Question for the experts.....

[daselbee]

J70ELCIM, 1981 70hp 3 cyl.

I think I have run into something I have not seen yet. I have good spark, compression is 135, 120, 135. I have rebuilt the carbs. The problem is that it only idles at 6-8 degrees BTDC. CORRECTION BTDC If you retard the timing slowly back toward TDC, it will stall. All this in neutral.
OK, so I did a cylinder drop test. #1 affects the idle slightly, #2 about the same, and #3 kills the motor.
All the time for these tests, the engine is running at 1200 rpm. Won't reliably go any slower.
Drop it in gear, and it really bogs the motor down, and it stalls within 10 secs.

I have a slight fuel drip from the front of #1 carb. I have changed that carb with another one, and still drips.

All of this is leading me to the conclusion that #1 and #2 are not contributing. But why? So, I think reeds, and then I thought crank seal ring between #1 and #2.

My question.....how can I absolutely test the crank seal between #1 and #2, (or maybe even the gelseal) between the two crankcases (#1 and #2) to eliminate that as an issue?

It seems as if the two upper cyls are not getting the same fuel charge as the bottom one. And, the fact that fuel is dripping slowly from the #1 carb says I am getting blow back somehow.

Any of this make sense? Is there an oldtimer's trick?

As always, thanks for your thoughts.

 

[Bosunsmate]

Re: Question for the experts.....

Thats what i was thinking, not sure if it makes sense or not either! but have you tried putting your hand over the carbs to feel if vacuum is approximately even on them all?

 

[daselbee]

Re: Question for the experts.....

Very good question!! They feel the same to me, as best I can tell. BUT!!! I can spray carb cleaner in the front of each carb, measured as best I can with a short quick blast, tried to make each spray the same, and the carb cleaner runs out, pours out the front of #1 and #2, slows the engine slightly, but when I spray into #3, all is sucked into #3, and almost kills the engine.

#1 and #2 are not sucking like #3 is.

I got a trick from an old timer that I will pass on to you. Remove the linkage from all three carbs that link the throttle butterflies. Remove the plug wire from #1, start engine and run on two cyls. Then, independent from the other two c arbs, open the butterfly manually for #1. That cyl has no spark, but now has gas. If the crank seal rings are leaking, the engine will pick up speed from fuel leaking from #1 to #2. Do test for all three cyls. Ingenious!!!

I also indexed the flywheel and all three are sparking the same, right now at 6* ATDC for each cylinder. That is way too advanced to be right.

Pulling the front now to inspect reeds. If the reeds are sealing, the only thing left is the condition of the bottom of the cylinder bores, I guess.

Please speak up if I am on the wrong track.

 

[daselbee]

Re: Question for the experts.....

Oh, and I did the oldtimer's trick as described above, and there was no affect to the running quality. SO, if the trick is valid, the crankcase rings should be OK.

 

[Bosunsmate]

Re: Question for the experts.....

Thanks for the tip, Im just wondering about that trick. Isnt the seal done via the crankcase centre bearing lube so you would probably expect a bit of a drip of of two stroke mix into the second cylinder from the top cylinder. But if the top seal has gone you would not get any change from that test as there would be hardly any fuel being drawn into the top carb and thus nothing to go down to the second cylinder.

If ive caught you i time before dismantling the reeds. try squirting some carb cleaner if you can under the flywheel to see if it gets sucked into the top seal

 

[Bosunsmate]

Re: Question for the experts.....

So if your top seal was gone the centre bearings between one and two would lean out causing both 1&2 to not affect idle much as you a finding.
Ive always thought the two stroke mix provided the sealing in those centre bearings, with the bottom bearing have a purging system in it to get the oil thats dripped down back into the crankcase and burnt.
Self taught so only quoting myself!

 

[tomhath]

Re: Question for the experts.....

Sounds to me like you might have both ignition timing and carburetor problems.

J70ELCIM, 1981 70hp 3 cyl.
The problem is that it only idles at 6-8 degrees ATDC. If you retard the timing slowly back toward TDC, it will stall.

That confuses me a little. Did you mean "advance" the timing toward TDC? Or are you firing 6 degrees Before TDC?

Also, are you absolutely sure the spark plug wires aren't mixed up? That's very easy to do...:grumpy:

 

[daselbee]

Re: Question for the experts.....

That confuses me a little. Did you mean "advance" the timing toward TDC? Or are you firing 6 degrees Before TDC?

Also, are you absolutely sure the spark plug wires aren't mixed up? That's very easy to do...:grumpy:

Yes Tom, I made a mistake....geez....let me correct it. It is firing at 6-8 degrees BTDC. As I retard it toward TDC, it slows and stalls. Very sorry...now I know you are reading carefully!!!

To repeat. The only way I can get it to idle at 1200 is to set the timing at 6-8 degrees BTDC which is way too far advanced.

I got the reed block off, and I see light between reeds on #1 and #2. HAve a spare parts engine, and the reed block is light proof on it. Will have it back together soon and will report back.

Have not sprayed under flywheel to check for top seal leak.

Index the wheel, and all cyls are firing right, so plug wires are not wrong. Will double check tho. I can see the timing hash marks when lighting #1, so, the plug wire is definitely OK for #1.

 

[Bosunsmate]

Re: Question for the experts.....

Thatl be interesting if two reeds have gone simulaneously unless its being only running on two cylinders for a while

 

[daselbee]

Re: Question for the experts.....

OK, I saw light on reeds for #1 and #2. Granted it was a very small sliver in no more than two places on each reed block. I would think that the reed would blow shut when back pressure hit it. But there was just a little light.

The reed block I used has NO light visible on any reeds.

I put it on, and the situation is improved. The gas drip from the front of the carb is gone.
It now idles at TDC at 1100 RPM in neutral.
When dropped in gear, it goes down to 650 and runs for 5 secs or so and stalls.
If I retard the timing toward ATDC numbers...like say 2* ATDC, it eventually stalls.

Things are a bit better, but this is still not the way it should be. When warm, I should be able to bump the key and have start. This one must have the fast idle lever raised before it will start. It sputters like it is flooded, smokes heavily, and then takes off and runs high, then drop the fast idle lever back down and it settles at 1100.....smoking normally.

Maybe just carb issues now....but I went thru them.....new OMC kits.....I am really beginning to wonder if the jets have been swapped sometime in the past. Three jets, and it is very unclear exactly which ones are called for. The parts list refs early production, late production, M suffix, 15in leg....sheesh....

It has 37 idles, 55 ints. and 52D mains. Best I can tell, that should be for an 81 20"leg 70 hp.

Fixed idle jets by the way. No needles.

 

[emdsapmgr]

Re: Question for the experts.....

I think you may be idling this on the trailer. Hard to discuss the timing at all at idle, as it does not mean anything. You must set the idle by rpm's. Set the idle rpm's when the boat is floating normally in the water, and is in forward gear. Set the rpm's to 650-750. Don't worry about the idle degree timing-it's different for every boat, depending on how deep the lower unit is on the water on your specific boat. Once you get it set, it will likely idle at 1100-1200 on the trailer. I'd agree that #1, #2 may not be contributing much. I'd have a look at the plugs and see if any of them look different. Do some look wetter than others. Any dry ones may not be getting fuel. You can put a timing light on each plugwire and note the flashes from the gun. They will show weak firing, misfires, no fires, etc.

 

[Bosunsmate]

Re: Question for the experts.....

Do you think 1 and 2 are sucking normally now doing your spray test?
Have you tried spraying under the flywheel?

 

[daselbee]

Re: Question for the experts.....

OK....things are still not right regarding the response from the engine when carb cleaner is sprayed in the carbs, one at a time.
Now, #1 bogs the engine, and #3 bogs the engine. Not much response from #2.
I did not try to get carb cleaner up under the flywheel. The TB is big, there is literally no room to get a decent spray up there, much less to see if it actually hits the upper seal. I'll will consider it....

EMD. The engine is in a 100 gal tank. I realize the fine tuning should be done as you suggest, but this is not running right at all, and is not to the stage of fine tuning it yet.
Already looked at timing light flashes...all solid and consistent.
The engine in the tank is in deep; waterline about 6 inches above the LU parting line with the midsection.

I am going to go thru the carbs again, paying particular attention to the idle circuits.

This may sound weird to you guys, but when you get one dialed in just right, there is a certain sound the carbs make. They don't just hiss, they have a throatiness to the hiss....I don't know how to describe it.....maybe the same sound as when you used to stomp the old V8 Chevy and the four barrels opened....only not near as loud.... This engine doesn't make this sound....I just don't think it is sucking right.

Right now I suspect that maybe the jets are wrong from some tinkering in the past, or that the bottom cylinder health is poor. You know, piston on downstroke cannot build enough crankcase pressure , causing a minimal fuel charge.

I put new plugs in tonight, will run for a while tomorrow and read them.

 

[Bosunsmate]

Re: Question for the experts.....

Yep thats what id do and id also have a bit of a look in all the sparkplug holes to see if any piston heads look different.
if you can post a video, keen to hear how it sounds.

 

[Faztbullet]

Re: Question for the experts.....

Dasel..that motor dont have crankseal rings, it has labrith seals on block halfs. If these are worn the cylinders will "cross talk" at low end but once ovet the hump will run fine on top end. Also this can be caused by pistons scuffed on exhaust side as crankcase pressure wil be low and it will have a "garble" from the carbs when advanced..

 

[emdsapmgr]

Re: Question for the experts.....

From your description, the #2 cyl seems to be the problem one. It should respond to the fuel test just like #1, #3. If you were going to pull the carbs back off, you might want to look inside the intake at the reed boxes, esp #2. What are the compression numbers on each cyl?

 

[seahorse5]

Re: Question for the experts.....

In your very first post you say the compression is 135, 120, 135. That is probably your major problem. Cylinder #2 being 15# lower than the others is a big red flag.

Have a knowledgeable shop perform a leak-down test on the cylinders and I'll bet that you will find your idle problem.

 

[daselbee]

Re: Question for the experts.....

Dasel..that motor dont have crankseal rings, it has labrith seals on block halfs. If these are worn the cylinders will "cross talk" at low end but once ovet the hump will run fine on top end. Also this can be caused by pistons scuffed on exhaust side as crankcase pressure wil be low and it will have a "garble" from the carbs when advanced..

Well I will be (fill in your own cussword)!!! No crank seal rings. Huh!!
I did that check I described above, and there was no noticeable change in engine operation. I did all three cyls. You think that test could detect the "cross talk" you describe?
And yes I distinctly remember many posts of yours that describe low crankcase pressure due to wear on piston skirts and lower cylinder walls.
Thanks very much for the reply Fazt.

I realize that #2 is low, but in reality, I just don't know that it would affect the idle so radically...I think it should idle ATDC not BTDC.
After all, the book says the timing PICKUP point when the mark aligns with the roller is supposed to be TDC. That tells me that it should be somewhere ATDC at idle in order to advance toward TDC to meet the pickup point on the cam/roller alignment. As has been stated, the exact idle timing is not set in stone, it is what it is when the idle speed is right.

Ummm Bosun...I will try for a video for you today. Not sure how to post it.....

 

[Bosunsmate]

Re: Question for the experts.....

Hi, i just set up a youtube account and upload it there. I then press the second on the far right icon in quick reply and paste the link there and iboats does the rest.
There is possibly a easier way.
I agree with you about timing being too far advanced and i also dont think compression is causing it but that that lower compression is probably caused by whatever is causing it.
If you can do a drop test on each cylinder on a video thatd be good.

 

[phillnjack2]

Re: Question for the experts.....

ok you have what i had with my engine.
you have gone about it pretty much like i did too, and ended up pulling ya hair out and getting nowhere.

its all wrong
start from scratch to do the link n synce, dont panic about the idle rpm till you get near it.

what i ended up doing was to take off all the carb linkages and realy start from scratch.

with engine spinning over realy fast with plugs out get the idle timming to what the engine specs are for that year.
once this is done then set all three carbs moving at the same time on linkage.

then have all 3 carbs fully closed and put your linkage back together and check the exact rod clearances in the book for this.

idle speed aint worth talking about just yet, and loads of these triples idle with just 2 pots working under 1,000 rpm.

then you can fine tune from there.

you will obviously already know all this but have missed something out along the line.

i couldnt believe it when i messed mine up why i couldnt get it running right, and the worse bit was i got a friends working fine over the phone !!!!!

people on this very forum helped me out big time, without the people telling me what to do i would still be trying to work out why mine was not running and sucking the fuel properly.

also on thse engines often the carbs dribble a drop of juice when idling if the front air box cover is not on ?
i found that out by checking the bottom of the air box while it was running with it on and no dribbles !!!!!!!!!
with airbox off it dribbled from the top carb.

once i completely started from scratch it ran great, i have no idea what i was doing wrong as i tried it every single way possible.

sometimes it would run and stay even at around 700rpm in nuetral and i would smile, then it would die like it was just winding me up.

i even tried telling the engine is was going to be melted down, that didnt work at all neither ha ha ha

so your not alone, you have just simply got something wrong along the way, that you already know how to do right.

dont try to get idle rpm right before the timing, its the other way round.
and i think on your engine your timing increases slightly before throttle movement unlike mine .

hope this possibly helps you.

p.s
have you tried to get the middle compression up with a tin of power tune or deep creep etc ?
as 15 psi difference is a lot.
.

phill