90HP Mercury backfires and loads up

[mainline4you]

Sorry if this is a duplicate, but I looked all over and couldn't find my answer. Anyways, I have a 1988 Merc 90HP. For awhile what would happen is that if you were running at a constant low to mid speed it would seem to load up and would chug for a couple seconds or more to get going when you throttle up. Been happening for years. The other day I was going full blast and the moter stopped like it ran out of fuel. I switched tanks and still wouldnt start. Primed and choked and still nothing. Half an hour later it fired up and ran like a champ. The next day I went out again. Running fine for a bit - then started spitting and died. This time however I was able to get it fired up again using the choke. Went to the dealer and asked for help and what they told me was the primer bulb and fuel pump gaskets were updated for everything prior to 2000. So I installed the new pump gaskets, primer bulb, fuel filter and cleaned the carbs (which were suprisingly clean). Fired it up using the hose in my driveway. Fired up right away not even using choke, but was only running on 2 holes. Shut her down, checked the plugs, fired up again - now was running on all three but backfireing every 5 seconds or so. Water?<br /><br />I plan on running this on the lake soon, but I guess I would like to know if you think there is something deeper than what I had fixed. Also, the air screws are at 1-1/4. I seen reports that have them turned all the way to 4. Can that be right? Anyways, feedback is welcomed since I really dont want to get stuck on the lake again with a dead motor. Was there something else I had to do with the fuel pump other than rebuild it and slap it back on? Also, the oil should flow in there right away once it starts, right?

 

[technostingray]

Re: 90HP Mercury backfires and loads up

Is this an inline 6? Sounds suspicious like a problem similar to one discussed earlier.

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

This is a 3 cyl.

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

UPDATE: I took my boat out tonight, after replacing the fuel filter, primer bulb, rebuilding the fuel pump and cleaning the carbs. Still dies after about half hour or so. I checked the primer bulb right away and it was soft. Tried starting and would only start on choke, but even that was a bear! When it WAS running, I played with the throttle and it would only stutter when giving it full - but then it just quit like I took its gas away. After awhile to get it running again, I was able to limp back to the dock, and if I tried to give it throttle again it would puke. Maybe I have completely the wrong train of thought here on thinking its gas related, but boy does it sound like it. HELP PLEASE!!!

 

[andrewkafp]

Re: 90HP Mercury backfires and loads up

Check the wires coming from the trigger to the switchbox for continuity as they can get corroded inside. The method I have used is a probe and test light at either end of each wire.

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

Checked the wires and all is good. Suprisingly all the wires on the switchbox were like new and tight! This is bumming me out. One thing - should the fuel bulb remain hard even after the motor is running or will it go soft? I guess I never thought to check it before.

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

Ok, heres another question. Judging from what I have already posted, and the reply about the switchbox and the trigger, will the symptoms I have explained be consistant with one of these items crapping out? I have spent a bunch of times looking at others posts and cant quite find one with the same things going on. Ones that are close, have ended up changing one of these things or the stator - but I cant believe its the stator since all holes should stop sparking at once and thats not whats happening with this one. This motor will die after a bit, but will pop and eventually run again, even if I cant throttle up off idle.<br /><br />I guess why I'm asking this is that I have a blown powerhead that I can get parts from that the electronics should all be good - like the switchbox. I dont have a puller for the flywheel however and only want to pay the 90 bucks for it at a last resort if I need to get to the trigger or stator.

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

Yet another question: I went through the manual and did the trigger tests which all came within limits. I did find that the white/black wire comming from the trigger had the insulation cracking and small peices were comming off. Could this cause the motor to shut down when warm and act normaly when still cool?

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

Anyone?

 

[Clams Canino]

Re: 90HP Mercury backfires and loads up

Trigger does not have a black/white wire.<br /><br />-W

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

It was a wight wire with a black or very dark tracer. According to the wireing diagram I have it was a black tracer.

 

[jrampey]

Re: 90HP Mercury backfires and loads up

Are you running this motor from a portable tank? Check the vent if so... If it if screwed shut you will build a vacuum in the tank resulting in fuel starvation. Small leaks allow it to limp along and restart after some time and run - until the vacuum eturns

 

[mainline4you]

Re: 90HP Mercury backfires and loads up

Yes I have two 6gal portable tanks I use, and when one tank is being used, the vent screw is made sure to be open. More I think about it, it's gotta be a heat/electrical thing. It takes around 20-30 min for it to die out and a bit longer to get it running again good. But then it dies out within a couple minutes again. So is it at first since the motor is cool it takes awhile to get hot - something happens and it dies. Then it cools down a bit, fires up, runs, heats back up and dies again. Could that cracked insulation on the wire from the trigger cause this sort of thing?<br /><br />One more thing, I have a clymer manual I use that covers all 1972 to something like 1989 40-225HP motors. (Im at work right now trying to remember the exact models covered - thats at home). I have a 1988 Merc 90 HP 3 cyl and looking at the books wireing diagrams, I am supposed to have 2 switchboxes and different colored wires. When I look at the 70hp diagram it is an exact match. anyone else run into this?