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GL1200: High RPM when hot / or clogged (?)

1967 Views 8 Replies 7 Participants Last post by  tire joe
Hi Guys,

I'm hoping someone has some experience, or can tell me what they think is going on with my bike.

I have an 84 GL1200 Aspy. A couple of times I've experienced this condition, then it seemed to clear up by itself.
The 'condition' is that after some time at sustained speed / RPM's (like 70 and 3,400). Then I'll get into town where I'll just be at more like 15-25 MPH and 2,200 RPM (approx)... The bike will be stuck revving at 3,000 or higher! Even at idle the RPM's won't come down. The latest occurrence (yesterday)... this happened, but it seemed ALSO to be influenced by the engine temperature... The bike was running very hot after a lot of slow twisties on a hot day and getting stuck in a bit of stop-n-go traffic. When the bike got hotter, the idle RPM got to about 4,000.
I managed to get home safely and park the bike.. by this time the bike would idle at 'only' 2,400 RPM... which I saw as an improvement. Later, I started the bike up... and thankfully it was idling normally (about 1,000 rpm)... But, I didn't do anything to fix it. Which is why I think the temp had an influence.

I suspect the issue is something to do with the fuel system... maybe a chunk of debris is blocking or holding something in the wrong place... But, could it be an electrical thing?

I know it wasn't the throttle cable or linkage... I was able to see and feel that all that was moving normally.
I know it wasn't the choke cable or linkage... I could see those components working normally as well.

I did rebuild the carbs recently, and USUALLY the bike runs very well and reliably.
There IS some debris in my gas tank still (rust granules) and I do clean my bronze fuel filter every few gallons. (which is why I suspect something is getting lodged in the carb causing the revving).

This type of thing has happened before, and I attributed it to debris in the carb. And it seemed to clear itself... But, this is the first time engine temperature seemed to play a role.

So... does anybody have any idea of what could be happening with my bike?

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Check for vacuum leaks first, as they can cause erratic idle and other problems.
Does sound more like throttle is not returning properly
Not familiar with the 1200 but generally speaking if the throttle plates WERE returning to idle position no way the engine could get enough air AND fuel to support a 4k RPM. Your throttle plates would not be affected by junk in the fuel line or tank. The junk in the fuel theory would have to effect all 4 carbs at the same time, if one carb were plugging something it wouldn't pull the other 3 up with it IMO.

The air AND fuel required for a 4k RPM must be coming from a different carb circuit. If you have enrichment rods for a choke system I would be looking there.

As a test with engine warm crank up the choke and see if you can simulate the fast RPM. There could be other systems in the engine which will increase RPM if an overheat is detected which I would not know about and might include a change in Ign timing also.
Wild Guess

This is just a guess, since I wasn't there playing with your bike when the high rpm idling condition was there. Next time it starts acting up like that, open up your faux tank and a) Fan it with a notebook or anything you have handy. b) Unscrew and screw back in the gas cap without necessarily removing it.

A while ago when my starter was acting up -only while hot- I stop and fueled up with the engine running. When the gas fumes were pulled by the engine, (air inlet is right there) the rpms went up, but went back to normal when I put the cap back on.

Good luck sorting this out, please let us know what it was when you sort it out.
Thanks for the tips!

As of this morning my bike is idling/running completely normal.. and I haven't done anything.

I did try the 'choke' test.. and YES. I can get it to rev up and emulate the problem I had... So, maybe the linkage to the plungers is not working all the time.

The throttle cables and linkage do/did seem to operate smoothly, and it was easy to see the linkage working... the choke rods are a bit more buried and I didn't look at the left bank of choke plungers... so maybe they were the culprit.

Since this problem is intermittent It may be some time before it happens again.. But, when it does... I'll check the items you've mentioned and post any updates.

Thanks for your input!
6/7/13 Update

The problem 'seems' to have cleared up. But, I'm not really sure what is different now. Here are a couple of things I did do that may have fixed my Revving (or slow to return to idle) condition.

1) The idle was set a little high (about 1,400 rpm). I adjusted it to be more like 1,000
2) I removed and re-inserted 2 of the carb sliders. (the ones that are easy to get to.) They seemed to be fine. the needles are clean and the slides moved freely.
3) Adjusted the throttle cable. After adjusting the idle screw I noticed the throttle didn't have any play at all. So I loosened it up a bit so that there is just a little play in twisting the grip.

Another thing that may have affected this was that In a recent tank, I added about 5 ounces of SeaFoam to the full tank. I believe the SeaFoam is pretty much out of the system now.

If the condition arises again, I'll be back with either more questions, or more solutions!

The key fact was the high temp, to me, since it makes things expand. This will sound weird, but sometimes when we pull, rebuild, and re-install carbs they need to "set-in" themselves. Things that are a bit too close spread out with heat and things that aren't perfectly sealed work themselves into perfection. I've had it happen many times and never had it re-occur. Hope that's your experience!:praying:

Got to have a little slack in throttle cable, vacuum leak when hot can give a higher idle,
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