QuestionQUESTION: My 1979 mgb appears to lack pick-up or power. Brought it out of 15 years of storage. Replaced brakes and clutch slave. Replaced fuel lines and filter, replaced numerous emmission system hoses, cleaned and rebuilt carb, installed new plugs and wires, set timing (10 degress at 1500rpm). Engine appears to run smooth (not much vibration). Drained all old fuel and replaced with fresher 92 octane. However, while test driving the car, it just doesn't seem to have much power or pick-up. I did notice that there appears to be a small leak coming the gasket of the exhaust entering into the catalytic converter. Could the exhaust be the problem? Could it be a vacuum leak somewhere, and how would I test for that? Could it be the fuel contaminated from old dirt still in the fuel tank? Could it be the Fuel is too lean or rich? Thank You in advance for any suggestions.
ANSWER: Hi Ernie. I was pleased to note that you have replaced the brakes and the clutch slave. After 15 years, just about everything made from rubber will have perished. Please note that the tyres will be hard and may have small cracks in the sidewalls. Also the brake hoses.
My immediate reaction is a sticking piston inside the Stromberg carb. Did you replace the rubber diaphragm? Also, did you remember to refill the oil dashpot on top of the carb? Any vacuum leak will adversely affect performance, and this model (with all the emissions equipment) needs all the power it can produce.
I don't think it is stale fuel. You cleaned the carb and drained the tank, so fresh fuel will quickly dilute any stale fuel in the lines. However, 92 octane is pretty low. This engine was designed to run with 98 octane, so please try some Super.
The vacuum system should hold a vacuum, but to test it you need a T-piece and a vacuum gauge. A classic car shop maybe could do this test for you.
Let me know what it was when you find it.
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QUESTION: Hi, thanks for your prompt response and help. A quick follow-up and question.
I have new brake hoses, just haven't installed yet. I will check into new tires as well.
As for the sticking piston in the carb, I did replace the diaphram. I DID NOT replace the O-ring on the needle system. I did notice my dashpot oil does not last long, so I will replace the O-ring this week. Could that be causing the problem?
Also, would the bad gasket at the catalytic converter cause any problems?
I will refill the tank with 98 octane this week, and get the vacuum test.
Thanks again. Ernie
ANSWER: Hi Ernie. I doubt that the O-ring is causing all this trouble, but it is worth changing it. Dashpot oil and a leak would do it. Use engine oil (20W/50) in the dashpot. Personally, if it looks expensive to fix, I would ditch the setup and fit UK specification twin SUs instead (if the law permits it where you live). This change would free up an additional 20 BHP or more.
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QUESTION: Hi again Barrie,
I dis-assembled the carb to installed the new O-ring and found alot of black oily residue. The piston was somewhat stuck with all the residue. I had just cleaned the carb about a month ago, and only ran the car periodically and test drives totalling maybe 25 miles. Do carburators get this dirty and black so quickly? Or is this a sign of another problem? Thanks. Ernie
AnswerHi Ernie. I guessed it would probably be a sticking piston.
No, carbs do not usually gum up like this when a car is used regularly. However, there was fuel in the lines when the car was parked up 15 years ago, and it probably turned to gum while it was standing. Eventually you ran fresh fuel through it, and some of the gum has now was washed into the carb. This will keep happening until all the gum has been flushed out.
Do you have an in-line fuel filter? If so, you should replace it. If not, you should fit one and inspect it regularly. Every time it looks dirty, replace it again. They only cost a couple of dollars each.
