Logo
FULL SITE MENU

Was weak spark on 1 now no spark on all 4

C

captain_crispy

New member
"Engine is a Johnson 85TL79R

"Engine is a Johnson 85TL79R
Had weak spark on cylinder 3, now no spark on all four. Here is what happened:
Just bought it last week. Engine started first time and ran great on flusher, but in the water it didn't rev very high, nor did the boat go more than 10 mph.
I checked the spark on the cylinders, 1, 2, and 4 were strong; # 3 was noticeable weak. Spark plug #3 fouled quickly, too.

I switched the ignition coils from the starboard side to port, and vice versa, in order to isolate the problem to the coil or the power pack.
Now there is no spark on any cylinder. I switched the coils back to their original cylinders [shouldn't matter, but what the heck] and still no spark.
I disconnected the red plug for the wiring harness, shorted the starter relay with the spark plugs removed and the spark checker installed.
Any ideas ?"
 
"UPDATE: Just went outside and

"UPDATE: Just went outside and put it all together. Started up, but sounds like it is only running on 2 cylinders. Obviously it is getting spark to some cylinders. I will go through the spark check again."
 
"possibly,low cranking speed..

"possibly,low cranking speed....chg battery,ck/clean connections,slice rubber off batt cables about 4" fr batt...if green color ,repl both cables.......and go to lgr size."
 
"Thanks for the input, but it

"Thanks for the input, but it isn't the battery. It is cranking plenty fast, and it will start and run for 12-15 seconds, sounds like on only 2 cylinders."
 
"It was running worse after I

"It was running worse after I switched the coils because I accidentally flipped the port side coils [ 2 was in 4, 4 was in 2]. I switched them back, installed a new coil on #3, cleaned the grounds to the power packs just for giggles and grins, and she fired up and ran beautifully, even better than when I bought it !
Checked compression while I was at it [I knew it was good, but didn't know how good]. It was 118; 120;120;120

I will put her in the water tomorrow afternoon and check hi-speed operation."
 
"I still have the same primary

"I still have the same primary symptom: No power at anything more than 1/4 throttle.
Compression is excellent.
The plugs on the two bottom cylinders are noticeably more dirty than the top two after 20 minutes run time. Not bad, though.
Also, when I start it cold, some fuel spills out of the FRONT of the carbs.
I checked spark again and I have good spark on all four cylinders [strong spark across 7/16th gap]."
 
"I am running it from a portab

"I am running it from a portable tank with new fuel through a water separating filter.
Timer base is advancing with the throttle.

Could a defect in the carbs cause it to put too much fuel in the cylinders ??

Is there any significance to the bottom plugs being so dirty after on 20 minutes run time ?
The insulators on the top plugs re almost white, but the bottom ones are dark brown [cylinder 3] and jet black [cylinder 4]."
 
I can look @ fuel delivery thr

I can look @ fuel delivery through carbs @ WOT. What am I looking for ??

I have not done anything to carbs other than use spray carb carb cleaner through the barrels.
 
"u would be looking for even s

"u would be looking for even stream of fuel spray being pulled from each venturi...spraying the the barrells,wont clean the carbs at all,in side...thats where any prob will develope...use a flashlite."
 
"and by the way,..i dont recom

"and by the way,..i dont recommend looking thru them,running down the lake.....on a trlr,or in a test tank w/a test prop would be perfect...short of that,..restrained,on a trlr,backed in fairly deep,w/prop on...... 2 people for safety."
 
"Remove the front cover from t

"Remove the front cover from the Carbs, observe if fuel is spitting out of the carbs at idle and at WOT if yes , you need re-build your carbs very simple to do on your type of carbs. pay special attention to your float adjustment
Your RPM issue seems to be electrical please do a Stator and Trigger test. It cheaper than swapping parts. Google it you will find a post if you have the manual all the better. I have the PDF for an 87 140 Looper not sure if it will work for you.
Good luck and keep us posted."
 
"As stated on 22 March, strong

"As stated on 22 March, strong spark on all cylinders across a 7/16 inch gap. After replacing the coil on cylinder #3, I am confident in the ignition system.

I disassembled and rebuilt both carbs today, found something I never thought I would see. Each carb has 1 high speed and one low speed jet [orifice] on each side.
On one of the carbs, there were TWO high speed jets screwed in on one side, one on top of the other. There was not a high speed jet on the other side.
After disassembling, cleaning, and reassembling both carbs correctly, it starts and runs great in the yard and when I give it quick revs on the flusher for 2-3 seconds. I will put it in the river tomorrow and see if the carb rebuild and correct assembly did the trick."
 
"Sounds like you found the pro

"Sounds like you found the problem. An improperly adjust float can also cause fuel to spill out of the carbs because it allows a constant flow to the bowl and floods the motor.

If none of this fixes your problem you might next look at the reeds. If they are cracked or bent it will allow pressurized air/fuel to blow back out the carbs. However, from your description it sounds like you found someone's botched attempt at a carb rebuild.

KJ"
 
"Very simple I paid 80 dollars

"Very simple I paid 80 dollars per hour to have mine done the same way last year, The good that comes out of this it forces guys like myself to learn. The money I wasted on a mechanic is now spent on me !
Enjoy and good luck"
 
"How the hell does somebod

"How the hell does somebody put one jet on top of another and not notice ???"


they did it all at the same time instead of one after the other.
 
"actually.............i have t

"actually.............i have to admit....i did that,...as a young mech,..back in 77....took me a whole day to figure it out......"
 
"but---as one of my old saying

"but---as one of my old sayings goes,..he that never screws up....is'nt doing anyting......."
 
Back
Top