Performance Boats Forum banner

1 - 6 of 6 Posts

·
Premium Member
Joined
·
5,115 Posts
Discussion Starter #1
Hey guys could somebody explain to me the difference in a dizzy with advance in it vs one that is locked ??

And why would you won't to run one vs the other??

Thanks
 

·
Living in a cage of fear
Joined
·
16,462 Posts
A locked distributor has no mechanical or vacuum advance capabilities.
Where you set the timing with the light is where it stays.
I've had a couple Vertex mags, neither had advance mechanism.

Most performance type boats/ Engines do not run at lower RPM's.
It isn't like a car where you pull through the RPM's gear after gear.

On mine, I have mechanical advance only. (It's in a Miller Jet, 454 BBC)
It has the lightest springs, and the biggest stop bushing in the MSD kit.
That gives it about 14* of mechanical advance.
Initial is 22*, basically just for starting it.
It is all in by 2200 RPM +-, at 36* total. (As soon as you give it throttle, all the advance is there)

So our boat would run no different with a locked distributor and the timing set at 36*, but might be a little rough starting, I've never tried it.
 

·
Registered
Joined
·
383 Posts
blower motors with there low comp. will turn over & start @ 32-36 of locked timing, try starting a mild built n/a motor @ 36* of locked timing, vacuum adv. only works on your car when you back off the throttle a little bit driving down the road, thats why you don't use it in boats. you want as much initial timing as possible when you start it & the mech. puts the rest (32-36) in asap.
 

·
Registered
Joined
·
4,318 Posts
N/A motors with larger cams thrive on as much timing @ idle as possible. As timing is advanced rpm increases, closing the throttle plates to get idle rpm helps keep the carb running on the idle circuit.
More timing @ idle also increases throttle response from idle. The only need for mechanical advance would be in a situation where running full advance @ cranking speed causes timing stall when starting the motor. MSD has a crank retard deal for their boxes. I'm on a budget,I run a stock type dizzy, limit mechanical advance to about 10* and run the advance springs loose enough so it runs -10 @ crank speed and full advance @ idle.
 

·
Premium Member
Joined
·
5,115 Posts
Discussion Starter #5
So witch is better in a jet boat??? My 540 is locked and the 477 is not

477 is a 1/4 miler and the 540 is a lake boat. Both engines turn over and start fine. 540 is locked at 33*
 

·
Registered
Joined
·
8,169 Posts
Answers....

So witch is better in a jet boat??? My 540 is locked and the 477 is not

477 is a 1/4 miler and the 540 is a lake boat. Both engines turn over and start fine. 540 is locked at 33*
IMO, the timing "curve", or lack of one, is all about driveability..... In a normal "grocery getter" vehicle the timing adjusts it's self to engine "load". This is still true today with computer controlled systems.. In our boats the engine seldom really "sees" a load like trying to move a 2 ton vehicle across an intersection from a dead stop. Because of that, we really don't need the fine tuning of the timing like you would in a car/truck.... When you hammer a jet boat, the motor gets "happy" pretty quickly, meaning the RPMs overcome the load almost at the "hit", so we don't need to "crutch" the motor. As far as starting the engine with a lot of advance in the initial timing, some guys prefer to use the available "retard" devices to save the starter and ring gear.... You can also use a separate switch to "light" the ignition after the engine is already cranking with a button. (you must disconnect the ballast resistor "by pass" wire from the starter solenoid) In your case(s), "if it aint broke don't try to fix it".....
Ray
 
1 - 6 of 6 Posts
Top