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MG Midget and Sprite Technical - Zenith-Strom-1500 flooding too easy on warm start

Hi guys,
My '76 midget is giving me a little trouble. It starts cold just fine, totally normal. It runs and idles just great. On a warm start, if I so much as touch the gas pedal before cranking, it's gonna flood. If I remember to keep my foot away, it will start fine. If it was just a trip to the post office or a couple miles, and I come out and leave the carb choked, it will flood if it was really warm enough to have gone without the choke.
What should I look at ?
Thanks for the ideas. It's getting to the time when I have to put the car away, but I'm hoping I can get a chance to still play a little.
Paul
Paul W 1976 1500

Hi Paul, I can't help you much I'm afraid. The Stromberg was only fitted to cars sold in the USA so I have no experience of them.

This reply, however, will bump you to the top again and some of our friends in the USA might care to pop by.

Rob
Rob aka MG Moneypit

Thanks Rob.
I had to tow the poor thing home from church on Saturday morning. I just didn't have time to wait for it to un-flood. It sat in the garage all weekend. I just took it to the post office and of course, it ran great.
If I were to get in it now, while the engine is warm, and I hit the gas pedal without thinking before turning the engine over, it probably would flood. It's odd....
Paul
Paul W 1976 1500

I think Strombergs were sold as Zenith carbs in the UK. I know I had one on a Triumph years ago. I have no idea why it should flood so easily.

Do they have an accelerator pump ? Maybe needs adjusting. Have you checked the float level and I seem to recall they include a diaphragm that maybe might have a split in it?
GuyW

Just found this web site, which might help:
http://tinyurl.com/gt57wgz
GuyW

Thanks guys.....I'll probably have to put this one off until the Spring.
I don't think the carb itself is flooding. I can't detect any gasoline leakage anywhere.
Paul
Paul W 1976 1500

Does it have an auto choke mechanism? Some cars did just before the introduction of electronics. They were always going wrong.

Rob
Rob aka MG Moneypit

No Rob, it's manual.....I wish all carbs were......
Paul W 1976 1500

I had twin Strombergs for a while on a tuned Moggie and seem to remember they were very fussy regarding float heights (which are critical)and fuel jet seats especially bits of crud under seats etc.Never really happy with them and changed them for a twin choke Nikki downdraft.

I would give the carb a good overhaul and clean out - check the rubber diaphragm and check the float height and fuel valve seats.
Also get an overhaul kit first as the float chamber gasket is an unusual shape an can tear easily !

Assume you have plenty of oil in the damper.
richard boobier

Hi Richard,
I haven't checked the damper in a while.
I'm starting to get the feeling that a carb overhaul is in order. The site that Guy linked looks pretty helpful.
The engine runs so well though, I thought I was in the clear. Something is causing this.....Just about to get the car out right now. Running to the post office and have to get over to vote. The last week or so, I mnake sure I park somewhere where I can leave the car for an hour or so, just in case.....
Paul
Paul W 1976 1500

I'm getting ready to scream.......
I get to the post office, come out and the car starts, and then just shuts off. An intermittent ignition problem has come back this season. I posted about it last year and tried all the recommended fixes. At first, it would only happen when it was exceedingly hot outside and the engine equally hot. I would be driving along and it would just shut off. No sputtering, choking or coughing. Just shut down like I pulled the ignition wire.
I first replaced the coil. No matter....ballast resistor.....then I got a 'red' rotor as per someones recommendation. Did the rotor, new cap, new wires. Was ok for the rest of the season, I thought I got it. This Summer, that problem started again. I figure the rubber fuel line was crimping when it got too hot (soft). It loops around pretty sharply coming from the tank and looping around to the fuel pump. I replace the hose. This problem continued. I replace the hose with a pipe, bent to accommdate the loop. Fine for a while.....Started shutting off again. I can't make it happen by jiggling wires, bending, crimping pulling twisting. Very intermittent. The engine would start again within minutes usually, and I would be on my way. Last week I pull the in-line fuel filter. While it looked fine from the top view, when I got it out it was full of crap where I couldn't see it. Put in a new one. Thinking 'that's got to be it'....
So anyway, I walk home from the post office, get the old cap and rotor and drive back. Replace those and it starts right up. It probably would have anyway, without the old cap and rotor. Just because I waited a while.....
It's getting me buggy.....
Paul
Paul W 1976 1500

Using Guys first question on ignition - 'did the tacho needle drop to zero' when it cut ?

If it did I look for a bad wire connection or ground fault - maybe within the dizzy - do you have after market electronic ignition - the wires going to the ignitor type units can give issues - especially when vac advance is operating.

The crap in the fuel filter may have built up in the float chamber causing your original fuel issue - so a carb service would be a good idea.
richard boobier

Hi Richard,
Yes, the tach dropped right down to 0. I haven't removed the electronic ignition module but I suppose I should. Yes, I hear you on the carb service idea.
Paul W 1976 1500

That is slightly ambiguous. The LT electrics fault test is if the tacho needle jumps erratically. Obviously if the engine cuts out and stops, the tach will go to zero, but its the wild flickering which is the thing to look out for.

If you do, then its likely to be a fault on the LT side of the ignition circuit. Battery, ignition switch, coil, dizzy or electronic module. Or any of the wires and connections between them. For intermittent come and go faults the ignition switch seems to be a common culprit for some reason.
GuyW

Paul, you can pump that puppy for all you're worth and it won't make a difference because the carb you have fitted does not have a pump like other carburetors do.

My car did the exact same thing. I'd have to pull the air filter out, wedge a screwdriver in to hold the needle thing up and it would start.

My problem was the diaphragm had stretched so far when it was warm, the vacuum could not lift the needle enough to allow fuel to get to the engine because of it.

Of course, when the car cooled, the rubber hardened and it worked like a charm so replacing the diaphragm cured the problem.

You see, the needle fits in a cylinder for lack of better description of the part. When the engine cranks over, it creates a vacuum in the area above chamber because the diaphragm seals it. The cylinder lifts in the vacuum lifting the needle and fuel flows, the engine starts. If the diaphragm is too soft, that rises but the cylinder doesn't. Can you see that in your mind?

Anyway, try it. It worked for my 1976 Midget.

Cheers,
Clare
C Ravenwood

Yes, it looks like a carb overhaul is in order. Thanks for all the great input guys.
I was thinking about the ignition switch on the intermittent shut down problem. I don't think that one is the carb. The switch seems to be a little buried though, at least in the casual reading I've done on it.I think I'm going to get a chance to pull out the ignition module on Thursday, so that will be a start.
I'll order a rebuild kit for the carb too.
Thanks again guys, My head has been hurting for some time in thinking about this. You know how it is.
Paul
Paul W 1976 1500

This thread was discussed between 06/11/2016 and 09/11/2016

MG Midget and Sprite Technical index

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