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Overheating problem - Distributor?

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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
Hi all.

just joined and first post.

I have a 73 BGT that has been rebuilt. I bought it nearly 5 years ago but it has been sat for the majority of 3 years due to me working away form home and not having the money nor time to enjoy it. I have all history of the rebuild and receipts of every nut and bolt that has been bought for this car. I'm getting it up and going again before it rusts away but seem to be having a problem.

Once it heats up and goes over the midway point on the water temp gauge it has a habit of cutting out, there's nothing to do except open the bonnet and wait 5 minutes unitl it cools down and then it fires up again, no problem. I've been diagnosing this problem for a while now and local mechanics (or so called mechanics) aren't sure what the problem is. Its not head gasket or radiator over heating or anything like that as they have all been changed and checked recently. I did notice a water leak on the water valve that sits above the dizzy so thought that this water might be making the dizzy wet and then when it dry's it starts again but im not sure. I ran it at the weekend with a plastic bag over the dizzy and it seems to be better but then it cut out again. Also the performance isn't ideal which my dad reckons is because of the lack of vac attachment to the dizzy

It has a 45D dizzy on it but I notice it hasn't got the vacuum part that goes to the carbs. Although the dizzy works, im thinking of putting on in with the vacuum attachment - my real question is - would any 45D dizzy work on here or not? i.e. one I could get on ebay for £50? don't want the outlay if it wont work. I believe the 73's should have a 25D but this is definitely a 45D and have the receipt to prove it. Its just weird that its a dizzy without a vac attachment?

I understand this might not fix my problem but im leaning now towards dizzy and/or ignition coil being the problem?

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nickj Avatar
nickj Nick Jenkins
Novato, Marin Co, CA, USA   USA
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1970 MG MGB GT
1972 MG MGB
I always suspect the coil in situations like that, but it's never been the coil. So far. This could be a first.

When I had this problem after resurrecting my '72, it was gunk in the carburetors. The engine ran okay with a super-rich mixture when cold, but once the car warmed up it just choked.


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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
Cheers for reply.

I've not taken the carbs to bits as that's going to be my last resort. Since I've had it, it has always run rich, 'hunting' my dad calls it. You can tell by the black on the exhaust. We've tried tuning the carbs at the weekend and its running better now but when we took it for a spin, I noticed gears 1 and 2 were great but 3 and 4 were sluggish, where obviously it was the other way round before we tried to tune it. It was running at 13/1400 at idle and we changed it to 1100 at idle when that happened.

BTW its the heater valve not the water valve that is leaking as I wrongly mentioned above - I've ordered a new one of them anyway.

It 'feels' like there is too much petrol getting somewhere and then it cuts out and when the petrol evaporates it works - I don't think its anything to do with the water temperature directly, its just the temp gauge is the only indicator that I can compare it happening to.

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HiPowerShooter Avatar
HiPowerShooter James Booker
Lake Winneconne, WI, USA   USA
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1973 MG MGB
When you say "cuts out"...do you mean as in it just dies? When it does, have you checked for spark? THAT would tell you very quickly if it's an ignition issue.



"One test is worth a thousand expert opinions"--Alvin "Tex" Johnston...Boeing test pilot.

"Who do you think you are? I am."...Pete Weber

73 MGB. Tires: Round, black, hold air. Oil: Sometimes old, sometimes new...always slippery. Oil filter: Yellow, usually full of oil. Carbs: 2 SU HIF. Distributor: Yes. Headlights: Not that bright but bright enough. A bunch of other stuff most cars have but not really important enough to itemize. Oh, wait...it has a cool sounding exhaust with stickers on the chrome tips. Really slays the ladies...

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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
Yes it just dies and cuts out and then wont fire up again. Ignition rolls and can hear dizzy turning but wont fire into action. It was MOT'd recently and all sparks were changed as it was sat for 3 years. I think its sparking fine. That's why I thought it was maybe cos the heater valve leaking onto the dizzy below it and making it damp but because engine was so warm it evaporated and then carried on. As I say, it 'feels' like water is evaporated or fuel evaporates before it kicks into life again?? Its a right teaser. The heater valve doesn't leak when the heater knob is turned on to full/hot. Only when heater is off.

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ErnieY Avatar
ErnieY Ernie Y
Albatera, Alicante, Spain   ESP
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A UK 73 will have HS carbs not HIF's as pictured by Nick and the float chambers on those are readily accessible for checking from above, that's some accumulation of junk BTW Nick !.

The lack of vacuum advance will not have any real impact on performance as it only comes into play when you're off the accelerator, it can have an affect on idling and fuel economy though.

When it cut's out is it instant or does it sort of splutter and die ?

Instant is usually down to ignition and spluttering down to fuel.

You said "Once it heats up and goes over the midway point on the water temp gauge" but normally the temperature should not go above the 'N' and with an over cooling mechanical fan and the British climate normal would typically be at about 7 o'clock.

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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
It normally sits (since ive had it) quite comfortable at 6 oclock, when it goes to 5 oclock is the cut out point. Its never gone above that since ive had it.. It has an extra fan on the other side of the radiator (which did have a thermostat turn on until the dozy mechanic who mot'd it and changed the head gasket and broke the sensor during the MOT) ive 'hard wired' it now though so it is always on (which I didnt think was a bad thing). Generally when it dies you hear it going, and revs dropping, its quite immiediate. Always generally at a junction when the revs drop, but when it goes, it will go know matter how hard you rev it to try and keep it going. Its hten a case of wheeling it to the side and waiting 5-10 mins.

so you reckon Ernie, a new dizzy with the vacuum attachment may not make much difference? I'm wondering if it is to do with the heater valve leaking? I know it not completely tuned properly and the carbs probably aren't properly balanced?

I'm a novice by the way but I'm enjoying learning how this great machine works...

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ErnieY Avatar
ErnieY Ernie Y
Albatera, Alicante, Spain   ESP
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It's hard to relate the engine cutting out to a relatively modest rise in temperature but to be absolutely clear as I understand you it's not cutting out instantly - as if the ignition had been turned off - but dies with some warning, is that right ?

At this juncture replacing the dizzy and getting the vacuum working will make no practical difference to anything, I'm assuming of course that you've at least replaced the points, condenser, and rotor.

You'd have to have a gush of water from the heater valve for it to have any effect on the dizzy nor would it recover from a dousing simply by waiting 5 minutes !

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nickj Avatar
nickj Nick Jenkins
Novato, Marin Co, CA, USA   USA
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1970 MG MGB GT
1972 MG MGB
If you've got HS4's, they're way easier to check. Just three screws and pop the float bowl cover. Check the float levels, mine were way off.

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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
Yes I hear you Ernie, when you say it like that it doesn't sound right. I used to have a mini and they were prone to dizzys getting wet and cutting out. But I suppose the heater valve shouldn't leak so will need replacing anyway. It does pour out a bit but I think your right, it would need a hell of wave to knock it out.

Its hard to describe the cut out. I suppose it is quite instant. The car has always spluttered a little bit when turning the ignition off and the recent meddling we did with it at the weekend did cause a few misfires. When I say it cuts out instantly I suppose it does just die, the time it takes for the revs to drop and it to cut out I suppose is pretty much like turning the ignition off. The rev counter simply drops and off it goes. Then when you turn the ignition there is nothing - no fire.

Nick - if your talking about what i think you are - we took out the three screws to the side of the carbs and took the lid off with the float attached and drained the fuel in those pots. The fuel was really quite dirty - it turned black on the drive where we siphoned it to. Wondering whether it may be a fuel problem. Thing is, this problem only developed after it was sat for a while, never had it for the first few years after I bought it when I was running it more.

The problem I have now is that its on my dads drive 330 miles away in Carlisle. I cant just nip outside and have a fiddle. I'll give him a ring and give him a few things to check...

They are HS4's btw.

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
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It has a 45D dizzy on it but I notice it hasn't got the vacuum part that goes to the carbs.

Andy,

If the vacuum advance unit is missing altogether, that will cause you performance problems, since the springy connection inside the distributor, where the vacuum advance unit attaches to a post on the breaker plate that carries the points, stabilizes the breaker plate. If the vacuum advance unit is absent the breaker plate can bounce around, giving you very erratic timing, which would certainly affect performance.

Suggest you address that issue right away. Also, suggest you carry a spare spark plug and, when the engine dies, attach one of the spark plug wires to the spare plug, lay it against a good earthing point like the cylinder head or alternator, and have a friend crank the engine while you look for spark at the plug.

You should certainly purge the fuel tank of old fuel. Also, try driving the car with the gas cap loose, since the vent may be clogged after the car sitting for so long, and you may be creating a partial vacuum in the tank if no air can get in to replace fuel as it's being used up...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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Badhoon Avatar
Badhoon Andy Woodyard
Ipswich, Suffolk, UK   GBR
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1974 MG MGB GT "Mutley"
Thanks Dick and all the rest of you - I'm gaining some good knowledge here.

It was always the plan to get a dizzy with a vacuum unit anyway, I was hoping it may fix my problem. We tried the 'spare plug' test at the weekend - although oi can remember if it was after the engine had just died and was at temperature. The spare plugs were sparking though - I'll check with my Dad if we did that test when it was warm or cold.

Ernie - i haven't replaced rotor, points or condensor or anything but i cleaned all the crud off the points and gave the inside the the dizzy cap a good clean (it was damp). If i order a new dizzy though - it should solve this problem anyway. I@m looking at this on ebay: guessing this one will fit?

http://www.ebay.co.uk/itm/MG-MGB-Brand-New-Replacement-Distributor-All-years-/390269464357?pt=LH_DefaultDomain_3&hash=item5adddf6f25


Another thought we had was that whilst it had been sat, my dad had been topping up the fuel form an old jerry can which we think had some water in it as it was leaking - I also took the fuel filter off at the weekend and cleaned that out - you could see water in there too. I filled the tank up with fuel before i left so am hoping if there was any contaminated fuel in the tank (it was on empty mind) - this would have pushed it out or displaced to the bottom by now - i think possibly draining the tank completely is a good idea - also I'll try running with the fuel cap off.

Will speak to my dad today and report back.

Cheers for all the advice so far guys.

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B-racer Avatar
B-racer Jeff Schlemmer
Shakopee, MN, USA   USA
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It sounds to me like your issue is an overheating coil, which is usually caused by high resistance plug wires or a faulty power input connection (feeding the coil with low voltage.) Plug wires should have 300-3000 Ohms resistance each, and power at the + terminal of the coil should be within 1 volt of battery voltage (well over 12 when running). A good set of wires and a new coil are probably in order.

As for a $50 replacement distributor, save your money. Don't buy cheap Chinese junk distributors. The car will NOT run any better. Since you're in the UK, speak with Martin the Distributor Doctor about getting a rebuilt original 25D, set up properly for your car. There's no such thing as a one-size-fits-all distributor, and that's what all the aftermarket stuff is marketed as. Let's just say that those are NOT ideal in any way! You're trying to resolve a problem, so I highly recommend not confusing the diagnostics with any more new parts than necessary.

If the coil and wires don't resolve the issue, my guess is that you have a fuel pump problem, overheating probably from poor grounding.



jeff@advanceddistributors.com

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LENZ Avatar
LENZ Jim B
Leominster, MA, USA   USA
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1970 MG MGB GT
1974 MG MGB GT "White Lightning"
whatever you do don't get a cheap Chinese dist. my GT had one, the main shaft was not even centered and the points were contacting at an angle.
I replaced with one built by Jeff S.

your issue does sound like a hot coil. your 73 should have a 25D if i'm not mistaken.



Edited 1 time(s). Last edit at 2015-07-30 10:26 AM by LENZ.

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EoinDubh Avatar
EoinDubh John Black
CA, USA   USA
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I have a 1972 GT and ran into the same issue a while ago. The first time that it happened was on the way home after a club tour driving up Hwy 1 along the California coast. We were driving at 65 MPH and the engine just shut off. I pushed in the clutch and cranked it over but it would not start. I downshifted a gear and let the clutch out but it would not catch. I pulled off at the only spot available and just before calling for a tow, I tried starting it again. It fired right up and ran OK all the way home. It was fine for a few months and then did it again. Over a few weeks it was becoming a more frequent occur more frequently.

The engine had about 4000 miles of a total rebuild with new carbs and a distributor rebuilt for the engine and can by Advanced Distributors. Spark was good, timing was spot on and it ran great except for when it didn't. I took it to my mechanic to have him install a new fuel pump and in doing so he found the problem. Another case of an idiot PO! There is a short fuel pipe that comes out of the gas tank that the hose to the fuel pump connects to. It is retained by a gland nut. At some point the nut had broken perpendicular to the pipe so that the threads were separated from the part that put pressure on the gland. It had been removed and rather than replace the nut together and put back on. Over time the solder just could not take the strain and separated so that, especially on bumpy roads, the pump would suck air not fuel. The nut was replaced with a new on and the new pump was installed and no more problems.

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