TOPIC: the next issue... rpm's

there isnt a tach on the motor/boat but, by ear I can hear it going up and down rpm as its running. Seems fine under idle but when you put it in gear and give it a little gas is when it seems to "act up". I havent had it in the water yet, just running on the hose.

Maybe needs a tune up?



75 70hp evinrude 3 cyl

Running it "on the hose" means open exhaust. No back pressure for the exhaust tuning to have an effect. Hose is to get it running, barrel for rough tuning, lake for fine tuning. Running in a barrel may smooth things out a bit if the leg is deep enough.

Agreed. Running on hose is not an accurate test.
Having said that, surging would indicate a fuel delivery problem, so carbs probably need a strip down/rebuild.

well, lake running ended up with same result. I was only able to get to wot for maybe 3mins and then it died back off.

try replacing all the hose's. Then a fuel kit and then go through the carbs. That should keep you busy for day. Then see how she runs.
Mike aka the pirate

Those 3 cyl are thirsty engines.
I have a 73' and a 76'
Check for a pinched fuel line.
I had the same issue on a maiden voyage.
If you put it in neutral for a few seconds and give it full throttle again does it run another 3 minutes?
If not be careful you are not over heating. Check your warning horn!

Also for everyone else, what kind of tach can be purchased for these engines? Any new one with 6 pulse setting?
I don't have a tach either and would like one!

I agree with the others. In fact on my 73' I replaced every fuel component due to it sitting for 17 years.
I will likely do the same for the 76'

I pulled the fuel pump off my parts motor and wamo, runs great on the hose. While I had it apart I replaced 1 of the hoses that looked iffy and new clamps to replace the zipties the factory had on it. It seems to be good now, starts with barly hitting the key and ran up thru the revs without miss. In the offseason I'll replace all the lines and rebuild the extra pump.

well now it doesnt surge... it just works when it feels like. Its really odd, we put in and it worked great, just seemed a little laggy on power. We ran up and down for a while topping out at 25mph (way slower than I would have thought it should). It never did seem to come to full song. After sitting for a while we decided to run a little. Thats when it started acting up. Basically I could go maybe 5mph but as soon as I gave it more throttle, it fell on itself and died. While the wife went to get the truck I tried putting up and down and seeing if I could get it. I pulled the gas cap thinking maybe the vent was clogged. At first that didnt help but then all the sudden I took off and was running great. Until I slowed for a john boat... right back to it. I took some video and as soon as I can find the camera Ill post it. The problem is only under load, revs up fine with the warmup lever

You have the classic "carbs need cleaning" syndrome.
You really need to do 3 full rebuild kits, PLUS all fuel lines with new ones. Not from a similar aged donor engine. Remember if gas isn't getting to a cylinder it isn't getting lubrication either.
Do it before damage occurs.

You have the classic "carbs need cleaning" syndrome.
You really need to do 3 full rebuild kits, PLUS all fuel lines with new ones. Not from a similar aged donor engine. Remember if gas isn't getting to a cylinder it isn't getting lubrication either.
Do it before damage occurs.

I went back and read your other posts. Did you change the impeller yet? Gear oil?
If not do so.

Carbs needing rebuilt does sound about right...

Is that thing reving up, but not going fast? (Spun prop)
What are we looking at in the video?

reved up was on the warmup handle... had to keep it reved up then shift into gear to keep it running to get it back to shore. Seemed to run rough but run as long as I didnt give it fuel.

The symptoms you describe are classic rebuild the carbs.
What is the known history of the engine?
Did you check compression?
Spark?

known history is about 30mins longer than you see in the video. I got it non-running with the boat.

Spark is nice and strong, didnt check compression

I went ahead and ordered 3 carb kits. Ill tear them down and start cleaning them up. Looking at the service manual, its not a huge job, prolly harder to get to them than to rebuild.

If compression #'s are good and spark jumps 7/16" or better then the next step is fuel issues.----Don,t forget to check the flywheel key !

Take pics before you take them off.
Did you get fuel line?

Jet, read the sync&link section of your book.......you do have the book dont you.......library if no on that. carbs need cleaning etc.
I dont mean to be a smarty pants but I am a factory train'd omc tech.......merc too.
On the side of the carbs there is a line that shows when the timing has moved enough forward that the carb should start to open. Alot of people advance the carbs to open too soon and they stall....alot! Older motors are usuly in dire need of a correct sync & link. I will be @ the Beloit show this friday and sat.

OH and I do have a 115 evinrude that would wake that boat up...

I have a manual with a sync section. Was already planning to take pics too... In the past I have taken stuff apart and then had to figure out how it goes back together.

I already bought new fuel line. Replaced some of it when I did the pump.

I looked at the pump I took off and its gummed all to heck. I dont see how this motor could have been running good anytime in the recent past.

At this point I have work, a rock crawling comp, a swap meet and the Beloit show Saturday. I know I cant make all of them and work is manditory (though could change).


Ponyboy... the wife already protested me putting the 85hp off the drag boat on.

I pulled the carbs last night to start the rebuild... When I drained them I noticed something... 1 carb had a nice full float bowl, the other 2 were prolly less than 1/2 full. Im guessing the floats have been sticking and freeing up and thats why the problem has been inconsistant.

I tore the carbs down and rebuilt them. They werent gummed and the seals were all good. When I pulled the float bowl valve seat on the bottom carb, it was packed full of metal debris. The other 2 carbs also had a little bit in them. To me, it looks like the fuel pump came apart and the parts went right into the carb since there is no filter between them. Luckily, it appears all teh pieces were big enough that they didnt get sucked into the cylinders.

I'll hose run in a bit, wont be able to lake it until next weekend most likely.