74' Bayliner 250 Chevy WOT nothing

Hey guys I have a 74' bayliner with the Chevy 250 6 cylinder. Last year the boat ran great, this year it won't go past 2,500 rpms. From 3/4 to wide open the rpms stay the same, whether the boat is loaded or not. I replaced the fuel line, filter, cleaned the fuel pump bowl, cleaned the carburetor, replaced spark plugs, cap and rotor look good, points and condenser look new and I adjusted them. I'm stumped. Please help

Look under the plate the points are mounted to.
Most likely the mechanical advance has frozen and the counter wieghts are not moving and advancing the timing.

Awesome I didn't even think of that I will try that! IF they're frozen what should I use to lube them? I have a few different greases and dielectric grease as well. Thanks!

first get them unfrozen if they are, then I would carefully remove them and scotch bright them clean and then reassembly with just some wd 40 or similar. light coating nothing extreme. Just don't break the springs..............!!!!! CAREFULLY!!!!

So I pulled the distributor cap and plate, the weights were pretty free...I lubed them and tested it and still low on power. With 6 people it'll hit 3000 rpms but no more. On take off it'll hit 2500 and slowly climb to 3000. I have a timing light and want to checj it, what should it be set at and what rpms to set it. Also is there a procedure for doing the timing, I know its mechanical advance so I figured just rpms set then time it in.

Connect to plug wire 1 close to spark plug. Adjust diatributor to set timing mark at 6-8 degrees btdc.
When running the timing should advance to about 30 degrees total..that would be 6 initial + 24 advance from counter wieghts.
If not the timing then what is the comression of each cylinder?
Maybe the motor is tired?

Based on your description the only other issue could be lack of fuel...

That's exactly what I've been thinking I'll get it timed and see what it'll do. I cleaned the carburetor, installed new fuel line with filter, flushed fuel tank, cleaned fuel pickup tube, now all I need to do is a compression test and a leakdown if the compression is low. Can I run a timing light at wide open throttle to check the mechanical advance? Thanks for the help I appreciate it.

That's the next thing to try. All you have to do is blip the throttle, in neutral,l to about 4,000 rpms. The advance should be all the way out by then.

Jeff

PS: That isn't one of those ignition systems where you have to ground a wire to se the initial advance? If so, the motor is timed way retarded.

I think that Jack nails it.
No gasser will reach it's optimum performance if the ignition lead is not correct.
Now.... we're talking about the Progressive and Total Advance.... not simply the BASE advance.

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mogas said:

So I pulled the distributor cap and plate, the weights were pretty free...I lubed them and tested it and still low on power. With 6 people it'll hit 3000 rpms but no more. On take off it'll hit 2500 and slowly climb to 3000. I have a timing light and want to checj it, what should it be set at and what rpms to set it. Also is there a procedure for doing the timing, I know its mechanical advance so I figured just rpms set then time it in.

Click to expand...

OK.... we have two camps here:
1.... those of us who like their digitally advancing timing lights and have complete faith in them.
2.... those of us who would rather see Real Degrees in Real Time.

I'm one who wants to see Real Degrees/Real Time.

If you're in my camp, you'll want to mark off your harmonic balancer up to approx 35* BTDC.

Two methods:

a... with the known diameter of the harmonic balancer, pick up a Mr. Gasket degree decal and install it.

b... make a circle template and layout a 35* spread and transfer this to the balancer OD.

At the exact radius of your balancer, use a compess style scribe, and set it at the 35* spread.
Transfer this over to your balancer OD from the OEM TDC notch towards Port side.
(see image below for the scribe method)

Now go back and set this for 5*.
Now transfer 7 of these 5* spreads over to your balancer OD until you reach the 35* mark.

Now your balancer is set up for Dynamic timing testing.

The ignition system doesn't care if the engine is loaded or not.
Increase RPM as you strobe the timing marks using #1 cylinder for the timing light's sensing.
Watch what the advance is doing at intervuls of 500 rpm.

Plot this out on graph paper throughout the RPM range up to approx 3,200 RPM.
This is your dynamic ignition curve.... and it will include BASE advance.

Compare this to your OEM specs.... be sure to add the BASE advance.

mogas said:

Can I run a timing light at wide open throttle to check the mechanical advance?

Click to expand...

Your concern is NOT what the advance is doing at WOT RPM.
Your concern is what the progressive and total advance are doing from just above idle RPM up to approximately 3,200/3,400 RPM.


Edit:

BTW.... set your contact points using a dwell meter.... point gap is an estimate only of correct dwell.

Make sure that the distributor shaft busings are good.... no wobble.... wobble will throw the dwell out of whack.

Im in the real timing light camp no digital advance. I gapped the points at 18 thousandth. I have an old dwell meter it has two wires and a plate. I thought setting the points gap was all I need to do. How do I check dwell. Do I check it after base timing is set?

Don't sweat messing with the the dwell if the points are set at the correct gap. You MUST get the base timing set right, then eyeball the mark as you jazz the throttle to see it move.

Jeff

The ignition system on your 6 cylinder engine is given 360 degrees of distributor rotation in which to fire all 6 cylinders.
In other words......... 360 degrees of distributor rotation in which to saturate (charge) the ignition coil, and then to discharge the high voltage to each cylinder within two full crankshaft revolutions.

This means that for each of the 6 cylinders, the ignition system contact points are given a 60 degree angle to do this.

Of that 60 degree angle, a portion is dedicated to coil saturation (points closed).
This is the dwell angle.

The remaining portion (points breaking) is given to spark firing and coil cooling.

At 1,000 rpm, this occurs 3,000 times per every minute.

Engineers have determined what the dwell is to be (per engine) for best performance.


Also, with a dwell meter connected, you will be able to see whether or not the dwell angle remains constant as engine speed is increased.
A ratical or unstable dwell angle represents a worn distributor shaft, etc, and will cause performance problems.

Setting gap only, will not let you see if all is OK.


Like said..... setting point gap is an estimate only of correct dwell angle.

Roll the dice if you prefer.:rolleyes:


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