1986 90hp inline 6 - runs then quits

[Vairpilot]

I'll try to keep this as short as I can, here goes! 1986 90hp I6 came with a boat, was sold as 'in running' condition. After getting it home I found that wasn't the case. I have replaced the fuel pump diaphragm and gaskets, took the carbs apart, soaked them in carb cleaner, blew them out with compressed air, put new gasket kits in all 3 carbs, and new inlet needles and seats. It DOES run better than before, I can get it started, and it will run somewhat normal for 30 seconds or so, but will slowly fade and quit regardless of throttle setting. I can't get it running long enough to start adjusting the carbs or doing a link and sync. It is getting spark at idle and throughout various throttle settings. I also replaced the impeller and gaskets just to make sure she was running cool. I've tried getting it running from about 1 turn of the idle needle out to like 4, doesn't seem to change much. I'm sure it is a fuel delivery problem, but not sure where to go next. None of the fuel hoses appear to have any leaks.

Any help is appreciated, thank you all!

Don

 

[Bob37814]

Re: 1986 90hp inline 6 - runs then quits

Don, Hopefully someone will shed some light on this. I just got my 115 Merc going today and it does the same as yours, starts and runs, you can rev it up with the fast idle lever and play with it all day but cant seem to get it to idle under 1000 rpm w/o dying. When you completely shut the fast idle lever it will continue to run for around 10 to 15 seconds and slowly fade and die. Then you have to pump the bulb to get it going again....I think I may have a fuel pump issue

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Another ? on this engine... I have a crappy aftermarket manual for this outboard that doesn't have the answer for this. I'm guessing this is WRONG, but the #3 coil goes to the plug on cyl #4, and the #4 coil goes to the #3 plug. Is this actually correct, or did the previous owner screw this up too??

 

[Bob37814]

Re: 1986 90hp inline 6 - runs then quits

Good eye there cause that too is wrong the mine are wired 1,2,3,4,5,6 from top to bottom, as with the coils

 

[AMD Rules]

Re: 1986 90hp inline 6 - runs then quits

Yup... coils 1 through 6 should go to thier corresponding plugs. Double check the wiring form the coil to the switchboxes though, as they are arranged differently. 1,5,3,6,2,4 from top to bottom. You can see those green wires in the attached image.

 

[achris]

Re: 1986 90hp inline 6 - runs then quits

Try pumping the fuel primer just as the engine is starting to die. If it picks up then you have a fuel pump problem. I know that with those engines there are several different gaskets for the pump and they are only subtly different. You have to be sure you have the right one. Make sure the pressure/vac holes (in the back of the pump) line up with the ports on the engine block.

Chris..........

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Thanks for the info guys, I'm going to take a look at the motor late this afternoon and will post back here with what I find. Dying to get the boat wet!!

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Alright... I got to work on the 90 a bit tonight, including checking the timing with a timing light. Timing looked good, got her running, seemed to have plenty of power. After 45 seconds or so it would slowly die. Sounds like it is starving for fuel, it will slowly quit regardless of throttle setting. The carbs have new gaskets, all passages are clean, and the floats are set per the manual. Fuel lines *look* alright, everything is clamped down with no apparent leaks. Is there something I'm missing?

I had the lower end submerged in a 90 gallon tank of water, it blew about 2/3 of that out within a few seconds of putting it in gear, couldn't believe how much water it could move!

I know she has plenty of power, just not sure what to be looking for now since I've hit everything that I can think of. Almost thinking of getting someone else to look at it, but I already have a sour taste in my mouth from a local marina/dealer that told me all the ignition parts and carbs would need to be replaced. This was coming from a so-called 'master mechanic' that couldn't even get it started. I guess I'll just keep plugging away at it since having someone else do it would be admitting defeat!

The fuel bulb remains fairly hard after the engine quits, and pumping it doesn't seem to do much. The fuel pump parts were replaced a couple weeks ago, but I took it apart anyway to check the gaskets, all are lined up correctly with the holes in the crankcase.

Thanks guys for any ideas!

Don

 

[achris]

Re: 1986 90hp inline 6 - runs then quits

.....The fuel bulb remains fairly hard after the engine quits, and pumping it doesn't seem to do much.......

Start looking for a fuel supply problem. The bulb shouldn't remain hard, it should go soft quite a bit if the pump is pulling fuel. Check the fuel pump output pressure and flow. I'm betting a pump problem.... Recheck the direction of the internal check valves.

Chris..............

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Yes, it seems to be a fuel supply issue. Ignition is good, and no problem getting air, so that leaves the fuel supply. Just in case there is a pinhole or something, I'm going to rip the fuel tubing out and replace it, which can't hurt. Might get some clear stuff if I can find it so I can actually see what's going on. Will also take the fuel pump apart again. When I took it apart last night, plenty of fuel came out as I pulled the gaskets apart, so I know at least one of the check valves is working correctly to keep fuel from flowing back out of the fuel pump. Unfortunately I won't be able to work on it again until Thursday, so I'll post back after I check it out again. Thank you guys for your ideas!

Don

 

[anzomcik]

Re: 1986 90hp inline 6 - runs then quits

Ok, i hope i can help. I just got my 86 L6 90 running after no joke 4 months of working on it. i had it at 3 marinas and all i got was the normal run around...

Ok when you cleaned the carbs did you disasemble them, or at least pull the main jets and the screws you could get out, out? i had alot of junk hanging by my main jets that i thought were clean.

check you floats, this is somthign i over looked many times, make sure they are not filling up with gasoline. they will dry out if left out for a while and you would never know. if one has a leak replace all three they are a couple buck each.

Check and make sure you are getting spark out of the even and odd cylinders, i bought a spark tester that went in line of the plug wire it showed i had spark, but it took me a long time to think of having some one pull the rope (i did not use the electric start for many reasons, one being it hurts oh so bad) and look for spark, turns out i had a switch box going bad.

Some other things i did to make my run is i was having trouble with stalling above idle, bump up two sizes on the main jet. this gets more of the junk gas that are at the pumps these days in you rmotor it made a big difference for me. and i took out the back drag jets ( ithink thats what they are called on top of the float bowl) you do not need them. they lean out your mid range.

my motor might run a tad rich but i know i will not fry a piston.

I also made a leak down test to see if my motor had cylinder tapper to them, luck i was in good spec. but make sure you check the floats if they leak, pull the main jet and at least make a note of its size, make sure the gaskets are good. clean the carbs until you think they are clean then clean them again (it took me three times to get mine good, but my inboard tank was dirty for the first two times, my bad) have a clean gas tank. check spark

good luck

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

OK, I'm on to something here. Last night I thought I had a fuel delivery problem, now I *know* that is the case. Gutted the fuel pump, one of the check valves was leaking both ways, that was the one feeding the carbs. I also did some more reading and research and found that the spring that was in my fuel pump probably shouldn't be there. I'm guessing the previous owner installed it as part of a rebuild kit. I removed it, but will probably have to get a new diaphragm since the one I installed a couple weeks ago is nice and stretched.

Speaking of new parts, anybody know the part # for a check valve kit compatible with my 90? The only part # I could find was 2130430A14, but am having trouble actually finding a place to buy them. All the fuel pump kits have the gaskets/diaphragms, but no check valves.

I'll post back here after I get her up and running!

 

[achris]

Re: 1986 90hp inline 6 - runs then quits

Give me an engine serial number and I will reveal all.....

 

[achris]

Re: 1986 90hp inline 6 - runs then quits

The number you have, 21-30430A14, is the right number for the check valve kit. The valves themselves are not sold separately... Mrec's philosophy, and I agree with it, is that in order to change the valves, you have to strip the pump, and in that case, they want you to use new gaskets and diaphragms.

You'll find the kit available at 3Ws dot mercruiserparts dot com.... It's $30.67...

Chris.............

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Thank you for the info, I just ordered a kit. I'd agree with your position too, might as well replace all the parts and do it the right way. I'll let you guys know how it works out when I get the parts put in.

Don

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

PROGRESS!!! I had ordered the new check valve kit yesterday, but couldn't wait for it to arrive. I took the old check valves and tinkered with them until they worked reasonably well. Put them back in the fuel pump and buttoned everything up. Gave the bulb a couple squeezes and hit the enrichener for about 10 seconds. Turned it over, it caught right away and ran... and ran... and ran!! About all I could manage before was 30-45 seconds, depending on throttle setting. It idles well around 800 rpm, I'm going to take it to the lake tomorrow to work on it and do some tuning. When the new check valves arrive I'm going to install them, might take like 5 min of work. I'll post back tomorrow letting you know how it works out. Thank you all for your help and insights!!

Don

 

[Vairpilot]

Re: 1986 90hp inline 6 - runs then quits

Well, a positive bit of news today. We had the boat out for a couple hours for her first run with 6 passengers. Motor started up easily, idled well, and pushed us around the lake for a couple hours with no stopping. Not even a burp! I do need to do the link and sync, it isn't developing anywhere near full power, could only manage 3000 rpm at the most. However, while we were underway I was able to open the engine up and play with the throttle I could get it up to 4000 rpm or so. I think that part of the problem is the linkage adjustment, so I'll play with that. I tell ya, it was fun regardless! Have a great week all, I'll post back when I've had a chance to tweak the motor.