Intro and Zenith Stromberg question

[John75]

I recently purchased a 75 Spitfire as a project for my son and I. It had been sitting a year and was running rough. I'm sure it will provide many evenings of bonding time between us, as we nurse it back to health and eventually a restoration project. We live in the Kansas City area. As a youngster I owned MGB's, so I understand the amount of time we will spend on our Spitfire. I'm also hoping to instill in my son the sense of joy and accomplishment that comes with keeping it running.

We are currently working through some rich running Zenith Stromberg (single 150 CD) carb problems. The archives have helped us immensely with tips and links, and we rebuilt it the other day with a kit and several new parts. However, it's still running rich but I'm confident we will discover the answer soon. My question to the group; does a list exist that matches ZS carberator numbers with what year it was made, or possibly what engine it was made for? I have the original brass tag with numbers on the carb and there is a number stamped onto the carb body. I've spent a few days lurking and I've been very impressed with the thoughtfullness of the group.

Thanks,
John

 

[Simon TR4a]

Congratulations on the Spitfire, John.
I don't think carbs are made "for" any particular car, the car manufacturer simply chooses which carb to use for his application, so I doubt the numbers stamped on the body would help you, they probably are production codes of some sort.
The brass tag may help, as it could tell you if this was originally one of a pair of carbs, or possibly even what needdle was originally fitted. I don't think any of the codes would tell you if the carb was originally used on a Spitfire or came from some other make or model.
Paul Tegler's site, Google "Teglerizer", is very good for SU or Weber carbs but I don't know of a similar resource for Zenith Stromberg. I believe that is the right carb for your car, so perhaps other Spit owners can suggest the right needle so you can check yours.
Sorry to be so long-winded!
Simon.

 

[sammyb]

John,
Chances are that your ZS carb was made in 1974 or 1975 and was made for the Spitfire (although it probably appears on other small-displacement English cars too.) It is an original-spec carb.

In terms of running rich, there are a few things to address.

First step: address the ignition system -- replace all the plugs, plug wires, cap, rotor, points, condenser. Ensure all the connections to and from the coil are clean and tight. Check that timing is correct. Remember that running rich can mean either too much fuel, or often it means too little spark.

Next you can ensure that there's an appropriate level of oil in the carb dashpot.

If it's still running rich, you can ensure your rubber diaphram in the carb isn't ripped (just take out the screws on the dashpot and pull it off and inspect the rubber diaphram.)

Next step-- set the mixture with a ZS mixture tool.

If it's still rich, your fuel float might be off -- this is very common in SUs (and easier to deal with, since the float bowl is separate.) In a Spit, you might be able to remove the float bowl without removing the carb. (You can't on a TR7, I found out!)

Good luck, and welcome to the group.
Sam

 

[gjh2007]

Eliminate the above issues, ign, etc, but take a peak at the attached link that explains how these carbs were designed to work.

https://www.keystonemg.com/tech/intro-zs-carbs.html

good luck:

 

[BritishCarMan]

Congratulations on the Spitfire purchase. I'm sure you and your son will enjoy working on it and enjoy driving it even more. It's a great first car.

 

[Paul Johnson]

Welcome, and congratulations. Being next door to Victoria, you have a big advantage, and perhaps that will help in your work with your son.

 

[AltaKnight]

I too had a heck of a tough time getting the mixture leaned out on my TR6 twin ZS's.
In the end I worked on the float levels by removing (as SammyB notes above) the float bowls with the carbs in situ.
I would first relieve reidual fuel pressure by pulling of the fuel hoses then remove the 6 screws underneath,(a little tricky till you get the hang of it) and eyeball the level in the bowl, after a couple of times tweaking it ( you lightly bend the brass tang that presses the valve) I managed to get it about right and could use the special allen wrench tool to adjust the mixture properly.

 

[John75]

This is a great group to get so many replys to a first time post. I've been out of town for work the last couple of days and just got a chance to check the relpys.

I think I've discovered why the rich running carb: I picked up a used exhaust manifold today to replace one that had a broken flang. When I took the old one off I discovered there were no lower retaining wings or nuts holding the intake and exhaust manifolds in place. The previous owner could never figure out why he couldn't adjust the carb. I won't have time to properly rebolt on the manifolds until Sunday afternoon, and see if it solves my carb problem.

I've already rebuilt the carb, including new diaphram and throtle rod. There was a missing seal on the throtle rod that I made sure got put in. I also discovered that the original distributor was replaced with a Lucas 25D4. At the least I'll look into putting a PerTronix Ignitor on it for a good spark.

Thanks again for all the great tips.
John

 

[John75]

Good news. After properly bolting on the intake and exhaust manifolds with replacement retaining wings and nuts from Victoria British (it's nice living 5 miles away from their city counter) the car is running without problems. The rich running was definately being caused by a major vacum leak from the missing nuts on the bottom of the manifolds.

Thanks again to the group,
John
1975 Triumph Spitfire