Stromberg not returning to idle?

[coldturkey]

More problems with my carb

Ok, so its running way better then when I first got it, but now being made apparent is that the carb doesn't return to idle easily after you have been at cruising speed.

Its basically like the accelerator cable is sticking, apart from the fact that the cable is loose as.

If I have been driving, ease of the accelerator and stop at the lights or something then it just sits there idling like 1500rpm or something, until I either open up the bonnet and push the throttle back against the idle stop, OR give the accelerator one quick stab - then the extra momentum the spring picks up seems to make the throttle return all the way to the idle stop.

What could be causing this? It also seems to be running a bit lean on the open road, it will top out at like 110kph and miss occasionally, but then if I pull the choke halfway out I can get significantly more speed out of it.

Cheers guys!

Edit: Its a Stromberg CD150 with temperature bypass thingy on the legendary 1256cc.

[KKtrips]

what have you done to it between when it was last running right and now?

[Seedy Al]

My suggestion. Remove damper, clean the shit out of it, get old oil out etc. remove piston, clean the shit out off it, make sure there is no dirt or anything around. check condition of your air cleaner, make sure that isnt full of dirt etc. Dirt is bad. If your filter is fucked replace it.

Maybe give both piston and bore a very light sand with wet and dry, Reassemble using very light oil on the piston, and full damper without over fulling causing oil to drain into carb, this can be hard, and not nesserly super important.

This may help, but it may not. However to me it sounds like your piston is sticking.

Oh, also make sure your needle on the piston isnt bent, and that the needle seat is correctly aligned with the needle

See how that goes

CDL

[coldturkey]

what have you done to it between when it was last running right and now?

It has never been running right since I have owned it (4 months). The last guy that owned it says he had it conditioned by someone that knew what they were doing, but im not so sure

[coldturkey]

My suggestion. Remove damper, clean the shit out of it, get old oil out etc. remove piston, clean the shit out off it, make sure there is no dirt or anything around. check condition of your air cleaner, make sure that isnt full of dirt etc. Dirt is bad. If your filter is fucked replace it.

Maybe give both piston and bore a very light sand with wet and dry, Reassemble using very light oil on the piston, and full damper without over fulling causing oil to drain into carb, this can be hard, and not nesserly super important.

This may help, but it may not. However to me it sounds like your piston is sticking.

Oh, also make sure your needle on the piston isnt bent, and that the needle seat is correctly aligned with the needle

See how that goes

CDL

Its a brand new air filter.

OK I will pull the damper assy apart and give it all a good clean and check clearances etc. Thanks!

Paul Walbran suggested it could be air leaking in around the accelerator spindle. I dont see how this could affect it returning to idle? It seems purely mechanical

[SloNLo]

add a second spring and call it a day

could be dirt/oil in the linkages, give them a blast of degreaser and see if it helps

[coldturkey]

add a second spring and call it a day

could be dirt/oil in the linkages, give them a blast of degreaser and see if it helps

haha yea thought about it. Different perceptions of 'solving' a problem

Well I cleaned out the damper assembly and put new ATF in there and its still the same. Damn.

So, this could be a noob question, but when someone is referring to the 'throttle spindle', which part is that in the following pic?

I assumed it was number 9 but i dont see how that could cause it to not return to idle.

[IvyMike]

I just had a look at my carb, could it possibly be the idle actuator? May have got dirt in it when you cleaned it? (Assuming you cleaned it)

[coldturkey]

I just had a look at my carb, could it possibly be the idle actuator? May have got dirt in it when you cleaned it? (Assuming you cleaned it)

I haven't cleaned it, but tell me more about this idle actuator, because when the engine is off, there is no resistance to the throttle movements at all but when its running there is some resistance there. Might be that thing.

How do I clean it?

[IvyMike]

I'm only assuming it is some sort of air bypass. So the butterfly won't actually shut with the engine running? Have you actually tried moving that little lever outlined in the photo with no load on it from the spring?

[Seedy Al]

did you remove the piston and diaphram when you said you cleaned out the damper or not? As this is where dirt can cause the piston to stick. As for the trottle spindle yes that is number 9.

if it is warn it can make the butterfly jam against the carb walls (for some reason correct term is escaping me) so this will keep for throttle open slightly. Same if the butterfly isnt set correctly on the spindle.

Also if its warn this can cause a vacuum leak.

I would suggest pull carb off, Check that butterfly is closing properly, as in try closing it slowly and see if it sticks, or if there is any differnece between butterfly location if you snap it closed.

However I still recommend pulling out the piston and cleaning it along with the bore that is slids in to make sure there is no dirt.

Seedy Al

[coldturkey]

did you remove the piston and diaphram when you said you cleaned out the damper or not? As this is where dirt can cause the piston to stick. As for the trottle spindle yes that is number 9.

if it is warn it can make the butterfly jam against the carb walls (for some reason correct term is escaping me) so this will keep for throttle open slightly. Same if the butterfly isnt set correctly on the spindle.

Also if its warn this can cause a vacuum leak.

I would suggest pull carb off, Check that butterfly is closing properly, as in try closing it slowly and see if it sticks, or if there is any differnece between butterfly location if you snap it closed.

However I still recommend pulling out the piston and cleaning it along with the bore that is slids in to make sure there is no dirt.

Seedy Al

Yep I removed the whole thing and cleaned it.

How much play is normal for the throttle spindle, i've got two carbs and both of them have about 1mm of play in the spindle (I can slide them in and out with ease though, until the butterfly touches each side of the housing).?

Ok, I might pull the carb off and try that, although when the engine is not running it seems to return to zero easily no matter if I do it slow or fast

[coldturkey]

I'm only assuming it is some sort of air bypass. So the butterfly won't actually shut with the engine running? Have you actually tried moving that little lever outlined in the photo with no load on it from the spring?

I'll have to have another look, I tried looking at this before but found it had to test when the engine is running (without revving the crap out of my poor little engine).

It doesn't have any resistance on it when the engine is off, thats for sure.

[Steelies]

i'm having the same problem with my SUs, after cruising they seem to stick (butterflies return to throttle stop for sure) holding the revs up around 2000rpm for a while before slowly coming back down. havent had a decent look at them yet, other than the initial cleanup on installation.

you running ATF coldturkey?

[KKtrips]

I did have a thought about this last night - pull the bell off and clean inside the damper sleeve then fill the damper with only JUST enough oil so it does not overflow when you put the piston in.. Would be interesting to see if this will make any difference..

I'm theorizing that the oil may be coating the wall of the damper sleeve and causing friction when it should be a microscopic "airgap"..

[coldturkey]

i'm having the same problem with my SUs, after cruising they seem to stick (butterflies return to throttle stop for sure) holding the revs up around 2000rpm for a while before slowly coming back down. havent had a decent look at them yet, other than the initial cleanup on installation.

you running ATF coldturkey?

Yeah im running ATF, but it did exactly the same with regular engine oil.

I did have a thought about this last night - pull the bell off and clean inside the damper sleeve then fill the damper with only JUST enough oil so it does not overflow when you put the piston in.. Would be interesting to see if this will make any difference..

I'm theorizing that the oil may be coating the wall of the damper sleeve and causing friction when it should be a microscopic "airgap"..

Cool, well its an idea, which is more than I have at the moment. I'll try part filling it in the weekend and see if 'just enough' oil makes a difference.

[Steelies]

ahh thats a good point kk, will try too

[Seedy Al]

yes, I agree with the above statement, so much so i think i included it in my first post, But yeah, i had a hell of a time with SU's on a Jag once, turned out air claner was full of dirt, and the oil over the piston was casuing it to stick

Allan

[KKtrips]

Oh I never saw that - well that may back up my/CDL's theory.. LOL

[coldturkey]

Well, I ended up pulling the carb off a spare 1256 i had and swapped them over. This one is running way better, its returning to idle properly, still hasn't settled in though few sputters here and there and cut out a couple times. But maybe I will run with this for a while and see how it goes. I think im getting a bit more speed out of it too, certainly doesnt seem to be running lean.

Kinda side stepping the problem but meh. Its real hard to not over fill them though eh, overfilled it even when trying super hard not to.

Got a carb kit coming tomorrow too, but now i dont know which carb to use it on!

On a side note, there was a bit of wear on the carb housing internals where the butterfly was hitting it, but I dont think this was the problem cause i was playing with it trying to make it catch on the edge but it wouldn't.