Backfiring

"Anyone have any idea why my M

"Anyone have any idea why my MD3 backfires when I try to start it.Recently had some work by a mechanic,had the head off to clean out the water jacket because of a cooling prob.Worked fine before.Mechanic doesn't know.Any advise much appreciated"

""It worked fine until the

""It worked fine until the mechanic worked on it."

That doesn't speak well of your mechanic. If it worked fine before the mechanic worked on it and it has a problem when the mechanic finished, it is very likely that the problem is related to something the mechanic did. The mechanic should go back over everything he did to find where he went wrong. If your mechanic can't find the problem himself and is leaving it up to you to find the solution on Internet message boards, he is certainly not a "mechanic". So - consider finding a different, more qualified mechanic."

There is not much to do wrong

There is not much to do wrong when removing one head or more than the valve adjustment.
The only other option might be that a water leak has occurred into the compression chamber when cleaning out the cooling channel.

"Thanks for responding,guys.Ye

"Thanks for responding,guys.Yes the mechanic's competency has been drawn into question.Rather than footing the bill for the mechanics 'by the hour'learning curve,I thought I would throw the question out there to try and narrow the search.Do you think an incorrect,improperly installed or re used original head gasket might cause coolant to enter the combustion chamber?"

"If Your mechanic has re-used

"If Your mechanic has re-used a head gasket on that engine, any for that sake, I would get a new mech!
With the age of the engine (Early 1970??), the minimum should have been to resurface the head and cyl, pressure test cooling system/head and NEW gaskets. Hopefully he at least did all 3 heads??"