9 replies to this topic

[NorthantsRob]

OK, I'm not quite a novice but go easy on me!

 

1959 850 Mini with standard HS2 carb, running perfectly until yesterday when I removed the carb dashpot to clean it up (outside only). I know to mark the dashpot to ensure it goes back on the right way etc.

 

I did also carefully lift out the piston assembly/spring and needle, wiping them gently before carefully re-inserting (only seems to go back in one way). Dashpot went back on (the right way, though I've since tried both ways also) and put oil into the dashpot to the right level.

 

The car starts OK and runs OK at idle, when engine is warm - all good at this point - but out on the road or parked on the drive, if I rev the engine (to say, 30-50% throttle movement at the pedal) then the engine dies. It then takes quite a few attempts to start again but when it does start, the same happens if I rev heavily.

 

Nothing else has been touched or altered and again, prior to dashpot removal yesterday, the car ran as sweet as a nut.

 

Anyone spot my (likely) schoolboy error??

[sledgehammer]

have you put the dash pot spring back in ?

 

what oil was it in the dash pot , try thicker oil

 

sounds like piston is rising to easily - making acc mix weak

 

(this is all a guess)

 

& no matter how good someone is on mini's we all have school boy errors

Edited by sledgehammer, 13 August 2016 - 03:44 PM.

[NorthantsRob]

Hi, thanks for your suggestions.

 

Yes, dash pot spring is definitely in there and I'm using a small bottle which is marked as SU dash pot oil. What would you suggest using, something like 20-50?

[sledgehammer]

that sounds like the right stuff

 

i would check piston moves to full extent both up & down

 

& look for pipes damaged / disturbed when taking off the dash pot

 

after that I'm out of ideas for something changing when only taking off dash pot

 

only other thing is a bit of crud under the dash pot seal stopping the vacuum

 

or have seen cheap pancake air filter with hole missing in the vent hole area stopping piston moving correctly

 

or even gasket between air filter & carb with hole missing

Edited by sledgehammer, 13 August 2016 - 03:56 PM.

[NorthantsRob]

Again, thanks sledgehammer - I'll go and make sure everything is totally clean - triple check everything. Appreciate your help!

[carbon]

+1 for sledgehammers suggestions, particularly checking the inside of the dashpot and outer edge of the piston are spotless and the piston moves up freely and also drops back down all the way.

 

There is very little clearance between the dashpot an piston, and very small amount of muck could cause piston to be sticky.

[NorthantsRob]

I've just taken it apart again, washed the inside of the dashpot out with petrol as well as the outside of the piston. Got the engine to normal temperature and on a 4-5 mile run, everything was ok. Stopped the engine for 5mins and set off again - almost stalled at the first junction and had to keep a bit of throttle on to keep from stalling all the way back.

 

When I had the dashpot off the piston was rising & falling OK, no sticking at all. I also put the slightest smear of light oil on the outside of the piston rod, as suggested in the workshop manual for the car. 

 

I guess I'll keep on looking and clean everything again - annoying this one! 

[sledgehammer]

just a pointer - don't put any oil on the piston outer surface it's self or dashpot inner surface

 

I don't think that is what you were saying - but just in case

 

any oil there can cause resistance & attract dust / dirt , which could cause sticking

[NorthantsRob]

Well guys, I think I might have fixed it!

 

Took the piston out again today and basically left it to soak in carb cleaner which I'd squirted into a pot - did the same with the dashpot as well, scrubbing them both with an old toothbrush. Despite workshop manual advice to the contrary, I didn't smear light oil on the outside of the piston rod (and no, there was none on the piston/inside of dashpot) and I put only a very small amount of oil into the dashpot when reassembled (I might have overfilled it yesterday).

 

Result = it seems to run well, cold and hot, idles nicely and when I rev, the engine returns to tickover without a hint of spluttering or stalling.

 

So, I got here in the end - thanks for the advice offered, much appreciated! :) 

[sledgehammer]

nice one