High Idle Speed - 85 XJ700

Great Website! Glad to see there are other Yamaha XJ Fans out there.

16 years after I sold my first motorcyle (1985 Red Maxim 700). I found another one that is almost as nice as the one I mistakenly sold all those years ago. I basically found the same bike I sold. Same year, same color, approximately the same miles (13K) in a shed that has seen daylight for 9 years. The bike looks mint. I was so happy to have found and pick up for what I consider to be a steal. I am biased towards this bike so others may not agree!

I knew since it had been sitting so long it would have some problems getting going. I drained and replace all the fluids. Other than the gas all appears good. The gas was bad and so was the inside of the tank. I got the tank clean so, on to the carbs.

Took the rack off and cleaned as best as I could. Some jets were clogged but appears to be in decent shape after cleaning. Put them back on and is firing on all 4 cylinders but idles really high, around 5K. It sounds good but will not come down from there. When I rev it up past 5K it appears to come down to 5K as it should. I have some Seafoam mixed in the gas. The boots are in good shape as is the vacuum line going to the petcock. There is a turn knob on the bottom of the two middle carbs. This may be the idle adjustment knob. If so which way do I turn to decrease idle? Is there something else I should be doing to get this idle speed to a normal range.

Any advice would be appreciated, please note that I am self & wife proclaimed to be "Mechanically De-Clined". The carb thing has taken me many, many hours & lots of notes just to make sure I got off & on correctly.

 

Turn the idle screw counter clockwise to decrease the idle speed.
Does the idle come down when you engage the choke?
What did you set the idle mixture screws at when you cleaned the carbs?

Nachoman

 

I'm not a XJ700 savy person but I do believe your observation on the idle adjustment knob is correct. That is the location of the knob on my older 650 and 750. Nacho's advice is correct for adjustment. Good luck to you and welcome to the forum!

 

Thanks for the tips.

What did you set the idle mixture screws at when you cleaned the carbs?
I am guessing the Idle mixture screws are the ones towards the front of the carbs on the top. This may be the problem. #1 will not turn. It is locked in place and the slot for the screwdriver is non-existant, #2,3 & 4 are 2 turns out. it appears that #1 is backed out farther than that. I will have to try & get this out. Do you think they still sell these screws at dealerships?



Does the idle come down when you engage the choke? Yes, but then it slowly starts to die.

 

The "standard" for mixture screws is 2 1/2 turns back from bottom.

I had an issue with high idle after replacing the throttle cable. Evidently the new one is just slighty shorter than the original and was pulling the revs up to about 5K rpm. I tapped (bent) the throttle cable bracket on the carbs down to give plenty of slack in the cable. In this case "loose" is a good thing. You might also check that the adjuster screw for the throttle cable at the throttle is all the way in. And for that matter, double check that the bracket for the throttle cable on the carbs has been remounted properly, and the cable is seated correctly. The smallest pull on the cable will shoot the revs way up.

Z

 

Those are the correct screws, right next to the choke plungers.
Like 'zilla said 2 1/2 turns from LIGHTLY seated is stock, although there may be some fudge factor in there.
Your results may vary.
Pulling the ckoke and having the Idle go down is a lean indicator.
Fill the offending hole with wd40 or the like and let it sit overnight.
Then line a screwdrive up with the old grove and give it a few light taps with a hammer.
This should loosen the screw an make enough of a grove to get the screw out.
Then cut a new groove in the head.
That should get you back in business.

Nachoman

 

this sounds very similar to what was hapening on my bike. I havent quite solved it yet, but im 99% sure its the butterfly shaft seals on mine. Just waiting for the fuel o-rings, before i do anything about it.

If adjusting the idle screw doesnt bring it down to normal iw ould say there is vacuum leaking past your butterfly valves,

also check to make sure throttle is releasing all the way.

 

Thanks guys for your advice!!

I got her running like a champ. I do not know exactly what fixed the problem but here is what I did and it worked.

1) the #1 Carb Idle mixture screw would not come out or turn in. I could also not get a screwdriver in at all. I let WD-40 soak overnight then I took a very small carbide burr in a Dremel and made a new slot in the screw while it was in the carb. (very carefully). This gave me enough of a slot to get a driver into. Then I made sure all were backed out 2.5 turns.

I made sure the Choke and throttle cables were correct.

Put the tank back on hooked everything up and crossed my fingers.

Fired right up and now idles smooth at about 1100. I appreciate all your comments & advice to help me figure out how to get this machine back on the street where it belongs.

 

Glad to hear she's back where she belongs. Good job Ringbat!

Z

 

okay well i know that this is an old thred...really old. but i recently had the same problem. dont touch the idle or syncing screws. instead cheak to make sure your all sealed up. no airleaks after the carbs. mainly the boots. thats ware my leak was. i had to replace the gaskets and boom. fixed the problem. an easy way to test is to get a can of carb cleaner and spary it all around the intake side of the motor. in a semi systematic manner. and if it idle up. thats ware the leak is. well i doubt anybody will read this. but if you do. hope it helps.