'90 15hp Merc. starts then stalls HELP

[swfl mike]

I bought the motor about a month ago and when the seller went to test run it, it was cold and it took a few pulls (5-10) and then it fired up and ran fine. I pulled the carb, took it apart and the fuel pump parts and carb seals/float looked like they'd been replaced not too long ago. I sprayed it with cleaner then blasted it with an air compressor.

I got the LU back today from getting re-sealed and put everything back together and tryed to fire it up in a bucket:

All my fuel lines are brand new, new tank open vent, good gas, I played with the choke, idle speed screw, and carb lean/rich adjustment for about an hour. Fuel filter is clean. New plugs. The best I could get it to do is fire up for for 10 or 15 seconds it would run fine then make a puff noise from the exhaust and stall out.

Can anyone diagnose my issue or point me in the right direction? Should I buy a cheap compression checker and check the comp.? Should I try and dunk the carb in fluid over-night?

Thanks for your responses

 

[Laddies]

Re: '90 15hp Merc. starts then stalls HELP

The carb still is plugged, probably the idle pickup tube, take it apart and use some spray carb cleaner and blow it all out.

 

[swfl mike]

Re: '90 15hp Merc. starts then stalls HELP

Thanks yeah I was still suspicious of the carb. The pin that gets pushed up and down by the float was getting kinda stuck in the up position. Not sure what that pin does or if it would be detrimental to carb operation???

I'll go pick up a gallon of carb cleaner and let it soak for 24hrs then blast 'er with the air sprayer; hopefully it'll do the trick

 

[Barnacle_Bill]

Re: '90 15hp Merc. starts then stalls HELP

That pin (needle) is what regulates the fuel coming into the carb. It must work freely. After cleaning properly, reassemble using new gaskets, needle and seat.

 

[swfl mike]

Re: '90 15hp Merc. starts then stalls HELP

The gaskets, float, inlet needle, etc. seemed to be fairly new looking. When the inlet needle was sticking in it's slot I wasn't sure if that was a bad thing, now realizing that it was i assume it was some gunky old gas that was keeping it from working

Do I need to buy a rebuild kit even though the parts I have look fairly newish?

 

[will941s]

Re: '90 15hp Merc. starts then stalls HELP

Don't know if this will help, and i'm no expert by any means. The kit is the same as a 25hp and I have cleaned my carb every year and replaced the kit in them every 2 years. I clean the carb with cleaner and compressed air, clean all the parts and inspect the needle, if it sets and falls freely I keep it and if don't I replace it. No doubt gum in the carb makes the you want to put a sledge hammer to the powerhead. Everytime I rebuild the carb I have to do a total link and sync on the motor. The same exact problem your having. Start and die. I can clean the carb and it will will run just fine, but if I rebuild it, link and sync. I have no idea why a carb kit totally screws the adjustments, but I have to readjust everything...even timing. After that, it'll run like a champ. I am going through the same thing right now as I speak. I pay a tech $85 everytime I rebuild it to make sure everything gets adjusted right........don't want to a lean condition to kill the powerhead.

 

[swfl mike]

Re: '90 15hp Merc. starts then stalls HELP

I should probably search this but I'll ask anyways... what's a link n sync? I'm gonna get a rebuild kit because I need reliability. It sounds like I need what your talking about aswell it is a 20 year old motor and it sat for many years

 

[swfl mike]

Re: '90 15hp Merc. starts then stalls HELP

Alright I somewhat looked into what a link and sync involves.


*Do I need a repair manual to do a link n sync on a single carb little motor?

*Is it difficult? I mean would I be better off paying a tech as opposed to buying a manual and attempting it myself?

*I'm fairly mechanically inclined. If it's not too complicated of a procedure, what does a shop manual usually cost?

Thanks again,

 

[will941s]

Re: '90 15hp Merc. starts then stalls HELP

I'm sure if I mess this up someone will chime in, but I will try. A link and sync is idle mixture, set along with throttle position, along with timing. All these things need to be at the right setting for the motor to run right throughout the power band from idle to full throttle....with out running too lean or too rich (thus fouling plugs from being rich or destroying cylinders from being lean). You can do it yourself, with a manual, timing light, and water to test it in......not muffs. I've never done the procedure myself, I've always had it done but I believe if you have all the above mentioned items and some know how you can do it. If you attempt it and need help, there are plenty of real experts on this forum that can guide you in the right direction. Good luck and you have a great, bulletproof motor.

 

[will941s]

Re: '90 15hp Merc. starts then stalls HELP

Oh yea, Merc manual....$9 or $10 Ebay used, about $35-$40 new. Worth the money.

 

[swfl mike]

Re: '90 15hp Merc. starts then stalls HELP

Cool thanks