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MG MGB Technical - Bad MGB Weekend

My '73 B has been running rich for a little while, so after giving up trying to adjust the carbs for myself I took it to someone to have them adjust them. It backfired off and on the whole way there and didn't want to go very quickly. I got there and he took a look at everything and started to adjust he carbs and then stopped and told me that I needed to adjust the timing and the valves. The distributor had welded itself to the block. The car ran fairly well driving away from there, but the further I got the worse it ran. As soon as I got to my garage I took the valve cover off and adjusted the vavles to .013" hot by the rule of nine. Some of the valves were tighter than that, but others weren't. Then went to work on the dirstributor, finally got it loose after applying some heat. Well got everything buttoned back up and went to check the timing. I turned on the ignition and went to look at the damper and I see smoke. Turned off the ignition and discovered that I now have a burnt wire from the fuse block to the coil. Go inside and call my dad, he says he will be home in a few minutes. Well, after a few hours of determining what is not the cause my dad notices that I had pinched one of the wires for the pertronix in between the distributor and the cap. Fixed that set the dynamic timing and fired up the car. Ran ok at first, so I started adjusting the idle speed and the after the car had warmed the whole engine started to shake. Turned it off and my dad re-checked the valves. Started the car again and now it is only running on one cylinder. My dad suggests that the cam has gone flat or one of the push rods is bent. Any other ideas?
Sorry for the long post.
Zach Dorsch

So, are you getting spark to the other 3 cylinders? Given your description, it really sounds more ignition related than anything else.
Barry Kindig

Zach,
Here's a comment I submitted a week or so ago. It sounds like you have the same problem with your HIF4 carbs. Same symptoms.


I had a problem with my '74 B that drove me crazy for a couple of months. The problem started suddenly and the symptoms were always the same. I could start the engine normally (cold start) using the choke. Once the engine began to warm up it would start to run progressively worse until it died. The engine would not start and run normally when warm and any pumping of the accelerator resulted in backfiring through the front carb. The plugs would foul with raw fuel as though the ignition was to weak to provide adequate combustion.
Since I was going to change out the tired old oil burning engine anyway, I went ahead and replaced it with a rebuilt short block. I also replaced all of the ignition bits and pieces (including a rebuilt distributor), the fuel pump and the carb. floats and jets. I figured one or all of those improvements should have solved the problem.
Nope! Same problem.
The only things I had not replaced or rebuilt were the HIF4 starter valves. That was it. The "O" rings were hard as rocks and were letting fuel flood out the engine as it warmed up. I replaced the "O" rings and valve seal and all was well. My '74 now runs like a champ. If you do the same thing to your B, be sure and not over-tighten the nuts that compress the valve seals. The seals will crack and become useless.
Gary Cash

Okay, update. Went out and messed around with the car for a while. I rechecked the valve adjustments. I rechecked the timing. I also tried switching around the plugs and cap. Well I think that the plugs were bad. It is still running very rough. It revs freely now without backfiring. What I am afraid of is that I may have messed up the vaccum diaphram on the distributor. Would another cause be misadjusted mixture?
Thank you for the replies.
Zach Dorsch

If you suspect the diaphragm is bad, simply disconnect the hose at the manifold end and suck on it a bit letting your tongue seal the opening to maintain the vacuum. If the vaccum is maintained, the diaphragm is probably OK. You should also see some baseplate movement as you apply suction.
I doubt that you have bad plugs if the car was running OK recently. Your plugs were probably fouled due to poor mixture.
Try adjusting the mixture on your carbs to see if the procedure improves your rough running. Check this site for carb adjustment procedures if you do not have a manual.
Gary Cash

I had a similar problem on a freshly rebuilt engine. It would run fine for a minute or two, then started running real rough and shaking. Turned out that the valve guides hadn't been reamed properly and a valve was sticking wide open. Some of the responses I received on this board when I posted my problem suggested that excessive carbon buildup could cause valves to stick.

Good luck,
Rich
Rich F.

Change over to a single weber.Will most likely solve
all your problems

AJ
alfred mitchell

This thread was discussed between 18/03/2002 and 22/03/2002

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