1914 roadster, vibrates/shudders when accelerating through15- 25 mph and is worse when under load. Once up around 30 35 mph fairly smooth.
Have tried reducing spark which helps a very little mixture change no effect. Engine was rebuilt using high compression pistons. quite noticeable when going up hill. Otherwise at low speed very smooth, easy to start and will idle very low rpm smooth.
Do you have the 2 wood side blocks between your motor mounts and frame?? If not, add them, along with the side bolts which some leave off, and test it out again.
Do you have a picture of the wood side blocks that your talking about? I don't recall wood block between the motor mounts and the frame.
Yes I've tried that .thanx
Daves suggestion about the U joint is something I had not considered. knowing the history of the car that might be worth a look!
Also a good time to check for babbit thrust washers!!
It's possible it could be an ignition problem. Especially with high compression pistons. It takes stronger spark to fire under high compression which is what happens when you accelerate and the high compression pistons will increase the compression beyond normal. Spark plugs or ignition coil problems on on or two cylinders could cause this problem.
A symptom of a loose universal joint would be a noticeable clunk when you back off the gas. If it clunks when you give it gas and when you back off the gas you have something loose in the drive train which could be a U joint. That doesn't fit the description of the vibration.
Also engine or transmission balancing could be a problem but are usually more noticeable at higher speeds.
Other vibrations which are not in the engine would be wheel shimmy or wheel balance problems.