Throttle issue

SHS93

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May 1, 2016
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I have a 78ish 115 hp Johnson. The throttle assembly doesn't move as much as I think it should. In reverse it hardly moves at all. Shifts into gear ok. Last week had it out and ran fine for a while then lost power. Had it at full throttle and wouldn't do much more than idle speed. The throttle assembly on the motor has a screw that limits the throttle from going past a certain point.

Do I adjust the screw or replace the throttle cable? Why would it run fine for about 20 min and then lose power?
 

flyingscott

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Apr 8, 2014
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Do not adjust the screw, look at the carb butterflies to verify the throttle is opening all the way. Check compression and spark.
 

SHS93

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Update: it's and 82 j115tlcnb: checked all coils with a multimeter. 2 bad 2 good. Replaced 2 and wires. Has new fuel line, fresh gas. Took out Saturday. No longer runs good for 15 min. Now has no WOT from the start. So.... Changing out all plugs now. All coils throwing good spark. I know cause I get shocked when I pull the wires off the plugs to do a cylinder drop. Even with rubber handled puller. Ouch. Carb look clean. I guess that's my next project. They where cleaned earlier this year though. So...

Any other ideas.

Oh yeah I've been running Ethonal free gas too.
 

emdsapmgr

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Dec 9, 2005
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The shifter is evidently not moving to your satisfaction. You can disconnect both the throttle and shift cables at the engine end. Shift the shift lever manually, and see if the shift cable will move front-to-back the same as the total movement on the shift lever on the engine. If so, they both have the same movement capability. That's what you want. So do the same with the throttle cable-disconnect it. Move the throttle lever through it's normal range of motion from idle to WOT. See if the end of the throttle cable will move to the exact positions of then you moved it manually-from idle to wot. Do the cables move fluidly, easily? Is one damaged or stiff?
 

SHS93

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May 1, 2016
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I've done that with the throttle. Don't think the throttle cable or those adjustments are the problem. WOT on the control opens the butterflies all the way. Haven't checked compression.
 

emdsapmgr

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So you really don't have a problem with the throttle cable movement...?
 
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SHS93

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Update again: changed all plugs. Champion as recommended. Gapped correctly. Cleaned both carbs. Fixed a busted check valve hose under bottom carb. Took out Sunday and it ran awful. Run fine at idle. When throttle applied it bogs and now has a miss. Can feel it jumping. Kind of like a cylinder is trying to kick back in. Did compression test all 4 are 120 psi.

Ran on hose after completing test saw some arching on cylinder 1 from where plug wire boot connects to coil. The plug wire that came with the 2 new coils seem cheap and small to me. But I'm not an expert. Also running ethanol free gas 50:1 quicksilver synthetic blend oil.
 
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boobie

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Have you checked the spark with an adjustable open air gap spark tester ?? Should jump 7/16".
 

oldboat1

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^^agree. and on those "some assembly required" coils -- sounds like rechecking might be good. If you have the ones with a couple of boots and spring connectors, will want to be sure each of the connectors securely punches through to contact the core wire, and the spring snaps over the post. Also, thinking there might be a different sized boot for the plug and for the coil on some assemblies. If so, reversing them might result in some arcing -- but first guess would be that the spring clip might not be installed quite right.
 

jakedaawg

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1. Is timer base moving when throttle applied?

2. Have you tried running with the lid off? If not, do so.
 

SHS93

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1. Is timer base moving when throttle applied?

2. Have you tried running with the lid off? If not, do so.

Yes to both. Fuel supply is not the problem. Checked fuel lines, pump, and filter today. All good. Lots of fuel flowing. Checking spark tomorrow. Too much rain today.
 

jakedaawg

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Yes to both. Fuel supply is not the problem. Checked fuel lines, pump, and filter today. All good. Lots of fuel flowing. Checking spark tomorrow. Too much rain today.

I was refering to the engine cowl, not the fuel cap. Fwiw

You should also check flywhell key.
 
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SHS93

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I was refering to the engine cowl, not the fuel cap. Fwiw

You should also check flywhell key.

Yes the cowl is off when I'm working on it. Don't really know about the flywheel key. I'll have to look into that.

I removed fuel pump to check for blockages. Found a bad hose from fuel line connector to the filter screen cap on the pump. Replaced with new. Ran with air silencer plate off and put my hand over the carbs one at a time. Hand got covered with gas each time and engine died. Does that mean it's getting gas? I guess so. Also check for spark with a light tester. All 4 cylinders lit up the light.
Kind of at a loss. Don't know where to check next.
 
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jakedaawg

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Jun 26, 2012
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Its a common misconception that a timing light will tell you something. It only tells you that you are getting enough to trip the light.

You need an open air gap spark checker. Set it 7/16" gap. Report back.
 

SHS93

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May 1, 2016
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Replaced bad fuel one from fuel pump to connection point where tank line connects to engine. Have had out 2 times since runs awesome. I think it was sucking in air.
 
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