon tubes) ... that extend down into the float bowl well. The Siphon Tubes need to be perfectly clean and unobstructed. Likewise ... the Metering Ports ... at the bottom of the Float Bowl Well ... need to be clean and unobstructed, too. Since these metering ports are some of the smallest metering ports in the rack ... it does not take much to foul or clog them. You'll need a tool that is small enough to fit those ports. Visit a well-stocked hardware store ... or ... a welding supply store and get a set of welding tip cleaners. The whole set is less than 5-bucks. There will be a cleaning probe in the set that perfectly fits every jet and metering port in the rack. Aside from fuel supply to the top-end ... you might check for a couple of other issues. Vacuum slides binding and vacuum diapragm leaks. They can "Leak" without being split or punctured. The leak happens when the top is replaced and the lip if the diapragm slips out of the channel. Good luck with it ... don't part it out! Be patient and put it on the hairy edge of fine tuning. It's just a matter of shaking-out all gremlins and tweaking the hell out of it! The XJ Engine is a screamer. And ... there's a few pitfalls in tuning one up that cam make YOU scream, too!
Be methodical and attack one issue at a time.

Rick Massey
Seca 900
750 Max

 

Thanks guys! I think that's just the pep talk I needed; it's back to the carbs again...

 

Okay. First rule of the noobie mechanic: "You're brand new at this; what makes you think you did it right???" One of the diaphrams either slipped out or pulled out of it's seat. (Rick: thanks for the tip on the welder tip cleaners for cleaning those darned holes! A bit under $4.00 at Home Dumpo, and I can actually get in there without worrying about screwing up those tiny holes!!)

So it's running now, but of course after taking the mixture screws out, I'm sure it REALLY needs the colortune treatment now. But heck, just hearing that engine run again without the choke is nice!

 

Forget the colortune ... pull the 4 piolt screws ... flush with carb cleaner ... oil threads on pilots ... insert ... screw IN -- EASY -- 'til they bottom-out.

Screw back OUT ... two and a half turns. 2.5 = Factory setting.
Run bike.
Bike runs good ... Ride!
Bike don't idle good?

Reset pilots to ... two and three quarter turns OUT

Idles? ... But a bit too rich???

Split the difference between two and a half and two and three quarters.

Go zooming. Colortune later.