Idle Frustrations

Ok...almost feel beatin down over this bike and I've never struggled so much be it bike or car...just seems hard to figure it out.

First what's been done, carbs house of clean preformed, throttle shaft seals replaced, float levels set and double checked..if its off by 1mm I'd accept that..but still just does not add up.

Idles fine when holding throttle but using the idle adustment either a has almost no effect, or will put the idle at 4k then back down a quarter at a time will eventually just drop all the way down to nothing and die.

had it at idle at one point so synced em and was doing good...color tuned still a bit off, but very close.

New plugs gapped right, no air leaks found, running stock airbox. Even road this weekend, good throttle ressponse..got back running good...then tried to run again this am and wouldn't idle after warm up. just at a stand still now. any insight?? Really hitting a wall with this project.

 

Try setting all your mixture screws 2 1/2 turns out from seated...I had a different problem...all my plugs were different colors and now they are all perfect. Don't know if it will fix your problem but its worth a try.

Good Luck!

 

Sounds like it might need a valve adjustment, or it's still a sync issue (or both, since out of spec valves will throw off your vac sync.)

What method are you using to vacuum sync the carbs?

 

Using a 4 vac sync setup, adjustable restrictors for a perfect view...plan right now is to take a look at the valves, had planned on doing so, just kind of suprised me it would have this kind of an effect on a motor with 15k on it...I realize they need to be checked and could be a bit off, but I assumed it would throw this big of a monkey wrench in things.

Guess I have to stay after it, but man I have to admit this project has pushed my normally great patience to its limits...I should have long been moving on to paint and fender mock up, but such is life...it was easy anyone could do it.


Had the idle screws set at 2.5 turns, but seemed to like being set at 3.5 which is closer to where they were from the factory.

 

SAVED by the bell! Hopefully anyway.

On the airheads, the original valve adjustment was to have been done at 3000 miles. Most owners ran the warranty period out time-wise long before they put 3K on the bike, so they didn't take it back to the dealer for an expensive procedure they didn't see a need for.

Adjustment interval is every 5000 miles after the initial 3000. As the bike changed hands, as long as it was running "ok" nobody ever bothered. How many miles have you added?

At 15K you are getting right to the point where if the valves have never been touched, you've got one or two that are critical (if you haven't burned one yet.)

I got my '83 with 7100 miles on it, valves untouched (thankfully.) Never done, not at 3000, never. Seven of the eight were tight, two getting critical. 7100 miles.

If yours have never been touched, you're 12K overdue. If they were done at 3000 like they should have been, you're only 7000 OVERdue.

So yes, it can and will have a major effect. And you'll need to re-sync after you adjust them.

Don't put it off any longer, you're jeopardizing your motor.

 

Is there a shim set to buy?

How long does it take to shim them in?

 

set the idle after it's good and warm, at least 10 min of riding, then when it's cold use the "choke" till it warms up

 

You generally do valve adjustments in two steps: Teardown, measure, order shims; replace shims. Kind of hard to buy a "set" without going broke.

How long does it take? A couple hours, total once you've done it a couple times.

Read: http://xjbikes.com/Forums/viewtopic/t=14827.html

And: http://xjbikes.com/Forums/viewtopic/t=29209.html

 

Hi. I've had the same problem with idling speed - I think most of us have, I think it's a symptom of this engine.

When adjusting the little wheel a quarter-turn at a time, allow a couple of seconds for your adjustment to take effect... I think there's some kind of built-in delay, or there seems to be.

Also check your mixtures (using the plug colour to judge). from the standard 2 and a half turns out.

After lumpy idling issues with mine, I adjusted one screw in a quarter turn and another in a half turn (one partially sooty and one sooty plug).

After doing that the bike seems to start up and idle more cleanly (time will tell).

PS. I re-shimmed my motor last year. If you're lucky some might swap positions, otherwise genuine Yamaha ones worked out around £8 each. Do them all at once - and you will need the shim tool.

PPS. I met a guy at a bike show last year who had owned his XJ from new. At 50-odd thousand miles he reckoned he'd never even lifted the cam cover, let alone changed any shims. It was still running.

With shims, the thing is that due to wear making things thinner rather than thicker, you're unlikely to get a valve not seating properly. The only problem you'd find would be a minute difference in valve opening/closing time (ie: less duration) which would be a problem if really slack.

Nige

 

Except that's incorrect, sorry. The shims and cams don't wear appreciably; that's not why regular checking and adjusting is needed.

What happens is the valves pound themselves into their seats, so as things wear, they tighten up, not get looser.

Once a valve gets to the point of being "dead" tight when cold, it won't seat properly once the motor is warmed up, and you end up burning a valve.

 

Go to your local bike shop with the shims you need to replace and 9 times out of 10 they will swap them for the ones you need for free.

The shop I go to said they haven't had anyone come in for the shims required for our bikes in a long time...hence them swapping with a smile!

 

I'll bow to your experience on that one Fitz..., though I'd have thought that valve-stem ends, both sides of the shim and the cam lobes would wear thinner too? I just know you're going to tell me that they are hardened to minimise wear.

Nige

 

Yep.

The "wear points" in the valve train are the valves themselves and the valve seats. So, as they wear, the valve clearances tighten up, counter-intuitive to what you'd assume.

Which is why checking clearances regularly is so important. As the clearances tighten, the valves are held open longer than they should be, decreasing compression, and eventually failing to seat fully; and that's when you burn a valve.

It really does work that way, too. I had one "getting quite close" valve the first time I did my '81; the next time I did the check, it had tightened beyond spec.

When I adjusted the clearances in my '83 for the first time at 7100 miles, seven of eight were tight. I'm interested to see where we are at the second check, at 12K.

One thing to note: This "pounding in" process seems to taper off as the motor ages; by that I mean once they've been through a couple of adjustments, they seem to "hold" for longer and longer. Once again, stressing the importance of the initial and follow-up checks, at 3000 and 5000 miles. You will find that fewer and fewer need actual adjusting with each subsequent check; but they have to be checked as specified or you're taking chances with the motor.

 

Check again for vacuum leaks. Take a can of carb cleaner and just start spraying around while the bike is running. If the RPM rises after you spray, then you found a vacuum leak. Spray the couplers between the carb and motor, spray the block, spray by the plugs, any head bolts, etc. I had a very similar problem and it turned out to be a vacuum leak.

 

:lol: Now Im looking forward to doing the shim work!

 

I think you have better local bike shops than I do. We have two big ones here in Colorado Springs. One sometimes will have a needed size shim in stock - better chances with the 13mm ones than the 29mm ones Yamaha uses. Even so, at least half the time they have to order it.

The other shop is very proud of the fact that they stock NOTHING for any bike older than 10 years. Since all the newer bikes use 9mm or so shims, that's all they stock.

The little shops don't stock much in the way of these kinds of parts, except one smaller one that's good for some used parts, some generic parts, and a lot of Harley parts.... still don't recall having much luck with shims there.

I got mine from Len.

 

I guess I am lucky then.

 

These bikes are not the only ones that use that size shim

 

I know that, and I didn't say they were. I didn't mean to confuse anyone on that. However, I still had better luck finding the 13mm ones my GPz uses in stock (at least used) than I did the 29mm ones the Seca uses.

But again, different shops, different cities (Colorado Springs is relatively small), different results.

I don't know how common it is to have a place like this (Rocky Mountain Cycle Plaza) that won't carry parts for or work on anything older than 10 years. (I forgot to mention before that they flat out will not work on old bikes.)

The other big place, Apex Sports, will work on older bikes, but only in the off season. In the summer they won't touch them. Period.

 

It is very common that bike shops wont work on the older bikes or stock the parts for them actually it is very rare that a shop will even touch one of these and to tell you the truth I do not really want anyone else touching any of my rides that includes my cars too