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High idle (Problem Solved)
https://www.ausmini.com/forums/viewtopic.php?f=2&t=20735		 Page 1 of 2
Author:  Hanra [ Sun Jul 02, 2006 3:11 pm ]
Post subject:  High idle (Problem Solved)
Ive just gotten my new manifold on, rebuilt both 1 1/4in SU's. Used all new gaskets for carb to heat shield/ shield to manifold. I have also thinned down the throttle shafts, fitted countersunk screws to the buttlerflys, smoothed out the rear of the carb just after the bridge all as per Vizards book. I also knive edged the both the butterflys.

Ive ditched the AH2 needles that i was running and fitted some 3's. I can set the mixture up quite well, though i still feel maybe on the rich side. The 3 is a bit richer than the AH2 but ive also got some leaner QW's to try as well.

The issue that i have is that i have the idle adjust screws fully wound out and i cant get the idle below 1100rpm. If it idles for a bit it will end up at 1000rpm. I would prefer it to be down around 800-900rpm. Previously with the AH2's i could get the idle riight down till it nearly stalled.

Ive sprayed around the throttle shafts/manifold/carby area with carb cleaner to check for air leaks but engine revs stayed constant. So kinda ruled that out. Ive confirmed that the throttle is fully closing, i disconnected the throttle cable to be 100%.

When i knivedged the buttlerflys i made dam sure that they still seated correctly inside the bore of the carb. U could not see daylight past the butterfly, so im pretty sure that is ok.

Any other ideas??

Cheers,
Author:  9YaTaH [ Sun Jul 02, 2006 5:39 pm ]
Post subject:  Air Filter
Hmmmm it sure sounds like it is rich at idle....I would like to see what happens if you remove the aircleaner element(s) to give it more air at idle.

Timing and points right :?:
Author:  Mini Mad [ Sun Jul 02, 2006 5:59 pm ]
Post subject: 
It's probably more beneficial to have it idle that little bit higher as it keeps a steady supply of oil to the cam and valve gear.

Mine idles at 1400-1600rpm :lol:
Author:  benjamin [ Sun Jul 02, 2006 6:03 pm ]
Post subject: 
maybe the choke cable is a little tight and pulling on the high idle , undo the choke cable completly to check
Author:  Hanra [ Sun Jul 02, 2006 7:53 pm ]
Post subject: 
I dont have a choke connected. Its never cold enough up here to warrant fitting it. I have been tuning it with the air cleaners off n still cant get the idle down. Timing is all correct, 10 deg adv, petronix elec ignition. Ill have to try the QW's that i have some time through the week n see if that makes a difference. I think from memory that the jet thickness is the same on the AH2/3/QW so idle mixture shouldnt of really changed???
Author:  supercharged 850 [ Mon Jul 03, 2006 12:45 am ]
Post subject: 
Could you have a leak around one of the gaskets???? Not impossible...... :?
Author:  Hanra [ Mon Jul 03, 2006 7:15 am ]
Post subject: 
supercharged 850 wrote:
Could you have a leak around one of the gaskets???? Not impossible...... :?
Thats why i was spraying carb cleaner everywhere, if there was a leak the revs would pick up even more. Will have to spend a bit more time on it this weekend i think.
Author:  Mick [ Mon Jul 03, 2006 10:05 am ]
Post subject: 
Just a thought , I rebuilt my twin SUs a while back and had the same problem for a while.

I had bushed the throttle shafts but hadn't pushed the bushes all the way in to the butterflies. This allowed air to get around the butterfly even when shut and the idle went through the roof, Or the throttle cable is a little too tight....

Might be worth a look.
Author:  Hanra [ Mon Jul 03, 2006 12:36 pm ]
Post subject: 
I think that is the area that i will have to look at. I cut the top half off the thottle shaft, So its not a slotted shaft any more. I also machined down the other side, then countersunk the butterfly and fitted countersunk screws. The idle is high even with the throttle cable disconnected. I didnt replace the bushes at all, but they are ok, no play or slop. 3 weeks ago b4 i touched the carbs i could get the idle down to almost stalling!!!!

With the idle screws fully wound out its idling at 1200rpm.
Author:  Morris 1100 [ Mon Jul 03, 2006 7:48 pm ]
Post subject: 
Have you backed off the linkage between the carbies? It could be that one carby is shut and the other is part open.
Try listening with a piece of hose and see if one carby is sucking more than the other.
I would not have bothered with Vizards carby tips. In one book he says you must do it, another book he says it is a waste of time! :roll:
Author:  Hanra [ Mon Jul 03, 2006 8:02 pm ]
Post subject: 
Im using a Gunsons Carb Balancer. They are both sucking the same amount of air with the throttle screws right out and the throttle cable disconnected.
Author:  drmini in aust [ Mon Jul 03, 2006 9:44 pm ]
Post subject: 
It sounds to me like you need 2 new butterflies....
Old ones often get worn at each end near where the shaft goes, to check, open throttle slightly and see if shafts have endfloat. If so, I bet butterflies (or bodies) are worn....
Author:  Hanra [ Mon Jul 03, 2006 10:15 pm ]
Post subject: 
Yeah there is a bit of end float, but 3 weeks ago b4 i touched everything i could wind the idle down to stall the engine. I did knife edge the butterflys though. I edged opposing sides n made sure the butterflies seated correctly on the body according to the edge that i had cut.
Author:  drmini in aust [ Mon Jul 03, 2006 10:23 pm ]
Post subject: 
Pffft I'd just go buy 2 newies then. 8)
Jury is still out on whether Vizard's carb mods are worth it.
If you want more flow, grab some HS4s... :lol:
Author:  willy [ Mon Jul 03, 2006 10:26 pm ]
Post subject: 
Or get yourself a nice DCOE.
You know you want to.
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