1977 70 HP puzzlement

Hi I have a 1977 Evinrude 70 HP 3 cylinder OB that has me a little stumped and I am hoping for some feedback and suggestions to fix her...

To start off with, this OB is on a 1972 16 foot Baja that my son purchased about 3 1/2 years ago... when we got it it ran OK, but seemed a little lacking in power..

I did head gaskets, thermostat, new coils, plugs and wires (one of the old coils was arcing over at the coil so it was decided to change all three) I also rebuilt all three carbs and replaced all the fuel lines under the cover...It ran much better, started up on first crank and made a little more power, but was still a little weak..

Two years ago, I "spun" the prop in the hub (and thought that might have been the lack of power problem) and replaced it with a new prop that has a replaceable hub in it, pitch and diameter were checked against all specs for the boat and engine and still it was weak..

Later that season I noticed that occasionally the starter would hesitate when starting and became concerned... long story short, there was a leak in the exhaust manifold that had caused water to get into cylinder #3 (bottom)... I removed & rebuilt the exhaust manifold, new gaskets and all the trimmings.. when I had the exhaust manifold off I noticed the sides of #3 piston were a little scored up and determined that this was probably why the engine wouldn't make the full 70 HP it was supposed to... at least I had my answer and it was confirmed by a compression test... #3 was off by more than 15%... so I accepted the fact that this wasn't going to be the fastest boat on the water, but it would be OK as long as the piston didn't get any worse...

The engine ran like a champ for the rest of that season and never gave anymore trouble with water intrusion after the exhaust manifold was repaired... Winterized it and fogged it and put it away for the winter....

My son joined the US Army last April, and in all the commotion and stuff, the Baja never got used at all... it sat all last year waiting to get it's bottom wet again...

Fast forward to two weeks ago, and I got the trailer out, and took off the winter cover and got the OB and boat ready for this season and my son's return on leave from Ft. Carson this July 4th... figured he would like to take his old boat out for a ride and have some fun...

Now for my problem (sorry it took so long to get here, but I am stumped and needed to vent a bit...) The OB sprang to life within three or four cranks after fresh fuel was put in the tank and a new fuel hose was installed .. ran it on the "muffs" for about an hour to make sure that the water pump and thermostat and everything else was OK.. changed the lower unit oil and decided to take it down to the launching ramp for a "spin"...

After launching, as I was trying to leave the dock, every time I put it into gear it stalled.... I had let it warm up for about ten minutes and the thermostat had opened and closed a whole bunch of times as evidenced by the water out the two holes in the lower unit...

After a little while I determined that the OB was only running on one cylinder..... #2
I couldn't get it to make any power when I did manage to get it into gear and try to throttle it up... put it back on the trailer and drove home in a "mood"..

Got back home and got out some tools, removed the airbox and checked the carbs... first I checked all the bowls for fuel... all had fuel... started it up (on the "muffs" again) and let it idle around 1200 RPM.. I figured the first thing to try was to open up the top jets of the carbs one at a time ... removed the screw and then loosened the jet and shot a little carb cleaner in to the jet ports and see if that got any results....

I removed the cap screw from #1 carb and nothing happened to the RPM's... I then tried #2 and the engine died...
restarted and tried #3 and no RPM change...

So I figured that I needed carb work again... cleaned the carbs as best as I could without fully removing them, but I still had a feeling that there was something else going on...

If I placed my palm over #1 carb as the engine was running, I would get vacuum at the carb and it would draw fuel up out of the bowl and "flood" the carb, but I couldn't get Cylinder #1 to fire....

If I "choked" #2 as it was running, it would stall from too rich mixture...

If I "choked" #3, I got FIRE in the cylinder as evidenced by RPM increase, and some extra smoke from the exhaust.... but it wouldn't keep firing on #3.... it would eventually go back to running on one cylinder.... now that was OK... it meant the #3 carb needed more attention and probably a good soak and ultrasonic cleaning... this wasn't going to be a problem... cylinder #1 however was giving me a headache...

I couldn't get #1 to fire AT ALL!!! i tried all sorts of things including a quick shot of ether down the throat of #1 carb.... NOTHING!!

Figured that I might have fouled plug or a spark issue now, so I pulled the plug and checked the spark.... it jumped almost an inch and a half when the engine was running on #2 cylinder.... OK, the spark is good...
Lemme try a fresh plug, in case the old plug is shorted or badly fouled..... NOTHING!!!

Now I was getting perplexed.... I started thinking , reed valves, cracked block... etc... If I "choked" #1 carb while it was running AND I had no spark I should see a wet plug when I pull the plug out, right??? Even if I sprayed something into #1 carb while it was running, I should see it on the plug... The plug kept coming out dry...

I can't think of any reason why a fuel charge won't pass through to the top end if you have vacuum at the carb (which would mean that the reed valves are closing and opening)... the ports in the cylinder walls control the intake and exhaust timing.... so unless I am missing something here I am stumped.....

I haven't done a compression test yet as that would tell me how bad the rings are, which wouldn't keep it from firing, just keep it from full power...


HELP ME!! I am stumped

I apologize for the LONG story, but I couldn't help it, I'm frustrated...

Any Ideas???


Rich

Re: 1977 70 HP puzzlement

welcome to iboats. Do the compression test.If all is okay we can go from there. If it is bad on number one then you know what is next. You sound like you know what you are doing, just seems like you are scared of what you will find. There is a service bulletin on this engine but if it ran fine before then the corrections have already been made. Actually, the service bulletin was for the '76 but my '77 needed it done too.

Re: 1977 70 HP puzzlement

I will hope to get home today before the forecasted thunderstorms arrive and do both a wet and dry compression test. Hopefully I will have favorable results. What was the service bulletin for the '76??

Rich

Re: 1977 70 HP puzzlement

The bulletin mentioned is for the 1976 70hp model only (Carburetor Modification). If your engine ran okay in the past, it doesn't need it.

Compression: What is the PSI reading of all cylinders?

Spark: With all spark plugs removed, the spark should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it?

If both of the areas above are as they should be, the usual cause of your problem is fouled, clogged, gummed carburetors. They will require removing, a thorough cleaning including manually cleaning the high speed jet that is located in the bottom center of the float chamber way in back of the drain plug, and rebuilding as needed with complete carburetor kits.

There are no short cuts when it comes to cleaning fouled carburetors.

Re: 1977 70 HP puzzlement

Hi Joe, the spark jumps almost an inch and a half, so I know it's not lack of spark. I am still at work so as soon as I have the compression test results I'll post them. My puzzlement is due to there being no combustion in cylinder one even if I manually spray gas or other vapors directly into the throat of the carb while engine is running. Number three will fire and indicates a bad idle and high speed circuit, but number one refuses to fire at all even with a shot of ether.....


Two strokes aren't all that complicated when it comes to running right, fuel charge gets introduced by carb into crankcase, pressurized by piston downstroke and reed valve closure, then up into head for combustion.... I can't figure out why number one is being so stubborn......

Rich

Re: 1977 70 HP puzzlement

OK, Here's the stats:

Cylinder #1 (top) 105 PSI dry, 115 PSI wet
Cylinder #2 (center) 105 PSI dry, 115 PSI wet
Cylinder #3 (bottom) 75 PSI dry, 112 PSI wet

I have removed #1 carb and am starting a thorough cleaning process, first by degreasing it, then boiling it in distilled water, then disassembly ultrasonic cleaning and reassembly.... If I can get #1 to fire up, then #2 and #3 will follow right after...

I can't think of any other reasons why it isn't running and as soon as the first carb is back on the engine, I'll post results..

wish me luck...


Rich

Re: 1977 70 HP puzzlement

rbser said:

OK, Here's the stats:

Cylinder #1 (top) 105 PSI dry, 115 PSI wet
Cylinder #2 (center) 105 PSI dry, 115 PSI wet
Cylinder #3 (bottom) 75 PSI dry, 112 PSI wet

I have removed #1 carb and am starting a thorough cleaning process, first by degreasing it, then boiling it in distilled water, then disassembly ultrasonic cleaning and reassembly.... If I can get #1 to fire up, then #2 and #3 will follow right after...

I can't think of any other reasons why it isn't running and as soon as the first carb is back on the engine, I'll post results..

wish me luck...


Rich

Click to expand...

After reading through all the comments, you still haven't confirmed that #1 cylinder is firing...You suspect that it is, but haven't confirmed it yet. SO...swap #2 coil with #1 coil and try again... See if your problem changes to #2 cylinder... Sounds like an ignition issue to me for the number one cylinder...

Re: 1977 70 HP puzzlement

@GM280.... After disassembling the #1 carb, I noticed that the reservoir that the draw tube sits in, on the bowl half (bottom) of the carb was clogged up. After removing the metering jet behind the drain screw, I was able to clear the clog. I also checked all the other passages and the low speed jet on the top of the carb. Boiled it all for 30 minutes in distilled water and blew it all clear with compressed air. A useful tool for carb cleaning is one of those little dental brushes your kids get from the orthodontist to keep their braces clean. Gets into all those small places nicely.
As for spark issues, I had reported that I had sufficient spark to jump a 1.5" gap from the #1 coil as well as #2 & #3 coils, so I had previously ruled out a bad coil or trigger as cause for no fire condition.
What I hadn't considered is if the crankcases are separated between all three cylinders..... If they share a common plenum area, that would account for there being no combustion when I choked the carb with my palm.
I am reasonably sure that this has been a carb problem all along.
As soon as the thunderstorms pass or when I get home tomorrow from work I will reinstall the freshly rebuilt and cleaned carb and fire her up to see if #1 cylinder will light off. Then if it succeeds I will do other two carbs and finally get the boat running.

Rich.

Re: 1977 70 HP puzzlement

Cylinder #1 (top) 105 PSI dry, 115 PSI wet
Cylinder #2 (center) 105 PSI dry, 115 PSI wet
Cylinder #3 (bottom) 75 PSI dry, 112 PSI wet

You have a 30 psi compression difference between the highest and lowest reading. Your first step is to remove the cylinder head to find out why. Possibly you have a blown head gasket, in which case... a easy fix. In any other case, don't be throwing money at that engine as a major overhaul is no doubt staring you in the face.

Re: 1977 70 HP puzzlement

I know about the difference in compression... already mentioned in first post, fifth paragraph....

.
Understood, and know what it's from... when wet the compression is within 3 PSI of other cylinders, so not a major issue... just a power loss issue...


Rich

Re: 1977 70 HP puzzlement

Success!

Carbs were the problem...

Fires on all three now....

apparently the "subtleness" of hearing the other two cylinders fire while on the muffs escaped me.... now that I hear all three firing, I can tell that number one WAS firing when I sprayed stuff into the carb throat earlier... just didn't hear it all that well... guess my age is catching up to me...

Is there any "trick" to synchronizing the carbs?? is it just a simple as making sure the throttle plates are all closed against their stops at idle and 180 degrees (perfectly flat) when the throttle cable is set at the WOT position???

On My 1981 Honda Goldwing, I would sync the carbs by setting three carbs to the "base" fourth one for equal vacuum readings... obviously there is no way to get a vacuum reading off the OB's carbs for a true vacuum "sync"...

I understand the sync-n-link process, but was looking for more practical applications of balancing the carbs for maximum HP at WOT and best idle...



Just askin'.......


Rich