I think I may have fixed the high start-up rpm issue

[Ken R]

I've been annoyed with the high revving of the engine on cold start-up since the motorcycle was new.  In really cold weather, it'd rev to 3,500 RPM (maybe more).  In 70 degree ambient, it'd rev to 2,500 RPM.  My Dakota Digital recorded and displayed highest RPM.

Because the plastic intake manifold has been suspect (and probably not a very good idea anyway) I bought a new S&S  55 mm manifold from California Phil and installed it last night and this morning.  (last night was disassembly, this morning was for putting it all back together)   
It's not an easy job with bolts just barely accessible, even using cut off Allen wrench. 

It appears that the manifold itself, may not have been the problem.  It looks pristine.
 
BUT, the manifold attachment to the front cylinder head had a peculiar brown ooze around the seal, on the head, and on the plastic. 
As far as I could tell, the seal wasn't making full contact with the head and gasoline vapor was finding its way out and I suppose air could get in.  The rear didn't have this peculiarity.  No brown ooze anywhere.   

I'm thinking that this was the result of an improper initial assembly.  I don't think that the front manifold seal was making full contact with the head, instead being recessed in the clamp for almost 50% of its circumference.  That seems a tricky area to assemble properly, I think. 

I wonder if, on initial start-up, it was running lean because of this intake leak causing high revving.  Could the fuel management have been compensating for it over several seconds of time,  trying to bring the mixture back to where it was supposed to be; thus taking the 20 seconds to lower the RPM to normal.  After that, the idle eventually reduced to around 1,000 RRPM as expected.

[-deuced-]

I think your thoughts of improper initial assembly sounds like a logical explanation.

It's my understanding that that's what any computer controlled fuel management system does.

What's your start up idle rpm like after correct installation of the new components?

[Ken R]

I think your thoughts of improper initial assembly sounds like a logical explanation.

It's my understanding that that's what any computer controlled fuel management system does.

What's your start up idle rpm like after correct installation of the new components?

I don't think there's any doubt that the seal wasn't pressing on the head.  And that's where the brown oozy stuff was located, on the head, the clamp, and manifold.

At 70 degrees ambient yesterday, it went to 2250 for about 3 seconds and then very quickly down to 1,550 or so.  Then in the next minute or two, down to around 1,000 (+/- 100) RPM.   


I'll know better tomorrow morning. It's supposed to get down to around 50 degrees.  Before my "fix", 50 degrees would have elicited a 3,200 or higher RPM.   So I'm leaving my motorcycle in the cold tonight for a start-up test in the morning.  I hope I'm not disappointed.

[rigidthumper]

It takes quite a few start/run cycles to relearn the idle configuration. Be patient...

[kd]

50 degrees, cold?     Sorry Ken.  I couldn't resist.  It's been snowing here most of the day. 

[Ken R]

The jury is in!
at 50 degrees, which would have previously elicited a 3,200 RPM or higher starting idle which might take 10 seconds or more to settle down, the idle went to 2,200 for a very extremely short time that wasn't even perceivable; then to 1,400 rpm and slowly settled down to 1,000 rpm in maybe 45 seconds to a minute. 


I just hope that it didn't mess up my engine's cylinder walls with dry starts and high revving over the past 2-1/2 years.  I might should have done this 2 years ago.  The dealership said it was normal more than once and more than one service manager. Obviously, I know now that it was not normal. 


Well, kd, 50 degrees isn't "cold" around here, either . . . but in mid April, it's about as cool as it's going to get.  Plenty cool to test the engine cold start.   

[Ken R]

Follow-up. 
It's working perfectly.  Start idle seems to be around 1,500 rpm and shortly goes down to 1,100 and eventually to 1,000. 

Pleased that I fixed something.

Ken