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MG MGB Technical - 1974 MGB won't start when cold

1974 MGB very, very hard to start when engine cold. After warmup, runs great. Confirmed dwell, timing, both carbs. Engine spits, sputters, acts like its running on two cylinders when it finally fires. Engine recently overhauled about two years ago. While chasing this issue, I have replaced distributer cap, rotor, points, condenser. Checked compression with engine cold (145 to 150 lbs all four cylinders). Vacuum gauge reads around 17 in. at idle -- after warmup (15 in. when its sputtering/etc) . Also checked fuel pressure -- 5 lbs.
IDEAS ANYONE????????????
THANX!

Larry Rousselle

Larry; Your fuel pressure is too high, probably the carbs are flooding. If you have an aftermarket fuel pump it needs a regulator to keep the pressure about half of what you are running. The presure from a properly working SU pump will be considerably less than you are running, I don't know the exact figure but I know it should be less than 5 psi.
Clifton Gordon

Larry - The proper pressure from an SU fuel pump is 1.5 - 3 lbs. 5 lbs is borderline high and could be causing your problem. Another possible problem area is the choke setting. Are you getting full choke when you pull the knob out? If not, it will also cause the symptoms your are experiencing. I would be more inclined to believe that this is the problem, since you are not having a problem when the car is warmed up, which you would if the excessive pressure was causing rich running.

For all who are interested in the specs and some simple troubleshooting of the SU fuel pumps, see my article, SU Fuel Pumps 101 on Les Bengtson's web page at:
http://www.custompistols.com/cars/articles/dd_su_fuel_pumps_101.htm
Cheers - Dave
David DuBois

Larry, you inferred you checked both carbs, and maybe you checked this also. If not . . . Choke!!!!! Is the choke cable slipping at the carb? Is it adjusted to give you enough "choke"? If it won't start cold, and will start and run OK when warmed up, must eliminate choke before doing more.
Daryl

I'm with Daryl. Move the lever on the choke interconnecting rod and make sure both jets are moving, then do it from the choke knob and check again. The choke interconnecting lever can be adjusted at both the ends with the clamp screws and in the middle with the cable. Unless the lever on the rod is horizontal when the choke is half-way through its travel it may not be moving the jets far enough.
Paul Hunt

This thread was discussed between 20/09/2003 and 22/09/2003

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