Any Stromberg Carb Experts Out There?

[chamba]

Hi guys, I've got a bit a problem with the Stromberg CD150 carb on my Herald. It's been leaking a lot of fuel and upon inspection it's coming out the arrowed hole in the photo. I can't for the life of me tell whether this hole should have had a screw or plug in it (can't really make out whether it's got a thread)or whether it is an overflow of some sort. On the exploded drawings I've got, it shows a bar that extends from the carb throat to the hole, but on my carb, the throat has a threaded metal 'bung' which sits flush (as you can see in the photo).

Not sure whether it's related, but I've also been experiencing idling problems when fully warm in that the engine will die down to a stall after a few 5-6 seconds. The exhaust note isn't particulary smooth and can't tell whether it was rich (should be a rythmic 'hunt') or weak (a bit all over the place). I've adjusted the carb this morning as per the usual Stromberg procedure and weakened off the mixture 3/8 of a turn - will see how it starts/runs on my drive home tonight.

Could the leak/running problems be caused by the piston not falling correctly? This *might* be happening but I would need to investigate further. Any help appreciated, carbs are still a black art to me!

[MrSpeedy]

Afaik, that hole should be plugged as it'sa leftover from production. It's a gallery drilling and shouldn't be open. You certainly shouldn't have fuel coming out of there (but I'm sure you know that)
I've a pair of cd150s knocking about off my Vitesse, I'll dig them out and study them closer.

[BenzBoy]

I think the float or needle valve is sticking or the float is holed and sinking, and the float bowl is overflowing. I can't remember for sure but I think that hole is the float chamber breather. That would also explain why the engine is running like pooh.

A rebuild will sort it!

[vitesseefi]

That hole IS the float chamber breather so clearly the float chamber is over-flowing. That drilling also comes forward to the airfilter gasket face (plugged in this case) and the more normal Stromberg behaviour is to dump fuel into the airfilter through this hole. This will also be causing it to run rich, especially at idle - hence your idle problems.,

Possible causes:

crud behind needle valve (very common - fit an inline filter!)
needle valve knacked
float has a hole in it and has sunk
float level setting incorrect
Crappy modern replacement fuel pump producing too high a fuel pressure

Nick

[MrSpeedy]

^^What they said!

I had a similar over fuelling issue when I first fitted my electric fuel pump.
Pressure regulator set at 2.5psi soon sorted that out

[chamba]

Cheers fellas, lots of very good advice there.

The car ran like wibblepoo when I bought it last year and it came with a carb rebuild kit so that was the first job I did and it ran fine afterwards. I never had conclusive evidence what was wrong with it, but was probably a damaged diaphragm.

Anyway, before posting on this thread, I had the fuel chamber open. The float valve opened and shut fine, the [plastic] float appeared bouyant. I measured the height too, but this wasn't actually too easy, so I wasn't as accurate I should have been, but I think it's correct. The fuel pump is a standard item and flow stopped easily with my thumb over the fuel pipe.

One thing I have noticed looking at drawings/photos is that that dashpot cover is probably rotated 90 degrees from where it should be, so I may spin that back round. Don't suppose that's causing the symptoms here though..... think I best take another look at that float. Damn it, I hate carbs!

[taurus]

By chance I came across a NOS Stromberg CD150 during the week - a bit mucky but unused. That hole is covered by a clip secured by a small screw in the threaded hole on the outer edge. The clip acts to allow the breather to breath, but keeps curse word from getting into it.

Other than that - it's as said above re. the float chamber

[MrSpeedy]

Aug 10, 2013 21:50:04 GMT chamba said:

One thing I have noticed looking at drawings/photos is that that dashpot cover is probably rotated 90 degrees from where it should be, so I may spin that back round. Don't suppose that's causing the symptoms here though..... think I best take another look at that float. Damn it, I hate carbs!

One thing I have learned about these carbs. If you're playing with the dashpots, when you refit it, make extra sure that the piston rises and falls freely. I've known them stick if one screw is as much as 1/4 turn too tight. It will affect running more than you imagine

[chamba]

Taurus & MrSpeedy, thanks for the very useful info there. Need to look at my carb strip down pics to see whether the clip was fitted previously. I couldn't find it my bag of old carbs parts, but it's not a show stopper either way.

I remember setting the needle centrally was a bit of a hit and miss affair last time round. Hope to get some time this week to have a play and let you know what the problem was, figners crossed.

[nomad]

I found some handy sites when I first started looking at my carb
Top tip - undo the needle holder in the carb base a couple of turns and tap it to center the needle jet
retrorides.proboards.com/thread/88892/1972-hillman-hunter-estate-lives?page=5

[chamba]

One week turned into 6 months! Reading up I found you could effectively change the float height by slipping additional washers under the fuel needle valve. Checking my rebuild kit this morning, there was a number of different thickness washers for this very purpose.

Slipping in another washer has got the float sitting from 15mm to somewhere nearer the 18mm it should be set to. Result - no fuel out the overflow or no idling probs!

Thanks for the help with this fellas!