Thoughts on slightly wandering idle

[pete]

Thanks Ian, that's real interesting reading... very keen to get into tuning my carbs or at least attempting to. Just gotta track down that mysterious time...

I must agree on a sync too, mine definitely ran better after the sync even without the proper tune...

Oh, almost forgot to say us Aussies were lucky and got adjustable needles too...

[Phil]

What is the throttle stop screw? Is this the same as the idle adjustment knob?

I'll be checking the valves once my order arrives from Boulevard with the valve cover gasket. Though I an hoping they all check out since I don't have the tappet tool and I am not quite sure how the zip tie method actually works.

I'll track down some of the Marvel Mystery Oil and see if it makes any difference.

I didn't read all the posts, but I'll throw in $0.02.

Do the valves first. Carb tuning is meaningless if the valves are tight and the risk of burning one is great. Do the valve adjustment first. Listen to the wise men who have kept these bikes running for 30 years for more. I'm not one of them but Mr. Nessism is

Sorry, this got long! So, the probable reason your idle is not stable is that the throttle stop screw is open too far and the vacuum controlling the slides is not getting shut off enough to allow the slides to close completely. There also might be some stiction happening in the slides. I would try backing off on the throttle stop screw a bit. The pilot screws should be somewhere between 1.5 to 2.5 turns out. Any more than that would be on the rich side. I would also try 2 or 3oz. of Marvel Mystery Oil in a full tank of gas. This will lube up the slides a bit.

Vacuum leaks either at the intake boots or in the carb diaphragms themselves can also cause unstable idle. It is mission critical that the boots and o-rings between the intake boots and cyl. head are fresh, viable rubber.

Carb sync is important and some will say that vacuum sync is the only way to do it, but I have never done it and my bike runs pretty well now. Having only two carbs greatly simplifies carb sync and I'm sure it is far more important on the 4 cyl. bikes. What carb sync does is ensure that both carbs are pulling equal amounts of vacuum at any given throttle opening. It can't be made absolutely perfect. What works at idle doesn't work at 4k rpm or 7k rpm. So one has to decide where in the rev range the most smoothness is desired and sync at that rpm. Out of sync carbs cause roughness and vibration more so at high revs than at idle. Bench syncing should be close enough to be able to tune for a decent idle.

I'm sure there's something else I haven't thought of, but those are the basics. The airbox can be wrestled back about two inches which gives you just enough room to get the carbs out. It's not easy but practice makes perfect. I had to replace the trumpets inside the airbox too because they got beat up from a few too many carb removal/replacements.

[tom203]

Idle adjustment knob = throttle stop screw
Putting anything in gas ain't going to lubricate slides- gas doesn't touch them. Closed throttle plates block air , this causes a high vacuum in intake manifold- any leaks can show up then often resulting in random high idle.
Just check your valve clearances to see where they are-this is important, so don't whip out the carbtune just yet. The ziptie is a means of holding the valve open (slightly) to take pressure off the shim so you can pull it out and replace it- it gives you manuvering room.

[Phil]

Update

Well I think the wondering idle really isn't the actual issue. After riding the bike for awhile, 20 or 30 minutes, I pulled over and set the idle to where it should be. The bike has been holding this idle fairly well on multiple rides over the past week once it reaches operating temperature.

So the real issue seems to be with cold starting. Like I mentioned in an earlier post the bike starts very weakly with the choke. It will stay on, but hovers under 500 rpms (if its any more/less than 1/2 on it will die out or not start). It also takes a bit to be able to take the choke off, but once it get to that point it runs very well.

I'll finally be checking the valve shim clearances at the end of this week and hopefully vacuum syncing the carbs depending on when the packages arrive.

I will see how it goes after those tasks before I get all excited.

[Phil]

Pic

Figured I should finally post a pic of the machine that is responsible for my golf game falling apart in the past month or so.

https://picasaweb.google.com/lh/phot...eat=directlink

The bike is pretty clean, but the picture definitely makes it look better than it does in person.

[tom203]

Figured I should finally post a pic of the machine....

The bike is pretty clean, but the picture definitely makes it look better than it does in person.

I've known guys who said that about their exgirlfriends!
At a cold start, you might have a lazy cylinder- not firing right away and forcing the other to do all the work till warm up- this often happens with out of whack valves.

[pete]

That's a nice lookin' machine Phil!

When you said it took a while to warm up, that's what made think of idle adjustment, figured like me you'd adjusted it too soon

+1 on valve adjustments, definitely can be a cause of hard starting.

[Phil]

Well the Carbtune arrived yesterday. (It's pretty amazing that something from the UK arrived before my order from Boulevard) I decided to try it out and see how it worked. The Carbtune seems to work great and was very easy to work with. The bike, how it is currently sitting, is pretty close as far as the vacuum sync goes. It was within 2 cmHg.

The Boulevard order should arrive today, so tomorrow or maybe Saturday I am planning on checking the tappet clearances. Hopefully that goes smoothly and I can find a way to get the shims I will most likely need without taking for ever.

[pete]

Yeah Boulevard can be slow... but everything's slow for me over here

Glad you got your Carbtune, and yes I agree, it's a great little unit. It made the carb sync so easy!

[Phil]

Update

Well the valves are all adjusted and now in spec, and thanks to tom203 for giving me one of the needed shims!

I am guessing that the valves haven't been checked in quite a long time due to the condition of the gasket which took about 2 hours to remove all the bits from the cover and the engine side. Three of the valves were tight and one was in spec.

I also installed a new petcock, new front pads and replaced the brake fluid.

The difference with the valves in spec is much more than I imagined it would be. The bike started right up with the choke, which now appears to be behaving normally (hopefully that continues), and warmed up quickly, and is holding its idle extremely well now with no wandering at all. It also seems a bit smoother under acceleration which surprised me since it didn't seem to be unsmooth before.

The only issue I have run into with all the work is that the new OEM petcock is slightly different then the original one. The point where the vacuum hose attaches is in a slightly different spot which means my hose is now a bit too short. Slightly annoying but obviously pretty minor.

So big lesson learned, check the valve clearances! Buy the new gasket, buy the feeler gauges, get a dang zip tie (which has got to be on the most simple and brilliant idea) and just do it!

Oh and the whole process really makes me glad that I bought a twin. I am happy to have only had to clean 2 carbs and dealt with 4 valves.

I've known guys who said that about their exgirlfriends!
At a cold start, you might have a lazy cylinder- not firing right away and forcing the other to do all the work till warm up- this often happens with out of whack valves.

[pete]

Well the valves are all adjusted and now in spec, and thanks to tom203 for giving me one of the needed shims!

I am guessing that the valves haven't been checked in quite a long time due to the condition of the gasket which took about 2 hours to remove all the bits from the cover and the engine side. Three of the valves were tight and one was in spec.

I also installed a new petcock, new front pads and replaced the brake fluid.

The difference with the valves in spec is much more than I imagined it would be. The bike started right up with the choke, which now appears to be behaving normally (hopefully that continues), and warmed up quickly, and is holding its idle extremely well now with no wandering at all. It also seems a bit smoother under acceleration which surprised me since it didn't seem to be unsmooth before.

The only issue I have run into with all the work is that the new OEM petcock is slightly different then the original one. The point where the vacuum hose attaches is in a slightly different spot which means my hose is now a bit too short. Slightly annoying but obviously pretty minor.

So big lesson learned, check the valve clearances! Buy the new gasket, buy the feeler gauges, get a dang zip tie (which has got to be on the most simple and brilliant idea) and just do it!

Oh and the whole process really makes me glad that I bought a twin. I am happy to have only had to clean 2 carbs and dealt with 4 valves.

Awesome news! Glad to hear it

And yes, I'm also very glad I only have 2 cylinders and carbs to deal with...

[Phil]

Well unfortunately it seems it is not starting normally with the choke. I guess there is something in the choke circuit.

...The difference with the valves in spec is much more than I imagined it would be. The bike started right up with the choke, which now appears to be behaving normally (hopefully that continues), and warmed up quickly, and is holding its idle extremely well now with no wandering at all. It also seems a bit smoother under acceleration which surprised me since it didn't seem to be unsmooth before.

[BigD_83]

Well unfortunately it seems it is not starting normally with the choke. I guess there is something in the choke circuit.

Can you explain further:

What do you understand as "normal" and what is actually happening now?

[Phil]

Normal would be that I should be able to engage the choke to some degree, usually somewhere in the neighborhood of halfway, and the bike should start from cold and not struggle to keep going.

Unfortunately, it seems to struggle and needs some amount of throttle to keep from stalling. Adjusting the amount of choke either doesn't change anything or makes it stall out.

Luckily it doesn't take very long for the bike to keep itself on without any choke.

At this point there can't be much else to cause this other than something clogging up the enrichment circuit.

Can you explain further:

What do you understand as "normal" and what is actually happening now?

[tom203]

Of course after the shim fun, you went back and checked/adjusted the mixture screws just in case ?? You said it was pretty close with Carbtune before valve fun, what about after?