140hp johnson cutting out...Help!!

Mojo353

Cadet
Joined
Oct 4, 2015
Messages
13
Hi guys, motor ran great over last few weeks but now can be difficult to start after warm up. Also noted at higher rpm it appears to get sudden bursts of power. I thought dirty fuel or carb problem. Cleaned fuel filter and ran sea foam through carbs, no real difference. I don't know the history of the motor but I believe it was rebuilt at some stage, it's too clean not to have been. Compression on all 4 cylinders is within 10psi of each other at around 120psi. What I have noticed is oil/gas seeping from behind one set of carbs... see attached photo. Im not exactly sure where it's coming from but I noticed the bolt securing the gear and throttle linkage arms (probably not the correct term) was loose and the oil/gas seepage is just below that or possibly coming from behind the bolt where it goes into the block which is behind the carbs. My question is .... is it possible I'm losing fuel from that lose bolt ? And is this what's causing he spurts of power at higher rpm ?
The motor also takes a while to build up speed or sometimes it's as if there is a delay once you push throttle forward. I'm hoping it's just this loose bolt as I've found other connections loose (electrical)
It was idling fine but now it's iratic and cuts out, does the same at speed also.
Any help would be appreciated.
I plan on doing a carb rebuild over the winter but would like to get the rest of the summer out of it as it is if possible.
Thanks.
 

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Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
I doubt its from that bolt as i doubt that bolt goes into the manifold.
Try priming your fuel bulb with engine off, does it go hard? How long does it stay hard? It should for at least a minute or so.
 

Mojo353

Cadet
Joined
Oct 4, 2015
Messages
13
Well tightened up that bolt, cleaned off the oil/gas. Suspect it was possibly grease from the bolt.
Ran the motor in a barrel not muffin and although it didn't cut out it still ran erratic. At 1500 rpm on warm up lever it still revs up and down over time. Haven't tried it under load but I suspect the same thing will happen, it will most likely cut out as soon as forward I'd engaged.
I may have found the problem though..... coil pack for cylinders 1&3 is arcing to the head. Only noticed it after the motor warmed up, dunno if that's the only problem, it would certainly a cause of the problems I'm having, let's hope that's all it is.
Also noted and I know it's common enough... cylinders 1&3 run hotter than 2&4... cylinders 1 @ 160'f cylinders 3 @ 145 cyl 2 @ 141 and cyl 4 @144 that's after running for a while at idle, they cool down at higher rpm, more water flow I guess.
I will start by changing the coil pack answer hopefully that will sort it.
The bulb stays hard for a few minutes after initial start. It's a new bulb.
 
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