Tough maiden voyage - 1970 250 Automatic

[Number400]

Been working on this for a few months now and in the garage it starts right up, idles at 900rpm and drops to ~600 in gear. Carbs are set up as instructed in the Kopp manual and it has been a journey of learning.

So I get my wife and kids in for the maiden voyage and just as I backed out of the garage (from level to a hill), the car hiccuped but then came right back to a lumpy idle. Once on the street, it sputtered but got going then stalled at the first intersection a block away. After many many neutral drops, I got it around the block but could not climb the hill back to the garage. When put into gear, she sputters and the idle drops to ~100. If the ground was level, it can putt along at almost a stall sometimes. Back to square one as it runs about the same as when I got it.

Any ideas? Could it be the float height? Since it was fine on level ground?
The Haynes manual said 21-23mm WITHOUT the gasket and the Kopp manual said 21-23mm WITH the gasket. If the level is truly that critical, then I will put a thicker washer under the valve. Maybe I am barking up the wrong tree but my patience is wearing thin and I need to get it off the street ASAP.

As for troubleshooting, I felt I was close. My accelerator pumps are pumping, I can rev the car cleanly, it can hold any RPM, e-chokes are working, secondaries hold, everything has been checked and is set up as directed to the best of my abilities so far.

I will check vacuum again tomorrow, it was a stable 15 at last check. Too low?

Just needed to rant for a bit. Any experiences?

Thanks,
Edmund

[BWhitmore]

Normal vacuum at idle should be 19-21 inches. Could you have a vacuum leak? This may explain the stalling and lack of acceleration.

[Number400]

Thanks, I will take another reading in park and then drive to see how low it drops before digging back into the carbs. I did just go back through the vacuum diagram and ensure that everything was routed correctly and that the fittings on the manifold were in good shape and hoses tight.

[Frank Reiner]

N4:

Some background information would be helpful.

- Length of ownership.
- When last in service.
- When valves last adjusted.
- Compression pressures.
- Ignition system w/ switchgear (amplifier), or w/o.
- Ignition timing, and advance mechanism working.
- Condition of spark plugs & wiring.

[ScooterABC]

If the car stalls trying to drive forward up the hill of your driveway, try backing up the hill of your driveway. That may enable you to get the car back inside your garage. It also would be diagnostically interesting. Also when trying to drive forward into your driveway put the gear selector in L or the lowest position so the car will actually start in 1st instead of 2nd.

[Number400]

She started up today and I was able to creep forward and then reverse up the hill and into the garage! Thanks so much for the helpful responses.

History on the car is it has been sitting for about 15 years and I purchased in January. Other than changing the oil, draining and flushing the tank, adding a fuel filter, disassembly cleaning and reassembly of the carbs, correcting the vacuum hose routing, new plugs and wires, I am just getting started on the revival.

The vacuum test today was again 15 inches and there was a miss every 5 seconds or so. Next step as suggested is to check valve tolerances and start over. I have new points and cap and rotor but have not replaced yet. I am just going to slow down and start with the valves and timing and getting the correct vacuum and then get back to the carbs.

[BWhitmore]

Good plan. Nice looking car. Great color.

[Number400]

Thanks. I snapped the pic to text to my Wife that it actually made it back up to the garage.

[barry12345]

Did you run it until the choke plates opened up in the garage? Just a thought. Did you ever bother to spray some wd 40 around the bases of the carbs. Air leaks where not uncommon.

[BWhitmore]

If while spraying WD40 around the bases of the carburetors the engine increases RPM that means you have a vacuum leak at the base.

[Benz Dr.]

A lean back fire is kind of indicating a fuel problem. It may have enough fuel volume at idle but not enough under load. You could always hook up a fuel pressure gauge in line and tape it to your windshield. If you can't maintain 3 or 4 pounds of pressure you may have a blocked screen in your fuel tank.

[ScooterABC]

Originally Posted by Number400

She started up today and I was able to creep forward and then reverse up the hill and into the garage!

OK, now I'm more curious about the angle of the carb (which is going to affect the fuel tank and the car float bowls).

Was it _difficult_ to get the car to reverse up the hill or was it easy? I am wondering if when the fuel is to the back of the float bowls is it starving of fuel (and it would be to the back going up a hill or accelerating). Will the car idle when up on a hill?

I also think Benz Dr. has a really good idea about fuel pressure (volume). The screen in the tank is easy to change (but the tank needs to be empty).

[cth350]

regarding float height, if you are 2mm too low in the bowl, you will starve the carbs while you are at speed for a bit. If you are too high in the bowl, you may well flood it at some point. Neither would the be case a block from home. Unless maybe the fuel return valve isn't closing.

Did you bring it up to 4,500 rpm and check the timing there? Sounds pretty loud when you are under the hood and wind from the fan is fierce, but she should be steady and happy there while you confirm the timing.

Things to check before that...
- Plugs clean? After what you described, I would expect them to be fairly black. Are they copper or platinum? Use the copper kind and make sure they are not the R8 kind (you want R0, or "non-resistor" plugs).
- Fuel pump delivery. Have the fuel dump into a metal can instead of the carbs. There's a spec for how much fuel should be delivered after 60 seconds of turning at starter speed. The suggestion of checking the fuel strainer is good one, presuming your tank is close to empty or you want to siphon it all out into a bunch of other containers.
- vacuum leaks. There are plenty of places for it to leak, find them and plug them.
- Carb linkages... You've got the carbs well balanced, with the RPM drop consistent between each carb? There's that little bit of slack in the arm so that touching the gas pedal impacts the transmission before it moves the butterflies on the carbs? The little gizmo on the front carb impacts the throttle the way it's supposed to and when its supposed to?
- Look down the throats of the carbs at idle. You should not see any gas flowing through the tubes that sit in the primaries at idle.

-CTH

[vwnate1]

The typ of miss isn't well described but as they say "99 % of all carby problems are in fact electrical in nature" so I'd be looking at the ignition system first as carbon tracks, failing coil or condenser will all allow the engine to start and idle normally but cut out under load.....

I assume this car has breaker points ignition still , consider Pertronix "Ignitor" breakerless system, no box to fail, it simply replaces the contact points in the distributor, no modification of the car at all .

Please keep us posted, lovely looking car .

[Number400]

Quick update. I advanced the ignition timing and am now in the green on my vacuum tester at 20 inches. My valve cover hose is cracked and will be replaced and I have not looked at the condition of the tube in the air box yet. I am working in balancing the carbs now and getting the vacuum dashpot dialed in. It is working but will be easier to set up with a helper so I can watch it when the car is put into gear. I tried the paper thickness but the idle still drops too much in gear at that setting. The adjuster screw was missing when I got the car so it's not a new problem.
My carbs were better balanced but I did some roadside adjusting and going to balance again. As it sits now, the front is pulling a lot more vacuum than the rear. Back to synchronizing the butterflies. Can anyone give me a baseline setting on the little grub screws (cO2)? I have them one turn out but I have no analyzer or reference to start with those. I already went back to 1.5 turns out on the air/fuel screws.

More updates this week as I go. She is insured now at least and I am getting my tag tomorrow. Trying to get her running so my daughter can drive it to her senior prom in a few weeks.

Thanks,
Edmund