Mercruiser 7.4 MPI Valve Job . . .

[Lou C]

Years ago we had a 1970 Ford Torino that was badly carboned up because the auto choke never opened up all the way. It was a second car my parents bought cheap back in '77. It was so carboned up it would not run without pinging even on high test gas so you had to retard the timing and then it had no power. Asked a few mechanics and they said to get a can of GM top engine cleaner and follow the directions on the can. Never mentioned the water trick. Well I did this on a winter day, and there was a snowbank behind the car. By the time I was done, there were chunks of carbon in the snow by the tail pipe! And after the ole 302 would run on regular with out pinging....

I might try this with my old '88 4.3. The last time I checked the compression test results were even higher than Teds:
1: 170 2: 160 (checked 8/5/2013)
3: 180 4: 180
5: 165 6: 165

BTW I checked them back in 2010 and they were about the same then.

 

[Scott Danforth]

Lou, GM's top engine cleaner has been discontinued. it is now Upper Engine Cleaner or UEC. it has been reformulated to not take out seals.

 

[tpenfield]

I checked a few cylinders with the boroscope and they still have quite a bit of carbon in them, even after a couple of seafoam treatments. So, I'm hoping the water does the trick. I have run some water through, but obviously not enough.