74B Won't Start...

[Obtong]

My 74B has been sitting in the garage for the past week avoiding the rain. Today was sunny so I thought I’d take it out for a spin, but unfortunately it wouldn’t start.

The fuel pump clicked away, but when I turned the ignition key all I got was starter motor going and the engine wouldn’t fire. The tachometer registered about 300-400rpm so I guess the starter motor is engaging and working. All the lights/indicators appear to work, but the horn doesn’t any more. I tried grounding the purple horn wire to get a sound, but it didn’t sound too good.

I checked all the fuses I could find, checked the rotor/points, and made sure the fuel filter and pump were doing their job. The battery was registering about 11volts, but even jump starting didn’t get the car going.

Does anyone have an idea as to what I should try now?

Thanks,
Dom

 

[Bugeye58]

Did you physically check to see if you are getting spark to the plugs?
Jeff

 

[Bret]

Hi Dom,

Sorry to hear about your problems. Here are some basic things you can try.

Ignition: Try to see if you are getting a spark to the plugs. If not use a voltmeter to do a voltage check & look at the connections between the coil to the dizzy. Anther cause could be bad points and/or condenser. Also water in the distributor will do the same thing. Water in the Dizzy is usually the result of a leaky heater valve positioned right above it.

Fuel delivery: If the ignition system looks good, try checking to see if you are getting fuel to you carburetor(s). The easy way to do this is to disconnect the fuel line from the carb(s) and put it into a jar and try to turn over the car again. Mind you it won’t start but you should be able to see if you are getting fuel delivered up to that point. If no fuel reaches the jar then check for a clogged fuel line, filter or sending unit.

Carburetion: Next check to see if the choke is setup correctly. If all of the above looks good then I don’t know what to tell you it could be something major. But the above tests should narrow down the possibilities for you.

Good luck!

[ 02-08-2004: Message edited by: Bret ]</p>

 

[Guest]

You didn't mention if the fuel pump stoped like normal after a few clicks. If it kept running, could be out of gas. I know that sounds elementry but it happens. Also the needle and seat could be stuck. Kinda unusual if you have two carbs though for both to stick at once.

Next, you said the tach was registering. That means the points are working so the problem must be in the high side of the coil through to the plugs. Like Bret & Jeff said, check to see if there is spark. Check distributor cap, rotor, wires and plugs. I had mine do this twice in 20 years like Bret said the heater valved leaked on it and filled the dist cap with moisture and it wouldn't run. Or this can happen right after you wash the engine off.

I assume you haven't changed any adjustments like timing.
Bob

 

[Obtong]

Thanks for your quick replies! I have checked the fuel pump and fuel is coming out of the fuel pump. I don’t have an SU pump, and you can always hear it clicking. My fuel gauge is a little off, so I put three gallons in. No difference.

I don’t think there are any sparks at the plugs. I don’t have anyone home to turn the ignition for me right now, so I set up my timing light on each plug wire in turn, and the HT lead to the coil, and in each case there was no light on the strobe.(And threfore spark at the plug? Bret, how should I connect a voltmeter to do a voltage check?)

The points and rotor look good and they don’t appear to be damp or corroded. No, I haven’t made any changes to timing or anything else. I last drove the car about a week ago and it sounded fine. It’s been garaged all week.

BTW, does this sound like a solenoid or a starter motor problem?

Dom

 

[Guest]

I just thought of something else. I didn't have this problem with my MG. It was a Dodge but it wouldn't start and I worked for a good part of the afternoon trying different things and still nothing. But after dark I was having my neighbor crank it and I was looking under the hood and saw flashing at the coil. Closer examination revealed the spark was going from the High voltage lead down the side of where that lead fastens to one of the low voltage leads. I cleaned this off and it cranked right up.

I wouldn't recomend checking the high voltage with a volt meter. It is 30,000 volts. You can check the 12v and check out the high voltage leads with the car off and the switch off by checking the wires out with the ohm meter.

Recap: your tach is working. It is taking it's signal from the low voltage side of the ignition at the coil so that means the points are working. You aren't getting anything on your timing light at any plug or the output of the coil. Therefore you must have either a short from there out to the dist or there is and open output wire from the dist or the coil is bad. I would check the ohm reading of that wire that goes from the coil to the center lead of the dist first. I just checked mine and it reads 13Kohms.

 

[chris roop]

If it flooded, your plugs won't fire. How long has it been setting? Points can corrode. The one that bites me time and again is the condensor.

 

[Bret]

As MRBASSMAN has said don’t use a standard voltmeter to check if you are getting Spark. The simple way to do this is to disconnect one of the plug wires and pull back the sparkplug boot to expose the terminal. Then holding it about ¼” away from the engine block you should see a spark when the engine is turned over.

From that point – use the voltmeter to check that you coil is receiving the proper voltage. I’m not 100% sure of the voltage readings for you 74B. But after looking over the 1973/74 schematic in my Haynes manual it looks like if you place the voltmeter with the red (+) lead on the positive (+) terminal of the coil and the black to ground or chassis your volt reading should be similar to the voltage reading of the battery approximately 12volts. But if you see a really low or no voltage check your fuses again. If they look good use the voltmeter in resistance (Ohms) mode and start doing a point-to-point continuity check from the fuse block back to the coil.

And another thing – while you are making your voltage & continuity measurements be sure to do a voltage check at your fuse block. I discovered (the hard way) that just because your fuses look intact doesn’t mean that the electrons are flowing. When I first got my 78B I had a bunch of electrical gremlins haunting my car. It wasn’t until I took actual voltage measurements on “both” sides of the fuse block that I discovered that I had an issue of corrosion buildup. The simple test is to use your voltmeter to measure the voltage on both side of the fuse block with the ignition key on. I know it sounds childishly simple, but take my word for it and take an extra minute or two to look at it. If it turns out to be an issue all it takes is a little elbow grease, some electrical contact cleaner and a wire brush.

Again – Good Luck!

[ 02-08-2004: Message edited by: Bret ]</p>

 

[Obtong]

Thanks for all your help with my MG starting problem. Over the last couple of days I have learned a lot more about how my MGB works!

Anyway, the problem turned out to be a poorly performing battery! The voltage readings looked a little low, and when I tried to jump start the car the battery began to smoke! I took the battery into Schuck's and within 10 minutes of dropping it off they phoned and left a message that the battery was bad. I bought a new battery and the MG fired up right away! Needless to say I was out running errands in no time.

The horn problem turned out to be a loose wire, which kind of through me when it came to figuring out the problem. I had begun to think that something major was the problem.

Thanks for you help guys! This is a GREAT forum!

Dom.

 

[piman]

Hello Dom,
a couple of points regarding your problems.

Ignition systems are not fused so there is no point looking in that direction.

Grounding the purple horn wire should have made an arc and blown the fuse that supplies the horn.
Horns are usually, unless fed via a relay, live and are operated by switching the earth return (purple\black wire).

Alec

 

[Obtong]

Thanks for that posting, Alec. I double-checked my horn wire and you are right, it is purple/black. I guess my eyes are not what they used to be...

Dom