won't idle/ overheating

[Lemonshark]

I recently installed a 3 bladed Indigo prop on my 1977 Catalina 27.I doubt if this is related to the problem. I ran the motor full throttle for a half hour or so and noticed the temperature gauge reaching 200. I shut the motor off and sailed back home, but could not start the engine when I got there--it turned over fine but did not even try to fire. A friend and I put new plugs and points in (the points appeared fried) and it starts, but runs only at higher rpm's. When I try to idle down, it quits. We tried adjusting the timing and adjusting the idle screw on the carb, but no luck. The engine used to start without using the choke after it had run for a while but now it needs to be choked every time to start it.
My first question is how to get the engine to idle, and my second question is did the overheating have anything to do with the engine not starting, and I guess my third question is what would cause the overheating. I have water coming out the exhaust and just last year flushed the system (raw water) with muriatic acid.

[Don Moyer]

The Atomic 4 is quite forgiving for overheating, and temperature excursions into the 200 degree range seldom result in any damage. This, of course, leaves the unlikely coincidence of your idling problem developing just in the aftermath of your 200 degree temperature unexplained, but we have no historical data to fall back on that would indicate any connection. On a long shot, you could check your compression using your thumb. As long as the compression blows past your thumb in each cylinder no matter much how hard you press, it would confirm that the engine didn't suffer from the overheating.

I'm not sure what adjustments you may have tried on the idle mixture, but I suggest trying to turn the adjustment all the way in against the seat and then backing it out no more than 1/2 turn. If that doesn't work, I would make the assumption that a piece of dirt got drawn into the idle system and the carburetor may need to be disassembled and cleaned.

Don

[msauntry]

I'm not positive this follows with Atomic 4s, but most carbs have an idle jet and a main jet. When at lower rpms, if the idle jet is clogged, it won't run or will run rough. When you open up the throttle, the main jet kicks in and it seems to run fine.

This seems to match your symptoms, so I agree with Don. A bit of carb cleaning should do it.

[Lemonshark]

won't idle/overheating

Thanks for your reply, Don. Before I read your reply, I reviewed the threads on fuel and tried screwing the idle mixture in and backing it out 1 1/4 turn. That seemed to solve the problem, and now it idles fine. But would it be better to back it out 1/2 turn?
Now to take it out and see if it overheats again.

[Don Moyer]

As long as the engine idles fine, I wouldn't touch the mixture screw. The idle system in our Zenith carburetors is much more problematic than the high speed system and it is not uncommon to have to tweak the idle mixture at the beginning of every season. If plugs are tending to become sooty frequently, I sometimes recommend an arbitrary 1/4 turn out (counterclockwise) toward a leaner mixture. If the engine still idles OK, you can leave the mixture there or try another 1/4 turn leaner. If you encounter idle problems, put the mixture adjustment back where it was.

Don

[tenders]

So, Don, when are you going to sell us a thumbscrew to facilitate this important tweaking process?

http://www.moyermarine.com/forums/showthread.php?t=1669

[msauntry]

Hasn't the poor man done enough for us? Now you want to put the thumbscrews on him?!

[tenders]

I would gladly contribute to another oriental carpet in Chateaux Moyer by purchasing from him yet another ingenious, high-quality, meticulously explained gewgaw!

[Don Moyer]

Thanks for offering to come to my rescue, but all the good folks in our shop were so impressed with the idea of a thumbscrew idle adjustment valve that they'll probably show up on our catalog before the end of the season.

Don

[tenders]

Those must be some skunks you've got back there in your skunkworks, Don!

That was last year's idea. The arm burns have healed, mostly, but I think my mix needs another tweak.

While you've got the gnurl-o-matic tool out, how about cutting a few of Baltimore Sailor's flame arrestor thumbscrews out too:

http://www.moyermarine.com/forums/showthread.php?t=1800

Sign me up for one of each!

[sunnnnseeeker]

GREAT idea! My fuel pump is in the way for easy screwdriver access to the idle adjustment screw. I tried like heck to turn the screw with my fingers but it is too small I can't get any leverage on it. I suggest that the screw head come out about another inch and it be 1 inch in diameter so one can easily turn it. I'll buy one as soon as available!

BTW - The new carb (from MMI) you see in the picture solved ALL my carburetor problems. The engine runs great, idles slow at 600 rpm (pushing the boat too), no hesitation on acceleration and decelerates back down to 600 rpm quickly without stopping. It is critical the engine stay running when docking!

I read the other news about the Rustoleum Marine Paint. Wish I had known about it before I painted my engine. The red paint you see is regular Rustoleum - it seems to be holding up well. I have about 5 hours, pushing the boat, on it since the rebuild and paint job.

FYI - Head nut torque: After I installed the head I ran the engine 5 times until HOT, let it cool and re-torque. The 1st 4 times the nuts needed a little turn to get them back to 35 ft lbs. The 5th time they were tight. Then after the 5 hours of pushing the boat I checked the torque again. Surprisingly the 2 nuts on the forward end (opposite flywheel) of the head took a little turn to get them back to 35ft lbs. I am satisfied the nuts are tight now and they will hold so I'll paint them. I tell you all this because we recently heard from a couple people about blown head gaskets on recently rebuilt engines and the likely cause of their troubles was that the head nuts were not as tight as they should have been.

Nathan

[tenders]

Hmmmm. I was thinking the adjusting screw could stick out MUCH farther -- maybe several inches. Maybe even close to the top of the head, if the fuel pump isn't in the way.

[sunnnnseeeker]

The fuel pump would be in the way on my engine or else a long screwdriver would work.

I forgot to mention a comment/question about the overheating stated above. For what it is worth, I don't see how overheating would be related to anything with the carburator. Could it be? How so?

Nathan

[SEMIJim]

Now to take it out and see if it overheats again.

Glad you got your idling problem solved, now about that "full throttle" comment you made originally: You don't really run at full throttle, surely? The maximum speed you can attain (limited by your boats hull speed) will be reached far before "full throttle" on the engine. That's about 6 kts on our Pearson 30. By pushing harder I can get her up to 6.25 kts or so--maybe a bit more, but the small gain isn't worth the much-increased wear-and-tear on the drive train, gasoline consumption and noise level.

If you're really running at full throttle, overheating would be no surprise at all.

Jim

[Don Moyer]

The knurled extension we're planning will come well past the rear of the carburetor mounting flange and should make "one-handed, blindfolded" adjustment quite easy. We talked about longer extensions, but we have some concern over the possibility of breakage or inadvertent movement if we put too much weight on the end of the needle.

Don