Either high idle or die

My XJ700X with Mikuni carbs is acting up... But I got it running! I couldn't care less that it runs poor! It is running! :lol: I did do a little dance!

But on to the problems:

It will idle at 1000rpm occassionaly - and then will jump up to 2000rpm or 500rpm. But I would not say it is hunting. All of this happens very slow - It will run at 500rpm one time I start the bike, and then next time at 2000rpm with no adjustments! Adjusting the idle screw gets me one of these two options usually. It does seem to idle better after warming up.

Also, it is very slow to come down from a high rpm under no load. Like if I rev it to 5,000 rpm, it will take about 4 seconds to come down to 1,000rpm. My local bike shop said that was because my carbs were not synched. This makes sense to me.

Would not having the carbs synched cause both of the above conditions? It seems to me like they would. I am just holding out for the North Texas Carb Clinic! Here I come Rex!

 

Yes it could cause these symptoms. What have you done to the carbs so far to get it running? It will help Rex to know so he is prepared at the NTCC. I will be there too as well as a "WeAreZilla". At least I hope he's there. Sounds like we need all experienced guys from last year!
Your symptoms are comon to an unsynced problem which allows too much air into one or more carbs. Running better once warm is another sign of a lean condition. I would use the unlit propane torch trick and check for any leaks around the intakes or airboots. This is done simply opening the valve of the torch and NOT lighting it, then with the engine running move the tip i and around the intakes listening for a change in RPM, either up or down. This would indicate an air leak and may be most of your problem. Tighten the clamps or what ever is needed to seal the leak and we'll see ya at the NTCC!

 

This bike was not running when I bought it. It has been sitting for about 6 years. I did a valve adjustment. Compression was good when I put it back together. Also - I cleaned out the carbs really good, and put in new needle valves (float valves). I did a rough sync with a vacuum gauge and an aquarium 4-way valve. I call it rough, because the valves were dinky plastic, and I know they were leaking a little. Other than that, I haven't done anything.

I wonder if one of my spark plugs is not working? Also - I wonder if one of my idle jets is fouled up? This would make sense, because my rpms stay at about 500, until I screw down on the idle speed screw enough, and then it all the sudden jumps up to 2000rpm. Does this make sense? I guess this could also be from having them unsynced.

 

If you didn't install new plugs I definately would. An unsynced condition is an imblance of fuel/air mixture in the carb bank. This is why we use the colortune plug and the carb sticks. One for the fuel and one for the air. IF you cleaned the carbs well then install an inline fuel filter. They are at your bike shop and are about $2. This will keep those pilot jets clean. If you don't have a colortune plug you can't check the mixture well. Most of those who have tried vacuum gauges don't like them. They will work but have to be restricted just right to keep the gauge from jumping around wildly and to let enough vacuum in to get an accurate read. We can take care of this at the NTCC. However if the carbs are not clean and one jet is plugged then it would be best to have that resolved before the NTCC.

 

You are right! I did buy new plugs, but I plan on pulling them today and checking the spark. I will also be doing a compression test, and checking the vacuum on each intake.

I do have a fuel filter, and I am 99% confident that the carbs were clean a month ago. However, I let them sit with gas in them on the work bench. But... I filled them with WD-40 also, so I thought that would stabilize the gas. If the above checks don't reveal anything, I will be pulling the carbs again. :x

 

I have to ammend my own post. For a while there I thought "WeAreZilla" was Gary in Austin who "was" at the NTCC last year. I checked his photo album yesterday and realized my mistake. Sorry about getting lost in cyber space guys!

 

ususally high idle such as that is cause by improper air/fuel mix. Running lean will cause the idles to take their time in coming back to normal.

Hope this helps!

 

Running lean causes high idle or a while for rpms to come down? That doesn't make sense to me... It seems like with less fuel, the bike would have less power, and the rpms would come down quicker than normal.

The thing that does make sense is that one cylinder is making more power than the others due to not being syncronized, and this would keep rpms higher for longer.

Can you explain the logic?

 

Sorry, my bad, that should have been running rich...too much fuel. I am on vicodin today for my knee, so my brain not worky so well. With too much fuel, it takes a bit to lean back out after a throttle, so the RPMS hang for a bit as if the choke is on. It should come back down, but may take a bit longer. Lean out your carbs via the air or fuel mixture screw and it should fix the problem. Yes, carb sync being off could cause this as well as the slide on a carb could be too low which doesn't let enough air in, so again, you get too much fuel.

Good catch Richard. Thanks!

 

So to elaborate running rich would mean you would need to turn the mixture (the ones that are capped) screws in and NOT out , correct?

 

Correct, in leans the mixture, out richens it.

 

That makes sense now. I will have to consider this... It is going to be kind of hard to work on the bike without knowing if I am rich or lean though. I am going to start with the sync, and if that doesn't fix it, start playing with mixtures. I appreciate the responses though! Good info!

 

A colortune plug is a good way to tell if each cylinder is running rich or lean. I personally have not used one, but I have one on order as I have heard that there is nothing better.

 

I want one! But I figure that I will wait until after the NTCC.

 

This has never been a problem for me as I'm neither. Oh, wait; you're talking about the bike...

 

That is too funny!

 

A lean mixture can cause the high idle and slow return to idle. I struggled with this also but remember these are CV carbs with the diaphragm sliders. When one rises up due to air leaking in fuel can be sucked in through the pilot jet.

 

Well, I just finished synchronizing the carbs. Stupid aquarium 4-way valve! It must not have been working right, because my number 1 carb was off by 2inHg! When I fixed this, it idled really smooth! I did another dance!

Now, the idle is fixed!

But now it does this and I don't know if it normal:
When I snap the throttle from idle really hard, the engine hesitates for a split second, and then revs really high. Is it normal to have a hesitation? I think it is, but I have never heard one of these bikes run right. :lol:
Remember also - I have an X with five valves, I think this would make a difference too! maybe more hesitation than with two valves? What do you guys think?

Also, after I release the throttle, the rpms hover at 2,000 for about a second or two before returning to 1,000rpms. Is this normal?

 

The other thing that I noticed was that it was smoking ever so slightly out of the right muffler when reved REALLY high - like 8,000rpm. Do you think this might be a rich or lean condition, or oil leaking? The smoke dissapated as soon as leaving the muffler - which leads me to believe it is not oil. Is this faulty logic?

 

Probably just a little lean still. You could open the pilot screws about an 1/8 of a turn and see if that does it. On the smoke I bet it is just condensation in the collector. If it is white then it is moisture, blue means oil and black means fuel from a rich mixture.

 

Tazzman, where is it you ordered your colortune plug from?

 

I got mine from www.etoolcart.com

 

Thanks Rich,ur all over it today!

 

From when my XJ750 USED to run right, I would say, no, neither of these is normal. Used to be a throttle snap brought an immediate pop in the revs and letting go brough it back to idle right-quick as well.

That said, my bike is currently behaving just like yours. Last plug check says I'm way lean (ashy white). My colortune plug is acting up and I don't have my YICS tool yet, so I'm going to hold off on running it much, but I do believe my latest carb cleaning did some good. With some tweaking an cajoling and tweaking, sometimes I can get a smooth idle from it. Which is more than I could say last week.

I just hope I dont' have any vacuum leaks. Just just checked the boots and replaced the header gaskets, so it shouldn't be that, but it might be those butterfly shafts.

We'll see. Good luck with yours.

 

Well, last night I was getting rock steady idle at 1,000 after synchronization. But today, on the way to work, my idle was 2,500? What is that all about? Something to do with cooling down? It was not running rough at all... So now I don't know what gives.

 

Yup, that's exactly what I'm getting. I can dial it in for a specific situation (cool, medium, or warm) but vary from that and it gets weird.

I'm waiting for my YICS tool and new colortune plug before I bang my head too much.

 

switz, I got my colortune from a company in Florida. It is an automotive shop called Eastmans. They are pretty good. And to whomever said it could be lean because they are CV Carbs is also correct. Another point I didn't consider as I have spent a lot of time lately working with Mikuni Slide Carbs.

 

Rich, Oblivion, my bike has same prob... Idle creep from 1000 rpm to 2500 rpm when warm. RPM does not come back down in between shifts very well.Im thinking about starting with carb rebuild and boots and going from there.

 

Don't forget the shaft seals, good source for a leak.
QR-011 quad rings are what you need

 

I did the propane trick, and did not find any vacuum leaks. I am thinking it may have something to do with idle mixture? Maybe synchronization. I just don't know. I need a colortune and mercury sticks!

 

Yep, that's exactly right! Mixture affects sync and vise-versa! You have to get the fuel right to get the air right and the air right to get the fuel right...or was it the other way around?

 

Well I just broke down and got a rebuild kit and new set of boots for $138.00 at partsnmore. Went ahead and splurged on the McCaster Carr O- rings as well. Hope this takes care of it.

 

Switz1,
You said you got "a" rebuild kit. I hope you got 4. You'll need one for each carb.

 

Yup got 4

 

I hope to get new boots for mine this winter.
This past winter when I had the money, partsnmore were out of stock on the boots, just my luck.
Good luck with the build and feel free to ask if you run into any problems.

 

Thanks, I may need it... Got the Haynes man. and the XJ cd coming soon I hope

 

Well, today on the ride home, it ran like a dream. Rock steady idle, and it hovers around 2,000 rpm for about a second before coming down. I actually like this, because when you twist the throttle again, you get a quicker response than from idle.

I can't wait to get it really tuned!

Thanks for the help guys!