140 HP Merc bogs, pings at high rpms

[drivin79]

I'm new to owning a boat, but have been around boats all my life. Since owning the 1985 170 wellcraft american as of april i've noticed after taking it out about 4 times that at high rpms at wot it bogs down and drops rpms and then raises back up to higher rpms then does the same thing over and over again. It idles fine and at about half throtle is fine, just as wot it does this. It will do this for a couple of minutes, then run fine, then start doing this again. After having to take it in to have it serviced for a leak in one of the bellows, i had the carb rebuilt and gas tested. Gas check ok. I put new plugs, wires, dist. cap and roter, anti siphon valve on fuel tank. Still has the same problem as listed above. Only thing i have left to do is change the fuel filter. Its hard for me to belive that the fuel filter would cause this problem. Maybe so... I'm thinking it could be the timing... or to rich/ lean. But how do I adjust the timing, find out if its right or wrong and adjust the mixture? Secondly on to the pinging noise... is this backfiring through the carb? Any suggestions. Am I totally off on the time, etc. I need all the help I can get.

 

[danond]

Re: 140 HP Merc bogs, pings at high rpms

To adjust timing all you need is a timing light and a wrench (and some basic instructions from the service manual). Sounds like you need to do that. Pinging can wreck your engine really quickly.

Backfiring through the carb would cause the engine to stumble really hard. You'd hear a pop vs a ping.

Change the fuel filter next. It's cheap and easy and sounds like you need to do it anyway.

 

[bruceb58]

Re: 140 HP Merc bogs, pings at high rpms

If you are running lean, that will cause you to ping. Although you really need to check your timing, it's more than likely a lean condition causing your problems,

 

[danond]

Re: 140 HP Merc bogs, pings at high rpms

Especially if he's starving for fuel at higher RPMs.

That pinging sound is your pistons being whacked at the wrong time (too early) by the exploding fuel. Kinda like hitting it with a hammer on the way up instead of a good push on the way down.

 

[drivin79]

Re: 140 HP Merc bogs, pings at high rpms

Well, to distinguish from the pop or ping, its probably more of a pop, I really dont' know what a backfire through a carb sounds like so i'm assuming that what it is. I don't have the original owners manuel for the boat/ motor, does anyone know where I can get one. I know I can print one off from the well craft website but I don't think that covers anything with the engine. I'll change the fuel filter today and get a timing light and see how that goes. I'll keep you guys posted.

 

[drivin79]

Re: 140 HP Merc bogs, pings at high rpms

well, I put the new fuel filter in, didn't help a bit. Still does the same thing, at wot it surges and occasionly backfires through the carb. I guess I'll check the timing when i get a chance. Any other suggestions?????

 

[bruceb58]

Re: 140 HP Merc bogs, pings at high rpms

Still sounds like it is leaning up. May want to run it off an external tank as a test to make sure it is not tank related.

 

[ken_23434]

Re: 140 HP Merc bogs, pings at high rpms

How many fuel filters does your boat have? By default it will have a fuel filter INSIDE the fuel pump and a strainer inside the carb at the fuel inlet. Most people will add an inline water separating fuel filter prior to the fuel pump.

A clogged fuel filter will cause the engine to starve for fuel (run lean) at higher RPMs, and this lean condition will cause a pinging noise.

In the "--Adults Only Sticky--" at the top of the forum, there is a link to download (for free) the genuine Mercruiser Service Manuals. No need for any other manuals.

 

[drivin79]

Re: 140 HP Merc bogs, pings at high rpms

I'm getting a timing light to check the timing. When I took it out last weekend i think i have confirmed that the pinging is really a poping. Back fired through the carb. Yeah, you are correct, one fuel filter inside the mechanical fuel pump and a strainer in the carb. No other fuel filters. I do need to get a fuel/water seperator filter installed. I know they replaced the fuel strainer in the carb though, when the mechanic rebuilt the carb. I'll try the alternative fuel tank and see if that might solve the problem. Here's the question, if it happens to be that the original fuel tank is causing the problem, what do I do to replace it/ clean it out? With as old as the boat is, I wouldn't be surpised that there is all sorts of crud sitting at the bottom of the tank. Thanks for all the help guys!!! I appreciate it!