Even stumped my mechanic (update)

[TenE307]

motor: 1991 100 hp 2+2<br />problems: 1) i have to disconnect the fuel line to get from 4100 rpms to 4800 rpms at wot.<br /> 2) 4th spark plug wont get dirty.<br />compression: 1-105 2-105 3-100 4-100<br />jets: 052 (i live at 6000 ft elev)<br /><br />this weekend i have tried to get some sign of black substance on #4 spark plug. cleaned the carb completely. checked the float and all was okay. #4 gets fuel and spark. checked the reed and no signs of cracking or breaking. i was at the mechanics most the day on sat and we tried all we could think of. he sent me home to rebuild the carb. sun hooked it all up tried some quick fast revs to see if i can get 3&4 to fire. #3 comes out like it runs in a 2 stroke, while #4 looks like it is still the brand new one i put in sat morning.<br />This has got me (and my mechanic) stumped. any help or other tests to run would be greatly apreciated!

 

[Laddies]

Re: Even stumped my mechanic (update)

A lower crank seal can give that kind of problem and a loose sleeve will drive you nuts, they will move around at higher RPM

 

[WillyBWright]

Re: Even stumped my mechanic (update)

It may be getting too much gas in #4. If it's too rich, it won't fire just as readily if it were too lean. Liquid gas would leave the sparkplug clean as a whistle. Besides the carb, there are two other possibilities. The fuel pump could have a diaphragm leak, or the #4 accelerator injector could be leaking. It's also possible that you have weak spark on #4 and it'll spark on an indicator and not under compression in a cylinder.

 

[TenE307]

Re: Even stumped my mechanic (update)

THANK YOU! i love this place! my town has only one cert marine mechanic and when this is stumping him, i always know i have here to try for other input.<br />we cleaned and inspected the accelerator injector this weekend. no prob (that we could see) other than i forgot to put the spring in the first time i put it back together. i rebuilt the fuel pump last year before my rebuild project started. ill take it back apart and see if there is any pin holes.<br />is there a way to test the amount of spark?

 

[emckelvy]

Re: Even stumped my mechanic (update)

The fact that it picks up nicely when you disconnect the fuel line is a Very good indication of overfueling in #4, as WBW stated.

 

[TenE307]

Re: Even stumped my mechanic (update)

If i remember correct. when i replaced the fuel pump last year, there was part of the pump that runs off of the pressure from the 4th cylinder. if there is a hole in that area, that has to be my problem. which would be the reason for having too much fuel and it sure looks like there is no oil in it. i am going to take the fuel pump apart tonight. that has to be the problem. THANKS AGAIN!

 

[TenE307]

Re: Even stumped my mechanic (update)

well i took apart the fuel pump. all looked good. i hooked up the (IN) fuel line and plugged all the three other holes and pumped away from the primer bulb. no fuel came out the port hole like i was hoping it would. i have tried all i can, any other ideas?

 

[wilde1j]

Re: Even stumped my mechanic (update)

You asked about checking spark. There are adjustable gap spark testers you could buy, but it's not hard to make one. You should get a clean blue spark over ~ a 7/16" gap if all's OK.<br /><br />I made one years ago for testing up to 4 cylinders at a time. Really easy to make one for a single cylinder at a time.

 

[TenE307]

Re: Even stumped my mechanic (update)

my mechanic set my plugs up on a board that made the arch jump about 1/2". i was thinking, i know that means trouble, when i rebuilt the fuel pump last year. on the two inner baffles the manual shows a rubber and a plastic circular flaps. when i bought the new fuel pump bebuild kit it only had the clear plastic circular flaps. could this be a result of me getting too much fuel?

 

[boatdoc]

Re: Even stumped my mechanic (update)

ibelieve the pump does use #4 for pressure,a defective diaphram would be the best thing to check

 

[boatdoc]

Re: Even stumped my mechanic (update)

i stand corrected,u should have had 2 black rubber discs in the kit also...the clear ones mount on top of them

 

[TenE307]

Re: Even stumped my mechanic (update)

i just called a marina that had the fuel pump rebuild kit in stock and they told me that there was only two circular plactic disks in the kit and there were no rubber circular disks at all. man this has got me so confused!

 

[clove]

Re: Even stumped my mechanic (update)

The rubber ones are no longer needed. I believe the reason Mercury has left them out is that due to the contents of todays gas they were out sooner than using just the mylar(plastic) ones. I rebuilt mine this year and have had no problems. <br /><br />Good luck!!!!

 

[Vlad D Impeller]

Re: Even stumped my mechanic (update)

I dunno, i bought a diaphram kit from Nappa, and it had both, the plastic check disc and the check valve rubber disc.<br /><br />I once tried using the plastic disc only and the pump did not function well, on another forum i was told that some pumps works just fine without the rubber valve disc and some don't <br /><br />Why not try it like boatdoc said, it works for me <br /><br />boatdoc <br />Member # 16605 posted July 26, 2005 11:04 AM<br />--------------------------------------------------------------------------------<br /> i stand corrected,u should have had 2 black rubber discs in the kit also...the clear ones mount on top of them

 

[Moody Blue]

Re: Even stumped my mechanic (update)

Agree with the above that BOTH the black rubber disk and the clear mylar disks are needed. The rubber acts as the seal and the mylar provides rigidity or acts as a backing plate.<br /><br />The instructions that came with my kit didn't even show or mention the rubber disks. When I took apart the pump both parts were there so when I rebuilt, I flipped over the rubber disk and installed the new mylar disks on-top as was the original setup. I then aquired a factory manual that showed BOTH pieces are to be installed. Glad I followed my instincts. Motor has run perfectly now for 20+ hours. I don't understand how some kits include the rubber discs and some don't. The kit I got was straight from Merc

 

[TenE307]

Re: Even stumped my mechanic (update)

so if quicksilver doesnt put the rubber ones in the fuel pump rebuild kit, who does? do all napas carry the same stuff? i am going to go to my mechanic again this afternoon to see if we can figure something out. i would try to use my old rubber check valves, but the reason for the first rebuild was becasue they were sucked through the holes in the fuel pump. is there any way to tell the difference between pumps that work with just plastic check valves and ones that work with both rubber and plastic ones?

 

[gss036]

Re: Even stumped my mechanic (update)

http://www.mercurypartsexpress.com/...ection/ServiceParts/PartSelectionframeSet.asp <br />Get the Sr# from/for your motor and look up the parts here and you can even order here and they give you a slight discount also. The peace of mind is, that you will get the proper parts. Some mechanics think they know it all and they too, don't realize that they to can make mistakes also. I paid mine to change heads gaskets 3 times, when I need thermostats, I asked why he had done them while he was doing the head gasket,"you didn't ask for them" OPPS! I now do my own,.

 

[TenE307]

Re: Even stumped my mechanic (update)

well i tried to take it to the mechanics yesterday, and he was too busy to look at it, so i did the next best thing. i took it to the lake and tested it. i rebuilt the fuel pump with some homeade rubber gaskets. cleaned the carbs. inspected the injector accelerator. the boat still runs the same as it did before. 0-2900 rpms does not affect the motor when i disconnect the fuel line. 2900 all the way to WOT makes it a whole new motor when i disconnect the fuel line.

 

[TenE307]

Re: Even stumped my mechanic (update)

i pulled my new spark plug in #4 and it has some darkness in the electrode, but the edges are clean as can be.

 

[dsrchamp04]

Re: Even stumped my mechanic (update)

i agree with laddies.