High idle suggestions

MikeM · Nov 12, 2014

The other day I was pushing my 71 750 around and when I came to the light it didnt want to idle down. I have dual OEM Amals.
Is there something I can do to settle it down at the light? I kicked it into 1st and it didnt like it. Rode it for a couple of miles and it mellowed out.
Is this just the beast or the carbs? Its been a little unsettled lately, I have a newly rebuilt engine and have been doing some miles. Simple solutions anyone?
Other than that, it runs great with the new engine.
Thanks MikeM

Bob Z. · Nov 12, 2014

A couple of suggestions...

If using original points/auto advance, check the auto advance unit for proper lubrication of cam and flyweights
If the AAU sticks the ignition timing advance will change and idle speed may increase

Check throttle cable for slack; if idling fast then gently open handlebar twist grip and when the cable slack is taken up the possibly worn slide might quit rattling around and stabilize/lower the idle speed

This is a pretty common problem you have

Nater_Potater · Nov 12, 2014

Bob Z. said:
A couple of suggestions...

If using original points/auto advance, check the auto advance unit for proper lubrication of cam and flyweights
If the AAU sticks the ignition timing advance will change and idle speed may increase

+1 I've had to disassemble/clean/lube my AAU twice in as many years for the same issue you note, and I'll be doing the same thing come next Spring. It shows itself as a high idle that can sometimes be "corrected" while at a traffic light by lugging the engine down with the clutch to allow the AAU's weights to drop back down. That is, unless a new EI finds its way into my Christmas stocking...

Nathan

Fullauto · Nov 12, 2014

Inlet manifold leaks.

olChris · Nov 13, 2014

Fullauto said:
Inlet manifold leaks.

+1 sucking air/induction side air leaks probably.... But thrashing around getting very hot and normalises down the road once it cools down... Is that a one off or every time????? Maybe go and try that same scenario.. New engine!!!!!!!!!!! go around and check every nut to ensure none are loose particularly carb/induction side..

toppy · Nov 13, 2014

If nothing is found to be loose or obviously leaking try spraying WD40 round joints as engine is running. If engine note changes as you spray a joint then the WD40 is being drawn into engine at that point.

Also check pilot air screw O rings are in good condition and not causing air leakage in pilot jet system which will affect idle speed.

htown16 · Nov 13, 2014

I found cable routing to be important. Works best if the cables go between the headsteady side plates instead of around them.

batrider · Nov 13, 2014

Also check for cracked or popped off balance hose on the carbs.

Chris T · Nov 13, 2014

Is high idle speed a bad thing? I'm conscious of posts that have suggested that it is wise to keep revs above 2000 on start up to get oil flowing around as soon as possible.

worntorn · Nov 13, 2014

For ease of operation, no gear clunking etc, an idle around 1,000 rpm when warm is nice. Yes, good to get oil flowing when cold, best not to let it idle very long at 5 or 600 rpm as some engines will. Most will die pretty quickly if the idle is this low, hot or cold.
Ideally, set the idle up for warm running, then use a throttle lock to keep a good idle speed at cold, and at that, minimize time spent cold idling. Best to warm it up while rolling down the road.

Glen

RoadScholar · Nov 14, 2014

If your Amals have as many years on them as your motorcycle it may be time to replace them. The slides and the carb bodies are made from the same alloy and it doesn't take a lot of action for galling to begin. Examine the slides if they are just beginning to gall you may want to consider the purchase of chrome slides, if the bores are galled as well consider upgrading to a set of Premiers.

Bill.

Hobot · Nov 14, 2014

I've put grease on Amal slides to find it allowed decent idle back down for 100 miles to diagnois how much new slides might help so bought anodzied ones with one half less cut out number to make up for the bore flutted wear and has worked a treat scine. Will try some Strongarm stuff on the AAU to see if that will keep it returning back to idle for some more years/1000's miles to avoid non Norton electronics.

mike996 · Nov 14, 2014

Could be any of the previously suggested issues but re the oem AAU - I had the same idle trouble a few years ago that was the fault of a sticking AAU. I discovered that the slots where the weight limiting posts fit (I don't know what else to call them) were worn and would "catch" the weights. Cleaning/lubing didn't help but disassembly and some work with a file and some 400 wet/dry smoothed the slots nicely and eliminated the problem. I ran the oem points for years (removed a Boyer that was on the bike and put the points back in for much improved operation in every way). I finally went to a TriSpark which I like a lot. But if I ever had any trouble with it, I'd reinstall the oem and forget about e-ignition.

Hobot · Nov 14, 2014

I like the contact breakers whole scope of behavior over all the best too so will be nursing Trixies current AAU along and have adozen+ to refab to keep Trixie honest and bone stock pleasing. We all need at least 2 Commandos, one or more to have our way with and one to test ones wits and skills and faith plus support long term venders part numbers.

High idle suggestions

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