irregular idle

htown16 · Jun 9, 2013

Every since I got my 72 back on the road it has had an unusual pattern to the idle.
When you first start the bike it idles right at 1000 rpm at each stop sign until you have ridden for about 3 or so miles then it jumps up to 1500. It will do this for the next 20 or 30 miles or so and then it starts idling down to 1000 rpm again and will continue to do that for as long as you ride. Everytime I ride it, exactly the same. Ambient temp has no effect.
It has done it with the original carbs and with a new set of Premiere. Different float levels. No inlet air leaks, I flattened the surfaces and checked with starting fluid.
Pazon ignition. Stobe timed spot on. Checked alternator output and its charging okay. New battery, measures same charge before and after trips.
I've got used to it and have quit messing with trying to set the idle screws any differently. Just puzzled as to why it does it so consistenly the same every time.

Rohan · Jun 9, 2013

Are these Premiere carbs jetted like the stock Amals ?
Does it have the stock air filter and airbox ?

How does it first idle when its cold ?

Checked the cable alignment and routing - not catching on anything when you first go canyon carving ?
Good fuel flow from the fuel taps ?

kevbo82 · Jun 9, 2013

i have almost the exact same scenario with new premiers, pazon sure fire, and stock air box. i only just put the pazon on and was still fussing with it, i dropped the bike off this weekend at the brit bike shop that rebuilt my motor to look at an oil issue and when i pulled in he heard it idling high and mentioned it to me. I told him about it and he said he would look things over while he had the bike, so i'll let ya know what he finds on mine. Do you have any trouble starting the bike at all? mine seemed harder to start. would get a few kicks where it would almost run and sputter out, i would change the stop screws on the amals and it would start up and idle around 1000 rpm's or so, then after a few minutes of riding be pushing 2000. i would adjust again to get back down around 1000 and next time i went to start from cold same thing again.

htown16 · Jun 9, 2013

K+N filter, stock jetting, needle in bottom groove. Pulls really smooth and strong from roll on all the way to wide open. Plugs look good. I tried a number of different jetting combo's which had effects on other parts of the throttle range, but no matter what I was using the idle pattern was exactly the same each time.
Wouldn't think if it was a fuel flow issue it would be such a consistent pattern.
Pretty sure cables aren't hanging.
Starts on one or two kicks cold, one warm.
Start it up and blip the throttle a few times and it will settle down to 1000 rpm. First couple of stop signs in neighborhood sitting at a 1000, ride about 3 miles to first stop light and she's up to 1500. Everytime you stop now its sitting at 1500.
Ride it out on the highway 20-30 miles and it suddenly drops back to 1000 and idles just perfectly. I've probably made 30 or 40 trips on it and it does this every time.
Like I said its something I can live with, but it just bugs me that I can't figure it out.

concours · Jun 10, 2013

Cold engine likes RICH(er) mixture, warm likes LEAN. Your symptoms suggest it's a bit lean... AS IT SHOULD BE. Chokes functioning?

htown16 · Jun 10, 2013

Yeah, chokes are mechanically functioning correctly.

concours · Jun 10, 2013

htown16 said:
Yeah, chokes are mechanically functioning correctly.

...and, does it want them when cold?

htown16 · Jun 10, 2013

I always put them down to start it and then gradually raise them after its warmed up for about 30 seconds or so. Never really tried it any other way.

JohnTy · Jun 10, 2013

Hi htown16
I am sure I read on this forum someone found some grease in pilot passage ways (thought it may be there from building by Amal) of their new Premier carbs. Must check mine when next off.
I have symptoms very similar to yours with an almost identical systems, although mine is a 920 with a Maney cam.
It is very difficult to get it to tick over much below 12/1300rpm.
Will watch the thread with interest.
Cheers
JohnT

pete.v · Jun 10, 2013

JohnTy said:
Hi htown16
I am sure I read on this forum someone found some grease in pilot passage ways (thought it may be there from building by Amal) of their new Premier carbs. Must check mine when next off.
I have symptoms very similar to yours with an almost identical systems, although mine is a 920 with a Maney cam.
It is very difficult to get it to tick over much below 12/1300rpm.
Will watch the thread with interest.
Cheers
JohnT

That was me. I have had my pilot jet and related circuit apart twice. The screw-in pilot jet itself has the 4 hole in the side which cross and one on the end which is very small, like #78 drill small.

The clear grease/lube was like the stuff to lube the oring. It seemed to have gotten over blobbed or something.

I am not saying that it is any bodies fault but these new improved carbs beg for an inline fuel filter if not already installed.

I stated in another post that I had hope these new carbs would have the pilot jet type that screws in the bottom of the body in the float bowl. This would have made them adjustable. The new screw-in jet is not all that easier because you still have to take at least one carb off. The other thing is I do not believe there are different sizes so we still have a proprietary issue. I hope I am wrong about this.

L.A.B. · Jun 10, 2013

pete.v said:
I am not saying that it is any bodies fault but these new improved carbs beg for an inline fuel filter if not already installed.

One apparent problem with the latest Amal carbs is that the recess in the metal fuel banjo is deeper than the Amal filter screen, so even relatively large pieces of dirt and debris can find their way through under the filter and become trapped under the the float needle causing carb flooding. I found that shortening the banjo so the filter bottoms out (with about 1mm compression of the filter, once assembled) cures this problem.

pete.v said:
I stated in another post that I had hope these new carbs would have the pilot jet type that screws in the bottom of the body in the float bowl. This would have made them adjustable. The new screw-in jet is not all that easier because you still have to take at least one carb off. The other thing is I do not believe there are different sizes so we still have a proprietary issue. I hope I am wrong about this.

It seems there are 5 sizes of Premier pilot jet
http://amalcarb.co.uk/mk-i-concentric-s ... t-jet.html

pete.v · Jun 10, 2013

L.A.B. said:
[It seems there are 5 sizes of Premier pilot jet
http://amalcarb.co.uk/mk-i-concentric-s ... t-jet.html

Good tip on the banjo lab.

When I click on that link, I see needle jets and nothing that shows anything like what is screwed into the sides of these bodies.

I can only assume that they do not have a picture yet and have used an old stock needle jet for a poor reference picture.

Well anyway, that's good news that they have them. I believe the 622/502-17 is stock. Seem to be a much more finite adjustment.
I still wish it was the other way though, with the pilot jet in the bottom. I guess I could have it that way, I've done it before.

L.A.B. · Jun 10, 2013

pete.v said:
When I click on that link, I see needle jets and nothing that shows anything like what is screwed into the sides of these bodies.

Yes, they've used the wrong image, however here's one of the actual Premier pilot jet.

http://amalcarb.co.uk/mk-i-concentric-s ... /jets.html

htown16 · Jun 10, 2013

Interesting stuff, but the situation I'm describing happened exactly the same with the old carbs as with the Premieres. Me thinks it is not in the carbs. Ignition advance fluctuating?

JohnTy · Jun 10, 2013

Hi
Sorry htown16
I got mixed up with Kevbo post, what ignition are you using?
I am running Pazon sure fire.
LAB do you have any issues with tick over varying, and what ignition are you using?
Cheers
JohnT

Torontonian · Jun 10, 2013

Worn or dry cables ? Worn or dry junction box ? Old or loose camchain ? Battery connections loose ?

JohnTy · Jun 10, 2013

Torontonian said:
Worn or dry cables ? Worn or dry junction box ? Old or loose camchain ? Battery connections loose ?

On all three machines?
JohnT

htown16 · Jun 10, 2013

Pazon

DogT · Jun 10, 2013

Happy with my sure-fire, but I wonder if the idle stab in the altair wouldn't help it some. I've got the wandering idle, but I attribute it to the old carbs and the wandering is not consistent. Air temp seems to have a bearing.

Dave
69S

pete.v · Jun 10, 2013

I can assume that you are running the SureFire. As with carbs, I have also been dealing with a couple ignition system. Without getting into details I have a theory of which I really cannot prove. I think that the pazons curve is a too little retarded at and near idle. I have to be very careful not to discolor the pipe. With the PA, I had no issue with the pipes but that was the only good thing about it.

I think people who are frustrated with fluctuating idle need to look into the TriSpark and move on.
Trying to get these bikes perfect is insane. I cannot tell you now many times my Norton was plenty good enough but I just have to take it to another level.

Expect magneto comments in the very near furture. The UPS truck will be here Wednesday.

irregular idle

htown16

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htown16

concours

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JohnTy

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L.A.B.

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