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MG Midget and Sprite Technical - Spark but no vroom vroom

Hi everybody,
I'm having some difficulty with a 75 midget timing and possibly not firing on all cylinders. The caveat is I have a 1275 Distributor on a 1500. (shouldn't matter right?) I'm getting plenty of spark, my fuel pump seems to be pumping plenty of gas. I also have put in new points, condenser and plug wires. It will start and idle for about a minute than die- it will not start up afterward and just turns over like it's not getting any spark. The ignition coil is getting very hot (which is a new development as of today) I'm wondering if this is a carb issue? I have a single zenith stromberg which has not been rebuilt- when in the process of turning over gas pretty much pours out of the bottom of the carb (yea obviously not good) Compression is at 120 across the board. Any direction would be much appreciated! Just kind of stuck in neutral with this.
Thanks!!!
MM75.

Mighty Midget 75

could be the coil internally shorting, especially if it is getting that hot very quickly. (I may not explain this well, but here is the rudimentary basics as i understand them) The coil is supposed to discharge when the distributor breaks its ground circuit, which is the spark that goes through the HT lead to the spark plug and fires the engine. it is not unheard of for the internal insulation on these coils to break down allowing them to complete a circuit independant of the rest of the ignition system. when an internal short happens, the distributor is unable to break the circuit so the coil just keeps getting hotter, but never discharges a spark. Often these break downs are dependant on temperature of the coil, (or so I am told), i.e. the coil is fine when it is cold, but once it heats up, the expansion of components or something allows the short to manifest. It will get progressively worse until the coil is shot. This could be your problem... Or i could be projecting because I think this is what happened to my coil recently. :)

either way, i would say your problem is more likely to be from the ignition/electrical side rather than carbs at this point because you said it doesn't spark when you try to re-start.

good luck, and hopefully some real experts will chime in too!
Cheers
Chris
Chris Edwards

Like any problem simple diagnosis is the key.

When the engine fails to start the first thing you should do is check the ignition circuit.

do you have a spark at the plugs?
Do you have a spark at the king lead of the coil?
Do you have a spark at the points in the dissy?
ETC ETC.

If all that checks out then you can sort out the fuel.

If you try to work simply by guessing you probably will end up nowhere.

Try this if yopu need help with ignition circuit
http://www.midgetregister.com/index.php?option=com_content&view=article&id=73&Itemid=66
Bob Turbo Midget England

you have a 1275 dissy in a 1500, Id imagine that the curve for a 1275 is differant then a 1500, I dont know that for a fact, but I think its a good guess

Id certinaly go to ebay and see if you can find the correct dissy for your car.

how long are your work sessions whith the ignition on, the coil can get fairly hot after 1/2 hour or so?

Prop
Prop

>>> I have a single zenith stromberg which has not been rebuilt- when in the process of turning over gas pretty much pours out of the bottom of the carb (yea obviously not good) <<<

Bingo - I have SO been there. Sounds like the float valve in your Zenith isn't shutting off fuel flow properly, and is letting the float chamber overflow. This is a big deal for two reasons - A. Your car won't run. B. All that extra fuel gets sucked into the engine, and since there's too much to burn, it gets forced past the piston rings into your oil. Check the dipstick - I'll bet the oil level is unusually high. And chances are good that your oil is very thin and smells like gasoline. This is a Bad Thing. It took me three oil changes one summer before I finally figured out what was happening with my car.

So then - the fix isn't too dreadful. Remove your carburetor, then invert it and remove the float chamber. First, check for crud at the bottom of the chamber. Mucky stuff can get into the float valve and keep it from shutting. Secondly, look at the float. If it has fuel in it, it's faulty and needs to be replaced. Thirdly, look at the float valve. If it has a shiny ball at the lower tip, it's a Grose Jet, and is crap. Replace it with a standard needle-type float valve.

When you think about it, the float chamber is essentially the same concept as a toilet tank. The idea is that the fuel pump sends fuel up to the chamber until the float raises and shuts off the flow. And how many times have we replaced components in a toilet tank to get it to shut off... same idea. When you start your car, it will run briefly until the chamber starts to overflow, at which time fuel will squirt through the jet - instead of being drawn off like an atomizer - and your engine will basically drown in extra fuel.

While I'm thinking about it, if fuel is leaking from the bottom of the carb, you might want to check the O-ring around the plug in the float chamber bottom. Also, if there really is crud in the float chamber, you may want to get an inexpensive fuel filter and install it just before the fuel hose enters the carb. I have two, actually - one at the carb, and another just upstream of the pump. If you use the clear ones, it's easy to see if you're getting fuel or not, which helps when troubleshooting.

Hope this helps! Whatever, be sure to check, and probably change, your oil.

-:G:-
Gryf Ketcherside

This thread was discussed on 25/05/2010

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