Leaking Water Jacket-No Fire on #6 Cylinder

[NJCinMN]

Here's what's up-1969 Merc 1000
no fire on # 6 cylinder
Power on plug wire (verified with timing light)
Spark at plug when grounded to motor

Out under light load
only turning 4200 rpm-17" prop
all plugs were new now brown to a little oily except #6 (shiny)
next time out switched #6 and # 5 plugs
Shiny plug now dirty after running in cylinder #5
dirty plug still dirty after running in cylinder #6 (hopefully ruling out water intrusion)

noticed water leaking out of water jacket around #6 plug
can this cause a no fire situation in the #6 cylinder or is something else
causing this dead cylinder? Thanks, Nick.

 

[daveswaves]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Here's what's up-1969 Merc 1000
no fire on # 6 cylinder
Power on plug wire (verified with timing light)
Spark at plug when grounded to motor

Out under light load
only turning 4200 rpm-17" prop
all plugs were new now brown to a little oily except #6 (shiny)
next time out switched #6 and # 5 plugs
Shiny plug now dirty after running in cylinder #5
dirty plug still dirty after running in cylinder #6 (hopefully ruling out water intrusion)

noticed water leaking out of water jacket around #6 plug
can this cause a no fire situation in the #6 cylinder or is something else
causing this dead cylinder? Thanks, Nick.

Do a compression check, sounds like number 6 is not firing due to low or no compression. The water jacket leak is not likely causing the problem unless it is shorting out your plug wires.

 

[NJCinMN]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Dave,
That's gotta be it right...#6 is the only one I couldn't check, all others 125 psi
I'll adapt my tester or get one with flexible hose
Should the compression check out whatda think?
I think ignition is all original-any components break down after time causing power loss? Damn thing runs great though. Fires right up & idles all day long?
I've done all the tuning I can other than new ignition parts.
I mean you're obviously a merc guy, this motor, when right, should push this boat with a 17" pitched prop about 40 MPH shouldn't it?

 

[daveswaves]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Dave,
That's gotta be it right...#6 is the only one I couldn't check, all others 125 psi
I'll adapt my tester or get one with flexible hose
Should the compression check out whatda think?
I think ignition is all original-any components break down after time causing power loss? Damn thing runs great though. Fires right up & idles all day long?
I've done all the tuning I can other than new ignition parts.
I mean you're obviously a merc guy, this motor, when right, should push this boat with a 17" pitched prop about 40 MPH shouldn't it?

Not sure you have described your boat, at least not to me, so I can,t speculate about boat speed. What I can tell you is that engine needs to turn more than 4200 at WOT and depending on boat and accessories (weight) a 17P may be ok. Remember, you still have to live within the laws of physics and a given HP will only move so much weight so fast. I run both a 17P and a 20P on my bass boat shown in the avatar. But I also run a jack plate and power tilt and trim so that if the water conditions are perfect I can run the 20P and squeek as much boat out of the water as possible to keep the RPMs up. For everyday running or bad weather I run a 17P and sacrifice a little speed. Lots of variables.

 

[NJCinMN]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Sorry, I didn't describe my boat to you, thought I did. It's a 1969 Glastron V-163. 16.5 ft runabout, closed bow, tri-v mix hull...appr. weight (when new) 700 lbs usually 4 adults, no gear, cooler, 6 gals of gas, no leaks. Maybe I'm right back to where I was about a week ago...ready to order a prop. Now I did take out all of the water logged foam under the floor but the entire corners between the splashwell is foam so maybe I should get at that. Anyway I know that running the rpms I am is a recipe for disaster so I really need to get this figured out. If motor does check out can I get a prop that'll push this inline to run beyond the 5200 manufacturer suggested max rpms?

Thanks, Nick.

 

[daveswaves]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Sorry, I didn't describe my boat to you, thought I did. It's a 1969 Glastron V-163. 16.5 ft runabout, closed bow, tri-v mix hull...appr. weight (when new) 700 lbs usually 4 adults, no gear, cooler, 6 gals of gas, no leaks. Maybe I'm right back to where I was about a week ago...ready to order a prop. Now I did take out all of the water logged foam under the floor but the entire corners between the splashwell is foam so maybe I should get at that. Anyway I know that running the rpms I am is a recipe for disaster so I really need to get this figured out. If motor does check out can I get a prop that'll push this inline to run beyond the 5200 manufacturer suggested max rpms?

Thanks, Nick.

Lots of different props available if it turns out to be just overpropped.

 

[NJCinMN]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Lots of different props available if it turns out to be just overpropped.

Dave, let me ask that more clearly. I guess my question is do you know if this motor minds to run beyond the 5200 rpm @wot say up into the 5500-5800 range as some other inlines? If it doesn't mind then I'll probably go down to a 13p 4-blade prop.

 

[NJCinMN]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Well I've got the results...122-125 psi on all six cylinders. Good, steady bright blue spark on all. I'm guessing that water may have been sucked in around the spark plug due to the leaking water jacket. I've read that the threads don't seal perfectly and I did run it long and hard the day the plug was cleaner than the rest. So I siliconed around the #6 hole and I guess I'm just over propped. Thanks for the advise. If anyone knows whether it would hurt to run this motor at higher rpms than originally suggested let me know.

 

[daveswaves]

Re: Leaking Water Jacket-No Fire on #6 Cylinder

Well I've got the results...122-125 psi on all six cylinders. Good, steady bright blue spark on all. I'm guessing that water may have been sucked in around the spark plug due to the leaking water jacket. I've read that the threads don't seal perfectly and I did run it long and hard the day the plug was cleaner than the rest. So I siliconed around the #6 hole and I guess I'm just over propped. Thanks for the advise. If anyone knows whether it would hurt to run this motor at higher rpms than originally suggested let me know.

I would prop for 5200 to 5300 WOT, Pick a prop that controls your boat the way you want it to as well. The 4 blade will certainly get you out of the water quickly.