70 HP 1987 Johonson won't idle unless......?

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Leopoldo

Seaman
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May 26, 2004
Messages
64
unless......I kick up the idle adjustment screw to 1500 RPM's + or -!<br /><br />Is that too fast? If I reduce the idle to around 1000 RPM's it dies!<br /><br />Trolling speed at 3.5 MPH at 1100 RPM's works fine.<br /><br />WOT is at 5100 RPM's at around 40 MPH. Should this be higher?<br /><br />In the range of 1500 to 2000 RPM's in gear there is a noticeable miss. Any higher it smooths out and planes well at 3000 RPM's.<br /><br />Am I overly concerned or should I be thankful as is? If you remember in my early post I figured the motor was seized because it was sitting for 4 years from the previous owner.
 
rickdb1boat

rickdb1boat

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Jan 23, 2002
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11,195
Re: 70 HP 1987 Johonson won't idle unless......?

Leopoldo<br /><br />Think I replied to you before that I have a 1991 70 HP Rude and it idles in gear at about 1000 RPM's and in neutral, about 1100. 1500 is too high. Did you ever try adjusting the low speed needle screws to 2 turns out from lightly seated position and then adjust your idle speed again? Generally, they will die at low RPM's due to a lean condition. It could also cause your "Miss" in that same RPM range. Give it a try and let us know what the initial settings on the number of turns that the screws were at. Jot them down for each carb, top to bottom. Remember, this is 2 FULL turns of the screws out and all of the carbs should be the same amount of turns out. You also need to get your RPM's up to at least 5500-5700, through a prop pitch change or raising the motor, if need be and see if that helps. Did you clean and rebuild the carbs??
 
H

Hooty

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Oct 2, 2001
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4,496
Re: 70 HP 1987 Johonson won't idle unless......?

I don' have the correct idle speed at my finger tips but it's probably in the 600-750rpm range. That's in the water, in gear. The miss could be a number of things, Carburetor adjustment, dirty or clogged low speed orfice or ignition breakdown. It'll require some trouble shooting.<br /><br />c/6<br />Hooty
 
rickdb1boat

rickdb1boat

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Re: 70 HP 1987 Johonson won't idle unless......?

Idle speed called for in Factory Manual is 725+-25 RPM's. Full throttle operation RPM is 5000-6000 RPM's. Mine likes it higher on the idle end. Always shifts into gear without hardy noticing. But then again, that's on a toon with a fairly flat prop pitched at 11". It does make a difference when shifting, as opposed to a 13" or 15" prop. I feel it then...
 
D

DJ

Guest
Re: 70 HP 1987 Johonson won't idle unless......?

Leo,<br /><br />If it won't idle at it's suggested RPM, the engine is sick.<br /><br />I doubt you can fix this with adjustments. <br /><br />What is the compression on all three cylinders?<br /><br />You cannot "adjust out" a sick engine.
 
B

Bass Runner

Senior Chief Petty Officer
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Apr 2, 2004
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746
Re: 70 HP 1987 Johonson won't idle unless......?

Originally posted by rickdb1boat:<br /> Leopoldo<br /><br />Think I replied to you before that I have a 1991 70 HP Rude and it idles in gear at about 1000 RPM's and in neutral, about 1100. 1500 is too high. Did you ever try adjusting the low speed needle screws to 2 turns out from lightly seated position and then adjust your idle speed again? Generally, they will die at low RPM's due to a lean condition. It could also cause your "Miss" in that same RPM range. Give it a try and let us know what the initial settings on the number of turns that the screws were at. Jot them down for each carb, top to bottom. Remember, this is 2 FULL turns of the screws out and all of the carbs should be the same amount of turns out. You also need to get your RPM's up to at least 5500-5700, through a prop pitch change or raising the motor, if need be and see if that helps. Did you clean and rebuild the carbs??
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You guys have adjustable jets on those 70hp motors? My 1974 70hp has fixed jets. I go along with the other post about the plugged or dirty jets that will also cause you to have to set the idle high to keep it running better rebuild the carbs, if it's running lean because of dirth carbs you will burn it up. :eek:
 
rickdb1boat

rickdb1boat

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Re: 70 HP 1987 Johonson won't idle unless......?

Well, DJ, I gave it a try. Hoping that it was leaned out too far and causing the low speed problem. Don't know how it ran 4 years before, so who knows. Oh well....
 
D

DJ

Guest
Re: 70 HP 1987 Johonson won't idle unless......?

Rick,<br /><br />No offense. Just want to make sure we're all dealing with something healthy.<br /><br />The 70 on our Whaler will die when engaged if everything is not just right. It's turning a 17" wheel. Even cranking up the idle speed won't help.
 
L

Leopoldo

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May 26, 2004
Messages
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Re: 70 HP 1987 Johonson won't idle unless......?

Thanks boys, I'll check this out on the lake again today. The prop that is on there is a 13 X 19. I do have a 13 1/4 x 17 would this be better? Also the only manuel I have is a Seloc. I find it has some discrepancies and is not as comprehensive as I would like. Pretty vague on the carburetors. Bass Runner has a point, I believe this Johnson 70 1987 has both fixed low-speed and high speed orfices after looking through the Seloc manuel. Is this correct?<br />I'll check the compression today. If I remember the bottom hole was 10 psi off!
 
rickdb1boat

rickdb1boat

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Re: 70 HP 1987 Johonson won't idle unless......?

Hi DJ. No offence taken. ;) I was just thinkng that if it was running too lean at idle, it would die out. I've had this happen on other motors, so that's why I suggested the richer mixture for starters and see if that helped. Look on the port side of the carbs and see if you have adjustable low speed needles. They are small brass screws on each carb. DJ is correct that nothing will help if the engine is not up to par. But the compression test will reveal that. Could be the carbs need a good cleaning if the engine is indeed healthy. A decarb may bring up that low cylinder compression and solve the problem, too. We'll see. Let us know what the compression numbers are now and we will go from there.
 
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Leopoldo

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May 26, 2004
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Re: 70 HP 1987 Johonson won't idle unless......?

Originally posted by DJ:<br /> Leo,<br /><br />If it won't idle at it's suggested RPM, the engine is sick.<br /><br />I doubt you can fix this with adjustments. <br /><br />What is the compression on all three cylinders?<br /><br />You cannot "adjust out" a sick engine.
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Leopoldo

Seaman
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May 26, 2004
Messages
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Re: 70 HP 1987 Johonson won't idle unless......?

You are right the motor appears to be SICK! 110 PSI, 110 PSI and the bottom hole sits at 90 PSI.<br /><br />I decarbed and that didn't bring up that hole!<br /><br />So what are the options? Use it as is until it dies, which seems fine for a novice (other than the idle problem) until I can afford a new 2 cylce 70 HP or higher?<br /><br />One other other question, do all new 2 stroke models come with the oil injection systems? I prefer to mix the 50:1...........L<br /><br />BTW: the plugs all appear the same in color, black and oil rich looking, not the dry and powdery look?.............L
 
W

Walker

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Jun 15, 2002
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Re: 70 HP 1987 Johonson won't idle unless......?

Leo, do you do a lot of trolling?? What sparkplugs do you have in it?
 
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Leopoldo

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May 26, 2004
Messages
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Re: 70 HP 1987 Johonson won't idle unless......?

Originally posted by Walker:<br /> Leo, do you do a lot of trolling?? What sparkplugs do you have in it?
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Actually I hate trolling Walker! :rolleyes: <br /><br />I have been putting this boat and motor through the paces, gobbling up gas like there was no tommorow, ilde, trolling speed, WOT.<br /><br />The recommended QL77JC4 plugs!
 
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Walker

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Re: 70 HP 1987 Johonson won't idle unless......?

Good plugs. Do you mean its using more gas than it should or you are just running it a lot??
 
O

ob

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Aug 16, 2002
Messages
6,992
Re: 70 HP 1987 Johonson won't idle unless......?

I'm with Rick on his earlier post. Run the 13 1/4 X 17 prop you have on that engine.5300 at wot is too low for the 3 cylinder loopers.And with a low compression cylinder on the bottom end the engine can use all of the breathing room you can give it.At 5300 wot rpm capability,that engine is being lugged at all throttle settings.<br /><br />I'd still give those carbs a once over cleaning as well.Could be that the bottom hole compression is a result of either a present or past lean condition.<br /><br />Also ,I don't know what product or procedure you used for the decarb,but you could try removing the bottom sparkplug after and engine warmup,rotate the flywheel until the piston is near top dead center and target spray some decarb(omc engine tuner) diectly around the cylinder wall. Let it sit for several hours.Then follow that with stroking the piston by hand ,using the flywheel,several rounds,and then a hose run for several minutes and recheck compression.This is under the assumption that there is possible heavy coking of the ring grooves from lugging the engine over time and could maybe improve the compression condition a bit.May or may not help ,but sure won't hurt.Good luck in any case.
 
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Leopoldo

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Joined
May 26, 2004
Messages
64
Re: 70 HP 1987 Johonson won't idle unless......?

Originally posted by ob:<br />I'd still give those carbs a once over cleaning as well.Could be that the bottom hole compression is a result of either a present or past lean condition.
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All plugs look the same excessive rich air-fuel mixture? Black, sooty, oily looking! What would cause the rich condition? Would running hotter plugs help and what would those be Champion's be ?????<br /><br />
Originally posted by ob:<br />Also ,I don't know what product or procedure you used for the decarb,but you could try removing the bottom sparkplug after and engine warmup,rotate the flywheel until the piston is near top dead center and target spray some decarb(omc engine tuner) diectly around the cylinder wall. Let it sit for several hours.Then follow that with stroking the piston by hand ,using the flywheel,several rounds,and then a hose run for several minutes and recheck compression.This is under the assumption that there is possible heavy coking of the ring grooves from lugging the engine over time and could maybe improve the compression condition a bit.May or may not help ,but sure won't hurt.Good luck in any case.
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I used Deep Creep Seafoam, but only through the carbs and not a very heavy dose at that. Thanks for the valuable info on this ob!..........L
 
L

Leopoldo

Seaman
Joined
May 26, 2004
Messages
64
Re: 70 HP 1987 Johonson won't idle unless......?

The follow up! Managed to Deep Creep the low bottom hole and this process allowed me to get that up from 90 psi to 94 psi, still trialing the other (2) at 112 and 111 respectively. Got the idle down to 1000 RPM's from a previous high of 1500 RPM's. Managed to get 5300 RPM's up another 200 RPM's without a prop change. Starts right up, picks up good onto a plane. Still a noticeable miss at lower RPM's.<br /><br />So that bottom hole is a bit sick I reackon since I can't pull up past it's 94 PSI reading. I guess I can live with it for the summer. Any guesses from you guys on what has happened to the cylinder?<br /><br />Also should I just run it as is? Thanks again in advance ............L<br /><br />BTW: I took a timing light with me and I am a little confused concerning BTDC and ATDC? Is ATDC going to the right with the minus numbers (-4) and BTDC is to the left with normal numbers up to 36? <br /><br />Also with this bad hole is it pretty much imposible to tune it at all? Again thanks.
 
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