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Question for Joe

G

gradywhiteman

Contributing Member
Joe, on my last post my question was about rebuilding the powerhead if needed, I have since put the boat in and have been running it. I was told by the mechanic where I had taken the boat to not go over 4000rpm or it will probably stall out, to this point at 4000rpm or over it runs fine. My biggest problem now is occasionaly stalling at low speed (1500rpm or so) when we are trying to get into the slip. It starts back up quickly with a little choke applied but always seems a little rough at that rpm. Is the weak cylinder responsible for this or can it be fixed by replacing some ignition parts, changing filters, plugs, etc. ?
 
I hate to see a post with no answers so....Joe posted a little while ago that he was taking a break from the forum for a bit. If you could put a little more information out on your problem maybe someone else can assist.
 
Thanks for your reply. As I mentioned it runs great from about 2000 rpm and beyond but it has a skip under those rpm,s. I was just looking for suggestions for probable cause. It seems the more we use it the stalling at low rpm goes away. Any idea why that would be?
 
In the water while leaving the harbor, usually about 1100 rpm,s. Another thing I noticed is a little harder to start if not run for a couple of days.
 
The engine is a 1987 225 Johnson, all that was done was a compression test by a local mechanic who told me I would need to re-build the power head. Before I go out and buy any parts I was looking to get some opinions on the problem. If it is the cylinder that is weak then I will use it as it is for the remainder of the season, but if could be something else I would try to fix it.
 
I had and older 65hp with a bad cly, when you put it in gear it stalled if you did not get the rpm up to 1200 right away and seemed to run fine above 1500rpm. I replaced the piston and it ran like new. About a year later the mtr blew a rod thru the side of the crank case, found some of the rubber gas line deteriorated and plugged up the jet in one of the carbs - leaned out the mix at full throttle, so if you are going to fix the mtr relace all the gaskets and fuel lines- take an old fuel hose let it dry out and then bend it- you would be suprized what may fall out.
 
A couple of questions...which cylinder is low in compression? How low is it? The problem could be something simple like a blown head gasket or something not so simple like a hole in the piston.
 
Looking at the back of the motor it is the lowest cylinder on the right. The compression on that cylinder is 60#, all the others are 95 to 100.
 
Pull the head off and take a look at the head gasket. Very possible there's a a bad gasket...at the very least, you'll be able to look at the cylinder wall, piston, etc. I wouldn't keep running the engine until I did the above.
 
The boat is in the water but with the engine tilted up I can probably take the head off to check the gasket. Looks like a fairly easy job, I would have to get a new gasket. I don't have a manual yet so would you know the torque specs and tightening sequence for the job?
 
thanks for your reply, the mechanic I took the boat to earlier in the season said he de-carbed it would that be the same as the sea foam treatment?
 
Yes, the seafoam treatment decarbs the engine. It's usually pretty easy to pull the head, even on a salt water engine, but it might be pretty difficult to pull the head with the boat in the water...can you put it on a trailer? Yes you will need a new head gasket and you should torque the head 18-20 foot pounds.
 
I will have to make the repair in the water most likely as my trailer is not registered. (that's a whole other story) I think I can do it without to much of a problem. By looking at the old head gasket how can you tell if it is bad?
 
Look at the gasket carefully in the area around the cylinder that's got low compression. You can generally tell if there's "blow by". Also check the look of the piston top...if it looks like it's been steam-cleaned compared to the others, that's also a good indicator of a blown gasket.
 
You can also pull the plug on the bad cylinder and see if there are small bits of shrapnel deposited on it. Also, if you bring that piston toward the top, you should be able to look at it through the plug hole using a good flashlight. Or, you could borrow one of those new-fangled bore cameras that will allow you to take a look inside.
 
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