'72 merc 1150 reed flutter

[monk-monk]

Still trying to figure this out...I had this powerhead professionally rebuilt last year. It runs good at low and mid RPM's, but when i try to open the throttle wide open it will go into a muffed kinda sound and it starts blowing gas out of the carbs. I can only run at about 3/4 throttle, anymore and it starts blowing gas...I have to pull way back on the throttle and basically start over throttling up again. All obvious things have been gone through, new internal electrical harness, complete new fuel system (except for the gas cans) carbs rebuilt per my Mercury manual specs for float lever clearance etc. Prop is original to the motor (17 pitch i believe)...timing is 21 max advance...What could be going on here??

 

[monk-monk]

Re: '72 merc 1150 reed flutter

Haven't gotten any replies to my post yet...figured i give it a little bump and see if anyone had any ideas...just can't get all the top end without blowing gas back through the carbs..

 

[Laddies]

Re: '72 merc 1150 reed flutter

After 1500 RPM the reed valves are wide open against the stops, reeds only function at startup and low idle. The flutter thing is BS.

 

[monk-monk]

Re: '72 merc 1150 reed flutter

Thanks Laddies...thats good news to me! I've been thinking about this very hard, i think the first thing i need to do is get a new up-to-date Tach (im using the original Mercury Thunderbolt Tach that plugs into the MerController) and i feel certain it's not 100% accurate and i need to know exactly what RPM's im hitting when this is happening...with the tach im using now, this problem starts at around 4200 rpm's at 3/4 throttle...Im getting a dial indicator to make darn sure where TDC is...i have put a timing light on it several times and it indicates 21 degrees max advance...Im beginning to wonder about prop slip/under propped resulting in over reving...COULD this be a possibility...??

 

[Dave1027]

Re: '72 merc 1150 reed flutter

Blowing gas sounds to me like a carb flooding problem.

Can you give specifics? What exactly is the problem? How do you know it's blowing gas out while you are cruising? Are you missing top end? Have you done a compression test?

What's a "muffed kinda sound"? I would actually like it if my motor was muffled at wot. I don't like to rev it because the damn thing is so loud. I cruise at 4200 rpm because the noise is bearable at that point. Any higher and it begins to roar.

 

[Laddies]

Re: '72 merc 1150 reed flutter

A fuel plume in front of inline carbs is quite common, over propping or the engine not making maximum RPM could make it worse under propping usually won't cause your problem.