Cd 150 metering needles

[Acollin]

series v twin stromberg cd150s

In trying to understand one thing more and more questions arise.

while fiddling with my carbs and a spare set, there were a few things that beg explanation.
1) some metering needles had stampings and other did not. I assume this suggests a) standard— no stamping, and b) a different size/thickness than standard That the stamping informs.
while I understand what a thicker and thinner needle will do, how does one determine what is best for ones car?

2) not all air valve pistons that fit into a cd 150 carb body are identical. How many are there and how is one to determine what is best for their car?

My carb issue: I have been experimenting a lot with mixture and slow running adjustment screws. When I get the car running “ great” I get dieseling at shut off— when I control the dieseling at shut off, the car hesitates and pulls away like an old man getting out of a recliner ( 1st hand knowledge) hesitates — stops and starts — until the full compliment of fuel is engaged.
Essentially: rich runs good, but dieseling/ lean runs badly no dieseling.

can some suggest a place to read up on better understanding my carbs that would explain metering needle markings and air valve differences?
How do I achieve —— runs great , no dieseling?

thanks all
Andrew

 

[hartmandm]

I have the Haynes Zenith Stromberg CD Carburetors book. It lists all the specs for each metering needle. They have maybe 300 metering needles listed with their dimensions. It is possible the part number is stamped on the needle. But don't interpret no stamping as being something 'standard'. You have to take measurements of the needle diameter every 1/8 of an inch to confirm what needle you have. The original needle for Alpines with CD150s is the 5M needle. I couldn't get my Alpine to run rich enough on ethanol gas with 5M needles. I bumped up to the 6J needles based on someone else's recommendation and it was a big improvement. The 6J needles were originally used in 2.0L engines, so they provide a richer fuel - air mixture.

It sounds like you are able to get your mixture too rich and too lean. Your current needles are probably fine.

I don't know anything about differences in air valve pistons, but I'd leave them in the same carb where you found them. Maybe there were minor changes to the parts over time. You don't want to be mixing parts and get a mismatched setup.

Mike

 

[husky drvr]

Just as an add-on for Mike's comment - from the same reference - the carb numbers for a sV Alpine are 150CD 3059(F) and 3059(R). Any other combination would mean a different combination of pieces and parts that wouldn't be comparable in some manner. For instance, 150CDS 3163(F) and 3163(R) are listed for the Mk. I Rapier (Alpine GT coupe for this side of the pond), would look almost identical, but are for a very different installation on a 1725 cc Rootes engine.

Hope this helps,

When I get the car running “ great” I get dieseling at shut off— when I control the dieseling at shut off,

Andrew,

Your over run issue might be a symptom, more than an issue. The electrical circuitry doesn't instantly cut off at the turn of the ignition switch. The alternator will continue to charge and feed the coil to some degree while it continues to rotate, after the ignition switch is turned off.

When you get your engine tuned where you are relatively sure you will experience run on after turning off the ignition switch, you might try this test.

Have someone else turn off the ignition switch. If the engine continues to run with the switch off, pull the power feed wire to the coil and see if it stops. As a double check, pull the power feed to the coil with the ignition switch still on and see if you have run on under that condition.

Just a thought,

 

[Acollin]

Thanks all, Good information.
I will look to buy the Haynes Book.

Mike: Are you suggesting that if my ”running on “ problem is fuel related and I can go to “too lean and too rich“ that I just need to strike the happy balance and will if I keep fiddling?

Husky drvr: I will try your testing tomorrow but are you suggesting my ignition switch could be the problem?

Be well
Andrew

 

[hdar5702]

Andrew,I don't know if this will help but it has answered most of my CD carb questions...so far.It also lists metering needle info.

stromberg cd carburetters​

tecb.eu
https://tecb.eu › onewebmedia › Tuning_Strom...

 

[hartmandm]

Mike: Are you suggesting that if my ”running on “ problem is fuel related and I can go to “too lean and too rich“ that I just need to strike the happy balance and will if I keep fiddling?

No. I don't know why your car is dieseling. I made that comment that you seem to be able to be too rich and too lean because I don't have any reason to think that switching to a richer metering needle will help with your dieseling issue.

Mike

 

[RootesRooter]

Has anyone with experience taken a look at your throttle rods to see if they have too much play in the housings? Worn rods and/or housings can play hell with the mixture.

 

[husky drvr]

Mike: Are you suggesting that if my ”running on “ problem is fuel related and I can go to “too lean and too rich“ that I just need to strike the happy balance and will if I keep fiddling?

Husky drvr: I will try your testing tomorrow but are you suggesting my ignition switch could be the problem?

Andrew,

I'm not sure I recall if you've ever stated what grade fuel you are using, regular or premium. I think Mike's "fuel related" is a suggestion to try a different fuel on your next fill-up - if you're using regular then try premium or a different brand.

As to your switch, I seriously doubt there's a problem with yours. It's just a thought about the way current is generated and flows through circuits in an old car. Remember, every circuit is grounded to a common point but if some circuit is poorly grounded, that circuit's current might find a back feed path to flow to the ignition circuit - maybe through some common connection after the "off" side of the ignition switch.

Hope this helps,

 

[Acollin]

Update

husky drvr: I have only run non ethanol fuel and I believe the octane rating is 92 or 93. ($5.50 a gallon) I have not yet done the coil wire test.
hdar 5702: outstanding book thanks for the file.

Before I get into the carbs on my car I use my spare set as a text book of sorts. I discovered that a metering needle can act as centered but not actually be centered. The metering needle on my front carb was slightly off but still moved freely. I was able to visually see that the jet was not centered as the gap between the jet and carb body was not consistent. I inserted a small metal rod into the jet oriface and was able to skosh it over a bit until I could see that gap between jet and the carb body was consistent. I had been “ sharp tapping”— (as per wsm) and things did not shift as much as they should have. The effect was profound. The dieseling is all but gone and I think I should be able to adjust it out. hdar 5702‘s book references using a rod to center the metering needle with no “sharp tap”. I think now that I can visually see if the jet is off center, I will go back through the carb adjustment sequence and try to eliminate the now very subtle running on. If anyone has more ideas and suggestions, please send them along!!

Thanks again for all the energy and information
be well all
Andrew

 

[puff4]

I made these quick and dirty tools many years ago, and although I’ve always said I’ll make a better set someday, these have served me surprisingly well ever since. I have them for S.U. and Z-S carbs.

To use them you remove the air valve (the bit that goes up and down) and then reinstall the chamber lid, without the damper cap. Then you slide this tool into the center of the carb, where the air valve would be. The larger diameter fits with a close fit into the air valve slide, and the smaller segment is meant to slip into the jet, with a similarly close fit. If it doesn’t slide in easily, then you loosen the jet and reposition it until it does. Then lock up the jet and you’re virtually guaranteed of having a properly centered jet. My days of “sharp tapping” are over.



They’re quite easy to make up - any competent amateur machinist could turn one in 30 minutes or less. But they’ll save you tons of time.

 

[hartmandm]

There was a commercial Stromberg tuning set sold by Schleyer. It has a procedure for centering the jet using a part similar to what Kevin has made up. It also has parts for other tuning processes. I picked up a tuning set, but haven't tried it yet. Instructions attached.

Mike

 

[puff4]

That’s true, Mike. I actually have that set. However, I don’t find it as easy to use as my centering tool - theirs requires you to remove the jet needle from the air valve piston, and then replace it with the provided insert. Plus, theirs centers the jet bearing, not the jet orifice, so if the orifice is slightly off, their tool won’t catch it.

 

[Shannon Boal]

I was able to visually see that the jet was not centered as the gap between the jet and carb body was not consistent. I inserted a small metal rod into the jet oriface and was able to skosh it over a bit until I could see that gap between jet and the carb body was consistent. ..................... I think now that I can visually see if the jet is off center............

I agree on the eyeball thing: like a Creedmore gunsite, it is very precise. (This from a guy who finally replaced those carbs with an Alpine Innovations Weber kit)