Leaking Choke

[Iain T]

I have recently stripped down the choke mechanism on my 150 CDS as part of a campaign to reduce the amount of engine cranking from cold. The discs are now in the correct orientation and I cleaned up all surfaces with 1500 wet and dry however the mechanism is leaking petrol. It may always have done so as the front cab always had a soggy bottom but I would obviously like to sort it out. If I now take it that the nice flat polished surfaces ( I used our quartz kitchen worktop as a flat base for the wet and dry, don't tell the wife) are petrol tight the only way fuel can escape is down the brass shaft. Over the years although there is a bush in the outer housing the shaft fits in there like the proverbial p***k in a bucket. It seems the way to stop or reduce the leak is to a) re-bush but that will only reduce it b) fit a grommet and washer between the spring and dished disc thereby stopping the petrol from creeping up the shaft c) fit a ring gasket on the shaft between the actuating lever and the outer body. Before you ask I do have a gasket between the cab body and choke.

Has anyone else experienced this? As always any other suggestions welcome (just keep them clean'ish)

The clocks running who will answer first Pete, Doug, ANO?

Iain

[Pete Lewis]

is there a problem with the choke pick up tube its in the float bowl area , ie can it suck up to much fuel. never looked at is it moveable 

but the problem is out the box so trying to think the same way ????

sorry being first               is not very constructive    ive not had any of these leakers 

is the rear carb choke outlet clear ????

Pete

[Iain T]

The whole design seems flawed as I would not expect mating bare metal parts to, over time, maintain a seal. Plus there is nothing to stop the fuel from creeping up the brass (there's no seal) shaft then out of the outer body...barmy. I'm going to try a seal and washer behind the dishes disc.

Fuel seems to be getting to the rear carb, not sure about the ball valve in the pick up pipe. As that involves taking the bowl off I'll try the seal first to rectify what seems to me a poor design.

Watch this space!

[Pete Lewis]

there is no seal as really  the fuel from the disc holes should be sucked direct into the barrel for mixing and has no reason to leak out the operating spindle 

but youve proved it can !!!!

is there enough fast idle to get the depression required to use all thats sucked in ???

 

Pete

[Iain T]

As far as I can see fuel enters via the slot in the disc and is then collected in the cavity created by this disc and the separate dished disc, when the assembly is further rotated fuel exits via the graduated holes to both carbs. Therefore fuel can escape by various routes a) poor fitting/scored disc to carb body b) poor seal from disc to dished disc c) along the shaft to the outside world through worn outer body sleeve. 

I have adjusted the fast idle to give about 1300 rpm max as before it was over 2000 which is not within spec. However it may be that this small lift in the throttle spindle is, in my case not, enough to suck all the fuel out of the 'disc chamber'. I have a Huco low pressure, 2.1 psi I think, fuel pump which shouldn't make any difference so I will give the fast idle a tweak to get more sucky sucky!

It is difficult to know exactly where the fuel is coming from, I suppose the last port of call is to take the carbs off and see if the pick up tube rattles (apparently that's a good omen) and if there are any other obstructions.

Good point is the new Burlen diaphragms give a nice even tick over and pick up but having fuel around a hot exhaust manifold is not ideal even if the leak looks as though it does stop when the choke is pushed in. In writing that is does rule out a leak between the rotating disc and the carb body.

I'll report back tomorrow, had to do one of my two days a month back at work today.......I thought I was retired!

Cheers

[dougbgt6]

Iain,

This may not be useful but have a look at Buckeye Triumph’s 3 technical articles on Strombergs, how they work, taking them apart and reassembly. They are 175s but essentially the same.

Doug

 

[Iain T]

Doug,

Yes I have looked at Buckeye, very good site but of little help with my chokes dribbling. I need to activate my little grey cells for an engineering solution.

I'm getting the big hammer and superglue out tomorrow!

Iain

[Waynebaby]

Iain,

If it is any comfort, I have the same trouble with my choke mechanism and I've never been able to resolve the problem (so I'm hoping that you figure it out!) Like you, my fuel leak started after I'd refurbished the carbs and like you I can't see how the design of the mechanism can do anything other than leak down the spindle.The fuel comes out as you describe and then drips down into the suspension upright directly below. As with your carbs it only does this when the choke is actuated, which is why I've not been too keen to disturb the carbs to resolve a short lived problem - I had a nightmare with rubber slivers upsetting the needle valves and have been paranoid about moving the bundy tube ever since!.

My fuel pump is the standard mechanical variety so that may save you suspecting your electric pump is the issue. 

Wayne

[Pete Lewis]

the vent holes on the cleaner face are all clear .not covered by any gasket or like 

Pete

[Iain T]

All graduated holes are clean and OK, like Wayne I think it's just a bad design.

Wayne, had a lights on moment, I'm going to put a washer behind the dished disc to see if more spring pressure has any effect. However it won't stop fuel going down the shaft, that may be phase 2!

Iain

[Pete Lewis]

im on about the holes  in the front /outer face of the carb .where the filter mates .  easy for gaskets to upside down and close off the float breather ports and more 

Pete

 

[Iain T]

Yes I think this is right?

[Pete Lewis]

yep

 

Pete

[Iain T]

I'll sprinkle some wizard dust on it, turn round three times and give it a stern talking to tomorrow.

[Pete Lewis]

odd its leaking, the depression in the throat should suck fuel up from the float, through the metering holes and into the mix zone behind the air piston 

if its leaking out the operating shaft  there must be some suck missing   ?????  just thinking 

is this due to having pancakes ????    if you have the orig with paper filters does it stop the leakage ????

pete

[Waynebaby]

Hi Pete,

Mine leaks with either the pancakes that were fitted by a PO or with the original set up (which I'm running now), so that's a dead end I'm afraid.

Wayne

[Iain T]

I've had my Quaker oats porridge this morning so watch out Vitesse!

Wayne, I think when I had the original air cleaner mine also leaked as there was always a wiff of petrol around the engine. I put it down to age and OCD, that's me....

I'm going to try a fibre washer between the outer body and the lever arm to see if the shaft is the culprit then take the choke off (yet again) and use a washer to give the spring more push. I polished all parts and mating surfaces so can't do anymore on that front.

Pete I agree fuel should be sucked out but to work there must be some sloshing about in the cavity created by the front disc and the dished disc. The fuel is escaping somewhere.

Iain

[Pete Lewis]

next idea float levels,,  on many the float has two valve arms and can be fitted upside down  whilst the float height setting may be 18mm the fuel level is quite wrong 

due to the float contour top and bottom is quite different    just more thoughts 

eg  file:///C:/Users/Peter/Saved Games/Pictures/Saved Pictures/Downloads/TR250_TR6+Carbs+Part+II.pdf

Pete

 

[Nick Jones]

Surely there should be a seal of some kind on that shaft? One that has long turned to dust?  That or a decent close fit between shaft and housing now worn.....

[Pete Lewis]

nothing shows in any of my manuals , if there was then i would expect a groove in the bore or an 0 ring ...as an idea

its design  similar to other  downdraft solex starting valves  again no seals on them either 

more strong tea and head scratching  

Pete

 

[Iain T]

I agree with above, I'm doing lots of scratching. Design for long term durability is bad.

[Paul H]

Is the choke setup under discussion the same one as CDSE ?? If so I had the same leaking issues and cured it with Wellseal. From memory Wellseal applied with cotton bud so no moving parts were affected . 

Paul 

[Iain T]

I think CDSE is the American or later spec and has a different choke mechanism. A friend of mine said get some Wellseal, and it's fuel resistant. I'm off now to have a play in the multi-storey car park aka my garage! Well at least it's dry but the lights are on timers so every 5 or 10 minutes I have to run around waving my hands to get the sensor to turn them on again.....I call it The Docklands Dance! Oh for a nice warm well lit garage.

[dougbgt6]

Iain,

CDSEs were fitted to UK GT6 mk3s like mine and yes, it has the same choke mechanism, ‘sept mine don’t leak. 😊 I suspect the spring isn’t strong enough?

Doug

 

[Iain T]

Doug now you're boasting 'cos you don't leak!

Have choke apart and in the kitchen again (wife not too chuffed) and ordered some Wellseal. 

Until it arrives and just to amuse myself I'm going to take a gander at my rocker assembly, when I last adjusted the tappets there seemed an excessive amount of movement on the arms. I notice Paddocks do a bushed assembly anyone know if it's any good?

Iain