78' 35HP Johnson Starting/Running Saga

[mnsherick]

After many hours of frustration, reading seloc's over and over, and even aquiring the help of my dad, I turn to you the experts.

First off I consider myself very mechanicaly inclined but lacking in motor/boat experience. Please take it easy on me.

Specs:

1978 Johnson 35HP MD#35EL78R
15' Lowe Line Aluminum Boat
Remote steering consol with electric start/choke


Back Story:
I was running this boat WOT and it kinda bogged down, almost like I was lowering the throttle 3/4 of WOT then down further about 1/2 of WOT. They phhhffff....nothing.

No chance for a restart. Got a tow back to dock....

What I've checked thus far:

Fuel filter...clean
Fuel pump...good flow (thought I lost the pump when it died on the lake)
Checked/replaced all fuel lines/clamps
Spark...good
Pulled plugs....I get fuel/air mixture when cranking over
Rebuilt carb...good fuel flow to bowl, float working, no build-up inside at all very clean.


Two things that I see as possible problems;

1) When cranking over with electric choke or manual choke engaged, I get a small ammount of fuel out the front of carb, and I get a 'back fire' sound after 4-6 revolutions of the motor.

2) Also cranking seems 'slower' or like it's having trouble cranking at random times, then the next crank it seems to crank just fine, and it almost starts I actually get a few 'fires' in the cylinders if I move the throttle to about 2/3 of WOT.

any help or advice is much appriciated in advance.

-Matt



EDIT* I forgot to mention one more thing, I'm leaning towards a fuel pump/fuel problem still, because if I use the choke it won't start, but the attempt right after a choke it almost always attempts to fire.

 

[jasper60103]

Re: 78' 35HP Johnson Starting/Running Saga

how's your compression?
Are your plugs fouling?

 

[kbait]

Re: 78' 35HP Johnson Starting/Running Saga

Skip the fuel pump, as if you can squeeze the bulb until hard, it's like bypassing it anyway. Check the compression, and spark (w/tester.. get 5/16" blue bolt). If that's good, maybe reeds? If fuel comes out the front of the carb, it's likely not a fuel starve issue.

 

[ba_50]

Re: 78' 35HP Johnson Starting/Running Saga

What about water in the gas. Put some Heet or sea foam in the tank.

 

[ezeke]

Re: 78' 35HP Johnson Starting/Running Saga

Check your flywheel key - you may have sheared it.

 

[kenmyfam]

Re: 78' 35HP Johnson Starting/Running Saga

Flywheel key shearing would explain a lot of the current symptoms. The "half fires" etc
Are the plugs getting wet ????

 

[samo_ott]

Re: 78' 35HP Johnson Starting/Running Saga

Gotta guarantee a good spark before going any further... did you use a spark tester or just hold the wire near a ground?

 

[mnsherick]

Re: 78' 35HP Johnson Starting/Running Saga

Update:

Checked spark with 'spark tester' got 5/16" gap and a good blue bolt.

Compression is :

55PSI MAX at top cylinder

40PSI MAX bottom cylinder


Pulled plug at bottom of carb fuel bowl after several attempts to start and fuel flows so fuel pump is good.

I'm including pictures of the two positions that the 'spark advance' is in when I attempt to start, one position it never fires, the other it 'trys' to start almost every attempt...I've marked them with tags on photobucket

Doesn't fire:
http://i300.photobucket.com/albums/nn33/mnsherick/IMG_0019.jpg

Trys to start:
http://i300.photobucket.com/albums/nn33/mnsherick/IMG_0020.jpg

One more note, I get a 'back fire' every time I try to start it choked, never had this happen regularly before this.

-Matt

 

[psteurer]

Re: 78' 35HP Johnson Starting/Running Saga

I sure don't like those compression numbers. That motor should easily have over 100 psi in each cylinder. What is more important though is that the two cylinders are not within 10%. Could the problem be a blown head gasket?

 

[mnsherick]

Re: 78' 35HP Johnson Starting/Running Saga

I sure don't like those compression numbers. That motor should easily have over 100 psi in each cylinder. What is more important though is that the two cylinders are not within 10%. Could the problem be a blown head gasket?

There are no visible signs of head gasket problems.


"maybe a leak between cylinders"?

I just can't figure out why it ran so good for several weeks during the opening of duck season, and now no start...

-Matt

 

[bktheking]

Re: 78' 35HP Johnson Starting/Running Saga

Pull the head off, you can see much more with it off, scoring, bad gasket etc etc etc.

 

[mnsherick]

Re: 78' 35HP Johnson Starting/Running Saga

After almost giving up, it started a few times, ran high rpms not wot but not idle, I had to crank it over 5-8 times with choke engaged, then crank it over 10-12 times with throttle at about 65% pic of spark advance above where I said it 'trys' to start, only ran 7-10 seconds...

should I put some fuel in the cylinders or try some starting fluid in the carb just to see if it's maybe a fluke fuel issue?

-Matt

 

[psteurer]

Re: 78' 35HP Johnson Starting/Running Saga

You can try that. But I afraid that if the compression numbers that you reported in an earlier post are accurate, then another issue or possibly the main issue will be other than fuel related. Possibly another compression test is in order to verify your numbers. If you get the same results, then removing the head gasket would be a good first step to see what is wrong.

 

[jasper60103]

Re: 78' 35HP Johnson Starting/Running Saga

yes, I agree on the retest. I borrowed a compression tester on 2 occasions from Autozone and results were very low both times. I borrowed another tester from Oreilly's and the results were much better. I guess this is a good reason to buy a quality tester. Of course a compression test won't fix your problem.

 

[samo_ott]

Re: 78' 35HP Johnson Starting/Running Saga

That compression is not good. I'd try a new head gasket and if that doesn't work, you could be SOL. Odd how it failed though while running though. Sounds like it could be a gasket failure. You said it looks ok. Can you post pics of the gasket and the cylinders?

 

[mnsherick]

Re: 78' 35HP Johnson Starting/Running Saga

That compression is not good. I'd try a new head gasket and if that doesn't work, you could be SOL. Odd how it failed though while running though. Sounds like it could be a gasket failure. You said it looks ok. Can you post pics of the gasket and the cylinders?

I've got another compression gauge, I'll give it another go, and I'll see about borrowing one from oriellys.

If the results are the same, I'll post pics.

-Matt

 

[mnsherick]

Re: 78' 35HP Johnson Starting/Running Saga

New compression test shows:

70/top
50/bottom

Since my dad was sure it was a fuel problem, today we tried starting it while squirting fuel into the carb:

It started right up and ran at about 40% of WOT sounded very good, just like always.

It would try to die, and he would squirt fuel in and it would stay running. After that we didn't get it to start again but it came darn close. We are thinking fuel problem still...I checked the carb bowl after running and it still has fuel in it. (Maybe plugged jet in carb?)

-Matt

 

[samo_ott]

Re: 78' 35HP Johnson Starting/Running Saga

That compression is still too low for an engine to run properly.

 

[kenmyfam]

Re: 78' 35HP Johnson Starting/Running Saga

New compression test shows:

70/top
50/bottom

Since my dad was sure it was a fuel problem, today we tried starting it while squirting fuel into the carb:

It started right up and ran at about 40% of WOT sounded very good, just like always.

It would try to die, and he would squirt fuel in and it would stay running. After that we didn't get it to start again but it came darn close. We are thinking fuel problem still...I checked the carb bowl after running and it still has fuel in it. (Maybe plugged jet in carb?)

-Matt

Your compression issue must be addressed. That is your starting point unless you feel that both compression testers were wildly inaccurate. Check the compression on something else for comparison.

 

[psteurer]

Re: 78' 35HP Johnson Starting/Running Saga

You likely do have fuel issues. Could be a clogged carburetor. But you definitely have a compression problem. Your fuel pump runs off the compression in the top cylinder of that motor. If you have low compression, it will not pump as efficiently and result in what you are experiencing. Scanning the posts from the experts that have responded here, I believe the consensus is to pull the head off and see what the cylinders look like. This could be as simple as a blown head gasket which is a fairly easy repair. You can post pictures of the cylinders and the experts here will let you know.