76 Johnson 70 hp slow to plane out

[64osby]

Have you ever weighed the hull to see if the foam is water logged. Might be one thing to check that is related to slow planing.

Hope the carb clean does the trick.

 

[Coltrickle]

I have not weighed the hull.. It's has been fully gutted to the skin

 

[lmuss53]

Lots of variables on the carb, fuel issues, but I think you are chasing the right stuff. All I have to add is I have an 85 model of the same motor on a Sea Nymph 17 footer with a 13 3/4 X 17 OMC aluminum prop that jumps up on plane with 2 big guys, gear and a 30 gallon bait tank, then runs out to 33 mph at WOT, 5400 rpm. I would try the same prop on your boat.

 

[Coltrickle]

I took her to the water today.. The idle seems to fluctuate from perfect sometimes to where it gets so low it dies when I put it in gear.... Sometimes it runs perfect and will launch like a rocket.. Other times when the idle falls of if I am able to get it in gear and keep it running it has a dead spot in the carbs.. I have to go from high idle to in gear quickly which is bad on my lower unit but none the less it will go and I have to go from a fast troll to wide open throttle or it will die if I gradually advance the throttle about half way through the progression..

 

[Coltrickle]

I have finally found my hole shot issue!!! While tinkering with the engine today I pulled the cowl off and looked at the linkage as I put it in gear and advanced the throttle. The trigger(timing) was only advancing in the first 1/4 of the throttle and stopping no matter if I pushed the throttle wide open.. Over the years I guess the trigger wire sheathing has hardened and prevented advancement.. I opened the wire clamp that the wires run through and spayed wd-40 on the shifter linkages and timer base... It tacs out like a big boy now!! I guess I never thought to look at it.. I was getting less than half of my timing advancement!!! Well after 3 carb rebuilds, coils, plugs, and several other parts I could have fixed it in 5 minutes and less a lot of labor!!! We live and learn!! I hope this helps someone!!

 

[Texasmark]

29 mph once it gets there just under 4800rpm. Thanks for the reply

Yepper you are over propped. As low as your rpms are and knowing what that engine can do...had one....I agree on the 15P...diameter will vary per the prop.

Tell you what. Change your thermostat, unless you just changed it! You have no over temp warning on that engine. If the stat sticks shut and you are at WOT when it happens it will cost you a powerhead. Now how do you think I know to warn you about that?

 

[Sea Rider]

For carb free issues, while flushing engine after each use, run carb dry till OB dies of fuel starvation....

Happy Boating

 

[airshot]

For carb free issues, while flushing engine after each use, run carb dry till OB dies of fuel starvation....

Happy Boating

OMC corp who built that engine strongly recommends NOT to run carbs dry on a two stroke with multiple carbs. Reason being that if one carb runs out of fuel before the other then that cylinder/crank will be running dry (without oil) and can cause serious damage to that cylinder. Only recommended for single carb engines!! That is posted right in the factory service manual and in my owners manual on my 1979 model.

 

[David Young]

I agree with the others. If your tach is right, a 15 pitch prop is what you should try.

 

[Texasmark]

For carb free issues, while flushing engine after each use, run carb dry till OB dies of fuel starvation....

Happy Boating

I did that for many years back in the 1958-88 time line. What made me stop was when I quit running pre-mix and had an oil pump. Sometime after that I picked up a tidbit on here that I had never thought of before and that is on a multiple carb engine, one of them is going to run out of fuel first. Question is, how long does it take for all to run out and while they are running out, what's happening to the rings and needle bearings in the one that ran out first........got to survive on what oily residue is left from when they were getting fueled. Made sense so I just quit the process.

 

[Sea Rider]

In a combo that has internal fuel tank would be a real PITA to disconnect fuel hose from OB entrance, unless has a quick release connector like the ones used on portable tanks. According to my personal experience with 2 stroke 3 cylinder, 3 carb OB's, not an issue, can connect a spare female connector on OB's fuel entrance so internal central pin of male connector remains pressed and open, that way while OB is on while flushing at idle, will consume most of bowl's fuel on each carb till OB drops dead.

This procedure is excellent if you're not hooked on constant boating, don't know when your next outing will be, one week, one month, several months ? carb will remain immaculate interior clean and gum, varnish free. I really laugh when boaters stops 2 strokes multicarbed OB's for 2- 3 + months and suffers starting OB at the marina. I have issues with E fuels, are evil on thin fuel pump diaphragms.

Happy Boating

 

[Texasmark]

In a combo that has internal fuel tank would be a real PITA to disconnect fuel hose from OB entrance, unless has a quick release connector like the ones used on portable tanks. According to my personal experience with 2 stroke 3 cylinder, 3 carb OB's, not an issue, can connect a spare female connector on OB's fuel entrance so internal central pin of male connector remains pressed and open, that way while OB is on while flushing at idle, will consume most of bowl's fuel on each carb till OB drops dead.

This procedure is excellent if you're not hooked on constant boating, don't know when your next outing will be, one week, one month, several months ? carb will remain immaculate interior clean and gum, varnish free. I really laugh when boaters stops 2 strokes multicarbed OB's for 2- 3 + months and suffers starting OB at the marina. I have issues with E fuels, are evil on thin fuel pump diaphragms.

Happy Boating

That's why Sea Foam was in every tank of gas in my boat. It prevented the problems you mentioned that others had. Course back when I used to run till dry, gas was good and I hadn't heard of sea foam and didn't have an onboard oil system.

 

[Coltrickle]

Well I thought it was good to go.. Took it to the lake and it ran like a scalded dog for about 5 minutes.. After I slowed back to idle it has all started again.. It starts and runs fine the long it idles the worse the idle gets.. It takes longer to plane and also even gets to the point to where the thing will not idle unless I have the fast idle up then dies as soon as it goes in gear!! Could this be an electrical breakdown?? Also my bottom plug is always wet with fuel!!

 

[ondarvr]

What did you check after it started running poorly again?

 

[Coltrickle]

I ohm checked the trigger but I do not have a dva adapter to do a voltage check.. How can I check to see if the plugs are still firing after being installed.. I have a spark gap tester and all 3 jump a good spark about 5/8 of an inch.. I just don't know what to do next?

 

[ondarvr]

Pull the plug wire off each cylinder one at a time, it should run noticeably worse on any two compared to all three. If there's little or no change when one is removed investigate that cylinder.

 

[steelespike]

A wet plug sure indicates too much fuel or not enough spark.
You might try switching plugs and or components.
Often components fail as they heat up.

 

[Coltrickle]

I will give this a shot.. I will post updates.. Thanks for your help

 

[Coltrickle]

I pulled off the plugs 1 at a time and all 3 made the engine start to miss.. I swapped around components and nothing changed. I did some electrical test I found on the Internet for the stator and trigger.. The trigger wires all ohm out between the 12-20 range around 17-18 for all 3.. The stator however says it should ohm around 500+\- 10% so 450-550 ohms.. My reading was 730 ohms.. From brown to brown orange wires.. And the voltage should be around 150v AC and is only around 90-95v. I know a little about electrical and an increase in ohms would correlate to an increase in amperage which leads to a decrease in voltage.. But I do not know if this is correct in the marine engine world.. Would it still run with low voltage from the stator and just be sluggish or weak.. Any knowledge is greatly appreciated!

 

[StarTed]

Sorry I can't help you. I'm interested in your findings because the engine I plan to use on my boat is a 1976 75HP that'll need some work.

As far as electrical is concerned, an increase in ohms will lead to a decrease in current. The voltage is lower as well because the power produced is less. I think you're onto something about the stator not putting out the power it should.