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Discussion Starter · #1 ·
First my bike made it on a 1750 mile trip with no major issues. I'm very impressed with my gl1200. We went from the 90's to raining for days and 50-60 degrees. Back to the 105 plus and cruising at 85mphs. It averaged 50 mpg peaked at 55mpg.
Now before we left the bike started idling high when hot and the outside temp over 80. It would idle at 1500-1900 once the temps went over 80. Also when I went let off the gas to slow down the rpms would stick at 2500 plus and some time increase. but drop down soon enough. During the last part of the trip when hot and 100 outside the idle would be as high as 3000, it would be very hard to restart when hot and when slowing down the rpms would stay or increase to 3500 for long time.
My fuel pump went out completely the second day home from trip good timing. I since replaced it with an 1985 prelude model. It starts,idles and revs great but still has the same issues as before. What causes the rpms to stay high and or increase after you let off gas and what causes the idle to increase if the its hot out and the bike is warmed up?

Sorry for long post. Ron
 

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1987 GL1200 Interstate
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Well, if you were really getting 50~55 mpg, I'd say leave things the way they are. But...
...have you looked at the slides?
...have you done an idle drop and sync?
...have you looked for interference in the cable's operation?
 

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Discussion Starter · #6 ·
Well, if you were really getting 50~55 mpg, I'd say leave things the way they are. But...
...have you looked at the slides?
...have you done an idle drop and sync?
...have you looked for interference in the cable's operation?
. Mileage was confirmed by the two other bikes riding with us. Cable operations is good nothing is binding. Adjusted with some slack, haven't open the carbs ever. Sync them in April plan on doing it again soon. I have had these issues since I got it in Jan but they are getting worse.
 

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I would take look at the choke cable and links at each carb, I found that the little piston can stick and the linkage restrict movement on my 84 Interstate, so that the choke/fast idle doesn't fully return to off even though the thumb lever is all the way home. A clean and spray lubricant may be all that's needed, but it might need a new choke cable.
 

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Discussion Starter · #8 ·
I should add the it only holds or raises the rpm once the motor gets over 2500-2700 below it won't do it?
 

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Does the 12 have a throttle return cable like the 15.

High heat can do strange things to carbs and linkages like a little bit of warping sometimes and under those conditions could be hanging a throttle plate open.

If the linkage or carb was hanging up when it does that you should have extra free play at throttle grip, got any. A return cable might make a difference though if you feel the play or not.
 

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The 1200s DO have a throttle return.

If you do pull the carbs.. may I offer one modification I made that I really like...?

I added a choke cable return spring. (See picture)

I bought a cheap simple spring at the hardware store, probably $1 or $2.00. And drilled a couple holes. Bolted it onto the bottom of the carb assembly. I have the spring under just a touch of tension when the choke is fully back. It helps a lot.

Anyway. the picture pretty self explanitory...
 

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It aint rocket science
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With a return cable that might blow that theory out the window you should be able to crank it back.

If you shut it down during the fast idle and start it right back up what is it doing then.
 

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Discussion Starter · #12 ·
The cable has slack even when the rpm is high. If I turn it off during high rpm its hard to restart idles higher then normal and if you twist the throttle it races again.
 

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Discussion Starter · #13 ·
I honestly don't think its an issue with cable because I loosened it while it was racing didn't change anything
 

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It aint rocket science
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Just a WAG but if it was linkage related shutting off and starting again should have no change, it should still be right where it was before.

Sounds more like you are getting vacuum somewhere it isn't supposed to be working on something.:? Make sense.
 

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OK, let's try again. What do the slides look like?
Have you done and idle drop to see how that affects it?
While this is going on, is the idle adjust screw resting against the stop?
 

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Discussion Starter · #17 ·
OK, let's try again. What do the slides look like?
Have you done and idle drop to see how that affects it?
While this is going on, is the idle adjust screw resting against the stop?
Honestly as soon as I have more then few minutes I'll open the caps and check the slides. I also want to sync it to. Yes the idle screw is bottomed out when the rpm is racing. Lower the idle does nothing while the rpms are racing.
I'm working 12 days straight 11-12 hour days. The bike is my only transportation right now and I need to use during work 3-4 days a week. Once I'm off I'll sync and look at slides.
 

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The cable has slack even when the rpm is high. If I turn it off during high rpm its hard to restart idles higher then normal and if you twist the throttle it races again.
On the restart what do you mean hard as in slow cranking or just wont catch. A big a$$ vacuum leak would make restart hard.

We need to back up a few steps here. When there is no problem what does the engine idle at. And check to see after starting cold with choke off how slow can you get the engine to run with the idle screw. Does it just go to 800 and stay running or does it stall and is the engine smooth when doing all this.

Come back with some numbers and behavior.
 

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I wonder if your throttle return cable is broken. ANd what you're feeling as slack is just no cable at all.

If the throttle cable was broke.. I could see where on occasion the return cable prevented the carbs from closing. The cable binding.

I could also see if the throttle valves were sticky, they would then hold open.

Remember, if you pull the carb caps.. The caps have to be installed with the slider in uppermost position.


Good luck
 

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Discussion Starter · #20 ·
Sorry still haven't had the time to work on the slides or sync the carbs. I did drop the idle cold down to 700 rpm the bike barely runs. I will update more once I get time off of work. I just don't want you all thinking I'm brushing off your advice and time. Thanks Ron
 
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