Strange idle problem

[Fritz The Cat]

Sometimes when I crank the fat lady, she won't idle. So I adjust the idle to 800 rpm and all is well until she warms up. Then the idle jumps waaaay up. Yesterday it went to over 3k. I had to pull over and and adjust it back down. Could something be sticking and then breaking loose on warm up?

[Gryphon Rider]

It sounds like you're trying to use the idle speed instead of the choke to make it run when the engine is cold.  If so, use the choke instead.

[PharmBoy]

If you use the choke for idle adjustment on start-up, don't for get and leave it on too long.  I am told that is possibly a cause for blue header pipes.  I have found that #38 slow jets solve a lot of start-up/warm-up problems...Jim

[Chrisj CMA]

Always adjust the idle speed with an engine fully warmed up.  Set it to 900-1000 and when its cold it will either idle low or not at all without the choke.  THIS IS NORMAL.  

I use the choke to hold the idle at 1000 when I first start her up only for a minute or two then the choke comes off and I use the throttle to keep it up there until I take off (which is a few seconds after turning the choke off) by the time I get to the first stop she is idling fine but  still below 900-1000 until it fully warms up (maybe 5 minutes of ride time)

[RP#62]

I use the throttle lock to set the idle at about 1200 when its cold.  As it warms up, the rpm will easily go above 2500, signaling that we're ready to go.
-RP

[Fritz The Cat]

It sounds like you're trying to use the idle speed instead of the choke to make it run when the engine is cold.  If so, use the choke instead.

No sir. I'm well aware of what the choke does and how to use it. After a several minute warmup I turn the choke off in preparation to ride and it dies. If I then adjust the idle, I can adjust it to wherever I want it. The problem occurs after I've ridden 20 miles or so.

Why the heck would I go to the trouble of using the idle adjustment as a choke? 

[Daniel Meyer]

It sounds like you're trying to use the idle speed instead of the choke to make it run when the engine is cold.  If so, use the choke instead.

No sir. I'm well aware of what the choke does and how to use it. After a several minute warmup I turn the choke off in preparation to ride and it dies. If I then adjust the idle, I can adjust it to wherever I want it. The problem occurs after I've ridden 20 miles or so.

Why the heck would I go to the trouble of using the idle adjustment as a choke? 

That's generally a sign of vacuum leaks...possibly the vacuum lines (look for splits right near the manifolds), petcock, or the o-rings between the manifolds and the heads.

[salty1]

I agree with Daniel as to the possibility of a vacuum leak(s). Sounds like the carbs may be OK.

[Ricky-D]

There well may be vacuum leaks but I don't think that's the cause of the problem.

The motor won't idle until fully warm, the choke is necessary to keep it running.

This is a symptom of a poor synchronization of the carburetors.
___________________________________

Comments regarding larger than stock idle jets are misplaced since larger idle jets are not a substitute for "starting without the choke" nor are they an answer for idle problems and clogged jets resulting from gasoline related problems.

[Gryphon Rider]

Now, I'm talking off the top of my head with no precise knowledge, but the ignition control module (ICM) has engine temperature as one of its inputs.  My understanding is that the ICM adjusts the advance according to whether the engine is hot or cold.  Perhaps the engine coolant temperature sensor is either disconnected or faulty.  It's shown on the schematic in the middle, about 2/3 of the way down.

[wild6]

Now, I'm talking off the top of my head with no precise knowledge, but the ignition control module (ICM) has engine temperature as one of its inputs.  My understanding is that the ICM adjusts the advance according to whether the engine is hot or cold.  Perhaps the engine coolant temperature sensor is either disconnected or faulty.  It's shown on the schematic in the middle, about 2/3 of the way down.

If the sensor was open, it would simulate a cold engine and advance the timing, so that's not the problem, but if it was shorted.........  Maybe?  Could be?  Anyone?

[Chrisj CMA]

It sounds like you're trying to use the idle speed instead of the choke to make it run when the engine is cold.  If so, use the choke instead.

No sir. I'm well aware of what the choke does and how to use it. After a several minute warmup I turn the choke off in preparation to ride and it dies. If I then adjust the idle, I can adjust it to wherever I want it. The problem occurs after I've ridden 20 miles or so.

Why the heck would I go to the trouble of using the idle adjustment as a choke? 

If you are adjusting the idle before you actually ride......well, then you are in a way using the idle adjustment as a choke.  I do agree if it is that cold blooded you should check all the vacuum lines because leaks will cause what you describe.  Also check unused nipple plugs and intake runner clamps (18 screws)....these are the areas vacuum leaks happen

[Fritz The Cat]

To be honest. I've only adjusted the idle before I ride twice, and both times the results were the same. Most of the time I just hold the throttle open a little till she snaps out of it and will idle on her own. I'm thinking it's not really a idle problem per se but like, others have suggested, a vacuum leak. Guess I'll have to pull the tank off and have a look.

Thanks all

[Chrisj CMA]

To be honest. I've only adjusted the idle before I ride twice, and both times the results were the same. Most of the time I just hold the throttle open a little till she snaps out of it and will idle on her own. I'm thinking it's not really a idle problem per se but like, others have suggested, a vacuum leak. Guess I'll have to pull the tank off and have a look.

Thanks all

If your '97 has never had the vacuum lines changed, you dont really need to look at them at all.....just need to change them.  To change vacuum lines taking the tank off is only a small help.  All thats really needed is to remove the fuel valve from the petcock (secret screw) so you can unbolt both ends of the tank and simply rotate the tank to the right a bit until you can see over the left carb bank.

You can reach in and hook the vacuum lines and pull them out over the carb bank and change them.  Read up on the string method in shop talk its very cool and makes it a snap.  Just plan on replacing all the nipple plugs too and while the tank is loose you can get to the last set of 6 intake clamp screws.  One set is readily accessible and one set you have to remove the choke slide chrome covers to get to.  You will be amazed at how loose the lower 12 screwes are if they have never been tightened.  The vacuum line from #6 intake to the petcock is the easiest to change

Good Luck

[Fritz The Cat]

Is there by chance a kit that includes all the parts needed?

[Willow]

Redeye Tech

[john]

bingo     

[Fritz The Cat]

Redeye Tech

Thank you sir. 

[Chrisj CMA]

Redeye Tech

Am I looking at that right $25 for vacuum lines?

I went to Autozone and bought 2 feet of 5/32ID fuel/vacuum line double wall so its far better than OEM for  3 or 4 bucks and it was way more than I needed

I also found some red nipple plug thinggys (they had other colors) that seem to be holding up real fine and they were a few cents each is all

[Willow]

Yes, and what you get at the parts store will probably work fine.  Redeye's kit is Viton which is supposed to hold up much better.  Obviously, cost is higher for a vendor dealing in small quantities rather than the auto parts chain.

Primarily, Fritz asked whether there was a kit.  Redeye is the answer to that question.

[Chrisj CMA]

Yes, and what you get at the parts store will probably work fine.  Redeye's kit is Viton which is supposed to hold up much better.  Obviously, cost is higher for a vendor dealing in small quantities rather than the auto parts chain.

Primarily, Fritz asked whether there was a kit.  Redeye is the answer to that question.

I understand, and Viton is good stuff.  However, the double walled fuel/vacuum lines I put in 3 (maybe closer to 4) years now still look good and no trouble with vacuum leaks.  I remember when I had never done a vacuum line change out, you dont realize how simple it is until you do it, and cutting a new vacuum line to match the old one is a no brainer.  Just trying to expose all the options here.

[Robert]

What ever lines you get I'm with Daniel on this one it sounds lean to me. I dont use a choke at all in temps till say 45 then its only to fire up then off. Its either dirty jets air leak unbalanced carbs way outside chance is bad plugs.

[Stratnick]

Now, I'm talking off the top of my head with no precise knowledge, but the ignition control module (ICM) has engine temperature as one of its inputs.  My understanding is that the ICM adjusts the advance according to whether the engine is hot or cold.  Perhaps the engine coolant temperature sensor is either disconnected or faulty.  It's shown on the schematic in the middle, about 2/3 of the way down.

My 2000 I/S is doing pretty much the same thing. It only idles really high after warming up. I noticed the other day that when the radiator fan came on, the idle returned to normal. Hmmmmm?