Hello Victor:
Another input. I had been having problems with my MD6A for two years. My
problems were similar, but not identical to, yours. My engine would start quite
easily and run OK for a minute or so, then slow down all by itself. Then, a few
seconds later it would return to the original speed. This cycle would
continue as long as I ran it. Also, as it increased in speed, it would put out black
smoke, but as it slowed down, it would put out gray smoke.
I finally removed the head and had it worked; cleaning and grinding the
valves and seats, and removing the carbon from the combustion chamber in the head
as well as the piston top. That solved the problem It now runs as well as the
day it was born. The work on the head cost me about $70.00 (US) plus the
gasket set, which was about $60.00. Volvo markets a "decarbonizing" gasket set.
The head was not difficult to remove and reinstall at all. I followed the
shop manual explicitly when putting it back together, especially the tightening
sequence of the head bolts. (Actually, they are nuts being tightened on studs
that are anchored in the block.)
Good luck. I hope this helps.
Smooth sailing.
Ed Davis, present (not for long) owner of Vesper, V1868 in Mystic, CT.
Another input. I had been having problems with my MD6A for two years. My
problems were similar, but not identical to, yours. My engine would start quite
easily and run OK for a minute or so, then slow down all by itself. Then, a few
seconds later it would return to the original speed. This cycle would
continue as long as I ran it. Also, as it increased in speed, it would put out black
smoke, but as it slowed down, it would put out gray smoke.
I finally removed the head and had it worked; cleaning and grinding the
valves and seats, and removing the carbon from the combustion chamber in the head
as well as the piston top. That solved the problem It now runs as well as the
day it was born. The work on the head cost me about $70.00 (US) plus the
gasket set, which was about $60.00. Volvo markets a "decarbonizing" gasket set.
The head was not difficult to remove and reinstall at all. I followed the
shop manual explicitly when putting it back together, especially the tightening
sequence of the head bolts. (Actually, they are nuts being tightened on studs
that are anchored in the block.)
Good luck. I hope this helps.
Smooth sailing.
Ed Davis, present (not for long) owner of Vesper, V1868 in Mystic, CT.