1967 250S cold start question

[dmtinker]

This car has a real hard time cold starting. If you shoot a little starting fluid into the carbs it fires right up. I suspect that it is either running lean or the float level is too low. Does this sound right? Does anyone have any possible suggestions?

[ggenovez]

could also be a vaccum leak.

Start the engine, and spray carb cleaner around the manifold around the head, the base gaskets of the carbs, and the vacuum lines.

Listen for any change in RPM.

Also the easiest way to adjust your fuel mixture, is to hook up a vacuum guage and turn the mixture screw until you get maximum vacuum. 14-17+ is the range.

Have you checked your timing? that could also cause starting problems.

[dmtinker]

Thanks for the tip. No I haven't checked the timing as I just picked up points, plugs, condenser, cap, rotor etc.... I don't have any of the specks for gap, timing dwell etc as I have not had a chance to get a manual and I didn't want to post asking for the info but I'm sure I'd get a link to the search engine or "tech help"...

If anyone happens to know all this and could post it, I would appreciate it.

I'll time it when I get the info. One question though, the plug wires I got are the resistor type as that is all they had. They didn't carry wires for my car so I had to get universal wires. I hope this won't be a problem.

[dmtinker]

Originally Posted by ggenovez

Also the easiest way to adjust your fuel mixture, is to hook up a vacuum guage and turn the mixture screw until you get maximum vacuum. 14-17+ is the range.

Pardon my ignorance, but where would I hook up the gauge?

[dmtinker]

I just went out and messed with the car. I noticed that when I sprayed around the base of the rear carburetor, the RPMs went up. I also checked the timing and it's 3 degrees BTDC.

[ggenovez]

Vaccum gauge can be hooked up to the vacuum advance.

There might be a plate on top of the front cassis that states RPM range and timing.

3 BTDC at how many RPMs?

Ok, you either have a loose carburator, a bad base gasket or a warped carburetor. You'll probably need to take off the valve cover to get to the back of those zeniths to try to tighten the 12mm nuts.

[Mike D]

The vacuum advance is carburetor activated. The vacuum retard (if equipped) is manifold fed.

You need manifold vacuum to adjust the carb mixture. You should have a vacuum fitting below each carb. Attach the gauge to there. You should actually use two gauges, one for each carb and alternate them to double check your readings.

3 degrees BTDC is about right for idle with vacuum connected.

[ggenovez]

Hey Mike,

On my zeniths the advance and retard both came from the carbs. The manifold fed the tranny and accessories. Was the 250 S different from that respect?

I've always used the ports off the carbs to individualy dial in the mixture.

DM, I forgot to mention the I use the vacuum for the dashpot for the rear, but I take the front vacuum line and plug it into the rear dashpot so the vacuum is taken at the same speed.

So just to recap, Advance vacuum connects to gauge, dial in, then front vaccum line connects to rear dashpot and rear vacuum line is used to dial in mixture. makes sense?

Mike if you have a different procedure, please let me know.

Thanks.

[dmtinker]

Well it's tough when you don't have it in front of you AND you're are not familiar with it to start with. If (and I know this is asking a lot) you could post a picture or even a hand drawing, that would be great.

[ggenovez]

Ok, first connect the vaccuum gauge to where the vacuum advance is,

Thane connect as following

[dmtinker]

Thanks, BIG help. I'll look at it tomorrow and let you know how much vacuum I'm getting.

[ggenovez]

Glad I could help.

Before you fire her up, I would take off the valve cover and see if I could tighten those carburator nuts, and see if it takes care of your vacuum leak.

Remember to go in a criss cross pattern, just like wheel bolts...

[dmtinker]

I thought about that. I recently spoke to a MB mechanic (both at the dealership and an independent) who said that the gaskets on these carbs are frequently installed wrong. The independent mechanic said that he actually had a box of Zenith's that he gave away as he refused to work on them anymore.

[ggenovez]

I find it odd that no body likes these carbs. I've found them pretty easy to work with once you understand them.

If you're going to pull them, might as well put a straight edge to them and see if they haven't warped. If they have, you can use something like a piece of glass and some sand paper to get them squared. Make sure you clean them well before you reinstall.

You might also want to put down some kind of gasket maker to ensure you have a good seal.

I've pulled my carbs off and I'm not sure how you can install the carb seal wrong.

Good luck.

[Mike D]

I'll defer to you regarding the Zenith's. You've been there and done it recently. It's been too long and too many carbs for me to remember.