Mercruiser 470 Problem

[LGMAZ]

I know, I know, a four banger question in a perfomance boating site, but here goes... Mercruiser 470: Starts cold beautifully, runs beatuifully, however, will not start when warm. Any suggestions?

[Ed Donnelly]

When the engine is warm, take the air filter off and check to see if the choke is partially closed. If it is re-adjust it ........Ed

[LGMAZ]

Will do. Thanks Ed.

[MOP]

Another couple of ideas, possible vapor lock or an over heating coil. When you shut it down go back and feel the coil it should be pretty warm but not hot and have no signs of oiliness on it can. Any hot sections of the fuel line can give you trouble, the fuel issue can be eliminated real easy. Go and grab some aluminum oven foil the heavy stuff cut it into 3-4 inch wide strips, crinkle it up a little then wrap it around the fuel lines by anything that can get it hot it will insulate it and draw the heat away.

The 470 is one of my favorite motors they are "TANKS" built very strong, I way back did a lot of rebuilds, a few were 470's the first one I tore apart I stood there in amazement at the size of the internals which were as big if not bigger then a BB. It had been rebuilt by a local shop down the road and had a funny knock, I pulled the rod caps all were perfect so I pulled the mains and found an uneven wear pattern on one. What the fellow in the other shop missed was the 470 has a special main cap aligning fixture to keep them straight while being torqued I slapped in one bearing got it back into the guys boat made a good buck buck and another customer.

[LGMAZ]

MOP: Just got back from the marina and the experts ( Read: guys standing around w/ beer) said the exact same things. They also suggested checking the fuel line fittings and clamps as they can expand when heated and cause the carb to suck air. I ran the boat for about 20 min. and it started back up w no problem. Still need to check these things as they don't tend to 'fix themselves'. Thanks for the advice, you guys are the best.

[Formula Jr]

The 470s, merc 165, all do this for some reason. I've had one for seven years. Cold she spins fine on start up. But when she is warm she cranks very slowly. On another board, where this is a more common engine, the slow start crankings when hot is often a subject. This is half of a ford 460 engine with an aluminum head. Does it spin oky while hot and not fire, or is it sluggish to spin while hot? Mine does the sluggish crank while hot and was a worry till I just let it cool down, before stopping. Then it starts everytime.
So my question is, will it crank fully yet not start, or does it crank over very slowly when Hot and not start. Mine likes full throttle and a bunch of pumps, then I have to be careful to throttle back very quickly.

the 4.7 is a great engine. If you ever come across the four barrel manifold for one of these, it is worth its weight in gold.
Interesting that they stopped making this engine because all the casting equipment wore out. Yet nothing better has really come along for a mid sized engine. It is used widely in small Hydro racing. This thing also sips gas. I have to plan the end of my seasons to drain the tank. That's not a bad thing these days.

When Mop says these are tanks, that is accurate. They are aso one of the most highly strung weight to HP Marine inboard engines ever made and offered in stock form. I think a 16 with one of these with a four barrel and raw water cooling, fresh water only, would be sweet.

[LGMAZ]

MOP: Changed the coil, problem solved. It's the first thing I've ever fixed myself on the engine. Can't believe it worked as I'm the guy that has to read the instructions on a shampoo bottle.
Formula: The starter would crank fine, it just wouldn't fire. Once started, it ran great.

Thanks again.

[Pismo]

4.36" bore.......thats bigger bore than a 454 and the new 496, almost as big as a 502.