Hey guys I have an old fishing boat that I acquired cleaning some land for a barn, "cut a tree down here and there and what do you see?? A '72 Bonanza Boat that's what!!" .......... The boat has a 72 or 73 Mercury 650 3cyl outboard on it. I've made it run, rebuilt the carbs, new impeller, fuel lines, etc.... My question lies with the timing. On the side of the engine there is a sticker that reads "timing 23 degrees BTDC" Is that the timing at Idle or WOT? The motor has a distributor that moves (advances?) when throttle is moved forward. The flywheel has timing marks from TDC to around 30 BTDC on it... Any ideas?? Idle seems extemely high when timing at idle is around 23 BTDC only way I can seem to bring it down is to retard the timing..

Thanks Guys
Brian

 

Usually, its at idle.

from other carburated engines I have worked on as long as the timing is close, it will run fine, it might take a little tweaking to get it to run its best.

btw, I have a merc 700 of about the same vintage.

for more info, parts and help try www.oldmercs.com

 

Say there Fronty Owner,I see that you were able to use that link I sent you.
Lots of info there huh?
I agree that he can find whatever he needs there.Ron G

 

Are you sure it is at idle. That seems like a lot of initial timing to run at idle. So when the vaccum advance kicks in, what will it go to? Timing light, and rev her to around 2000 and see what it reads. Most timing advance has come in at 2000-2500 rpm.

 

Kinda what I was thinking. If I set timing at Idle at 23 BTDC then when at WOT and the timing "self advances" the timing wont even show up on the timing marks?!?! way too far over the limit... So I am guessing that 23 BTDC is a max spark advance for full throttle.. So going on this (could be completely wrong) what should I set the timing at at Idle?? close to TDC??

Thanks Brian

 

do a search on google for that model engine and all. See what comes up. Surely the specs will be there somewhere. If all else fails, call a local boating place that sells the stuff. They ought to be able to at least look it up in a book for you while you wait on the phone. But honestly I am thinking around 7* of timing initially, but I do not know how far the dizzy advances. Maybe try it at top dead center and see if it will crank and run, then idle up to see how far it will advance. When you get it revved, and see where it advances to, just subtract that from 23 and that should work for your initial timing. Then re-check it after setting that and see if it advances to 23*.

 

I think 23* at idle is a little much......that would advance A LOT when running it up in the RPMS!!! I'd start with maybe half of that at idle and see how it runs......if it runs like crap then adjust it some more and see what happens???

The thing that kinda boggles me, is why would anybody every want to set the timing when the motor is reved up high.......seems weird to me!!!! You would think it should be at idle....but who knows......some people are goofy when the build stuff!!!


~Nick

 

Well you have to remember that on a vacuum advanced system there are two timings. there is initial timing which is for starting and idling purposes. Then there is advanced timing for when your engine speeds up and runs at the higher rpm. Almost all older ford engines had vacuum advanced distributors. When the engine increased rpm, the vacuum in the intake was greater. A vacuum line would be attached from the disributor to a port on either the carb or intake. This vacuum would pull the internals of the distributor as to advance the timing so that the spark would come in at a more opportune time that would yield a better and more efficient burn.

This is a common practice that a lot of auto makers used. And I guess outboard makers did to.

Note: Most racecar engines are locked out at the timing needed for peak RPM power. Like on a box you see it say such and such intake 1500-6500 RPM. Most builders will lock out the timing to that it is at the point where it is most beneficial at 1500 rpm so that it is used in the power band that the parts were designed for.

 

Yeah that is true.........but you'd think that by setting the first timing before it advances would set the secondary timing after it advances. Everytime I've timed a car it's always been at idle and everything worked fine!?!?!?!?!

I'm not timing guru so I really don't know a whole lot about it.........so I could very well be wrong, just seems weird to me but so do a lot of things!!!!LOL



~Nick