symptoms of broken reed

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
About two years ago,I was on the lake going about fifty five and suddenly ,bammmm ,sounded like a bang and chatter,I stoped.Steam was comming from my engine as the water rushed to the back of the boat.
I figured I blew a cylinder.After a little wait I started the boat, drove it home. I think that is when I lost some power not really sure.
Tore it down that weekend and found nothing wrong.No I didnt do a compression check before I took it down. Dumb huh! It now has 120psi on all six cylinders My boat is a 1985 v6 mariner serial # A137316

My problem is I have lost 1000 rpms.The boat used to run 5500 to 6000rms.Now I'm stuck at 5200 rpms at full slugish full throtle. I have been trouble shooting this and found that on muffs I have good spark on all six cylinders .When i run it on the lake at full throtle and then take the plugs out,five are a little wet and one,
the top on on starboard side is dry.

I had a tech tell me today to take the plug wire off that cylinder while the boat was running on muffs and listen for a miss,there was no miss and there is fire on that plug,so that tells me that that cylinder is not getting fuel,correct? I had also installed a fuel pump kit today.
I took off the top carb today and dissambled and examed.All passages were clear and cean including the jets.
Tomorrow I am going to reassemble and run it on muffs and spray some fuel on that carb port of that cylinder and see if it changes the sound of the engine.
My question is ,could that sound that I heard have been a reed? if so could that reed be blocking the exhaust?
Could that be why I have no fuel on the top clinder and loss of 1000 rpms on top end?:facepalm:
 

kodibass

Master Chief Petty Officer
Joined
Apr 10, 2010
Messages
864
Re: symptoms of broken reed

I think it could be the reed, have you ran it under load and pulled that plug wire off, I would take it out for a quick run, while under load pull that wire and see if the sound/rpms are affected. just because you see a spark outside the engine does not mean things are fireing as they should in the cylinder. Let us know after you reinstall the carb what you get.
kb
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: symptoms of broken reed

If you loose a reed at WOT the engine will lose about 100 rpm but still run normally at WOT unless it damages the cylinder as it passes thru. The bang and chatter are a different problem. Also a reed will cause a cylinder not to draw fuel at idle as crankcase cannot form a vacuum, it will sometimes have a dead miss at idle, a huffing noise from air silencer cover,fuel mist fog emitting from that cylinders carb throat.
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: symptoms of broken reed

Faztbullet it will lose 100 rpms or did you mean to say 1000rpms? I am going to take a closer look at the carbs today while running on muffs to see whats going on Faztbullet.
Yes Kodibas ,I will keep the post current. I have not run the boat at full throtle with that plug wire off yet.
 

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
updated symptoms of broken reed

updated symptoms of broken reed

Well,it wasn't the reeds.
I did not install the top carb,just went ahead and tore it down to the reeds,They look fine to me and all was clean.
I did notice this as seen in the pictures....
I think I will change all the gaskets before I reinstall.
Have to order them, so it will be a few days.

Anyone have any thoughts on the pictures?Could someone please answer why the top port in the block has a black reducer in it and the other two ports do not? The top port is the one that supplys fuel to the top two cylinders and one of those cylinders is not getting fuel.The top port on the block with the black reducer is not stopped up.

Its the picture on the right side.
 

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