Running on one cylinder

Kenny1

Cadet
Joined
May 8, 2010
Messages
14
I have a 2003 Johnson 2 stroke that only runs on the top cylinder. I bought this boat as is. I have checked compression and both cyl. are 140psi. I installed new plugs. I used a spark plug gap checker and it jumps 7/16' gap on both cyl. I removed carb. cover and placed my hand over top carb. opening and the engine died. No affect on bottom carb.I squirted fuel in bottom carb. while cracking open throttle a little and still no affect. Both carbs have been rebuilt. I even swapped top carb to bottom with no affect. HELP
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
Bottom seal on crankshaft ?------Or cylinder sleeve out of position ?
 

Crosbyman

Rear Admiral
Joined
Nov 5, 2006
Messages
4,908
Not much behind the carb to stop the in rush of the squirted fuel / air mixture except the reeds

can you at least feel the air being suck in the lower carb during the compression stroke. (try a sheet of paper on the carb face)

compare it with the top carb inflow

could be bad/stuck reeds behind the carb I suppose or general loss of suction due to a bad seal as indicated by racerone
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Broken reed valve???

EDIT: Crosbyman posted same thing at same time.
 

Kenny1

Cadet
Joined
May 8, 2010
Messages
14
Hey guys. I removed the reed valves and they seal good. There isn't any suction on bottom carb unless I open throttle up and run at higher rpm. The suction is not as strong as the top carb. How do I check the crankshaft seals. I tried pumping up crankcase by disconnecting pulse hose and connecting a vacuum/pressure tester. Can not get any pressure in crankcase. I think I might have to pull head and have a look.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
Was the piston at top of cylinder / bottom / do not know.----When you tried to pressure test crankcase ?-----Looked for holes / cracks in the crankcase ?------Inspected fuel pump ?------Does it still have the VRO pump ?
 

jakedaawg

Rear Admiral
Joined
Jun 26, 2012
Messages
4,275
Before tearing stuff apart you may consider hooking up 2 spark checkers Simultaneously to ensure that the spark alternates evenly...
 

Crosbyman

Rear Admiral
Joined
Nov 5, 2006
Messages
4,908
I must have missed something…. which motor model is it ?? 2003 johnson 2 stroke is vague for some reason
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,033
A 2 cylinder and 2 carburetor would make it a 40 / 50 HP model I think.-----Just guessing.
 

Kenny1

Cadet
Joined
May 8, 2010
Messages
14
Can anyone give me the link and sync measurements for 2003 Johnson 50 hp 2 stroke? I think my spark control rod is way off.
 
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