Spark/Fuel Mercury Rookie. Help!

[davejohnson]

Hi from Georgia. I just acquired an antique boat with a 1978 Mercury 900 inline 6. Runs fantastic, even wide open when connected to the earmuffs & hose, but stalls immediately when in the water and any load whatsoever is placed on the motor. Starts back up fine, but stalls again on the first turn of the prop. Thought it was bad spark: changed spark plugs, no change. Clymer book says bad spark symptoms sometime mean bad fuel pump. Is this possible? Is it a big job to rebuild fuel pump? Thanks for helping out a rookie.

 

[andrewkafp]

Re: Spark/Fuel Mercury Rookie. Help!

Don't run motor WOT on muffs, as it can cause damage. Just run it a @1200rpm. Is your fuel pump a single external type or (1 per carb) "integral" type. The external pump is quite easy to rebuild, you need to make sure that it is the thing causing the problem. If could need a carb rebuild. Be very careful of "Lean condition" on these motors as it can cause detonation.

 

[tmcalavy]

Re: Spark/Fuel Mercury Rookie. Help!

Do a compression check. Then check the fuel system from tank to carbs. Uni is right bout external fuel pumps, not hard to do at all. Could be that or varnishy carbs or maybe timing and carbs aren't in synch. The FAQ forum is a good way to diagnose. Good luck.

 

[2cycle]

Re: Spark/Fuel Mercury Rookie. Help!

You may/probably have your idle speed settings set too lean for proper acceleration. My inline 150 did the same thing and I had to set the idle mixture scres on each carburetor at around 2-3 turns out. The maual will give a detailed explanation of the procedure, but I found that it works best setting them at the lake as opposed to on the hose. Just do a search for idle mixture and you should find volumes on here to supplememt Clymer. Good luck.

 

[davejohnson]

Re: Spark/Fuel Mercury Rookie. Help!

Thanks to all for responding.