1972 merc 1150 timing/fuel issue

[monk-monk]

Need some advice! I have a '72 merc 1150 and heres whats happening: I put the boat in gear and throttle up, it comes out of the "hole" pretty good, it runs good at low and mid throttle, but once im on the fly i still have more throttle remaining on my MerControl so when i advance the control lever towards the max point of throttle it will start spitting gas out of the carbs and it nearly kills the engine...I have to pull back on the controller to stop this fuel spitting out the carbs...its like it hits a certain RPM and then blow-back from compression occurs at the carbs...Im very knowledgable of carbs and have rebuilt them per my mercury manual specs, so i don't think its a carb issue, more like a timing issue where cylinder compression is getting blown back through the carbs...and heres something i find strange, though my max timing advance is 21 degrees, when i put a timing light on it at idle...the timing mark on the flywheel shows up WAY passed TDC (retarded)...but max advance still shows up at 21 degrees BTDC when performing the link and sync...

 

[DHag]

Re: 1972 merc 1150 timing/fuel issue

Sounds like over-advanced timing to me. Or possibly the reeds aren't closing properly at speed. Do you know the timing specs for your motor?

I just timed my '78 150 using the Merc manual for it. If it's like mine (probably is), then there are multiple adjustment points. Here's the process for mine. Yours is probably similar, with slightly different specs.

-- Take out the plugs. Insert a dial gauge into #1. Turn the flywheel to put #1 on TDC (top dead center). Zero the dial gauge.
-- Turn the flywheel backward until the gauge moves about a half inch, then bring it back forward until the dial gauge reads 0.462". Funny number, but that's what the book says.
-- On the front of the flywheel cover, move the timing mark to match the ".462" mark on the flywheel. This is the "zero" timing point.
-- Put in the #1 plug, and attach a timing light to it.
-- Take the throttle loose. Turn the idle speed adjusting screw way out. Press the idle timing screw against its stop.
-- Crank the engine and check the timing. On mine, adjust the timing to 7.5-8.5 degrees ATDC.
-- Open the throttle, and push the max idle timing screw against its stop. Crank the engine and adjust this screw to get specified max timing. On mine, that's 18 degrees.
-- Disconnect the timing light.
-- Sync the carbs: Loosen the carburetor shafts' screws. Adjust the idle speed screw until it just touches the carb rod cam. Tighten the carbs' shaft screws.
-- Open the throttle to WOT. Adjust the WOT throttle screw so the carb rod cam has about 0.010" of free play.
-- Install the rest of the spark plugs.
-- Hook up the throttle to the control. Fire it up (on water or on the hose), and adjust the idle speed.

 

[monk-monk]

Re: 1972 merc 1150 timing/fuel issue

Thanks DHag...Im still at a loss here...it just seems like when i try to get the rest of the throttle it just kills the spark then starts blowing gas out of the carbs...the prop is correct original...I can get up to about 3700RPM and when i ask for more it just wants to shut down...it's like the ignition gets confused and the motor just goes into a funny muffed kinda sound.

 

[Catarama]

Re: 1972 merc 1150 timing/fuel issue

Well hot dog - I thought I was the only one in the world with this problem. Here's what mine does - it starts fine, runs fine, I mash down the throttle and it's quicker'n a scared Chihuaha out of the hole. BUT to get it to max out, I have to pull the throttle BACK to where the economizer collar used to put it. I gain 200-300 RPM by doing so. Going back to WOT just loads it up when it seems to me that such a move should have no effect if the throttle was mashed down to begin with. I'd wonder about altitude effects but it acts the same at near sea-level, and when new in '72 the throttle and economizer worked as expected. The timing was checked but that assumes the mechanic knew how to time & (more importantly) adjust the electro-fuel system on a 6-cyl Merc. Anyone else out there have something similar? If so, please tell me how you fixed it. It's probably a trivial thing but I just like machinery to operate as intended.

 

[monk-monk]

Re: 1972 merc 1150 timing/fuel issue

Im still examing/troubleshooting this Catarama...i get my 1150 to about 4000 RPM's and still have plenty of throttle...timing set at 21 BTDC...and any more throttle and it will go into a muffed sound, spit gas out of the center and bottom carbs...then you have to reduce throttle, let the motor gain its composure, then you can go again...

 

[Chris1956]

Re: 1972 merc 1150 timing/fuel issue

You may have reached max power with that propeller. What kind of boat and what kind/pitch prop. Is the motor trimmed to max? Up on a jackplate?