Cold Start Problem - what else is left to try...

Hi,
the car is a 1975 MGB with the single Zenith carburetor with a manual choke conversion. Most of the smog equipment has been removed. I bought the car 6 months ago and and enjoyed it for about 2000 miles since.
A few weeks ago it developed a serious cold start issue to the point where it is almost impossible to start. How long can a starter motor survive this I wonder...
When I say cold start - I live in SoCal so it is not really cold. Temps now are always between 60-80ºF

Anyhow, if I get the car to run it runs absolutely perfect. Nice idle which I can set to anywhere down to 600 and under load or full throttle it runs real nice. Mixture seems to be just right. Once the engine is warm, I can start it without problem throughout the day. Until it gets cold again..... trust me, i already thought of getting up every three hours at night to start the engine for a few minutes...

Here's what I did so far:
- new rotor, cap, points, properly gapped
- new spark plugs, tried both Bosch Platinum and Champion, gapped to 0.035 first, then 0.030
- new spark plug wires
- new coil
- rebuild carburetor: throttle shaft rubbers were hard as a rock, float needle assembly was fixed pretty badly by PO. So now it has the propper CA 45H needle, new gaskets, fuel jet
- adjusted float level (16.5mm from carb body)
- Cleaned power connection from battery to frame
- jumped battery to 2nd running car to eliminate battery capacity as possible cause
- Mixture: seems OK, whenever I get the car to run the plugs have a healthy brown/tan color after driving for an hour or so and are dry
- Enrichment unit seems ok. I loosened the three bolts that hold the body in place and rotated it into different positions to see if that has an impact. None.
- I adjusted the ignition timing (dynamic) to 12º @ 2000 which is about right for the 75
- I adjusted the valves a few months ago
- compression test is 120psi on all four
- firing order of plugs is correct (1342)
- gas is in the tank (89)
- now running out of ideas on what else to check
Does anyone have any idea?
Also: where is the connection from the frame to the engine for the ground connection? That one I would like to check as well.

With no specific experience with the Zenith, all I can do is guess that something is interfering with choke action.

I think this is an "automatic" choke (?) if so it's controlled by water temp (called, I think, the "water choke"). There are some converted-to-manual choke Zeniths out there, I presume (since there's a kit for this) and it is possible a PO did this.

search the forum for "water choke" or "cold starting"--you might also check youtube fro John Twist's videos, he may have one on the Zenith.

right, it was a "water choke", but the PO replaced the "water" part with the manual activation, just like a regular choke. So I can just pull the cable on the dashboard and it activates and enrichens the mixture. If the engine runs and i pull the choke the engine slows down and stalls eventually, i.e. making it run too rich as it should. I wonder if it is still running to rich on idle, but as I wrote earlier, the plugs are colored properly and idle is good (not too smooth/rich either).
I have to admit that other than taking it apart, looking at it in wonder, making sure it is clean and putting it back together (carefully) I did not do anything to it. From what I saw inside of it everything seemed to be working OK. Should I mention that I have never seen the inside of one of those before?

What is the voltage at the + coil terminal when the engine is cranking? When the engine is running? Is the coil you are using supposed to have a ballast resistor?

Clifton

I have not checked the voltage yet, I'll be heading home now to test. I don't think the 75 uses a ballast resistor. The car ran fine on this setup until it got worse, so i assume this setup is correct - I will check with the shop manual though. Thanks, and I'll post the voltage readings shortly.

OK, so I was able to start the engine with much agony, but somehow I convinced it to run. It is warm today, prob 75º so not really cold...
The voltage at engine running is 10V on the + terminal, 11V when cranking, 6V when ignition is on and not cranking. I am no expert, but shouldn't it be 12V?

Here is something I just found:
I fiddled with the idle mixture adjustment screw turning the big yellow nut, not the bolt. It made absolutely no difference. I actually turned it all the way until I was able to take it out and hear the air go through the bypass. The engine idle did not change a bit - now that can't be right.
Then I put my finger on it to emulate the bolt being screwed all the way in and still no difference.

zugvogel Wrote:

Mac,
yes, the choke is turning back to normal. Everything is turning freely.
I am not sure I understand your second question correctly. From my understanding the fast idle on the ZS is activated by the fast idle lever. This is sitting on the throttle shaft and depresses the idle pin on the enrichment unit when idling. When i open the throttle the idle lever goes back and the idle pin comes out.
I am not sure this is the best way to describe it but I hope it makes sense. Is that what you are asking for?

Rene, Your voltage is probably about right if the original wiring is still being used, I would have thought the running voltage may be a little lower. You should be using a 1.5 ohm coil. A 3 ohm coil using OE wiring with built in ballast will reduce the voltage/current at the points (you said you have points) and may not be enough for easy starting.

Clifton

Clifton,
the coil I put it is from Moss:
143-230 COIL, ignition, ballasted system
How do I determine whether it is a 1.5 or 3 Ohm coil?
The wiring looks like it is still original - I am not 100% sure but it doesn't look like it has been changed

Rene,
12 degrees timing at 2000 is WAY too far retarded. It'll NEVER run well at that setting. Try 10-14 at IDLE with the vacuum line disconnected from the distributor and plugged (if you have one). This will transform your car!

I agree with Jeff. I have about 20 degrees BTDC at 2000 rpm on my 18V.

Hi there,
so I changed the timing to about 20º and was able to start the engine. Whereas before it did not start at all, now I got it to a point where at least I got enough ignitions to let it putter for 5 minutes until it finally ran. So it did help but there is obviousely another Gremlin at work.
Taking this behaviour into account, I am now focussing in on the enrichment unit again, since everything else seems to be working fine as soon as the engine is somewhat warm.

So here is the new question:
The ZS enrichment unit has a threaded whole on the driver's side of the enrichment unit body. This whole is pugged with a rickety little plastic cap which by no means can seal it. Is that supposed to be that way? My assumption was that the unit needs to be airtight. If it indeed has to hold a vacuum, this plug ain't doing it - there might be my problem. I sealed it with Silicon now waiting for the engine to get cold again to start all over again...