I have what appears to be a late 70's Evinrude 70 hp outboard. It will run great on the muffs or in a barrel without a load, but with a load i can open the throttle all the way and it takes longer than usual to get on plane, sometimes with a sputter and then it sounds like it catches up. It may plane eventually depending upon the weight in the boat. With only a few people and some tackle it picks up quickly sometimes, but sometimes it still drags or hesitates. I have taken the carbs apart and cleaned them and checked for sticking valves and it ran great right after that but then went back to its loss of power. Compression checked at 100 psi on all 3 cyl. Once on plane it runs great, but it seems to be lagging to get there. I do smell excess fuel and it leaves a little in the water when sitting still. I also see quite a bit of excess in the breather box when i take it apart. I have done a few backyard tests to try and figure out if it is a carb or powerhead issue and from what i have been told it sounds like carbs. Any ideas from anyone with more experience would be greatly appreciated. I am tired of taking the carbs on and off and not getting results i need. I have rebuilt them already and was thinking about replacing them, but if it is a powerhead issue there is no reason. Thanks!
A couple of thoughts, have you done a compression and spark test? Spark should jump 7/16" and be bright blue.
You didn't list your model number, but I am assuming you have 3 carbs. You can remove the 7/16 plug in the bottom of the carb bowel and that will give you access to the high speed jets. Remove and check the jets for restrictions, it don't take much to block them off. You did remove and clean all jets and blow out all passages when you rebuilt your carbs didn't you?
You should probably replace the fuel lines if not done already, they tend to flake inside and plug jets.
If that does not help, use an inductive timing light to check spark when engine is preforming poorly, have someone run the boat for you. If you are dropping a cylinder it should show you which one. What do the spark plugs look like?
Ever hear of Occam's Razor? Usually the simplest solution is right? Not always, but I had a similar issue with a 75hp 1976 Johnson. I replaced the powerpack, rectifier and coils (also had the marina rebuild my carbs). Still had the same problem! Believe it or not it was BAD gas. After running about two cans of seafoam through the fresh gas and oil it came alive. Be certain you have checked all the simple solutions first. Do you by any chance have any air getting in the fuel line? For about $10.00 you can re-due your gas line and eliminate that as well.
Thanks to all for your help! I have done a spark test and am getting good spark on all plugs,which are a little wet, i did use kits to replace the internals and adjusted to the correct float specs, i also pulled the 7/16 plug and thoroughly cleaned the jets. I also have replaced all the fuel lines. The motor is used almost every weekend and gas is pretty much new and doesn't get over two weeks old most of the time. It ran well after i rebuilt the carbs, but only for a few months. Since the problem has started i have taken the carbs back apart and cleaned and made sure floats were adjusted correctly and valves were opening and closing properly. I have noticed a small amount of fuel spitting out of the top carb when i run it with the covers off in the yard. But the vavle doesn't seem to be sticking when i take it apart and check it.
Thanks again for the replies!
100 should be fine, a little worn but nothing to cause concern, I think if they are close across the board you are in good shape. At this point if you are confident the carbs are clean and in good shape i'd start looking deeper, gas spitting out the carbs is a sign of carb issues (which you are confident you ruled out) the the reed valves could be damaged, pull the intake and check them out.
Thanks bk. I have def not ruled out the carbs, i have just taken them apart and cleaned and checked them so much i feel like a pro at it! I def wanted to make sure it sounded like a carb issue before i spent any more money on the carbs themselves. I was contemplating just trying to replace all three and trying that. However buying these older parts for an ok price may mean trading one problem for another. I will keep workin with the carbs though and hopefully i can find the one that is causing the problem and get rid of it.
Evinrude 70 hp power loss
1983 Thundercraft 16.5 * 1983 Johnson 90 v4 * 1983 Johnson 9.9 * 1965 Evinrude 9.5 * 1955 Evinrude 7.5 * 1951 Viking 3 **Latest-76 Evinrude 15
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