spark advance on a 86 350 with thunderbolt ignition

[lime4x4]

Having some power issues on a 1986 searay with a 350 4bbl carb engine. Tonight i was checking timing. Base timing is set to 8 deg when running the engine at 2000 rpm's i aimed the timing light and i had to adjust the dial to 30 to get the mark lined up with 0 deg on the timing tab. According to the mercruiser manual at 2000 rpm it should be around 12 deg advance.

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

You should be seeing 20? at 2000 rpm, not 30?.
The charts don't add in the initial timing in degrees, so you have 8? plus 12? = 20?.
Check the ign. amplifier connections.

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

okay then i actually have 38 deg at 2000 rpm. If the connections check out could it be a bad ign. amplifier?

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

okay then i actually have 38 deg at 2000 rpm.

No, if you are seeing 30? with your timing light, you subtract 8 from 30 which means you actually have 22? of advance at 2000 rpm, not 12.

Yes, if the wiring is ok, it's probably the amplifier going out.

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

you think with it advancing the timing that much at a low rpm would cause the following. When floored the engine tachs up to 3500 then it takes almost 2 minutes to go from 3500 to 4000 rpms. My max rpm that i can get is 4100 rpms.Motor was replaced 2 years ago. Just did a complete tune-up. I've had this problem for the last 2 years. The other night i decided to check the timing advance

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

When floored the engine tachs up to 3500 then it takes almost 2 minutes to go from 3500 to 4000 rpms. My max rpm that i can get is 4100 rpms.

Are you using the trim at all, or are you just running it with the drive all the way down?

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

start off with the trim all the way down. Till she gets up on plane. even if i trim the drive up all the way no rpm change. She planes at 3800 rpms.New alpha drive unit,correct prop no growth.When in neutral the boat tacks up past 5500 rpm.It just seems when under load she maxes out at 4000 to 4100 rpms. Thats why i was looking at the ignition advance .

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

When in neutral the boat tacks up past 5500 rpm.

It'll probably go a lot higher than that, no rev limiter. but checking rpm in neutral is a non test and is meaningless. You could do that with only 4 cylinders firing.

correct prop

How do you know that? You should be seeing between 4200 and 4600 rpm.

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

Have you looked at the Adults only sticky at the top of the forum, at the list of causes of WOT?

 

[cooter2506]

Re: spark advance on a 86 350 with thunderbolt ignition

I personally would do a compression test also. I had same rpm numbers on my old boat and turned out it had two cylinders at 30lbs remaining six were at 150lbs. But if you go to the adult stickys section at top of page there is a whole list of reason for no WOT. good luck to ya.

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

yes i read the sticky. compression is 125 to 130 all cylinders.the prop is a mirage plus 15 3/4 X 15 which all the prop selection tools show as correct and i've talked to other people who own a 268 searay weekender and they use that prop with good results. carb was rebuilt last year.The only thing different is that i run a marine grade electric fuel pump

 

[J. Mark]

Re: spark advance on a 86 350 with thunderbolt ignition

What is your fuel pressure at the carburetor with the electric pump?

How is your fuel consumption?

If the timing is not advancing properly your engine will not produce normal power. Have you looked at the plugs to get a reading on how the engine is performing?

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

plugs look clean.I haven't checked fuel pressure since i installed the electrical pump.I have fuel flow gauge installed and i know once on plane and engine running at 4000 rpm the gauge is showing 15.4 gallons per hour

 

[Bondo]

Re: spark advance on a 86 350 with thunderbolt ignition

Ayuh,... Just a Shot in the Dark....

This thing hasn't run Right since the new motor,... How,+ What happened to the Old motor,..??

If there was an Overheat involved,...The shutters melted,+ are Clogging the Y-pipe.?.?.?.?.

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

when we bought the boat it had a blown motor. 3 rod bearings went out on the original motor. Replaced block with a newer one that didn't have a provision for a mechanical fuel pump.I guess i'll have to remove the y-pipe and verify nothing is in there

 

[Don S]

Re: spark advance on a 86 350 with thunderbolt ignition

I guess i'll have to remove the y-pipe and verify nothing is in there

Slow down and think, you're jumpinig to conclusions.

First, you have to remove the engine to remove the Y pipe and check it.
Why don't you just pull the drive and look thru the exhaust bellows into the bottom of the Y pipe.

Back to your prop. Just because all the books, and prop charts and other peoples similar boats may say that is the right one. You boat may be heavier or something. Try a lower pitched prop.

120 to 130 is not great compression for a new engine. 140 to 160 range yes, but not 120 to 130.

 

[JustJason]

Re: spark advance on a 86 350 with thunderbolt ignition

It sounds like your on the wrong plug wire, or your firing order is messed up. Are you sure you don't have 1 and 3 backwards or something to that effect?
Double check your fireing order wire by wire.
Aside from messing up your timing (especially if numero uno is switch with something else) If you had just 2 of the wires on the wrong cylinders your not going to hit WOT.

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

i'm in the process of looking for a 15x13 prop.To c if that helps. I did look thru the exhaust tube before and i saw nothing laying in there

 

[J. Mark]

Re: spark advance on a 86 350 with thunderbolt ignition

The reason I asked about fuel pressure is that an electric fuel pump can produce a lot more pressure than a mechanical. If your pressure isn't regulated down to about 6-7 PSI the carburetor can't handle the pressure and fuel blows past the seats and you can never get it to run properly as it is always rich and will remain down on power. It is an easy check and even if it isn't the primary problem it will be something that needs to be verified to prevent chasing down imaginary gremlins.

Is timing supposed to be 8 degrees BTDC and is it set at 8 degrees ATDC by chance?

 

[lime4x4]

Re: spark advance on a 86 350 with thunderbolt ignition

i'll check it out but i doubt if that's it.If the pump was putting out more then 7 psi then the engine should run really rough at an idle plus my fuel flow at idle is 0.84 gallons per hour. Since it'a an electric fuel pump the flow is constantly the same. But it never hurts to check