Noise from exhaust

howie123

howie123

Senior Member
I have been working on this for awhile. I have a Model A speedster with a stock 1928 engine, Zenith carburetor, fuel tank in the rear with electric fuel pump back by the tank. When driving under power above about 15 mph, I hear a noise which I think is coming from the exhaust. It is more like a spitting noise than a backfire and occurs every few seconds. The engine starts good, runs well at a slow, smooth idle with the GAV about 1/4 turn open after warm-up. The fuel pump was connected to the ignition switch but I changed that by running a wire from the fuse block to a switch and then to the pump without any change. I am not sure where to look next. Any help would be appreciated. Thanks. Howie
 
Sounds like you have a slight exhaust leak? Possibly from unburned gas in the pipe. Is the tail pipe original or did you make your own?
 
Long shot: Is the fuel pump mounted in rubber or solid to the frame or body? Is it a pulse-type pump that 'rattles' when it is pumping? Maybe you're hearing the pump as it fills the float bowl, then stops for a brief time and pumps agian when the carb needle valve opens. Try switching the pump off to see if the noise stops.
 
Look for black soot spots around the connection between the maniford and the pipe. Drive it far enough for the soot spots to appear. If you find any soot spots(black) you have a small leak. Use muffler seal or high temp. silicone to seal the joint but be sure to follow the directions and don't start the engine for overtnight. Worked good for me.
 
Well, now I'm not sure it's an exhaust noise. I checked the exhaust pipe to manifold connection which did appear to be leaking. I replaced the brass gasket with Permatex exhaust system sealer. I also reworked the rear clamp which was pulling down on the rear of the pipe. I also retorqued the manifold. The noise persists. If deffinitely sounds like it is coming from the rear but it's hard to tell which side. It could be a squeak or creak but I can't pin it down. It doesn't seem to happen under 15 mph which has me stumped. The fuel pump and lines are all secure. I have greased all major lube points. Any ideas would be appreciate. On the bright side, the car starts easily, runs smoothly and has never left me stranded. I will keep driving until I figure it out. Thanks again. Howie
 
I use my shop-vac to find the leaks. Connect the shop-vac hose to the outlet, exhaust, of the shop-vac. Connect the other end of the shop-vac hose to the tail pipe. Get a spray bottle with soapy water. Turn on the shop-vac and spray the suspected area with the soapy water. You should find the leak if there is one.

Bob
 
Well, I definitely have a leak around the manifold. Thanks Bob for the suggestion. It was a quick and easy test. The manifold is now off the engine. I will take it to the machine shop for resurfacing. Does anyone have suggestions on the best gasket to use. The gasket that was in it was two peice with gland rings. It didn't look like there was a metal layer but hard to tell. I put it in so long ago I can't remember. Any suggestions on reassembly would be appreciated. Thanks for all the help. Howie
 
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