Mcm 170 bogging out

[tony-e]

I have a 1986 mcm 170 3.7 liter I took the boat out today and it ran fine . I went back to the dock and went home for a little when I got back on the boat and left the marina it ran fine for about 10 minutes then it started to lose power and kept bogging out and turning off. We just put a new coil, cap, spark plugs and the carb was rebuilt last year. So I am stuck on what it could be. Is it the timing or the carb is shot or is it something with points. I tried to run it at full throttle and I could only get the rpm to 3000 and it kept bogging out. Thanks for the help

 

[stonyloam]

Re: Mcm 170 bogging out

. We just put a new coil, cap, spark plugs and the carb was rebuilt last year.

You seem to have left out the one thing that should have been first on the list. Points! Regardless of whether or not they are the cause of the problem, points, timing and dwell are probably more important than all the rest combined IMHO. Are you getting spark when it dies?

 

[tony-e]

Re: Mcm 170 bogging out

You seem to have left out the one thing that should have been first on the list. Points! Regardless of whether or not they are the cause of the problem, points, timing and dwell are probably more important than all the rest combined IMHO. Are you getting spark when it dies?

I'm getting spark it just seems to lose power

 

[generator12]

Re: Mcm 170 bogging out

Tony, my 170 was acting just like you describe, except that it continued to degrade until she wouldn't even re-start. I eventually found that the wire to the tach was the cause. Disconnected it and she ran fine.

This wire checked out fine with a digital multimeter, too. No low resistance to engine ground, no discernable cross-talk between it and any voltage source that I could find - but it definitely caused my problem as I could bog the engine down by simply touching it to coil negative (it's normal connection point) and free it by removing it. I've been good since I replaced it. I suggest you try running without it.

 

[Motor Tech]

Re: Mcm 170 bogging out

Tony, You should start by making sure your fuel/water seperator is functioning properly and not full of water or plugged. Then see if the fuel pump itself is working too. A lot of people bring their boats in with similar problems and I'd say 50 percent of them are fuel related.

 

[tony-e]

Re: Mcm 170 bogging out

Is the water fuel separator generic or boat specific. Thanks a lot for all the help this is why I love this forum

 

[Motor Tech]

Re: Mcm 170 bogging out

Well, it can be boat specific. If its older, it might not have a seperator, just a filter located right under the fuel pump on the side of the block. Make sure it is supplying enough fuel. If thats ok, you could check the fittings and make sure they are all tight and not sucking air. Make sure the pickup tube in the tank has not come loose or fallen off too.

 

[tony-e]

Re: Mcm 170 bogging out

I changed the fuel water separated and check the points it ran good for around an hour I took it around the lake and ran it at 4000 rpm and then went full throttle and it started to bog out again and kept dropping rpm but not as bad as yesterday . It seemed when it warmed up than it ran crappy .so now Im thinking the carb is the problem it's beyond my repair knowledge so I'm having my mechanic take a look tomorrow

 

[nola mike]

Re: Mcm 170 bogging out

clogged fuel vent can also cause your symptoms. try unscrewing your gas tank cover next time it happens. oh, and change the points.

 

[tony-e]

Re: Mcm 170 bogging out

Here's is an update I pulled the boat and brought it to a mechanic he stated that the engine had to much oil and the carb needed to be rebuilt. The mechanic rebuilt it did the points the oil timing and dwell. I put it back in the water yesterday and it ran great for the whole day until I went to get fuel. I ran the boat at 4000 rpm and the engine started to do the same thing but not as bad as before. So I
Spent 500 on the mechanic and it's not fixed. I noticed when I trimmed out the Boat I noticed when I go the boat on plane I noticed when I hit the trim switch it would bog the engine out. When I got to the fuel dock the attendant said there was a lot of air in the tank. So is the fuel pump ignition or something worse? Thanks guys for all the help

 

[nola mike]

Re: Mcm 170 bogging out

When I got to the fuel dock the attendant said there was a lot of air in the tank. So is the fuel pump ignition or something worse? Thanks guys for all the help

Air pressure, like gushing out when you open the tank? If so, see my last post...

 

[Eric 3.7LX Alpha 1]

Re: Mcm 170 bogging out

Here's is an update I pulled the boat and brought it to a mechanic he stated that the engine had to much oil and the carb needed to be rebuilt. The mechanic rebuilt it did the points the oil timing and dwell. I put it back in the water yesterday and it ran great for the whole day until I went to get fuel. I ran the boat at 4000 rpm and the engine started to do the same thing but not as bad as before. So I
Spent 500 on the mechanic and it's not fixed. I noticed when I trimmed out the Boat I noticed when I go the boat on plane I noticed when I hit the trim switch it would bog the engine out. When I got to the fuel dock the attendant said there was a lot of air in the tank. So is the fuel pump ignition or something worse? Thanks guys for all the help

What exactly does that mean?

If you have a tank with 1/4 of fuel, the rest is filled with air. That's the way it works. When you fill the tank, the new gas added displaces the air that's in the tank, that's why you have a vent on the side of hull. The air leaves thru that vent as fuel is added, and air is sucked into the tank from that vent when your running the engine.

If the vent is not working(blocked), the engine will eventually draw enough fuel from the tank to cause a vacuum in the tank which the fuel pump can't overcome...... engine runs bad.

It does sound like fuel related, could have water in the tank if the vent checks ok. If you had gas in there over winter and keep adding to it, the water could still be in there.

 

[tony-e]

Re: Mcm 170 bogging out

Vent checked out ok ran the boat today and it ran great. Same thing happened when I went over 4000 and the engine would bog down but not stall. The tank was taken out of the boat over the winter so there is no water in the tank. My next thing to check is the fuel pump and the condensor. Any one have any other ideas

 

[Golflover]

Re: Mcm 170 bogging out

Following having my starter replaced, my 3.7 did the same thing about a couple years ago. Started great, but bogged down. I rebuilt the carb, checked for blockages in the fuel line, changed the distributer shaft, battery, gaskets, plugs, condensor, points, wires, connections to the voltage regulator,........... I think ultimately it was a ground on the transom side of the motor was not properly secured. I'm not sure if that's what it was, but the boat has never run better after that. It's worth the look.

 

[tony-e]

Re: Mcm 170 bogging out

more great news for me. while out on the lake doing a test run i started to smell something plastic burning so i opened up the engine hatch and saw that the voltage regulator was smoking really bad while im in the middle of the lake. so i called for a tow. now do i have to buy the voltage regulator or can i go with the conversion alternator kit.

 

[Eric 3.7LX Alpha 1]

Re: Mcm 170 bogging out

Do yourself a favor, get the conversion kit. Breezeworks.net sells em and many on here have their kit.