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MG MGB Technical - New MGB Owner with a few bugs

Hello folks,

Fairly new to the MG world and am hesitant to get my hands too dirty without some sound advice.

I have a 78 MGB and am looking for a little help with the following:
1. Upon start-up, the engine does idle quite fast, over 10K. Is that normal for an MG at start-up? It does not sound like it should be like that. If not, any simple ways to adjust the timing without getting down and dirty with the engine?


2. After shutting down the car, the motor continues to run until, it seems, all of the gas inside the carb has been used up. Makes sense since the fuel pump should shut off after you turn off the ignition. The former owner blamed it on the new throttle cable he installed but I have not had much luck. The throttle appears closed but when you feel the cable you can feel some slack. I purchased the Haynes manual but that has not been very helpful since I cannot match my carb with any in the diagrams. It appears that I have a normal double barrel carb but, again, not too sure.

Any thoughts?

3. There appears to be a leak in the clutch line somewhere and would have to pin it on the rubber hose feeding the slave cylinder. Any easy ways to deduce a clutch leak without having to lift the car? I would like to have an idea and the parts ready for when I do get under there. Also, when I fill the clutch fluid reservoir, I get a small puddle of fluid on the driver's floor mat most likely from the fluid overflow dripping down the line.

Again, any quick thoughts? Is this something major I should fix or is simply refilling the fluid when its low a good solution until I can get under there?

4. Right next to the clutch fluid reservoir is a disconnect electrical wire with a three prong contact. The wire has a blue covering which leads me to believe that it is the power for the windshield washer pump. The Haynes manual is not very helpful for this except for a short single paragraph blurb. If this is the washer pump power cable, where does it plug into? If not, any thoughts as to what it could be?

5. Attached to the rear of the engine block is a metal line that has a rubber fitting (about 3 inches long) on the end. It travels from the left side of the engine compartment in the rear to the right and it is attached to a bolt on the engine cover and is allowed to swivel. This appears to be an air line of sorts but, again, my manual does not seem to help. Besides the obvious need of having to purchase the Chilton manual, any thoughts?

Thanks in advance for any help you can provide to my small problems. Keep in mind, the car runs beautifully for a 25 year old vehicle. With gas so high and my Suburban constantly thirsty, I am enjoying the MG as much as possible and would like to rectify these issues before I begin restoring the vehicle (cleaning up the engine compartment, sprucing up the interior, etc).

Regards,
Jim
JFB Berlinger

3. No way to tell unless you get under there and have someone pump clutch. Puddles on the drivers side is usually leaking master cylinder. Replace with new. Don't rebuild. Generally I would replace the whole mess (master, slave and hose) and never have to mess with it again. Bleed it backwards using pump style oil can and plastic tubing....it's a bear to bleed otherwise.
5. Sounds like vacuum advance tube. If you follow to the left side (distributor side) of the engine it should attach to the distributor. The other end with the 3 inch rubber tubing should attach to either a vacuum take-off (tube) on the intake manifold or possible the carbs...but for your year...I think...the intake manifold.
J.T. Bamford

I would guess that you have a Weber carb, most likely a 32/36 style if it is a 2bbl.

I had the same problem with the running on until I went on a 200 mile cruise averaging about 60-65 mph. I suspect the earlier owner only ran about town for short hops. It may have needed to have the carbon cleaned out by the steady running at a higher rpm to prevent the running on.

If your car was "de-smogged", the wire may have more to do with a vacuum control that was removed in the process.

The "B" has a water line off the top of the rear of the head that originally was for carb heat (I think?). It is attached to the head with two 1/4 inch studs. I made a small flat plate to block mine off as I also have the Weber 32/36 on my '77 "B".

Likewise about the gas mpg! I average about 24/25 around town at stop & go. On the highway top up and running 55-60 mph I get 40-43 mpg or a little better if I drive carefully. If I drop the top and run 60-65/70 mph it hits me for about 8 mpg, dropping back to about 34-35 mpg.



D Maples

1 and 2 should be helped by a good tuning and driving as suggested. If the PO says it's the throttle cable I'd check that it's properly connected. But it can't hurt to throw a new fuel filter, plugs and plug wires, points, rotar cap and rotar button in there. Set the timing and then tune the carb.

For 3 I'd have to agree with JT. Do it once and forget about it.

4 I'm absolutely guessing that it's maybe the circuit for the brake warning light. That's just my SWAG. There are many electrical experts around who probably know off the top of their heads.

No clue on 5 but my Haynes has served me well.






Brad Batchelor

Thanks for the advice guys. Now that I may know the carb I have, I can refer to the appropriate diagram.

I will check both the carb and intake manifold to see if I can get that line (vacuum or water) attached to something, if necessary.

Just as an FYI, I did just take a nice voyaget with the MG, about 150 miles this past weekend in 85+ degree heat with the car average 50 or so but I still get that dieseling effect.
jberlinger

Hi Jim,

Welcome to the world of MGs, I hope you're good friends with your bank manager!

1. Do you mean 10K? I think that's off the scale on my rev counter! 1000 RPM sounds more feasable. Depending on the condition of the engine it could take a couple of seconds for the oil pressure to build up, so high revs at startup are not a good thing. I think the Haynes manual mentions warm idle speeds between 500 and 800 depending on the engine.
Does the engine speed settle once it's running? If so how long does this take?

2. How long does the car run-on for? This is fairly common, my '71 BGT sometimes runs on for a couple of seconds. I remember from somewhere that retarding the timing can cure the problem, although it's always a trade-off against something else (performance?). You could also fit an anti run-on valve.
Matt Bagshawe

Nice catch Matt!

The 10K rpm was one of those things you recognize after you hit send even if you proof-read it 20 times! You are correct, I meant 1000rpm.

On a typical VA day, mid 70s, it takes about 30 seconds for the rpms to come down, but that is after rev'ing the engine once.

As for the run-on, it depends. If it has just been running for over an hour, it may sputter for about 5 to 10 seconds. Most of the time it is around 5 or less.

As for the banking piece, after hearing from J.T., D, and Brad, I may have to open a line of credit with Victoria British!

Thanks again.
jberlinger

Jim,

Looks like you've been given the best advice by the other guys - a tune up and service then see where you need to go from there.

More of an anecdote than a recommendation here, but some people cope with run-on by stalling the engine in 4th gear while it's spluttering. Just a thought...

Anyway I hope you enjoy your MG, they're worth every late night and every split knuckle in my opinion.

Good Luck!

Matt "what's that bit do?" Bagshawe
Matt Bagshawe

The high idle, and "run on" condition can both be caused by a throttle that isn't closing all the way, and/or a vacuum leak somewhere between the carb and the head. Disconnect the throttle cable from the gas pedal (very easy, take a look!) and MAKE SURE the throttle plates are closed (take the air cleaner off, and look down the carb throat). Remember to check & see that the manual choke cable is also slack. If not, this will raise your idle, as it has a cam that opens the throttle just a little when you pull the choke out. If all is okay, go to the carb base itself. If you do, in fact, have a Weber you may find that it is loose on the manifold. Locktight the studs in the manifold, and snug that bad boy down. Make sure you have a good base gasket, too. Next check for any air leaks in the intake manifold itself; leaks around the power brake fitting, etc. Lastly, check that the intake is making a good seal to the head. If all is good, your idle should come down and be easy to set to factory specs. Oh yeah, make sure the vacuum advance hose (rubber) is hooked up & not leaking/split, etc. All of these checks should be made with the engine off. One trick to check gasket sealing for air leaks is to spray some WD40 around the suspect area while the car is running. Any waiver in RPM's (generally, the RPM's will drop slightly) indicates a potentional leak. Make this check after you have made sure the throttles are closed, and before you start taking things apart to actually look at the gaskets. Keep after it & you'll succeed! Good luck.
Mike Koval

Jim Your running on should go once you can get your idle speed below 800rpm, 750 seems best for me.I have always said my car never runs on, but it did the other day and I found that the choke was slightly out causing it to idle fast. It might pay to make sure the choke at the carb is going right off when the knob is pushed in. Also if the PO has played with the carb it can be that the throttle buttiflyes are not aligned, causing them to jam before they close to the correct idle position. You can check this by losening the idle stop adjuster right off and try and close the throttle a little more by hand. Then see if the throttle has a jamed feel (still by hand)they can usually be aligned by slightly loosening the buttifly screws and tapping them fully closed then tighten the screws. A very worn throttle shaft can also do the same thing. Of coarse you must remove the carby to make this adj. and the screws must be retained (threadlock,burred over etc).
Anyway just a few things for you to think about if the good advice from the previous threads dont fix the problem. I agree with the others about the clutch leak, the parts are cheaper than being stranded.
Good luck with the new toy. Denis
DENIS

Thanks for all of the great ideas guys! It is great to see advice from all corners of the world.

I may have to hook up with Brad since I am in Virginia Beach and he is only a couple of hours away in Rocky Mount.

I will begin my quest next week and keep you all posted. I am on a plane in the morning to see the family in CT and will back towards the end of the week. The MG will get some well deserved rest. If the odometer is true at 59K (which all previous owners have said it is), my little Tahitian Blue gem has not been driven this hard in quite some time, if at all.

Have a great Memorial Day weekend to those in US and a great weekend to you folks in the Kingdom and Down Under.

Jim
Jim

Fixing the clutch hydraulics was one of the first jobs I did on my car. I agree with the guys do the whole system and froget about it. I bought a new master cylinder, a recon kit for the slave cylinder and a new flex pipe.

It's a trickey job but all possible. You'll find it difficult to remove the screws on the master cylinder(s) cover. You need a long screwdriver to get inbetween the cover and the wing(fender). The flex pipe is pushed through a bracket and a ring nut put on. You can access this from above with a long socket extension. Don't do it up tight until you have the slave cylinder in place.

Bleeding in reverse, slave cylinder up, makes it easy. Email me if you need any help.
Richard Evans

This thread was discussed between 28/05/2004 and 29/05/2004

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