Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing tuning SU HS6 carbs in a '67 +4?

Could it be a small air leak either on one of the carb gaskets or the carb/inlet manifold gasket?

Popping on the over-run is usually unburnt fuel exploding in the exhaust.

"Popping on the over-run is usually unburnt fuel exploding in the exhaust."

Yes, that sounds feasible. I need to tune the carbs better. I believe that may be right with the mixture not being perfect. I tried the Colortune, but didn't get far since sunlight was gone fast with our switch out of daylight savings time. Then it isn't the distributor and cables?

Is there an issue if the engine doesn't heat up enough even after an hour of driving? I fear I don't have the gas/air mix perfect, so perhaps the engine doesn't warm up enough. I only noticed it this past weekend when it was in the 50s (F) and testing the car. Of course during the summer it was always hovering around the middle of the dial. Now it doesn't seem to reach the middle. Is that a bad thing? Or a good thing?

Budster,
I tested the carbs for any leaks and didn't find any... I sprayed starter fluid all around.

An air leak in exhaust system can cause that sound.

My first Midget always popped and banged on the over-run and I quite liked it!

Ha ha... It does sound ferocious.

Ok, funny thing happened to me. I changed the spark plugs,distributor cap, wires, and rotor. I took it for a long spin and all seemed to work wonderfully. The popping noise subsided, it was still there, but it was much lighter, more of a putt putt as I slowed the car in gear. I still have to get the mix right and will do soon. I got home, idled for a bit, and gave a little gas. I waited just a second until it went to idle. When I switched it off, the car diesled a bit and poofed up a bit of smoke from the carb side.... oh no. I then tried to turn it on again, and nothing. No lights, no nothing. I feared for the worst. Good gosh, my novice mechanic abilities may have ruined my car. I went to the internet to see whether others had this problem on their TR4A. I found several remedies, and one that seemed like the first thing to check was to check the battery connections. I did, and found the clamp on the battery switch was too loose. I tightened it and the car started. Life is good again.

If the dieseling becomes a problem, you might consider fitting an anti-run on valve. Fitted as standard to the MG Metro,(and other BL cars) it's a simple solenoid, energised by the ignition, When switched off the valve opens and dumps air into the inlet manifold. It has a swiched live terminal, an earth terminal and a servo hose connection which must either go via a T piece into the brake servo hose, or if you don't have one, into the inlet manifold direct.

Dave, Thanks for the dieseling suggestion. Sounds a bit complicated. I know the car isn't tuned perfectly and hope that has something to do with the dieseling. It did it during hot days of the summer. I does it sometimes when I rev the engine and then turn it off. If I let it idle for a little bit, and then shut it off, it usually doesn't diesel. I heard some recommend giving a flush with Seafoam gas additive to clear out the cylinders of buildup. After I get the distributor refurbished and the carbs tuned right I hope the dieseling will go away.