84 Rude keeps dying under load

[mjm91673]

Have a '84 70hp evinrude that runs fine on muffs, however once on the water it acts as if it is getting no fuel and will die once under load. We have replaced fuel filter, fuel lines, cleaned carbs, cleaned fuel tanks, changed plugs all to no improvement. Did a compression test and found one cylinder to be low #1 and #2 were 150psi #3 was 125psi. We have know removed the head to inspect and everything looks good so am assuming we may have a ring issue. Anyway while tearing down found what we believe to be the two temperature sensors. Here lies the question if these sensors would sense too much heat would they in turn cause the engine to shut down under load?

Thanks

 

[Seasport]

Re: 84 Rude keeps dying under load

No. If your motor has SLOW feature, if it overheats the motor revs will be limited to 2500 and the motor will shake. You'sd also expect to get an overtemp alarm.

Your compression seems OK although you would expect all to be similar.

You should check your throttle & ignition linkages and make sure that the ignition timing is being advanced smoothly as the throttle is opened. Make sure that the timer base is rotating freely uner the flywheel.

Does the problem go away if you manually pump the primer bulb. If so could be a fuel delivery problem.

 

[The-Machinist]

Re: 84 Rude keeps dying under load

Do you have a good hot spark on all 3 cyl?

 

[tashasdaddy]

Re: 84 Rude keeps dying under load

the difference between 150 and 125 concerns me, but a decarb may cure that. when you did the carbs, did you remove the high speed jets that are deep inside the front drain plug on the carb? requires special screwdriver to get them out. if there is the slightest varnishing of these jets, it will cause your problem.

 

[mjm91673]

Re: 84 Rude keeps dying under load

No the problem does not go away while pumping the primer bulb. And yes it has good spark to all three cylinders.

 

[mjm91673]

Re: 84 Rude keeps dying under load

Also did not remove the special jets, took carb down to there and cleaned with carb cleaner but did not remove the jet.

 

[tashasdaddy]

Re: 84 Rude keeps dying under load

carb tool required, i made mine from a screwdriver with the belt sander. you wasted your time, also did you use a rebuild kit.

 

[mjm91673]

Re: 84 Rude keeps dying under load

How do the jets come out? Do they screw or do they need to be popped out?

 

[Seasport]

Re: 84 Rude keeps dying under load

They screw out. You just need the right screwdriver shape to get to them properly. Nice work Tashasdaddy.

 

[tashasdaddy]

Re: 84 Rude keeps dying under load

F_R_ gets the credit for that, the picture of the 3 tools are his, and i made mine from his directions.

 

[mjm91673]

Re: 84 Rude keeps dying under load

alrighty thanks for help so far guys, I've got carb kits, head gasket, thermostat and gasket, water pump etc etc all ordered , hoping to have in this weekend. I'll post back later.

 

[mjm91673]

Re: 84 Rude keeps dying under load

Here's what was found this weekend. Took cylinder head off and found bad thermo switch. Cleaned all sealing surfaces, replaced thermo and temp switches, thermostat, relief valves, water pump, lower unit oil, and rebuilt carbs (found what I believed to be pine needle in middle carb). Haven't actually got to put on the water yet but have ran it on the muffs and it appears to be running good, although it would run fine on the muffs before. Also have put seafoam in it and will report back on if that increases compression or not.

 

[AQUASPORT17.5]

Re: 84 Rude keeps dying under load

Hi Mjm,

I was just wondering how toygh was it to replace your thermo, I belive that mine on my 115 oceanpro needs replacement

 

[mjm91673]

Re: 84 Rude keeps dying under load

Sorry for the late update, finally got the boat out to some open water. Runs like a champ now probable the best since owned. The only problem we have had since is the fuel line in the engine compartment needs to be modified because of the engine cover "pinches it when on" causing the motor to surge.

As far as switching the thermo switch it is relatively easy, you just need to have the correct gaskets when putting back together.