91' XJ600S misfire at idle on 2 cylinders

Hello everyone, My first post- Im new to street bikes as my friend gave me his 91' XJ600S due to him buying a ZX10 Anyway, this bike is a Cali model and has been in storeage for 5 years with fuel in the system. I cleaned the carbs, main and pilot jets are now clear except this cali model does not have a pilot air screw to clean or even one at all. This bike now misfires at idle on 2 cylinders but cleans up well after 1/4 throttle, my friend said it idled like this from day one- but I think he is crazy. Please click the video below as i think its way to rough. Note in the video you can here the misfire of the cylinder really well when i place my hand behind the pipe- and when i put choke on halfway threw the video the extra fuel causes the engine to smooth out and race to 4,000RPM.... please let me know what I need to clean out to get my idle smooth. Thanks, Joe

 

25 views, im thinking this is a normal idle?

 

Welcome to the site Jthumper.

I went to Yamaha's web site to check out the carbs on your bike and could not find a listing for a 1991 XJ600.

I did find a 1992 XJ600SD Seca II and below is a cropped section of the parts blow up. They show the typical plug # 28 covering the pilot screw set # 5.

There is only one set of carbs listed with an insert of a few extra hoses for the California model.

I would check your carbs in the area shown on the parts listing and look for that cap, under it you will find the adjustment screw.

 

Did you say, "Gave You?"

WOW! nice ride

welcome to the best bike info site on the net.

Cant say I can hear the miss!?!? Maybe these cheezy speakers.

 

Did you say, "Gave You?"

WOW! nice ride

welcome to the best bike info site on the net.

Cant say I can hear the miss!?!? Maybe these cheezy speakers.

 

Ok I saw video but i couldn't figure anything wrong.
Maybe I am hearing impired

If she is misfiring check pilot mixture screws. They can be reason for low rpm misfiring. They should be covered with some type of plug on your bike. They are located on aft side of carb under float chamber near carb outlet (Mikuni BDST 28 on my bike, on your they should be Mikuni BDS26 according to that previously posted drawing). Turn one screw in until fully seated (don't force it!!!) and count turns. Write it down. Turn it out at exactly same setting. Repeat for all 4 carbs. Take care not to mix up settings.

As much as I could found, those XJ since 1991 or '92 have very lean idle mixture (ecology) which causes rough idle and misfiring on all cylinders. Try to enrich mixture by 1/4 on all carbs. Repeat until you get steady idle without missfiring. Colortune will be of great help. After additional opening of all mixture screws you will probably have to reduce idle speed with idle screw located between carb No. 2&3.
I set up my XJ properly for first time after I got Colortune.

Check this topic, it may help:
http://xjbikes.com/Forums/viewtopic/t=5396.html

 

thanks everyone, yeah its lean throught the entire range but idle is worst as something is clogged on those 2 cylinders as i can remove the spark plug caps while its running with zero change in RPM. Looks like I must pull the fuel tank and air filter to get in there?

 

It would be helpful to share with us which cylinders do misfire

Can You smell gasoline from exhaust? Don't sniff to much, be careful :roll:

It is not good idea to pull spark plug cap and leave it like that while engine is running. That way you can damage electric circuits...

To gain access to carbs remove seat. Leave petcock at "on" or "res" position to prevent gasoline for pouring out. Remove petcocks handle (screw in middle), disconnect vacuum hose from petcock (smaller diameter), disconnect fuel line from petcock (larger diameter hose). Remove small M8 hex screw from front top side of fuel tank (just under top joke) and larger M12 from aft side (which keeps seat holder on place). Be careful with this seat holder because it probably will start to turn so hold it with something. Before removing tank from bike, there is overflow hose connected under tank on aft left side, just behind petcock.

I hope this will help

Do check everything else before messing with carbs. Have You checked intake rubber boots? Usually they become porous after 10 years or so. Maybe there is heavy air leak at them...

 

Maybe pilot screws are fuc... up.
Some people like to touch stuff
Try to check position of screws first. I still think that that is the initial and easiest idea.
:|

 

thanks everyone, he bought the bike new- so everything has never been touched and it sat since 2002 with fuel in it, I have had the entire carb rack off and removed the gelled fuel from the carb bowls- these carbs are close to my quad's 37mm carb just more of them and smaller. I have clenaed the main and pilot jets and float valve. its the 2 outside cylinders that are dead below 1/4 throttle, so im sure its the pilot screw with gum in the passageways... gotta love it, so on this carb- is turning the pilot screw in lean and out rich? I also have experence with CR250R's and they are a AIR crew so when you turn them in, its rich as it blocked air.
Thanks, Joe

 

just returned from my first ride on pavement, wow i must admit that i have never wached the road so close! The carbs clean up well at throttle. Question- im new to street bikes but this thing sure rev's hard at 70MPH, im like at 4,000+ RPM with alot of vibration... I also had alot of spark knock and pining at lower speeds once the engine got hot, prob the lean condition on those 2 carbs? It doesnt even lift the front end when floored threw the gears, is this normal for this 600CC machine? My honda CRF450X dirt bike is twice as fast 0-60MPH

 

Did you sync the carbs?
That could be the problem if you had the carbs apart.

Also I recomensd the use of a ColorTune, makes all the difference in the world.

 

You're best bet is to remove the rack and strip it right down to Brass Tacks. You'll have to have the Anti-Tamper Plugs removes and the Mixture Screws Removed.

First you try having the rack Sonic-cleaned.
The bad news is ... sometimes the Sound Cleaning won't get the Pilot Fuel & Air Passages Cleaned on Horizontally configured Carbs with "Petro-fried" and fully impacted passageway.

The Old Fashioned Way would be to Boil them. Not always good for the Carbs and not always successful.

You may very well have to resort to having a Blind Plug drilled and "Excavating" the hardened fuel residue out of the passageway.

You may have someone recommend "The Cheat Method" of drilling into the passageway (away from the stock plug) ... and going after the clog with Pipe Cleaners.

A failed attempt at "Cheating-it" is going to add Pipe Cleaner to the already Fuel impacted passageway.

 

""Did you sync the carbs?
That could be the problem if you had the carbs apart.""

No, i didnt- i only pulled off the bowls- how does one snyc a carb? these are just vacuume slide carbs- they all open at the same time right?
I will see what I can do by simply takeing out the pilot screw and blasting cleaner in there- Im working 55 hours a week, so not alot of time

 

The Butterfly's on the Carbs need to be synchronized to allow the same flow of air drawn into the Carbs on the Intake Stroke.

The Slides should open at the same time; but a bike that's been sitting around for awhile gets attacked by oxidation and dried-up fuel that can cause the slides to become frozen or stick pretty badly.

To get the performance that bike is designed to provide, you really should take the Carbs off and Clean and Clean-tune them.

All the component parts and passages Cleaned right up and out.
The Emulsion Tubes and Bores Cleaned and scrubbed out.
The Diaphragm Piston Bore refinished and Polished to a fine, friction-free surface.

Then, flushed out.
Pilot Fuel and Air Passage ... Opened and Cleaned-out of any contaminate.
Main AIR Passage Clean and Flushed-out to get the most out of the Powerband as the Slide rises and lets Air through the Emulsion Tube to draw-up the Main FUEL Jet supply.

Most of all ... the Starting Circuit needs to be clean and free to have the bike start and run without hoping to have the Pilot System do it alone.

 

Bear in mind all that stuff Rick said, yep it needs to be done.

If you will search past threads you will find very useful and necessary info reguarding carb rebuild, sync, and colortuning.

Until you've done those things you probably will fight with making your bike run marginally but not very well.

The sync screws are on the linkage between the carbs there are 3 of them you will need sync sticks to get them all working equally, and yes I do realize they are vacuum diaphram valves (bt the way those valves need to be super polished to slide absolutly free in the carb body and so does the carb body.

There is some chance that the Blaster will but up some stuff and get you running again, but all this stuff will need to be dine sooner or later.

Your hoping for later, right?


Good Luck

 

There's a set of your Carbs on ebay ... right NOW.

Since you got the bike for free ... they be a dam good investment. If they get you going Burp-free ... well worth the money.

Then, you can have your Carbs Cleaned and Staged.
No need to fool around.

Up and running upon arrival!

 

Hey Rick

Which carbs are compatable with an XJ700N ?
Can I buy carbs for a 650 or 1100 for parts on my 700?

 

Hi, new user here. I've been reading posts on here for three days now, and I still cant get a definite answer as to whether this screw set #5 is actually a pilot-air or a pilot-fuel screw. It appears from the dialogs to be a pilot-air, but then again it appears to be on the output end of the carb, which makes me think that its a pilot-fuel, and it looks like its on top of the pilot jet.

Which one is it? Before I go in there I want to have an idea of which way it will need to be turned to get my California lean condition richened up.

 

I want to say that all these bikes are pilot fuel.