Timing vs. WOT

[FreeBeeTony]

I rebuilt my Mercruiser 165 IL6 last year, just bought it last year. It's pushing a '78 20' Grady White. When I first put it in the water I had a 19P prop on it and could only get up to 3200 RPM's. This is with a 1.65:1 outdrive. I had to go down to a 15P prop to get close to 4000 RPM's. I checked the tach and it is calibrated. How much of an affect does the timing have on WOT? Would a couple of degrees too far advanced make that much of a difference?

 

[Bhamil]

Re: Timing vs. WOT

Absolutely! Loosen the distributor hold-down clamp, start the engine and let it warm to operating temp. Slowly advance then retard the spark and listen to the effect it has on RPM, and you'll answer your own question. If your distributor is failing to advance with an increase of throttle you will certainly have limited RPM increase and you can test that manually. I advise buying a Clymer or SELOC manual and follow their test procedures for testing the distributor. Set the timing, point gap properly, and use a timing light to adjust to TDC, also following the books procedure. Oh, and be sure to follow the RPM requirements when you do this. After you've done the set-up, see what you get with WOT and post your results. One word of caution; if your engine uses an external cooling source, you're using muffs running the engine out of the water, be careful of the high RPM's and watch your temperature. You can regulate the temperature with the flow of water from the hose but the loading on the engine is not the same as it would be in the water, in gear, and under load. That's your best test platform; put the boat overboard, double up your lines, and run it at the pier if you have room and time. Post your results. This is just my opinion, other's might disagree.

 

[FreeBeeTony]

Re: Timing vs. WOT

I forgot to add that I installed a petronix electronic conversion kit. I know that the timing is advancing when accelerating.

 

[Buttanic]

Re: Timing vs. WOT

Unless you can determan exactly what the timing will be at wide open trottle stick to the stock setting. Overly advanced timing at light loads can help fuel economey but at WOT and high load it can cause pre-ignition and detonation which can destroy pistons. See the thread on timing.<br /><br />Buttanic<br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=24;t=004877

 

[daveswaves]

Re: Timing vs. WOT

Tony I answered your question in another section as well, I think your timing might be too advanced. Pay particular attention to the distributors thread that Buttanic posted, near the end of the thread there is a link to mercruiser bulletins and yes, our old distributors are there. Total advance on these old things kicks in at 2100 rpm. If you have too much initial advance you are going to hit the wall early....no top end. The method I suggested uses a vacuum gauge because you cannot see your timing marks.

 

[FreeBeeTony]

Re: Timing vs. WOT

Thanks again Dave. I figured I would start a new thread here to see if I got any other opinions. I am going to check the timing with a vacum gauge in the spring. I hope I can get the 'plug' out of the top of the manifold so I can install a nipple in order to check the timing using a vacum gauge. I also plan on installing a FWC kit.I hope you're right and I am too far advanced. So all I have to do is install a vacum gauge and using the distributor find the 'sweet spot' (the highest vacum reading) and back it off some? Is the amount of vacum affected by RPM's?

 

[daveswaves]

Re: Timing vs. WOT

Yeah Tony, you can only do it at idle, at WOT vacuum is zero.

 

[Buttanic]

Re: Timing vs. WOT

I do not recommend setting timing with a vacuum gauge. A vacuum gauge is used to set idle mixtures on carburators. You may end up with way too much advance using the vacuum gauge. Put a timing light on it, its the only safe way. Automobiles can usually get away with too much advance because they rarely run at high loads and RPM. Boat engines generally do run at high loads even thought the RPM may not. High load is anytime the throttle is wide open no matter what the RPM is. This is the time when detonation will occure if timing is too far advanced.<br /><br />Buttanic

 

[daveswaves]

Re: Timing vs. WOT

Hey Buttanic, I agree, normally I don,t reccommend timing with a vacuum gauge, in this case Tony has no timing marks. Given that this is a 30 year old engine technology I just offered a way to do it without the marks.

 

[Buttanic]

Re: Timing vs. WOT

It shouldn't be that difficult to put a pointer and a degree wheel on the pully and find TDC then remark the pully. If it is a degree or three off no big deal but if it ends up 10 or 15 off using the vacuuum gauge I see $$$$$ for an engine rebuild. Exactly what marks are missing. The mark on the pully or the tab on the cam cover.<br /><br />Buttanic