Increasing tickover speed

[TimB]

Hi, anyone any ideas on why the tickover speed should get faster and faster on a B20 engine as it warms up? I have checked the linkages and it has nothing to do with the fast idle cams on the SUs as ther is still clearance. Likewise the throttle linkage itself is not effecting the butterfly spindles as there is also plenty of radial free play (I think that's just a posh way of saying you can rotate the spindle before it touches the 'C' shaped connector to the throttle pedal linkage.
It is really odd, however I set the idle to about 800-900rpm when warm, it still creeps up after driving right up to 1800+. The idle is otherwise fine and regular on a normal 'C' type cam and standard SUs

[222s]

Knackered throttle return springs?

[mike gilbert]

just a guess but what if there were an air leak between manifold and carbs or manifold and block. As the engine got really hot from driving the expanding gaskets and metal would block the leak and thereby make the mixture richer than it was when the idle was set. Might that then increase the idle speed?
Mike

Any joy fixing this?

I had a similar problem which I discovered was down to using the wrong oil in the SU dampers. I had mistakenly used a multigrade gearbox oil. I'm now using SAE 20 monograde (although I understand ATF works well too).

The symptoms were similar although I found blipping the throttle brought the revs back down...sometimes.

Damon

[TomTom]

I have exactly the same problem using the same SUs and cam set-up. I've also been told that it is most likely an air leak. But I'll try changing the dash-pot oil and see. For me it's not too annoying but must be wasting petrol.

I must say that my higher revs sometimes dip down to normal in the course of the drive, but then go up again; this wouldn't quite go along with the expanding gaskets, unless something else is moving and affecting the mixture.

Tom

[classicswede]

A few posssibles on these.
badly balanced carbs
air leaks
gummed up butterflies
worn butterflies
worn spindles
sticking linkages
incorrect oil (engine for SU's ATF for strongbergs)
and the other one with twin carbs is some manifolds (for us market) have a extra pair of butterflies in them - these manifolds cause no end of running problems. If you have one it is best replaced

[amazondean]

I totaly agree with Dai. If you have one of those manifolds with the extra butterflies, get rid of it. I had similar trouble with one once, and tried everything. I stripped the carbs and rebuilt them. Changed plugs, points, condenser, rotor arm, cap, leads, fiddled with the timing. All to no avail. I even tried different carbs off one of my other cars, and still the same. I then spoke to a specialist ( i forget who) and straight away he said dump the manifold. Instantly it sorted it out. What a relief. They are notoriously crap I have since found out and was only introduced to try and get emissions down on idle for the MOT. Lose the retarding distributor as well if it's fitted and replace with an advancing one, or even no vacuum advance at all.

One reason why I chose an amazon for my daily transport is because among other things, they are incredibly simple animals. Get rid of all gadgets and life will be soooo simple.

Dean.

[classicswede]

The manifold was introduced to reduce emmissions for the US. This manfold is most common on 140's and the odd P1800. I've not seen one on an original 2carb spec amazon.

[TimB]

Thanks for all your input. We have been following the same line of attack. As a compromise I have taken out the secondary butterflies and blanked off their spindle holes. I would love to replace the manifolds but don't know anyone with a spare...Any offers? I suppose I will have to replace the exhaust manifold too as it currently has a twin downpipe.
Incedentally I have asceetained that the vacuum system on the distributor is one of the 'retard' type. I have found that it indeed runs better with it disconnected and I have done this and blanked off the vacuum pipe.
The inlet manifold really looks like a weird arrangement. I have a B18 powered P1800 with the basic type and it runs like a sewing machine by comparison!

[mike gilbert]

If you can find an early aluminium inlet manifold as used on Amazons and 1800's up to 1966, then mate it with an injection exhaust manifold (they are a perfect fit for each other) you will have the best set up. The early mainfold is light and easily polished inside and the injection exhaust is a larger bore twin downpipe. I did this on my '69 1800 after getting grief from the original manifold.
Mike