1977 Evinrude 70 HP: Trouble idling in water and cannot reach WOT

[SHSU]

Howdy All,

Been chasing engine problems on my Starcraft rebuild I finally got back in the water (2 1/2 year project). If your interested in that, please see link in signature. As a note, since I have put so much blood, sweat, and tears into this project would really like to keep/use this motor vs buying new. I know its probably not the best decision and could be/has been expensive, but if you take a look at what we have done on the boat project you will understand the sentiment. Otherwise, looking to get some more assistance from ya'll on the motor and hopefully next steps. Please see information below and comment accordingly. As always, appreciate the assistance in advance.

Boat: 16ft Aluminum Starcraft

Motor: Evinrude 2 stroke

Make: 70773S

HP: 70

Power head Year: 1977

Cylinders: 3

Total Hours: Unknown


Background Info
1. As part of my original engine rebuild 2 1/2 years ago, I took the power head off and installed all new gaskets from exhaust to head. I did not crack the engine block as all the pistons looked good. Did complete rebuild of carburetors.

2. I did not replace any electronic components during that time. Fogged out the engine for storage while I worked on the boat. Did not plan on taking two years to finish the boat....

3. Fast forward two years, put the engine on the boat and fired right up. Ran for a little while on muffs then I shut it down, tried to start it again and noticed I got no spark.

4. At this time, I decided to replace a couple electrical components as they looked sketchy anyways as part of my "rebuild". Installed 3 new iridium spark plugs, 3 new Sierra coils, new CDI power pack, and new Sierra rectifier (Rectifier is what failed).

5. Took boat/motor out for first time back in July for maiden voyage at Lake Sommervile. Motor ran great and was able to reach WOT (~4500 - 5000 RPM)

6. Two weeks later, took it out to Texas City Dike (Saltwater) and started fine. Idled fine. Was able to reach WOT. Then I slowed down and put motor into neutral. Motor died, started back up, advanced the throttle and couldn't get past 2000 rpm.

7. Have troubleshot a couple things and taken it back out with no improvements.

8. Side note, live about an hour from any body of water I can test in. So only way to simulate back pressure on exhaust easily is to put it into a trash can at idle. (I know, not in gear and only for a short while as the water heats up quickly and doesn't provide proper cooling).

Things I have tested and tried since then (not exactly in the order below but tested):
1. New, non ethanol fuel, mixed with Pennzoil 2 stoke oil at 50:1 and sea foam stabilizer

2. Checked fuel filter/water separator, verified no water in fuel

3. Suspected fuel pump. Changed it out. No improvement (Threw this part at it....).

4. Checked compression, all three cylinders have 120 psi

5. Test I have done on Fuel system
a. Hooked up kicker fuel line to main motor and still had same issue. 8 hp Mercury 2 stroke kicker runs just fine and has been our "main" motor every time since my "Fixes" haven't worked
b. Verified all carburetors had fuel
c. Manually pumped fuel bulb and motor would not surge. Bulb would get hard and stop accepting fuel as the carburetor bowls were full while running.
d. Rechecked all the fuel lines. Redid all the fuel line clamps.
e. Cleaned out the carburetors again. Had issues with #3 cylinder (bottom cylinder) as pulling spark plug did not cause any major difference in RPM. Once cleaning done, RPM would drop when plug was pulled
f. Found some minor evidence of water in the #1 cylinder so changed out the head gasket again. I noticed the piston head looked way to clean through the spark plug hole and a couple little droplets on the spark plug head. Also, spark plug head looked much whiter then the other two. Installed new head gasket and made sure to properly torque the bolts down to 20 ft lb (Didn't do that before). Engine ran much better on the muffs but still issue once in the water.

6. Test I have done on ignition system
a. Moved coil packs around. Verified all coil packs working
b. Moved spark plugs around. Verified all spark plugs were firing and had good spark
c. Started engine on Muffs, individually pulled plugs. As stated above, 3rd cylinder had issues and were fixed by carb clean out again. Now, can pull any plug and RPM drop.
d. Checked idle Spark advance with a timing gun. Its showing at 4 degrees after TDC. SELOC Manual says it should be between 3-5 degrees after TDC

7. Changed prop to a 15 pitch from 17 pitch to reduce strain on engine. Figured with older motor it would help it out by reducing the strain.... Plus I wanted a better hole shot.

Current State:
1. Engine starts fine and idles fine in driveway. Sounds great too... But as others have stated, running on muffs anything can sound good

2. Once put in the water (back pressure on exhaust) engine has trouble starting/idling. When cold, engine will start and then quickly die out after 10-15 seconds.

3. If I start it and immediately shift into gear, give it a little throttle (While still cold) it will run for about 20-30 seconds before dieing out.

4. If I start, immediately shift into gear and advance throttle to WOT. Motor will get to ~2000 rpm and hold there. So we are moving at ~6 mph.

5. If I try and trim the motor or back off the throttle, the engine will die out. If I leave it alone, it will hold steady. Sounds like its not getting enough gas, but everything I have tried says fuel system is good.

6. Once "warm", it will idle a lot better and idle for longer periods before dieing out.

7. Often when it dies out, I have to try a couple times and choke the motor to get it to start.

8. The exhaust is a whitish gray. Originally was more blue when I first restarted it back in July, but think that was because #3 cylinder wasn't firing properly and had a lot of excess oil dripping out of exhaust pipe. Now, no oil drips out of exhaust pipe when sitting.

9. As we have gone out, the issue becomes worse and worse. Meaning after three trips to the water, idle time becomes shorter and shorter before it dies out, plus harder to start in water.

Next Steps/Question:
Not sure.... Hoping ya'll can help point me toward something I have done wrong or should check next.

1. Should I get a DVA to check the stator?

2. Should I recheck the power pack?

3. Any ideas on what my culprit could be?

As stated before, Thanks in advance

SHSU

 

[jimmbo]

Can the spark jump a 7/16" gap on all plug wire?
What is the Max Timing advance set to?
This Idle timing you called it, is not a timing spec for timing at idle, It is where the timing needs to be at a certain point of the when all the slack is taken out the carb linkage. The timing at idle will end up being what what ever is needed for the engine to idle at the correct speed in gear.
You are/were on the low side of the engines WOT rpm range, which is 4500 - 5500 rpm
That engine would probably run not too bad on the hose with only one cylinder firing. Sitting in the water is a different matter all together.
Get rid of the SeaFoam
What exactly is your Starting Technique?

 

[juno pierrat]

might change plugs back to champions L77J4 , original recommend.

 

[JerEazy]

Check the timing and timing “linkage” - and double check the carb sync

 

[SHSU]

Thanks All,
So I was able to work on it again this morning. Things I checked:

Went to auto store and picked up a Spark Gap Tester (Not a spark tester, have one of those already). Before I tested by just holding the plug near the head to see it jump, but at this point decided needed a real verification. Verified all three cylinders jumped a 7/16th gap and then some with ease. Nice strong spark with a lot of pop. One thing I did notice was that 1 and 3 cylinder would cause a small drop in RPM if I pulled the plug, but if I pulled the #2 cylinder it really was a noticeable drop. So it sounds like number 1 and 3 cylinder aren't working nearly as hard as #2 cylinder. Does that mean anything? Should I see the same level of drop across all three cylinders?

At this point, filled a garbage can full of water so I could simulate some back pressure on the exhaust and not just use the muffs.

As requested, checked the timing linkage again. Looked it over and used the timing light. As jimmbo pointed out, my timing looked off. I adjusted the linkage. Found that at idle and not in gear, my spark was firing a couple degrees before TDC. I am guessing that is what was causing me to stall out. So I had to adjust linkage so it would fire at ~2 degress after TDC while idling and not in gear.

Disconnected the gear shift so I could simulate putting the boat into gear without it actually engaging the prop. Wanted to see what my advance was once the throttle started to move forward. Found that it was at ~4 degrees after TDC which is where it should be before it started to open the carbs up. I believe that is what jimmbo was clarifying for me.

Also as requested, checked my spark timing for WOT the same way by manually moving the timing lever without engaging the carbs. Verified that it was at ~16 degrees after TDC. SOLEC manual says it shouldn't be anymore then 17 degrees. So that looked OK.

Here is a picture of the linkage the way I have it setup now and the engine running. One thing I noticed was that the carb linkage was getting hung up. So when we tried to open her up, the butterfly valves would not be opening all the way, so the motor was starving for air. Looked like it may have only been opening to half what it should have been at WOT.



Here is another picture of the motor running in the trash can. Engine is not in gear, just all the exhaust being forced out causing the water to bubble like that



Last thing I am dealing with now, is I can't get it to idle well below ~1600 RPMs, or so my Tach reads. If i try and manually reduce the idle (not in gear) I can get it down to about 1000 RPM before it starts to sputter and then die. I know the manual says I should be at ~700 RPM. But I can't seem to get there. Any ideas? Other ways to test to make sure I am getting the proper reading?



Also as requested, my starting technique:
1. Check primer bulb to make sure it is hard
2. Engage the push choke and try to start
3. Give it a 2-3 second count and if it doesn't cough or try and start with stop trying
4. Will repeat 2-3 until I hear the engine trying to catch
5. Will disengage choke and try if the motor hasn't caught
6. Usually by this time the engine fires right up.

So that is what I have tested thus far. Appreciate all the suggestions. Please let me know your thoughts on what I have done and if ya'll think I am on the right track or need to start looking somewhere else.

As always thanks for the assistance.

SHSU

 

[racerone]

Shift linkages tell me that it is NOT a 77 model powerhead.-----Or perhaps an earlier lower unit was installed and linkage had to be changed.----The linkage I speak of is the one at sort of a 45 degree angle.

 

[jimmbo]

Retardation of the Timing is how the idle speed is regulated. That is the reason I said that there was no timing spec for Idle.
The Maximum Advance is checked without the engine running. Just advance the throttle fully, and crank the engine, with the plugs out and the plug wires grounded. and using timing light.
As I mentioned before, there is a pick-up timing spec. That is a point in the timing advance where all the clearance in the linkage to the carbs is taken up, or in some cases the carbs have opened a specific amount. Misadjustment of this can make a engine behave oddly.

The Throttle linkage on most 2 strokes is designed to almost advance the Timing to the Max before any opening of the carbs happens, as the carbs open a tiny bit the Timing is advanced to max and then the carbs open up. You have be tinkering with the linkages so...

 

[SHSU]

racerone
You are correct, the power head is a 70773s on a 70473m lower unit. I didn't realize that until I was tearing it apart during my original rebuild. Don't know all the adjustments they had to do to make it fit.

jimmbo
​​​​​​​
Much appreciate your assistance, so with what you have read and seen me do, should I adjust the linkage some more to advance the timing earlier during throttling up or leave it alone for now?

Also, any suggestions on my RPM at idle? Does it sound normal? Any suggestions on lowering it or leave it alone for now as well?

As always, thanks in advance.

SHSU

 

[jimmbo]

You are going to start from scratch. Set maximum advance, then setting the pickup timing. After which the idle speed(usually 600 -650 in gear under load) is set, then the throttle cable length is adjusted. If you adjust the idle mixture, the engine idle speed may need resetting, and the throttle cable length will need readjustment after.

 

[SHSU]

Thank you jimmbo
I will go through that at home and check again out on the water.

From what I have read and seen, the idle screws on my unit are fixed so no adjustments can be made, but maybe I am wrong on that too.

Again, really appreciate all the advice

SHSU

 

[oldboat1]

Are you operating using the remote throttle lever? Try disconnecting the remote cable and operate using the throttle controls at the engine. If proper idle is achieved using controls at the engine, adjust the remote cable to match the engine and reconnect.

Might have missed it, but what is the operating temp.? (should be around 130-140F. 160F would be an overheat.)

 

[SHSU]

Howdy Oldboat 1
I have been using the throttle controls on the engine. But realize now I wasn't setting the control cables right. I was adjusting the length of the cable to control the revs. So when I go back and resync this weekend, will remove the control cable, set the engine, and then adjust the cable length.

Also, engine temp is around 130-140 when we are out and about. It did get up one time when we were running WOT at the lake according to my temp gauge, but haven't seen a repeat of that. Also, I haven't been able to run true WOT since that one time either...

Thanks again,

SHSU

 

[jimmbo]

A lot of OMC engines did have no Idle Mixture adjustability. Just more reason to make sure the carbs are spotless internally, and that the Float is set correctly.
An added note. When you do adjust the cable length when done, you need adjust it a wee bit long, to have a bit of preload on the cable to ensure consistency in idle speed. No preload, and the linkage might not return to the idle stop, too much and it gets difficult to shift into Neutral

 

[oldboat1]

Also, engine temp is around 130-140 when we are out and about. It did get up one time when we were running WOT at the lake according to my temp gauge, but haven't seen a repeat of that. Also, I haven't been able to run true WOT since that one time either...

Think I stepped on jimmbo's earlier post re. cable adjustment (agree with his advice, above, and learned something about preload).

Anyway, your description of the brief overheat episode is curious, given your inability to hit WOT again. Perhaps this is also a cable adjustment issue, and the overheating is coincidence. But if the water pump and circulation is top notch, it seems to me there should be no instance of overheating. Maybe when done with cable adjustments try running at the top end again with an eye on both rpm and temp. See if there are remaining issues.

 

[jimmbo]

That engine has a Temp-Pressure regulated cooling system. A Stat ensures a warm engine(to reduce fuel puddling and resulting misfire) at low, especially idle speeds, and at higher speeds a pressure valve ensures more water for cooler running at higher speeds(where the vapourised gas is moving fast enough not to fall out of suspension.(at least that's how most Outboards cooling systems work, OMC did have some different systems on their 1960s 40 HP and pre 69 V4s which recirculated the water back to the Water Pump.)
You might have a bunch of Salts and Minerals clogging up the cooling passages, on a motor run in salt water, guaranteed, but some fresh water isn't much better. It is a 42 yr old motor

You say it got hot, but I can't see where you posted a value as to how hot it got.

 

[SHSU]

Howdy jimmbo ,
Sorry for the late update. I was able to get a couple hours of work on the engine in the driveway. Dealing with some medical issues and just don't have the energy I used too.

I was able to adjust the pick up timing to TDC. I tried to do the WOT timing as you described, but didn't see much of a change, no matter how much I adjusted in the WOT timing. So I returned the WOT stop to about the same place and will have to check it on the water.

As for the Temp, I have a sierra 62728P. From their website its a gauge that reads between 120-240. At Idle, it reads at a quarter which I interpret at about 140. I have hit the exterior of the powerhead with my laser temp and it reads at ~120. So I don't know if the temp gauge is reading high, or just because of how it is mounted (internal of the powerhead vs external of the powerhead with the laser temp). So when i say it might have overheated, the temp gauge read close to middle, which I figure to be close to ~160-170. Don't have a temp reading at WOT with my laser temp gauge.



Also, when I did the original tear down, I cleaned out all the water passages. So no clogs and do a freshwater flush after every trip.

Thanks again,

SHSU

 

[jimmbo]

If you are adjusting maximum advance, and you don’t see the timing change, then I would be checking for interference. You are doing these adjustments with the throttle cable disconnected?

 

[SHSU]

Sorry let me clarify. Idle pickup is set to TDC - ~1 degree BTDC. When I do WOT setting, it goes up to ~16 BTDC. Then when I adjust the stop under the fly wheel, it doesn't really move the BTDC beyond ~16 degrees. Hence why I said it doesn't really change. Truthfully ~16 BTDC is close to the recommended 17 degrees anyways. So if I can achieve WOT again it won't matter.

Again, really appreciate all the help

SHSU

 

[SHSU]

Just wanted to update ya'll

Was able to take the boat out for a couple hours this past weekend. Timing was adjusted to below:

Idle Neutral: ~900 - 1000 RPM
Idle In gear: ~800 - 900 RPM
Timing: ~TDC - 1 BTDC

WOT: Still having issues. Only able to get to ~2000 RPM
Timing: ~17-18 BTDC

Now that the timing has been corrected enough to rule that out. I was able to monkey around with the fuel bulb and believe I have a fuel restriction issue now....

Symptoms: We can get to about ~2000 RPM then if we advance the throttle anymore the engine will die. Also, if I manually pump the fuel bulb I can make it hard and stop no real change in RPM; however, if i continue to try and force gas through with the manual pump after bulb is hard, i can get the engine RPM to slowly increase a liitle. Once I stop trying to force it, it will come back down. So i believe that I am forcing gas through the high speed jets, which means I didn't clean them out well enough the first time...

So plan to pull the carbs again and do another full cleaning.

Also, one thing that I have read was that the top carb (Carb1) runs lean a lot because of how the gas is pumped for these 3 cylinder outboards. Was thinking of adjusting the fuel lines and instead of having the main line go into Carb 2, then split to Carb 1 and Carb 3. Have the main fuel line split at Carb 1 and feed Carb 2. Then have the out feed of carb 2 go into carb 3. Hopefully that makes sense. If anyone has any thoughts on it, please let me know.

As always, really appreciate all the help.
Thanks,

SHSU

 

[racerone]

No the reading you have done is misleading you.------They have made these 3 cylinder motors for about 30 years.----Never an issue with fuel not filling the top carburetor !-----Checked the flywheel key ?----Are you sure the orange wires from powerpack are going to the correct coils ?------Checked the reed valves ?-----Did you have this motor apart ?-------I was not there during this " rebuild ", but are pistons 1 and 3 installed correctly ?----You say that pulling the plug wire off makes hardly any change compared to #2 cylinder.