Fluctuating Vacuum Reading on 4-stroke

[Philn]

Thought I would check the sync of my carbs since my 65 HP 2001 4-stroke Merc was running somewhat poorly.
All four vacuum guages on my sync tool were flucuating rapidly from 15-0 at idle cold and same thing at fast idle warm.

Checked for any obvious vacuum hose rot, etc. all looks ok.

Engine idles rough but will achieve full rpm after some babying. Will cruise well at certain rpm's but at other throttle positions will surge at cruising speeds.

Any idea where do i go from here? I believe this engine has the Yamaha powerhead. Thanks

 

[ENSIGN]

Re: Fluctuating Vacuum Reading on 4-stroke

My vacu-mate does the same thing,it's never always steady I've considered changing to liquid filled gauges but haven't found them yet. Your running issue sounds like a lean carb,they have been a pain in the a## since day one.start by checking the gas for dirt and water,If you don't have a water separating filter put one on.

 

[Philn]

Re: Fluctuating Vacuum Reading on 4-stroke

Thanks, Ensign
I do have fresh gas/fuel filter/water seperator

Shop manual says carb sinc tool should be mercury filled.
So is wildly flucuating vacuum more a symptom of using standard vacuum guages (for motor cycle) rather than Merc's sync tool?

How can I get these carbs to run richer?

Should I start with complete carb removal and cleaning and see if that helps??

 

[CharlieB]

Re: Fluctuating Vacuum Reading on 4-stroke

Definitely start with a very thorough carb cleaning then link and synch following the directions in the factory service manual. Also ensure a complete tune-up is done, including new spark plugs, spark test, timing, and valve adjustment.

Vacuum synch sticks with a common mercury pool work very well but availability may be tough since EPA has limited mercury usage.

Any liquid will function, the height of the column is determined by the weight of the liquid used.

 

[Faztbullet]

Re: Fluctuating Vacuum Reading on 4-stroke

If the engine has set up a while you may have some varnish build up in carbs that will require removal and cleaning.Also if it is a 4-stroke(couldnt find 65hp 4 stroke)change the filters going into carbs(see picture) part #804195 as these can stop up and restrict fuel flow.