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Cough, Sneeze, predetonation, afterburn, what is this?

R

RyanM29

New member
Hi Guys.. this is my second thread..

Bit of Background: http://www.marineengine.com/boat-fo...1553-1987-J150hp-v6-one-problem-after-another

Since then, I noticed the engine was heating up a LOT, so I replaced the cylinderhead/head/stat gaskets on one side of the v6 then noticed that the other side really needed it done too, was operating at 130F for the good bank and 200F for the bad one.. So Removed the head cover/head and of course sheared a bolt flush with the case.. after a few weeks of messing finally drilled out the bolt and retapped the hole.. replaced the gaskets and torqued it up just nice... but I think it has overheated at some point in the past.

Now I have this: https://www.youtube.com/watch?v=sc9Zc30uss4 running pretty sweet except for the sneeze/cough/burp etc, seems worse at low revs.

Any idea what it is? I had previously seen this before the woes of the gaskets/overheating.. and I have had the carbs off for a cleaning... (not much of this engine hasn't been on my garage floor recently)

Thanks
 
Did you replace the deflectors / water guides in the block when heads were off.----Post your compression numbers.-----Sneeze is often caused by a lean condition.
 
Hi, nope I didn't know they even could be removed. Gave everything a very thorough cleaning though.

Haven't got compression numbers..yet, I'm guessing poor compression could cause the sneeze? Would you call it a sneeze from that video?

I have got a set of carb rebuild kits that I think might be wise to put on it.

Thanks
 
That sneezing condition is normally caused by a lean condition of at least one carburetor.

If that sneeze is more of a very mild backfire coming from the carburetor area.... with the carburetor face-plate removed and the engine running with that condition existing... stick two fingers into the carburetor throats, acting a a manual choke.

When the engine picks up somewhat and runs a bit smoother, you've found the offending carburetor.
 
​I dunno, I'm thinking a cylinder firing out of time. But it's hard to tell and I very well could be wrong anyway.
 
fdrgator said:
​I dunno, I'm thinking a cylinder firing out of time. But it's hard to tell and I very well could be wrong anyway.
Click to expand...

Yep, could be a blown diode in the pack causing two cylinders to fire at the same time, something on that order. I just like to get the carburetors out of the way first if possible.
 
Well in that case it could be that I've mixed up the cables going to the coil's and got 1+5 the wrong way around when I did the first gasket replace.. AFAIK its still the original wiring so the colours should be correct.. will also try that tomorrow
 
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