"bucking" at high power settings

[Nigel70]

My 88" petrol S2A is "bucking" art high throttle settings under load. It's as if you floor the accelerator and let off, and floor it again, then let off and then again full throttle. Eventually if I don't let off the gas it will stall. Letting off the gas will temporarily correct the bucking but by that time I have lost momentum and must start in 1st gear again. It is also sputtering at idle. I have replaced the carburetor, fuel pump, fuel filter and installed an electric auxiliary fuel pump as well. My mechanic says I need a new distributor because it doesn't hold correct dwell. Would a new distributor help? Or, is my problem fuel starvation?

[Snowboy71]

My 1970 88" 2a had a very similar problem last summer. I replaced the points and condensor which solved the problem. Not sure if the same will work for you but it was an inexpensive and fairly quick exercise.

[roverp480]

I have had similar symptoms a number of times over the years. 1) Failed condenser being the most common. Replace Condenser 2) Poor petrol , refill with good quality branded fuel. 3) Carburettor issues, but that was sticking none return valve on a S1 LR with a different carb. One other electrical item could be a coil breaking down .
As your mechanic states the distributer cannot hold the dwell, I do wonder if the advance springs have broken or weak, allowing cam with the rotor arm to float around. Also if the vacuum advance has broken or become detached , the base plate with the contact breaker points can float around . The obvious way would be to replace with a known good one but I appreciate that may not be easy. If you can find any Lucas 25 D4 distributer off a 1960's British car such as an MG it could be swapped in to prove a point , but as it would inevitably have the wrong ignition advance curve , just run it up briefly to see if the problem ceases .

[Nigel70]

Thanks. I am having a new distributor installed and hoe that fixes the problem.

[Nigel70]

Thanks for the reply. I am installing a new distributor tomorrow and hope that corrects the problem.

[jimrr]

i'm betting it's fuel starvation. though initially you may get a good flow from the tank via the fuel line, let it run a couple minits and see if it diminishes for oft times there is something in the tank that moves into the outlet port blocking.
I mean to say, on start up it may run fine, and make it around the block ok but after a bit and when the engine demands significant fuel flow it then isn't avaiable though after while at idle or low demand a dimished fuel flow will "catch up".

[erik88lr]

Thanks for the reply. I am installing a new distributor tomorrow and hope that corrects the problem.

So.... is the problem fixed? If not I'd suggest connecting a fuel pressure gauge at the carb and see if the pressure drops to zero under high load / high RPMs.

Mine did, and I had to install an electric pump.