Hanging idle at stops

Advance springs

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michigander52
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Hanging idle at stops

#1

Post by michigander52 »

I'm re-visiting an issue on my '76 FXE that I've been living with/trying to correct since I got this bike. I have searched the knowledge base but haven't found must info or where anyone has solved this issue.
When pulling up to a stop the idle hangs high for a few seconds before settling to what I believe is around around 700-800 RPM. It doesn't idle well at that speed and will try to die if I don't blip the throttle a bit. If I try to raise the idle speed just a touch the idle increases abruptly and I can't obtain an idle in the 900 RPM range. I believe that the advance is kicking in and causing the idle to jump to high. I have replaced the advance mechanism and also installed silver springs but this hasn't made a significant improvement. I'm thinking about ordering a pair of the gold springs and giving those a try.
Have any of you guys dealt with this before and if so what have you done to solve it?
Steve
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Re: Hanging idle at stops

#2

Post by 38ulh »

I've had that issue a few times with the advance on my 79 shovel. I only tune ignition when it starts running bad. I don't use a lot of lube (but I lube it) on the advance mostly corrosion prevention. Eventually I expect the problem to return. I've decided the only new advance units money can buy are of marginal quality at best so I consider them all consumable tune up parts. I've even tried the one with roller bearings it still wore out just not at the bearings. I just keep mine clean and lightly lubed and I get a pretty good life out of them. My two cents.
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Re: Hanging idle at stops

#3

Post by RooDog »

Don't treat the symptoms, cure the problem.
Get rid of that 50 year old technology and get a good electronic ignition like the $&$ Hi-4N, or any other similar offerings. I have two vintage Crane Hi4s in my big inch Evo, and stroker Shovelhead, for over 20 years with no issues. You will be glad once you have done so, and your wallet quits smoking.....
....RooDog....
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Re: Hanging idle at stops

#4

Post by nifty »

I'll second Roodog, modern electronic advance ignition is so much better, its like night & day, even on flatheads.
Nifty
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Re: Hanging idle at stops

#5

Post by Excalibur »

Talk is this problem is more common with EI because you don't get the braking effect of the point heel rubbing the cam adding retard bias.
Two other things you could possibly do in addition to new stronger springs.
1/. Add extra spring tension by wrapping the hook end of each spring around the post a little tighter. I've done this to my EI equipped bikes.
2/. Reduce the weight of the weights themselves. I haven't done this so it's only theory at the moment. Actually my Pan will get this soon.

Another thought is intake air leak. I'd bubble test with 10psi and eliminate this potential. The thought is if there's air leaking in, you'd have to richen the low speed to compensate. On the over-run intake vacuum is high. Air plus fuel, what else can it do but race.
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Re: Hanging idle at stops

#6

Post by Mongrel505558 »

If you choose to keep the advance weight method vs. going electronic; here's what I did and I haven't had the sticking advance problem in years:
- Remove advance assembly, disassemble and clean thoroughly with parts cleaner, brake cleaner, alcohol, or whatever your preference.
- Clean points cam and timer shaft where it rides, too.
- Reassemble advance unit with the next stiffer springs (I forget the color) if you haven't replaced the original springs already.
- Use that thin liquid moly lube that comes in a bottle with a steel syringe to get all contacting surfaces (pricey stuff, a little bit goes a long way) and work the mechanism a few times. It should snap back quickly and smoothly. Reassemble to timer.

Make adding a few drops of the moly lube part of your maintenance routine. I like it because coats the parts and flows easily. You don't have to take the advance apart every time. Just take the cap off and inject a few drops down between the points cam and the timer shaft.

Jim
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Re: Hanging idle at stops

#7

Post by michigander52 »

Thanks for the replies all. For now rather than going to electronic ignition I'm going to try replacing the springs with a heavier set and clean and lube the advance mechanism. I do like the idea of electronic but if I can get the stock unit to cooperate I would prefer that.
I'll post my results once I get it back together.
Thanks again
Steve
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Re: Hanging idle at stops

#8

Post by RooDog »

Do bear in mind that stiffer advance springs slows down the advance rate. This may be OK for an under powered & heavy machine, but is death to a performance bike. But since you want to retain the antiquated mechanical advance, I'll assume performance is down low on the list of parameters.
But do check for a vacuum leak both at the juncture of the manifold to the heads, and also the carb's gaskets and spacers.
You do have the carbby properly supported, and not just counting on the manifold clamps to hold everything together, yes?
....Best wishes....
....RooDog....
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Re: Hanging idle at stops

#9

Post by panheadrider1961 »

Agree with Roodog sounds more a carb issue sticking cable, do you lube it? What type of carb ? Stock bendix check bind on accelerator pump binding on pump rod ,you riding in 100 degree heat? Vacuum locking, are you running heat block on intake as pointed out manifold leak usually compensated with high idle to over ride leak vacuum lose, damage to piston by running lean at highway speed good luck
michigander52
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Re: Hanging idle at stops

#10

Post by michigander52 »

RooDog wrote: Fri Jun 24, 2022 10:15 pm Do bear in mind that stiffer advance springs slows down the advance rate. This may be OK for an under powered & heavy machine, but is death to a performance bike. But since you want to retain the antiquated mechanical advance, I'll assume performance is down low on the list of parameters.
But do check for a vacuum leak both at the juncture of the manifold to the heads, and also the carb's gaskets and spacers.
You do have the carbby properly supported, and not just counting on the manifold clamps to hold everything together, yes?
....Best wishes....
....RooDog....
RooDog, while I was waiting on the new springs I took the carb off to check for manifold leaks. I made a adapter plate to connect an air hose to pressure test the manifold and that checked out with no leaks. And yes there is a support on the carb.

Also while installing the advance mechanism when looking in the manual for the torque spec for the cam bolt I'm seeing conflicting information. In the electrical section for servicing the advance unit it states to tighten the cam bolt to 60-80 in-lbs however in the general section in torque requirements the cam bolt torque is listed at 20-24 in-lbs which seems to me to be correct for the #10 size bolt this is. I expect the 60-80 in-lbs is a typo?

Anyone have an idea what the correct torque on that cam bolt is?
Steve
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Re: Hanging idle at stops

#11

Post by RooDog »

I don't sweat the published torque specs on this particular part. Try locating an industry standard chart for a hi-grade bolt and use that spec if you really want one, but beware, that OEM screw with the big hex head is a trap. I toss that screw and replace it with a black Allen screw and an appropriately sized flat washer. That combo is way better than the MoCo's way of doing it.
If in doubt, do your own torque test. Clamp a duplicate screw in a vice and pull a torque wrench on it until it breaks. Then you will know the upper most limit for that screw. I have twisted off OE screws which is why I don't like to use them.
Put some blue Loctite on it and you'll be OK. It is not a stressed fastener. It really doesn't hold anything heavy in place, only the center parts of the advance mechanism, and is not much more than a place holder.
....RooDog....
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Re: Hanging idle at stops

#12

Post by Excalibur »

My tip is to use a real short spanner. This way you'll get a much better feel for tightness.
michigander52
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Re: Hanging idle at stops

#13

Post by michigander52 »

RooDog wrote: Fri Jul 01, 2022 2:29 pm I don't sweat the published torque specs on this particular part. Try locating an industry standard chart for a hi-grade bolt and use that spec if you really want one, but beware, that OEM screw with the big hex head is a trap. I toss that screw and replace it with a black Allen screw and an appropriately sized flat washer. That combo is way better than the MoCo's way of doing it.
If in doubt, do your own torque test. Clamp a duplicate screw in a vice and pull a torque wrench on it until it breaks. Then you will know the upper most limit for that screw. I have twisted off OE screws which is why I don't like to use them.
Put some blue Loctite on it and you'll be OK. It is not a stressed fastener. It really doesn't hold anything heavy in place, only the center parts of the advance mechanism, and is not much more than a place holder.
....RooDog....
Thanks RooDog, I like the idea of using a Allen head screw.
I think I opened up the can of worms today. I thought while I was getting the points, timing and carburetor all in tune I'd go ahead and check the lifter adjustment as I have never been in there yet. Glad I did. Some one with heady hands had been there before and didn't do any favors. I was hoping to just get them adjusted without replacing the o rings at this time however when I got to the third pushrod I noticed two small pieces of metal wedged around the lifter. I pulled the lifter out to see if the piece had come from their but the lifter looked good. It appears that none of the pushrod tubes have the thin washer between the seal and spring on the middle seal. Until I looked at my parts book I didn't realize that there should be a washer there. Also didn't know that the bottom seal on these motors is larger than the top and middle one's.
So I'm ordering some more parts and half afraid to check anything else out.
I'm wondering if I should flush out the lifters or just wipe them down?
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michigander52
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Re: Hanging idle at stops

#14

Post by michigander52 »

Excalibur wrote: Sat Jul 02, 2022 12:25 am My tip is to use a real short spanner. This way you'll get a much better feel for tightness.
Thanks for the tip, if I replace the screw with an Allen the Allen wrench should be short enough to get a good feel. If I keep the factory bolt I'll use a short wrench or maybe a 1/4 drive ratchet.
Steve
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Re: Hanging idle at stops

#15

Post by RooDog »

There is a small check ball up inside the small end of the lifter. A paper clip works well to unseat the ball, and allow the lifter to collapse. It should then be squeezable by hand, collapsible and rebound with no effort. I would put it back in and set the preload half way between fully extended and bottomed out, +/- 1/2 turn. Once the engine is running it will fill with oil and be OK. This may take a few minutes.
I don't run hydraulics, but that is the way I did them at the H-D Dealership, back in the late 1970s....
Yep. Put the flat washer back in between the spring and the seal....
....RooDog....
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