Evinrude 70 hp 3-cyl 2stroke dies at high throttle

[Bernt]

I tried to find the reason for my problem for weeks now but failed.Please help!
Have a 3 cyl 70 hp from 1986. It starts well, runs very well on ilde and slow speed, responds well and even on throttle when not under load ( in neutral or when tested on land). But when throttle gets to about 60% and under load (running with my 20 foot speed boat), the engine hesitates when I try to pick up speed and dies until throttle is pulled back again. The impression is something like when you active a choke on hot engine ( too much fuel) or the opposite when a fuel filter is clogged ( too little fuel).

Gas flow is good to carbs, filter is good, fuekl pump works, carbs are cleaned and in great condition, spark plugs looks good, compression is good and even on all 3 cyl. Replaced the pump just in case but same issue. Checked and replaced some fuel lines. Even bypassed pump and hand.pumped gas to carbs directly, same issue. I suspect it is some ignition issue but I'm not sure how to test and correct that, I'm a mechanical type of guy. The VRO is disconnected and well plugged.

Sorry for language issues, English is my 3rd language. Any tips what to look for? Thanks in advance!

 

[flyingscott]

Did somebody replace the VRO with a non VRO pump

 

[oldboat1]

Get an open air adjustable spark tester, and measure spark. When at the auto parts store for the spark tester, buy or rent a compression tester. Post results for compression and spark tests.

 

[Bernt]

Did somebody replace the VRO with a non VRO pump

The VRO was on but oil inlet plugged. We suspected it to be faulty, so installed a standard pump from lawnmower. But exactly same behaviour.

 

[Bernt]

Get an open air adjustable spark tester, and measure spark. When at the auto parts store for the spark tester, buy or rent a compression tester. Post results for compression and spark tests.

Compression 10 on all 3 cylinders. Don't have a spark tester but will get one. On idle and up to mid throttle, all 3 have spark.

 

[Bernt]

The VRO was on but oil inlet plugged. We suspected it to be faulty, so installed a standard pump from lawnmower. But exactly same behaviour.

The issue comes quite distinctly at a certain throttle and under load only. If the pump was not giving enough fuel, this could be the reason, so thus the test with another pump. But no difference. And no difference when manually pumped to the carbs. Ignition issue most likely?

 

[oldboat1]

Sounds like you need to see if there is spark at high throttle -- can be done with a repurposed timing gun. Check for flash at each lead/plug wire (no flash means no spark).

 

[racerone]

How does it run if your assistant operates the manual fuel pump ?----A standard pump from a lawn mower ??----Put the pump on from a 3 cylinder 70 hp motor a 1983 model .----Or find the 3 cylinder 65 HP model from say 1990 and use one of those pumps.

 

[Bernt]

Sounds like you need to see if there is spark at high throttle -- can be done with a repurposed timing gun. Check for flash at each lead/plug wire (no flash means no spark).

Thanks, good idea. Will try today. Might be hard as it dies so quickly, but worth a test. Could it be relayed to the mechanism for variable ignition? The whole assembly moves easy back and forth, and start to move approximately when the engine starts to hesitate. Is it correct that it only start to adjust at say 60% throttle and up? Quite small movement, maybe 2 inches.

 

[Bernt]

Thanks, good idea. Will try today. Might be hard as it dies so quickly, but worth a test. Could it be relayed to the mechanism for variable ignition? The whole assembly moves easy back and forth, and start to move approximately when the engine starts to hesitate. Is it correct that it only start to adjust at say 60% throttle and up? Quite small movement, maybe 2 inches.

How does it run if your assistant operates the manual fuel pump ?----A standard pump from a lawn mower ??----Put the pump on from a 3 cylinder 70 hp motor a 1983 model .----Or find the 3 cylinder 65 HP model from say 1990 and use one of those pumps.

Thanks. We tried manually to pump but no difference. We even bypassed the vacuum pump and only pumped manually. Yes the lawnmower pump is also a vaccum pump although for smaller engines. But from what we see, OEM pump is the same size from 10 to 115 hp so probably not critical. And the behavior is identical with VRO and lawnmower pump. The problem lays elsewhere. I lean towards ignition but why only at high throttle? Thanks!!!!

 

[Ferg01]

Try your power pack

 

[juno pierrat]

bogging at 2/3's throttle, sounds like one or two high speed jets maybe clogged, happened to me after carb cleaning, inspected again and found clog, is this engine new to you or just started this problem?

 

[Bernt]

bogging at 2/3's throttle, sounds like one or two high speed jets maybe clogged, happened to me after carb cleaning, inspected again and found clog, is this engine new to you or just started this problem?

It's new to me. Bought and tested it last fall, ran well, installed on new boat and the problem started directly. I'm 99 % sure the carbs are clean. Can the ignition arm movement be incorrectly adjusted, after disassembly and assembly of the control wires? So ignition is adjusted too early or late? We disconnected the arm moving it, and on land ( no real load) we can't tell any difference when it runs. Good or bad....?

 

[racerone]

Fuel pumps on these motors run with a crankcase PRESSURE pulse and not so much with vacuum.----Post results of a compression test.

 

[Bernt]

Fuel pumps on these motors run with a crankcase PRESSURE pulse and not so much with vacuum.----Post results of a compression test.

10.5 to 11 bars on all 3. Good.

 

[Bernt]

We just found a faulty ignition cable to one cylinder. It was good enough to allow a spark, but resistance is way to high. Out theory is that the spark is nor strong enough once the advance ignition steps in, which is exactly when we loose power. Our initial test was just spark yes/no, I retrospect too simple. So need to tow it down to water and test again, as I can't test with load at home. Will order a cable now and test next week. Big thanks to all, will report back!

 

[oldboat1]

Measured on an open air tester (not the inline variety), a strong ignition on your motor should easily produce a 3/8-1/2 inch spark.

 

[juno pierrat]

if you didn't move the stop that the "ignition arm" hits at high throttle, i say timing is good , timing set at factory, no need to mess with that stop

 

[Bernt]

Hi again folks, many thanks for all replies and suggestions. Unfortunately I still have the same problems. Johnson 3 cyl 70 hp, 1986. Starts easy, runs well on idle and slow speed, responds well and even on throttle when not under load (when tested on land). But when throttle gets to about 50% and under load (running with my 20 foot speed boat), the engine often hesitates when I try to pick up speed and dies until throttle is pulled back again. At a few oocassions I managed to pick up speed and then it runs well at high rpm ( + 30 knots, sat 500 rpm), especially if I increase throttle very very slowly and gradually. Following is done:

1. Compression test, OK. About 10 bars/145 psi on all 3 cyl.
2. Carbs inspected and cleaned. Great condition as fast as I can tell, but not an expert
3. Coils measured over 1/2 side, all same resistance 250 ohms. Earthing ok.
4. New spark plugs, gap 0,75 mm / 0,03 inches
5. New fuel pump. Also tried with hand pump, both thru and bypassed pump. No difference
6. Spark plug cables measured, one was bad, replaced it, no difference.
7. Tried to manually adjust ingnition advanced by moving the "arm" and it seems to work. Engine dies if advance is moved back, and pick up again when back as it was.
8. When removing mone plug cable after another, the ilde falls down a bit, same from cylinder to cylinder. So seems it's running on all 3 cyl (idle, no load) but somethign happens when under load/throttle
9. Removed the air inlet box and looked at throttles under operation. All "flaps" opens and closed evenly when operated

QUESTION 1: I just noticed that the top carb spits out some gas! With the inlet cover removed, I can see a fine drizzle of gas leaving the carb thru air inlet. Nothing on carb 2 & 3. What is happening? My feeling from day one was that one or more cylinders is getting too much fuel, and maybe this is what I see? What could be the reason?

QUESTION 2: is there a fuel/air mixture screw? I can´t see any, is the mix facory set? Never seen carbs like these, no needles, just 3 small holes after the flap.

QUESTION 3: Can I find a free manual online? Googled for a while without result.

THANKS in advance, ran out of ideas, and now half summer is ruined. I am mostly able to fix engines but this time......!!! Frustration!