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High Idle Causing Redlining and Excessive vibration.
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Sat Jul 26, 2008 3:43 pm    Post subject: High Idle Causing Redlining and Excessive vibration. Reply with quote

Hello,

Commando 850cc 1973 Roadster. Boyer ignition, clean Amal original carbs.

The bike starts right up (one kick) and idles at around 1500 rpm's cold. The Rpm's continue to climb at idle as the engine gets hotter.

I have made adjustments to the throttle screw and pilot screw. If i screw the pilot in any more the bike will not idle. Same with the throttle stop, it wont bring the idle down without a complete stop in the motor. This seems to be the "sweet spot", however at 1500 rpms its just to high.

Any suggestions? Anything else besides the carbs that can be adjusted to bring the idle down while maintaining a strng tick-over speed?

any help will be apprecaitesd
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panic



Joined: 20 Sep 2005
Posts: 53
Location: Hempstead, New York

PostPosted: Sat Jul 26, 2008 3:55 pm    Post subject: Reply with quote

Vacuum leak.
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Sat Jul 26, 2008 4:12 pm    Post subject: Reply with quote

Ok..

Vacuum Leak. I'm game and i have all day tomorrow and monday to fetter.

Any tips or suggestions on how to find the leak? Anything i should be on the look out for or quick tips?
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Stuart SS



Joined: 21 May 2004
Posts: 269
Location: Australia's Far tropical nth

PostPosted: Sat Jul 26, 2008 4:36 pm    Post subject: Reply with quote

jsouthard

Quote:
clean Amal original carbs.


But what are the wear factors like in the slides/ bodies.. sounds typical of what I have experienced with flogged out slides ~

(I used to pull at a set of lights and the revs would surely climb .. but if I engaged first gear and then just let the clutch out to load the thing , the revs would return to low revs ~ ????? )

You can run successfully with worn slides ~ even the point of being able to hear them rattling IMO , but there is a point of critical mass ~ Shocked
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Sat Jul 26, 2008 5:16 pm    Post subject: Reply with quote

The slides have never been "sleeved" so there may be an opportunity there.

However the RPM's get so high so quick i CANNOT keep up with highway traffic without exceeding redline.

I can feel lots of room in the throttle and the bike responds very strong. Good off the line and if i open the throttle up she moves quick. Just redlines so fast. when i'm in 4th gear i hit 7,000 RPM's at 50mph.
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trinorman



Joined: 16 May 2007
Posts: 33
Location: Ventura, California

PostPosted: Sat Jul 26, 2008 9:58 pm    Post subject: Reply with quote

I'm a little confused from your last line (...if i open the throttle up she moves quick. Just redlines so fast. when i'm in 4th gear i hit 7,000 RPM's at 50mph.) I don't get what this has to do with a high idle problem. This sounds like you have a slipping clutch.


.
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cash



Joined: 10 Nov 2006
Posts: 419
Location: west cumbria

PostPosted: Sat Jul 26, 2008 11:16 pm    Post subject: Reply with quote

Or the rev counter is fast? Might explain the high tickover? Rolling Eyes

Cash
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grandpaul



Joined: 15 Jan 2008
Posts: 533
Location: Laredo (south) Texas

PostPosted: Sun Jul 27, 2008 6:39 am    Post subject: Reply with quote

To find intake leaks, use starter spray (ether0.

Squirt some on a joint area, and if the idle increases, you found the spot.

However, you need to get it under control first, so start by snugging up EVERYTHING.

ALWAYS start with the bloody hard-to-reach manifold mounting bolts, then the equally fussy inner carb mounting nuts.
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Mon Jul 28, 2008 7:58 am    Post subject: Reply with quote

Doesn't seem to be a vacuum leak. I sprayed all the areas that could be effecting the idle and nothing changed.

I have have seen the idle lower to about 900 rpm's at startup. I went through and tightened everything, continued to adjust the pilot screw and it seems to be ok. It does want to live around 1100 - 1500 rpm's once it warms up and has be run a bit. It may be time to look at a more modern carb.

thanks again for everyones help. i think it was the combination of the tightening, incorrect tach and frustration that was the problem.
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cash



Joined: 10 Nov 2006
Posts: 419
Location: west cumbria

PostPosted: Mon Jul 28, 2008 11:43 am    Post subject: Reply with quote

Before you start spending big money check the slides are falling onto the stops and it's not mal-adjusted cables and splitter box that's holding them up.

Cash
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dave M



Joined: 19 Oct 2005
Posts: 309
Location: Hong Kong

PostPosted: Mon Jul 28, 2008 9:39 pm    Post subject: Reply with quote

Great minds think alike Cash, I have previously bought brand new cables that have insufficient slack to allow the slides to bottom out in the carb body and also that were slightly different from each other in length thus requiring individual adjustment at the carb top, both cables need to allow the carbs to open exactly together and close together.
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Tue Jul 29, 2008 1:16 am    Post subject: Reply with quote

ah... ha!

One of my throttle adjustment screws is broken. they lift the same but this may be causing the slides to stay up once i get going.

I'll replace the cable which is still the original '73 and the screws. Hopefully this will do the trick.
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Gino Rondelli



Joined: 03 Jan 2008
Posts: 44
Location: Perth Scotland

PostPosted: Tue Jul 29, 2008 5:32 am    Post subject: Reply with quote

If its not that then have you looked at the balance pipe between the carbs, can cause all sorts of problems!
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jsouthard



Joined: 26 Jul 2008
Posts: 42
Location: Detroit Michigan

PostPosted: Thu Jul 31, 2008 5:11 pm    Post subject: Reply with quote

So the low idle lasted about 30 miles.

I'm back to 1100 - 1500 rpm's with rattling slides and shaking arms.

I balanced the slides, cleared the pilot crews, re-set the carbs to an even tick over thats strong, the balance pipe and filters in good shape and spraying starter fluid on every possible leak made no difference.

It idles low (600) but uneven at first start. At the first stop light i'm back to 1500 rpm's?

Any other ideas?
Mad
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norbsa48503



Joined: 07 Apr 2004
Posts: 995
Location: Flint, Michigan

PostPosted: Thu Jul 31, 2008 5:38 pm    Post subject: Reply with quote

Well I am right up here in Flint if you can make it 60 miles. I am betting you have a warped carb body. It gets warm it gets worse. I have the service tools to fix it. I will work on it for some doe if you like. PM me
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The Unapproachable Norton Commando

At the end of 1967 the Norton Commando was announced.

The Norton Commando was greeted with a certain amount of scepticism because on first sight the commando appeared to comprise of the old Norton Dominator twin cylinder engine mounted at an inclined angle in a set of new cylinder parts.

It was not realized that the new Norton Commando Isolastic method of engine suspension damped out all engine vibration and produced a machine which had uncanny smoothness for a vertical twin. In due course the critics were silenced and the Norton Commando had the distinction of being regarded as the first of todays so called superbikes. There can be little doubt that the original design concept of the Norton Commando has proved correct, since comparatively few modifications of any real consequence have been made since production commenced during 1968.

Now nearly 40 years later Norton Commando riders like us are a breed of our own, and as far as we are concerned its still more fun to go for a blat on the old Norton Commando, and fast. As a Norton Commando owner and enthusiast, my goal here is to promote and give credit to those who keep the Norton name going.

It is more deserving to give credit to the Commando itself, for after all these years it continues to be respected. The original Commando designers like John Favill are those who deserve the credit for developing this incredible motorcycle.

The Norton Commando Roadster and Interstate of the late seventies, never died. Although the Norton Villiers factory dispersed the tradition lived on. Today Kenny Dreer in the USA is developing the new 952 CC Norton. What a great looking bike this is, and its engineering is still based on the original layout. It will be interesting to see how the new 952CC Norton does in todays tough motorcycle market. One thing is for sure, I would own one if I could afford it.