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MG MGB Technical - WHAT IS IT?

Converted to twin HIF-4 on my 80 MGB and car seemed to run well for a while. Kept getting carbon the plugs and finally one would foul out. I was out trying to tune in the carbs the other day and while doing so, ran out of gas. Got gas carried in a few days later and the car won't run hardly at all and cannot rev it up at all. Will not idle and I noticed the ignition light not going off. I took the alternator off and had it checked and they said it was good. NOW for the big question-----
since the plugs were carbon and a couple were wet with gas---- could I have lost a good spark to the plugs and not be burning the gas? The coil and amplifier are the original ones that came on the car when we bought it new in 1980. Being a novice at this I really need some help! Any takers on this one??
Dale & Barb Mast

Water in the new gas?
Wet ignition cap, wires etc?
D Sjostrom

Could be anything. First check the system voltage (i.e. on the brown at the fusebox) with the engine running at say 1500 rpm, it should be about 14v. If 12.8v or lower the alternator isn't charging, and if the battery is running down will affect spark. If that is OK clip a timing light on to the coil lead and each plug lead and check you are getting regular and consistent flashes. If not check the dwell, it should be steady and consistent, although the factory electronic system may have a higher dwell than points systems. The 45DE4 system is quoted as the same as for points (51 +-5) but the 45DM4 is not mentioned. If the spark is OK clean the plugs and try again, or ideally replace them unless they are very new. Disconnect each plug lead in turn and the revs should drop by the same amount. One or more not dropping at all or less than the others indicates weak firing on that cylinder. Could be plugs, even if new, swap them round and try again, or fuel. When the ignition system (and valve clearances) are correct set up the carbs from first principles for air flow and mixture balance. When doing this watch out for one carb needing more adjustment from the basic starting position to reach balance than the other.
Paul Hunt

Get rid of the factory electonic ignition, that is failing. If the car has got over 80k miles the factory unit is know to fail with the symtems you posted.
George

Thanks for the replys so far. Problem is, the car will not run hardly at all so I can check anything!
Dale & Barb Mast

Whoa there, only the Opus system (with the amp on the distributor) was known to fail, and most people who had them have replaced them by now. The newer ignition with the external amplifier used a rebadged GM ignition amp. That one is solid and reliable, and it's probably the one he has. Before trashing the entire ignition system he should determine that there's a problem with it.

I think Paul has a good systematic way of isolating the issue. Don't be tempted to try this-n-that, just do the steps in a sensible order (check ignition, then check valves/compression, then check fuel) and you WILL find the problem. Checking good working systems takes very little time and can save tons of time if the system that's failed isn't the system you thought it would be - for example, rebuilding your ignition would be silly if the problem was a stuck needle valve that's got you running on only one carb. However, checking a working ignition system is quick and easy and frees your mind from having to wonder whether ignition might be the problem. Checking each system guarantees that wherever the problem lies, you'll find it. The mind you save may be your own.
Sam

You need to approach this like a doctor. First be sure there is spark. You can do this by pulling a wire and holding it close to a ground or the plug end while someone cranks the engine. If you are not getting spark you should make sure the distributor and all its parts are in good order, i.e. cap not cracked, contacts on the rotor clean, I take it you have electronic ignition, I'm not sure how to diagnose that. You might want to change all the wires and plugs. The coil can go sometimes but I believe that would cause stalling and not running at all, but if it's original it pprobably needs a change. If no improvement try the fuel delivery system, is the fuel pump sending fuel or did it fail, is the gas filter clogged, I am not familiar with your carb set up but are there any air leaks into the intake manifold, this can be checked either by spraying a little carb cleaner around the manifold and listening to a change in RPM, but you say it is hardly running at all. Was it timed correctly? Are the plug wires on the proper recepticles on the dizzy, is it set up to fire in the proper order? The clue here is that it was running ok prior the gas run out, I would tend to suspect the fuel system. As for the alternator light coming on and staying on, my "B" will do that briefly when first started until I get the revs smoothed out and up a bit, if your car is barely running the alternator is probably not sending a charge to the battery.
Lewis

Well guys-------
Thanks again for the responses! I am trying to get all the ideas you have out there. The car will NOT rev and last time I tried, it would not even start. It has some wet plugs and a lot of black on the others as well.It just acts like it is not fireing the gas altogether. I am going to hang around to see if one of you can help some more. I really appreciate your time and effort to help me!
Dale
Dale & Barb Mast

It appears you are getting gas since you say the plugs are wet with the stuff, so you probably aren't getting spark. I read your post on the MGB general web about a yellow colored spark. I may be wrong but I would guess the coil. But to be sure (and before you buy one) is there someone you can borrow one from to see if it makes a difference? The only reason I guess coil is a fellow in my town was broken down on the road with his 79 "B", he determined it was the coil (it was), and all the car would do is crank but not start.
Henry

Take a fouled plug, clean it up, and cut the entire electrode off of it. From now on, use that to test for spark. If it won't jump the huge gap, you don't have good spark. Check the spark at each plug wire AND from the coil. Replace what you need to.
Jeff Schlemmer

A big thanks to all who responded. I still am in need of help. How about some input from you wiring guys who know more than me?
Dale
Dale & Barb Mast

Yes, electonic ignitions will fail. Everything old and electronic will fail eventually. There are a few things to check. The coil can fail and they do sometimes. If its a new rotor, it is entirely possible that it is failing. Its happened often. The spark passes through the rotor and grounds on the distributor shaft. Since it is an HIF car, check the plugs on the sides of the intake manifold. At times a strong backfire can pop them out (I have seen it, wierd but true). If the plugs have fouled and their Champions, throw them away as theyll never be right again. Check all the vent lines coming off the carb as any air leaks will let it crank but not fire. One thing that sticks in my mind for a lack of revs is improper float height. If its wrong, the car will idle but not rev as it starves for gas. If it is the electronic ignition that is doing it, it wont even start and you wont see any spark. I doubt it is that but if it is, put a pertronix in it and forget about it. Also, check the timing and carb fuel settings.
Jarrod Hills

Hi there. Any luck yet?
Going back to your original problem, you only had a fouled plug before you started tuning the carbs. Are you sure you ran out of fuel and just didn't 'tune' them a little too much? Could be that's why the car didn't start when you put new fuel in - because that wasn't the problem - just a thought. I recall playing with the twin SU carbs on my mini and got my 'adjusments' all out of whack when out on a road test (trying to do it in a car park in the dark). What method were you using to tune the carbs?
Chick
Chick

Chick UK-----------
No, the little "B" ran completely out of gas! Still working on some ideas and hope to answer what was wrong!
Dale
Dale & Barb Mast

If your spark is good, check the float levels in the carbs and confirm that the float needle is closing off the fuel properly. Sounds a bit like flooding to me.
Richard Smith

This thread was discussed between 15/04/2005 and 26/04/2005

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