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Engine developed a miss

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Bruce L. Wiley Avatar
Bruce L. Wiley Bruce Wiley
Vidalia, Louisiana, USA   USA
1965 MG MGB "Daisy"
I drove the MGB for about 45 mins yesterday at which time it developed a miss and almost died at a red light. It is barely noticable at speed except an occasional slight fluctuation in the RPM gauge (+ or - 100rpm). I pulled each wire to see if any change and each plug caused a worse miss. The fuel pump is pumping and the mark on the dizzy had not moved. I tried cleaning the points with no effect. Any suggestions?



If you can't find time to do it right, where will you find the time to do it over?

It's not ownership, it's a relationship.

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ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
Possibly a fouled plug.
When last changed
What plug model ie. BP6ES
Loose plug wire
Inspect



"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"



"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972



Edited 1 time(s). Last edit at 2017-03-19 09:59 PM by ohlord.

ken472 Avatar
ken472 Ken Petersen
Luverne, MN, USA   USA
Pull the valve cover and check for stuck valve or broken spring. Or even a loose rocker

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steve12955 Steve B
Massachusetts, USA   USA
1970 MG MGB "Emma"
Possibly the condenser if the misfire is more significant under load/acceleration and smoother running at idle or at steady RPM.

B-racer Avatar
B-racer Jeff Schlemmer
Minnesota, USA   USA
Ohm out your plug wires and the carbon brush in your cap. As installed, you want no more than 5000 Ohms resistance through your cap, wire, and spark plug for each wire. I'd be willing to bet you're double that?
Check timing with a light to see if your timing mark fluctuates when the rpm fluctuates. If so, there's likely a mechanical distributor issue at play.

Then again, you could have water in your fuel or rust in your tank.



jeff@advanceddistributors.com

Bruce L. Wiley Avatar
Bruce L. Wiley Bruce Wiley
Vidalia, Louisiana, USA   USA
1965 MG MGB "Daisy"
I've done all the checks and have narrowed it down to the Weber DGV. Engage the manual choke, she smooths right out. I am assuming, please help if I'm wrong, that I have a vacuum leak in the carb.



If you can't find time to do it right, where will you find the time to do it over?

It's not ownership, it's a relationship.

nickj Avatar
nickj Gold Member Nick Jenkins
Novato, Marin Co, CA, USA   USA
1970 MG MGB GT
1972 MG MGB
A vacuum leak would most likely result in a high idle, which doesn't sound like your issue. It does seem to be carb-related, though, not ignition.

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Bruce L. Wiley Avatar
Bruce L. Wiley Bruce Wiley
Vidalia, Louisiana, USA   USA
1965 MG MGB "Daisy"
If I listen closely, I can hear an intermittent sputter inside the carb. I think a rebuild may be in order. At least a thorough cleaning. Jets clogged?



If you can't find time to do it right, where will you find the time to do it over?

It's not ownership, it's a relationship.

RAY 67 TOURER Avatar
RAY 67 TOURER Ray Marloff
Fort Bragg, CA, USA   USA
1967 MG MGB "My Girl"
Look again for a vacuum leak. I fired up my Samurai, after an 8 month rest, and it ran great for a few miles and then wanted to stall out. The first thing that I checked was the vacuum lines. Sure enough, I found one that was loose and one that had a crack in it. Cut off 1/2" and re-installed it. It now runs as good as it ever did. KISS. Keep It Simple Stupid. RAY

Bruce L. Wiley Avatar
Bruce L. Wiley Bruce Wiley
Vidalia, Louisiana, USA   USA
1965 MG MGB "Daisy"
I have a single Weber DGV courtesy of the PO. I took it off, minor dismantling, sprayed copious amounts of carb cleaner, and hosed her down with the air compressor. 30 mins later and back on, good as new. It IS the simple things.



If you can't find time to do it right, where will you find the time to do it over?

It's not ownership, it's a relationship.

terryke5hwe Terry Halbert
Rogers, AR - Arkansas, USA   USA
1978 MG Midget 1500 "Blue Eyes"
1979 MG MGB "Money Pit!"
I had similar issue with my 1979 B and the dist cap had some metallic dust inside. Maybe a loose fit? Saw uneven wear on the contact's, replaced and miss stopped but I want to get a good 25d to replace the aftermarket 45d.

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