My starting carburetor (aka choke mechanism) on my 3.8 is misbehaving. The prior owner removed the temperature sensor and wired it to a switch under the dash. When it's turned on, it will stay active for a short while, and then disengage. Worse, it will find its own ground periodically and activate when the car is hot, flooding the engine.

My mechanic was musing if there was perhaps a more modern alternative to the mechanism. Anyone find an alternate solution to ease cold starting and keep the car running until it's warm?

Thanks!

 

you either have a wiring issue or the body of the electric SOL is failing. Just fix what you have as they give little issue. Many folks do the "switch" as they do not understand the proper way or are using bad parts. Either way is fine but if you forget to switch off you will foul plugs and have very poor fuel mileage.

 

Hi George,

It's not happening reliably so it's hard to test, but my mechanic is confident that the body is going to ground when it shouldn't. For the time being, I'm probably just going to reverse the action of the switch: wire to ground (+) directly, and then have the switch send negative power. At some point I'll take the thing apart and rebuild it, but for now I'm just trying to avoid the flooding / fouling problem.

I was under the impression that most people who replaced the temp sensor with a switch did so because the temp sensor kept the enriched mixture on too long.

Thanks,
Doug

 

Doug I have heard all sorts of "reasons" but can say when properly set up and adjusted they work fine and properly.

 

Okay, after more examination and experimentation, I'm convinced that the problem I was having with the solenoid inadvertently activating was due to the previous owner-installed under-dash switch shorting against the cigar lighter body. When I removed the switch, I saw that the spade connections to the switch were not insulated, and the switch was basically right against the cigar lighter Hence, any significant vibration could've grounded the wire, thus activating the solenoid.

My problem now I that the solenoid is clearly not configured properly. When activated, the car will not start, even from cold. I believe this is because the mixture adjustment screw for the starting carb is set all the way in, thus I think that, when I activate the starting carb, the mixture is way too lean -- all air, no fuel.

The Mark VII service manual that I have (section attached) shows the same part as on the Mark IX, and instructs to unscrew the mixture adjusting screw to make the starting carb mixture more rich. But I don't see a set screw on mine, or any way to hold the mixture adjusting screw at a fixed position. It seems that, if I unscrew it some, it will be very loose and unreasonably susceptible to vibration. What am I doing wrong?

 

There is a small steel lock tab that mounts under one of the screws that hold the needle assy in place. Once adjusted engage the lock tab and it will not move. that said you really need a parts manual for your car. I am a bit confused though--you have a MK IX right?

 

Thanks, George. I *barely* see the lock tab in the image from the Mk VII service manual that I have (and which I uploaded to the prior post). That makes sense; the lock tab is completely missing from my starting carb. And you're right; I have a Mk IX, but when I first got this car, someone kindly sent me the service manual for the Mk VII / XK120 electronically, and so much of the motor is similar, I've been using that as a reference. I don't use it for torque setting or anything really critical, but the component descriptions and diagrams are usually very helpful. I'm not sure what a 'parts manual' is; are you talking about the service manual?

The reason I was originally seeking an alternate solution to the starting carb is that, I presume, the enrichment adjustment probably needs to be different for different seasons; no? If you have one of these on your car, does it work reliably across different ambient temperatures, or do you find that you need to fiddle with it as you move between seasons?

 

Well it is a manual that shows ALL of the parts (or lists them) for your car.

 

I got the parts manuals for the car from a nice guy at Welsh Enterprises, so thanks for that tip. And my mechanic had flipped the lock tab over just to hold it on the car since he had put the starting carb out of service until we got the electrical issue resolved. I'm now convinced we've got the electrical problem resolved, and we put the starting carb back in to service, but it's clearly not adjusted right because the car just barely runs when it's activated. He took it apart and noted that the needle valve appears to be in perfect shape, so I'm not sure why we're having so much trouble getting the mixture right. I know he knows what he's doing because he got the SUs adjusted and synchronized beautifully. It's still quite warm now, so I think he is hoping the starting carb will behave more normally once the weather gets cold and the enrichment is actually needed to get the beast running on cold mornings.

 

Hallo und guten Abend, ich schreibe mein Problem hier weil George Camp sehr kompetent geantwortet hat und mir vielleicht auch helfen kann. Wenn ich.meinen MK9 nach 1 bis 2 Monaten starten will muss ich mehrere Minuten immer wieder den Anlasser betätigen bis der Motor anspringt. Dann läuft er im Kaltststart einwandfrei und wechselt dann in den Warmlaufmodus. Wenn ich nach 1 bis 2 Tagen starten will funktioniert der Kaltststart immer sofort einwandfrei. Wo könnte da der Fehler sein? Über eine Antwort wäre ich sehr dankbar. Martin aus der Schweiz

 

From your description the cold start is working properly. I would look at what changes during the long storage period. Is the battery low or on a tender? Is your fuel fresh? There are so many variables but as said I would look elsewhere. One question is after the lay u when you switch on the key do you hear the enrichment device engage? If you do it is elsewhere.

 

Danke für die schnelle Antwort. Das hilft mir zu hören, dass das Kaltststart System nicht die Ursache sein kann. Dort hätte ich gesucht. Zu den anderen Fragen: die Batterie lade ich immer regelmässig und wenn ich den Schlüssel drehe höre ich die Benzin Pumpe und warte bis das Schwimmergehäuse voll ist, beziehungsweise man die Pumpe nicht mehr hört. Einzig der Kraftstoff ist dann ein paar Wochen alt. Aber nachher klappt die Zündung ja auch mit dem gleichen Benzin. Freue mich auf weitere Anregungen 😊, danke.

 

Google Translate provided this, so that's what I'm going to respond to: "Thank you for your quick response. This helps me to hear that the cold start system cannot be the cause. I would have looked there. Regarding the other questions: I always charge the battery regularly and when I turn the key I hear the petrol pump and wait until the float chamber is full or the pump can no longer be heard. Only the fuel is then a few weeks old. But afterwards the ignition works with the same fuel. I look forward to further suggestions 😊, thank you"

Given that your car appears to be running perfectly cold and warm once the engine fires, I'm wondering if you've got an electrical problem. On my Mark IX, I was having a very similar problem, and I *think* it was caused by some weak electrical connections that lowered the voltage going to the coil while the starter was engaged. My car is negative ground, so I proved this by running dedicated lines from the coil to ground, and from the battery negative lead to the distributor. Mine fired right up. I did further testing and eliminated the ground as the problem. I couldn't locate a failure point on the negative side, so I ultimately wound up inserting a relay that would feed dedicated negative power from the battery to the distributor whenever the starter was engaged. Worked like a charm.

 

I should also point out that I've replaced my original distributor and coil with Pertronix Flame-thrower components for higher reliability and performance:

I saved my original parts for the next owner in case they want to revert to original, but I think they'd be crazy to willingly revert back to minding points and gaps for anything other than a concourse vehicle.