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88HP bogging down at 3/4 speed

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west500

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I have 1995 88HP that has recently began to feel like it had trash in gas line, because it would runs great at startup and seems as the engine got hotter it would bogg down like it was running out of gas, but I could increase the throttle and seems to run ok. I have replaced the spark plugs and fuel/water separator hoping this would correct, but it still does the bogging down. This problem seemed to start out as a small miss only once in my fishing trips and has got worse on each trip fishing. The carburator and fuel pump has never been checked.

Has anyone had problems similiar to mine and what suggestions do you have in repairing. Thanks in advance for the help.

West 500
 
These motors have a history of breaking the piston rings.------Myself I test compression first before looking at anything else.----Once the overall condition is established you can do other trouble shooting.--------Have a 135 HP Mercury V-6 right now to be rebuilt.----Lowest compression was 85 PSI and highest was 120 PSI.--------The higher reading one also had a scored piston.
 
west500 said:
I have 1995 88HP that has recently began to feel like it had trash in gas line, because it would runs great at startup and seems as the engine got hotter it would bogg down like it was running out of gas, but I could increase the throttle and seems to run ok. I have replaced the spark plugs and fuel/water separator hoping this would correct, but it still does the bogging down. This problem seemed to start out as a small miss only once in my fishing trips and has got worse on each trip fishing. The carburator and fuel pump has never been checked.

Has anyone had problems similiar to mine and what suggestions do you have in repairing. Thanks in advance for the help.

West 500
Click to expand...

Most likely you have a carb problem. Make a couple basic checks though first to be sure you aren't wasting your time.

Check compression; I'm not sure but I think that's an engine that will only be ~90 PSI. Difference in highest to lowest cylinders is the most important factor (ballpark of 10 PSI is good). There is a compression gauge available at Auto-zone for like $25 that will do the trick.

You can isolate the fuel pump as a source by keeping the primer bulb tight (not so tight as to force gas through the carbs, just enough to keep the bowls filled) while trying to reproduce the "bog". If it won't bog when playing with the primer bulb then your fuel pump is not involved. Based on your description it does not sound like the fuel pump (would not normally get better as you increased throttle with a bad fuel pump).

Take a quick look a the way the carbs open/shut, be sure when you open the throttle the butterflies all move in sync.

If the above checks out as not the issue, get a repair manual, the repair kits, and clean/rebuild the carbs. This is something to be expected at least every 5 years under perfect conditions; for some it's probably needed every couple years. While you are at it - flush out the fuel lines and replace the filter on the engine itself (to assure if you have any crap in the fuel lines it will not re-infect your rebuilt carbs).

There is a chance this behavior is due to something being out of sync (throttle/timing), but since you are saying it's getting worse, it's probably the simple common issue of clogged carbs.

Jon
 
I should probably add in no way am I saying that "good" compression means there isn't a scoring problem, as racer points out.

I've seen awfully ugly cylinders that still produced "good" compression; just those engines also ran OK as do most with "good" compression.

Jon
 
I had technican check my engine and found broke ring. I guess I will just trash this motor. I had to put a piston in this same engine in1998.
Thanks for all the help.
West500
 
I wish I would have mentioned your advice to the technician which could have saved me some money. The technician went into the engine after a check of low compression on one cylinder to find a broke piston ring. I will probably have a big bill of his work and nothing to show. I am not going to do any repair to this engine at this time.
Thanks for the post
West 500
 
Should not have taken more than 20 minutes to determine the broken ring / cause for low compression.----Only 6 small screws and the bypass cover is off to inspect piston and rings on the cylinder with low compression.-----Nothing to this at all in my book.
 
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