As an addendum to the closed point situation I mentioned, this reminded me of an an old Audi a car dealer sent to me one time. This car had been taken to an import shop and he was quoted 400 bucks for fixing a fuel injection problem Every car that goes through the door there has an FI problem that requires 400 bucks.
The car would only run well at elevated RPMs and would buck and jerk at idle and low RPMs. Problem? Closed points. At elevated RPMs the weakened point spring was allowed the points to bounce. Normally bounce is not good and only occurs at very high RPMs. When they’re closed up you need all of the bounce you can get.
Regapped the points, added a drop of cam lube, and the car ran like a new sewing machine.
Hit the simple stuff up first before expecting the worst.
“When we first began restoring this car it had sat for 15 years and so we replaced, points, condenser, spark plugs wires, fuel filter, etc… did all the little things, and it ran great, started right up, ran very well. We didn’t however change the fuel tank at the begginning, we just ran it off a portable tank of gas so we could set the carbs and just work on it… Well we cleaned the tank by running gas thru it and started running it off the old tank, thinking it seemed pretty clean, we were wrong apparently cauze that’s when all our problems started and it hasn’t run right since… At first it just started dying after we’d drive it a certain distance, then it would only idle with the choke pulled so we assumed that we must’ve ruined our carbs, so we replaced them and you know the rest…”
So at the beginning, with new points, condensor, etc., and OLD carbs it ran fine from a separate gas supply. After hooking up the original gas tank all the trouble began, unaffected by replancing the carbs. It sounds like the the old tank had dirt in it, plugged up the fuel system with the old carbs, plugged up the fuel system with the new carbs, and now the fuel system (somewhere) is plugged up with a new tank in place. Sounds like everything in the fuel system needs to be cleaned out downstream of the new fuel tank.
Unfortinately they didn’t originally have a fuel filter. It’s very easy to splice one into the line under the hood. It’s a cheap investment. I have one on my MGA. Works well. They relied on the float bowls of the SU carbs to make what little dirt did get into the system to settle into bottom of the float bowls. Eventually they had to be cleaned out, but they might go years before needing the treatment.
NOW that we know about the problem coming up after you started using the original tank, I think you do have a dirty little problem there. The Weber carb is probably full of rust and assorted other junk that was in the original tank.
Granted, I missed the post where the OP stated that points, condenser, and whatnot was replaced.
The post with that little bit of trivia was apparently dated a week after the original posting. Along with the other trivia about only idling with the choke on.
The points were replaced. The question remains; are they gapped properly and adjusted on the highest point of the distributor cam?
What about the timing question? On the money or way retarded?
It can’t be a fuel system clog. The OP states the car will run at high RPMs and high speed is where a system clog will be most noticeable.
Given the added bit about only idling with the choke on then it sounds like a gigantic air leak exists somewhere, there is a restriction in an idle circuit, mixture screws are shut off, etc.
Not all SU fuel pumps are equal. If the fuel pump has twin dome type inlet / outlets secured by a metal ring with 2 screw, it will likely have metal mesh fuel filters unless someone has removed them.
is it a side draft weber or down draft if its the dd carb i think the accelerater pump stroke is adjustable you may not be getting enough fuel at low rpms if you have sd carbs you need to pump up that wheezer of an engine too much carb!!! check your ig. timing if you have the photo dizzy u r screwed
I want to add two more things to check. First, remove the distributor cap and turn the engine until the points rest on top of one of the lobes. Then insert the correct feeler gauge in between the points and push on the distributor shaft in the direction of the points. If the open up some more, you have a worn shaft bushing. This can cause the symptoms you are experiencing.
One other thing is to measure the amount that the valves are depressed when the engine is turned over. Here you are looking for a “flat cam” lobe. If the cam was ever reground, it might not have been case hardened after grinding, in which case, it will go “flat” very quickly.
I wonder after reading texases most excellent reply we are looking at clogged carb needing cleaning especially at the idle set screws and a fuel filter. Thanks tex for restating what may have been missed, still looking for my mid life crisis mg, if you want to sell it let us know. It is not a hard carb to clean, but we have been round and round so often on this,
I was surprised a dwell meter was not available at the auto parts store or farm and fleet while trying to fix my 66 Evinrude 4 cyl 4 barrel carb dual point 100 hp engine on a 15’ boat. I have one at home but can’t believe they are as dead as dinasaurs, If you don’t have a dwell meter make sure you check point gap at the high point on the distributor cam, cam grease is good, too many options.
I’m not an MG expert by any means, but I did a lot of work on a '79 Midget a couple of years ago. I remember a similar problem with that car. I replaced a bad ignition module with a Pertronix unit and that cured it. Much more reliable than the OEM unit and not too expensive. The original was some weird old thing (Piranah?) that you couldn’t find anyway. Good luck!
Just to clarify… We didn’t use the OLD tank with new carb… and we blew the lines out several times before we hooked it up to the new carbs… it seems to be getting sufficient fuel supply… Also I have had several people tell me that it could be a vaccuum leak or ignition problem. But One said because of the way it idles fine, but if you push the gas slow or soflty it catches and dies but once it gets up to high rpm’s runs fine, they thought it could be a SMALL vaccuum leak causeing it to run bad at low rpm’s. They also said the didn’t think that it could be ignition cause ignition wouldn’t get better with higher rpm’s… Does that makes sense to anyone???
OK…if it idles well, runs well at high rpms, but stumbles going from idle to high rpm my guess is (if all possible vacuum leaks have been checked an eliminated) it is something in the carb. Ignition problems might do this (I don’t know how), but I can easily understand how a mis-adjusted or mis-jetted carb would do this.
My carb is a downdraft… I am pretty sure we checked the timing and that it was fine, but I’ll make sure… And I will also check the distributer and points stuff you guys mentioned… Thanks!
One little update I forgot to mention is that my dad messed with the distributer vaccuum advance the other day and now it seems to be doing a LITTLE bit better… That is if you call hitting the gas once fast to, we’ll just say, “release the catch it has”, THEN hitting it again FAST before it DIES to rev it up… It seems to rev up GREAT if you hit it twice like that… I don’t know…
"They also said the didn’t think that it could be ignition cause ignition wouldn’t get better with higher rpm’s… "
You seem to have ruled out fuel and vacuum and most basic ignition parts. My car (93 suzuki swift) has a similar issue. Idles good and runs well at high rpm. It’s the in-between part that sux. Oh, and that’s on an EFI vehicle.
While you’re in there, some day check the intake manifold for cracks and the gasket. Ignition can always be a problem. Be sure the advance is working right. Glad that you did look at the vacuum advance. Best of luck. Check firing order again. People can get 1-3-4-2 messed up really bad by forgetting which way is CW and which CCW. Sometimes the engine even idles OK.
Play with the timing setting. Factory spec may not be correct. You may have to adjust timing by engine sound rather than by what is shown with the timing light. Keep experimenting with the setting & I beleive that you will find a setting that will result in proper acceleration.