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Top speed twin 318bs 30 ft silverton

Can you rev past 2700 in neutral? Is your problem only under load?

If your problem is only under load then I still suspect a fuel delivery issue. Check to see if you have anti siphon valves and if they're getting stuck.

-JJ
 
I can rev past that at idle... New Fuel Pump and filters.... siphon valve no clue what or where that is. I do doubt fuel issues I'm going to pop open the dist and check the advance mechanism.... thoughts?
 
under load I max out at 2900/3000..... but it has not been maintined well prior to my purchase... So i have done alot to this boat
 
The easiest way to check for the advance working properly is with an "advancing timing light" (that you can borrow from Auto Zone). You MUST see a change in advance of at least 20 degrees between where the mark is idling. Now, with the motor at 3,000 rms, adjust the timing light (approx 20 degrees) to put the mark in the SAME place and read what that is. Again, it should be around 20 degrees. If it's only 10 or so, the advance is sticking.

If so, it's time for the "famous" Fastjeff Distributor Repair Method: Remove the cap, get comfortable down there, and then flip the rotor all the way and release it--then repeat this for a minimum of 5 minutes. (Put a few drops of oil UNDER the rotor on that felt wick first.) Then retime the motor.

Jeff
 
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Jeff,

Doesn't the advance operate the same regardless of engine load conditions? If he's getting rpms in neutral but not under load, would you still suspect distributor advance?

-JJ
 
Is it just one motor giving you problems or both? An anti siphon valve is a one way check valve that stops fuel from siphoning out of the tank uncontrollably in the event that the fuel line is ruptured. They are usually located above the pickup tube at the fuel tank. See the circled valve in the image below. Ignore the arrow. If this valve is stuck partially closed or is clogged with junk from the tank then it can starve your motor under load at elevated engine speeds.

247565.jpg
 
Ok so the springs looked shot but there were to.diffrent sizes amd the larger one didnt.do.anything just moved freely. So I replaced one of them and noticed a significant difference. According to the instructions on the springs replacing both advances timing at 1600rpm instead of replacing one where ot advances at 2600... To me makes no sense
 
Holy crap! I just saw the photo of that rusted distributor! It's gotta be the problem.

Jeff

PS: Same one I have. Mine was sticking, and it was spotlessly clean compared to that one!
 
i just replaced one spring since for some reason the instructions on the slring said only replace both for streeet racing didnt make much sense. mzybe tmmrw ill replace both. i lubed everything so it moves more freely. it got better just windering about the other spring
 
Where did you find your stationary mark? On the front of the motor or the bell housing? I can't find a stationary mark on either place on my 73 318.
 
Whats with the mechanic bashing right after the thread hijacking? I WAS interested in the numbers for a twin screw 318 silverton

Your talking to mostly mechanics BTW,

your problem is obvious like jeff said,COMPLETELY rebuild that dist.
 
maxxumnys said:
what kind of max RPM's should I be seeing?
Click to expand...
This is where you'll need to look at your OEM specs. I'd not guess at this, I'd look up what the OEM recommends.

sandkicker said:
"4000 RPM WOT = heavily loaded engine
4400 RPM WOT = lightly loaded engine

Max cruise RPM 75 to 80% MAX WOT
Spoke to an engineer at Chrysler marine many years ago on this issue. Engine life a WOT is measured in hundreds of hours. Engine life at 80% WOT (as I recall) 2000 hrs... At 75% WOT climbs to 3000 hrs. (assuming FWC) All these hours assume engine can reach specified WOT RPMS
(closer to middle, the better)."
Click to expand...
Good info!
WOT RPM is not intended to be an operating RPM..... it is a test RPM ONLY!

fastjeff said:
Yes; that boat should plane IF the motor is running properly. Either it is not, the prop is wrong, or the bottom is needing cleaning.
I suggest you put a timing light on it and see if you are getting full spark advance AND full retard; it's common for the advance mechanism in those distributors to stick. If they stick advanced--and someone times it that way--then you won't get full advane and the motor will be a dog at full throttle.

Jeff
Click to expand...
Bingo! As usual...... smart man! :)

jp253 said:
Jeff,

Bottom newly painted, timing has beem done t times but.i.dont know.that anyone was aware of what you were talking about.
1.... How can check mechanical advance manuelly?
2.... Id like to do that before i start prop shoping
Click to expand...
1.... JP, you cannot check this manually.
You'll need to perform a dynamic advance check by strobing the timing marks while the engine is running..... and not only at low speed, you'll need to increase RPM as you jot down the numbers.
Your critical RPM range will be where the ignition discontinues to advance. This will be your "Full-In" RPM, and it must meet OEM specs! (yes, the specs that are apparently non-existant:mad:)

Then you can plot this out in graph form and look it over... perhaps post it here.

2... No successful WOT RPM test can be performed until this is done. It just doesn't work that way! I/B's or I/O's... it doesn't matter.
It's just plain physics!


.
 
Apparently I missed these earlier.

jp253 said:
This is the dist i have... is this a mechanical one?
View attachment 5023
Click to expand...
Yes, that is Chrysler's VR style triggering ignition with a mechanical advance unit directly underneath the plate.

jp253 said:
Ok so the springs looked shot but there were to.diffrent sizes amd the larger one didnt.do.anything just moved freely. So I replaced one of them and noticed a significant difference. According to the instructions on the springs replacing both advances timing at 1600rpm instead of replacing one where ot advances at 2600... To me makes no sense
Click to expand...
The two flyweight return springs are always of two different spring tensions, and size appearance.

These control a very sensitive load against the centrifugal force at the flyweights.
IOW, these completely control not only the amount of centrifugal advance, but when it occurs in terms of "crankshaft angle" and RPM.
Spelled "Advance Curve"!
Springs that may be too heavy, do not pose detonation potential, but definitely cause performance issues.
Springs that may be too light, DO pose detonation potential..... and this is why I generally suggest the following:

Be very careful when replacing these springs without the aid of distributor machine, or at least the knowledge of how to check this "On-Engine", and with your OEM specs on hand!
It can be done!

Many owners have never seen piston detonation damage, and don't give it much thought.
2 or 4 degrees at the distributor, is 4 or 8 degrees at the crankshaft.
As little as 4 degrees off, in favor of too much/too early, can cause marine load ignition induced detonation, and it ain't pretty.

DetonationFailure01.JPG


JJDebeers said:
Jeff,
Doesn't the advance operate the same regardless of engine load conditions? If he's getting rpms in neutral but not under load, would you still suspect distributor advance?
-JJ
Click to expand...
Simple and short answers.... YES and YES!
Engine load makes no difference as to how/when the mechanical advance begins the progressive and offers the TA.
A no-load engine will increase RPM even while the ignition is not advancing adquately.
Under load.... different story, and is often why igniton advance is brough into the mix as a potential for the problem!

Many simply look to fuel, fuel filtration, carburetion, compression readings, etc., and give little to no importance to correct ignition timing, other than BASE advance.
We've got to look past our noses!
(this in not aimed at any member..... it's just a general statement)


jp253 said:
i just replaced one spring since for some reason the instructions on the slring said only replace both for streeet racing didnt make much sense. mzybe tmmrw ill replace both. i lubed everything so it moves more freely. it got better just windering about the other spring
Click to expand...
Nine times out of ten, these spring kits are intended for automotive us, not Marine.

Again, see above caution regarding changing these return springs.


JJDebeers said:
This thread is chaos. Let's stick to one person and one issue at a time so we can actually get something done.
Click to expand...
Agree!
Let's apply this to ALL threads!

.
 
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