Hanging idle problem with Zak's bike. Old problem. Been through a lot.

So, here's everything we have ruled out. By the way, at one time Junior had the same problem and would not go away until the head was swapped.
89-00 2 jet carbs. So....

1. NO AIR LEAK - read on and you'll see why
2. Replaced gaskets on carb boots. No leak there.
3. Replaced can chain tensioned gasket (oil leak due to PO leaving half of an old gasket on it)
4. Lunchbox filter - swapped with brand new OEM 89-00 air box (yes, I have new old stock). Though carb set #1 did have backfire issues with both, but less with OEM air box.
5. Swapped carbs with a set just cleaned by PJ Motor Sports (set #2). Runs fine but still hanging idle. That rules out the carbs.
6. Lots of WD40 - no leaks.
7. Tried NGK and Brisk plugs. Same results.
8. Gas was new (took from one of my bikes)
9. Carbs have long mixture screws so we can easily adjust the mixture with the bike running. 1 turn to 4 turns results in no difference. Well, 3 turns helps slightly but ever so slightly. Both sets of carbs have the long mixture screws.


So, by
a) swapping carb sets
b) swapping air boxes
c) new carb boots

We have ruled out carbs, air box and all air leaks as possibilities.

Supposedly problem started when a cam journal was stripped and then repaired.

Remember Junior had the same problem and it went away when heads were swapped.

Ideas? What in the head could cause this?

Tomorrow we will swap heads to see. We will try lunchbox with carbs #2 (cleaned by PJ Motorsports) to see if jetting was the cause of backfiring, though that is a separate issue not related to the hangining idle.

Runs fine otherwise, or no? Also, what work was being done when the journal bolt got stripped? I imagine it wasn't opened up just for fun.

Zak can fill in more.
But he did say there was hanging idle BEFORE the head was worked on. Hanging idle was the reason to open things up.
So a few months later and work, and it is back to where it was.

So much has been swapped and fixed. One of the advantages of more parts than a dealer at the West Seattle Bike Cave.

Right now all I can relate to is the same unknown issue on Junior that did not go away until the head was swapped.

Thoughts on what in a head can cause this?

Also, valves were checked.
As I recall about 0.05 on the intakes and 0.07 on the exhausts.

( probably unrelated) but during any repairs could any MINUTE metallic fragments got in where it shouldn't have been? carbs ruled out, what about floats, they as they should be?

2 sets of carbs. One set just cleaned by the pros at PJ Motorsports.

As far as being in the head... valve timing/seat condition/sticking and head gasket should all be verifiable with a compression test. Outside of that I can't think of what in the head would do it.

With your fancy idle mix screws -- were those a common variable in both sets of carbs? I'm thinking if those leak, it could cause the problems as well as explaining why adjusting them doesn't make a huge difference. Also make sure the o-rings are good and  it goes screw-spring-washer-oring with the spring ground flat on both ends for even pressure.

You could try disconnecting the throttle cable at the carb end and try running the bike without it. If it idles correctly you can suspect the cable or twist grip is binding and holding the carb open 

Supposedly problem started when a cam journal was stripped and then repaired.

Remember Junior had the same problem and it went away when heads were swapped.

The above comments are screaming `cracked head` to me   


Get yourself a `dye-pen` kit, you will love it.......just follow the instructions TO THE LETTER!

http://www.rocol.com/products/non-destructive-testing-kit

So I ran into a similar issue on my 74 tx500, went though every thing for a few months and almost gave up on it. Between mixture adjustment, a faulty choke and ignition timing. Most of my issue was the faulty choke, however the points still played into it.

I know these bikes don't use points but it wouldn't be a bad idea to inspect the ignition system.


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A TX500 eh?

Now that WAS a bike with a reputation for cracked heads 

The problem occurred before the head was worked on. The hanging idle was the reason the head and carbs were worked on.

Would a cracked head show up in a compression test sledge?

Things are pointing to the head. Something happens as the bike warms up. Cold - OK. Hot - hangs.
We're pulling the head.

Twp points:
1. Problem started afterthe head was repaired
2. At first, there was a leak around the head

So, wither damaged head or bad seal between it and the jugs.

Oh, no....a solution looking for a problem....hope it all works out OK.

One other thing. When head put on before it did not get torqued down enough and leaked.
Then it was torqued.

We removed the head. The gasket was oily.

Theory: Re-torquing an oily head did not result in correct torquing because oil was between the head and gasket. Torquing done when cold.

Now, when motor is cold it was OK. Hot it hung. So maybe when it heats up, the head/jug seating opens up due to that old oil there? Then when cold, it closes up and engine runs OK again.

Thoughts?

I had a hanging idle on my 97 GS that I bought new in Mar 99. The first summer it starting hanging when hot.  I managed to eliminate it by adjusting the idle speed knob.  I would turn down the idle speed as slowly as possible until the fast idle just fell off without going any further.  Adjusted it several times that summer and it never did it again after that summer for the rest of the 80k miles I putt on it.  Never had the problem on my 02 GS with the 3 circuit carbs that replaced the 97 in 03.  I always attributed the problem to the leaness of that 2 circuit 97.  Both bikes went all the way with stock carbs.

Quote from: adidasguy on January 26, 2014, 05:15:38 PM
One other thing. When head put on before it did not get torqued down enough and leaked.
Then it was torqued.

We removed the head. The gasket was oily.

Theory: Re-torquing an oily head did not result in correct torquing because oil was between the head and gasket. Torquing done when cold.

Now, when motor is cold it was OK. Hot it hung. So maybe when it heats up, the head/jug seating opens up due to that old oil there? Then when cold, it closes up and engine runs OK again.

Thoughts?

Possible... but the studs are steel, correct? Steel studs with an aluminum block/cylinder/head should result in tightening when it heats up. I feel like any form of leakage through the head gasket enough to be noticeable in performance would easily show on a compression test.

I agree with what you say. Just all the things we have swapped out and it still hangs when hot points to the head - and since it started after the head had a bolt helicoiled and the head put back on.
We are planning to put it back (Saturday) on with all new OEM gaskets and insure all surfaces are spotless.

On order is a leak down test tool,valve lapping tools, as well as spare piston rings and other engine parts. (We have a few engines for upcoming projects so parts on hand will help if not needed now, and not go to waste).

Quote from: Badot on January 26, 2014, 11:40:11 AM
Would a cracked head show up in a compression test sledge?

Depends.....It would have to be in the chamber and quite substantial to show up under a compression test. If it was hairline it might not neither would it show if the crack was between the inlet port and the atmosphere.

Sometimes cracks and poor head gaskets only become apparent when things get hot, the metal expands and it opens it up.......go figure!!

Head cracks are very rare with modern machines unless they are abused and I have never heard or read about a GS5 suffering from one but I wouldn't rule it out, neither would I rule out the head gasket if, as we are being told all the other possible and usual causes for the hang-up have been thoroughly investigated

Cleaned the head. Replaced a number of farkled gaskets the PO messed up.
Lots of other little things which may have made a difference.

Now, after everything back together still hanging idle.
Well, I had to figure it out. Hard to believe but the timing was off by 1 tooth. One tooth backwards.
Fixed that and all is perfect.

I doubt all these weeks of work we had the timing off. There were other issues of oil leaks and do forth.

But the final peg after making sure EVERYTHING was spotless and put back together was the timing. I am sure everything came into play and previously other issues were the problem.

IIt is easy to get timing off one tooth since the engine is tilted and the diagrams are not tilted.

Now, we had triple checked the timing before. I I think it was everything that had an effect. One word of advice is: if everything is perfect, you might be one tooth off on timing OR your timing rotor might have become rotated a little off. (forward, due to using it to rotate the motor but that was not our issue)