89 Volvo Penta AQ271C ignition or carb, maybe something else

[Dillon36]

Update from this weekend
-New ignition module (dizzy) = no change,
-New carb = No change
-Removed Rev limiter = No Change
-Distributer tested good

still 2800 rpm, no secondaries.

 

[Scott Danforth]

compression is good and equal across all cylinders

what are the compression numbers? should be 140-150 psi across all cylinders

secondaries wont open until the RPM's get up over 3500 RPM

what props are you running on the boat. should be B2's or B3's

 

[Dillon36]

what are the compression numbers? should be 140-150 psi across all cylinders

secondaries wont open until the RPM's get up over 3500 RPM

what props are you running on the boat. should be B2's or B3's

Compression was about 147 on all cylinders, I don't know the prop size off the top of my head other then it's duel prop and was running great all summer, then one day all this happened.

I'm going to try a new coil again and retrace all the plug wires but I'm getting to a loss.

 

[Scott Danforth]

147psi is good

are your plugs black? if so, you could have a blown power valve (from a backfire) or the fuel tell-tale hose is full of fuel indicating a bad fuel pump

can you smell the engine burning rich?

what is your timing set to? should be all in at 32 degrees BTDC at about 2800 RPM (its on the decal on top the carb)

 

[Dillon36]

147psi is good

are your plugs black? if so, you could have a blown power valve (from a backfire) or the fuel tell-tale hose is full of fuel indicating a bad fuel pump

can you smell the engine burning rich?

what is your timing set to? should be all in at 32 degrees BTDC at about 2800 RPM (its on the decal on top the carb)

We had fouled plugs before adding the new dizzy but now they look good. Our Carb Mech installed a new power valve last week along with a new fuel pump. I checked the timing again yesterday and it's spot on with the sticker and tech info on the engine over, No backfiring or sputtering at all. Just wont go?

 

[Dillon36]

We had fouled plugs before adding the new dizzy but now they look good. Our Carb Mech installed a new power valve last week along with a new fuel pump. I checked the timing again yesterday and it's spot on with the sticker and tech info on the engine over, No backfiring or sputtering at all. Just wont go?

Is the

We had fouled plugs before adding the new dizzy but now they look good. Our Carb Mech installed a new power valve last week along with a new fuel pump. I checked the timing again yesterday and it's spot on with the sticker and tech info on the engine over, No backfiring or sputtering at all. Just wont go?

perfect running up until 2500-2800 RPM, then just lays over.

 

[Scott Danforth]

Is the

perfect running up until 2500-2800 RPM, then just lays over.

check the fuel pressure. may be easiest to remove the fuel line and drill a 1/8 NPT port in the Y-block (its a steel block with 3 holes drilled into it and the 3 lines brazed in place)

you can also get another bowl inlet plug and plumb the fuel gauge there

 

[Dillon36]

check the fuel pressure. may be easiest to remove the fuel line and drill a 1/8 NPT port in the Y-block (its a steel block with 3 holes drilled into it and the 3 lines brazed in place)

you can also get another bowl inlet plug and plumb the fuel gauge there

Ugh, what a pain

 

[Dillon36]

Ugh, what a pain

I'm going to try a new anti-siphon valve since its a quick check.

 

[Scott Danforth]

Ugh, what a pain

you have to do the diagnostic work to know what is going on.

being "all of a sudden" I would lean toward bad fuel or blown power valve or bad compression.

 

[Dillon36]

you have to do the diagnostic work to know what is going on.

being "all of a sudden" I would lean toward bad fuel or blown power valve or bad compression.

Correct, I have good compression, new power valve, and good fuel.

 

[Lou C]

OK you have a Prestolite BID unit, correct? I believe that those have mechanical (centrifugal) advance just like the points distributors did. Have you verified that the advance unit is in fact advancing the timing the specified amount the the specified RPM? They have centrifugal weights that can rust up and stick. There is (at least on the points distributors) a lubrication wick in the distributor shaft, you just oil it with a few drops of motor oil each year to keep it working right. Pull off the rotor and look...
you can see it in this pic....
you need an advance timing light to check this....I have this ancient Sears Craftsman one from the '80s...

 

[Dillon36]

OK you have a Prestolite BID unit, correct? I believe that those have mechanical (centrifugal) advance just like the points distributors did. Have you verified that the advance unit is in fact advancing the timing the specified amount the the specified RPM? They have centrifugal weights that can rust up and stick. There is (at least on the points distributors) a lubrication wick in the distributor shaft, you just oil it with a few drops of motor oil each year to keep it working right. Pull off the rotor and look...
you can see it in this pic....
you need an advance timing light to check this....I have this ancient Sears Craftsman one from the '80s...

Yes,that was one of the first places i looked. I even removed the entire unit and had it tested at a distributor shop.

 

[Dillon36]

Does anyone have a picture of the timing mark on both the harmonic balancer and the block? I have a sticker on the balancer

 

[Scott Danforth]

Does anyone have a picture of the timing mark on both the harmonic balancer and the block? I have a sticker on the balancer

You have timing tape on the damper. It's used to validate full advance the groove is TDC or 0

Timing tab is standard SBC. The big V is TDC

At 2800 RPM, your total advance should be 32 or 34 (see decal on vanity cover)

 

[Dillon36]

You have timing tape on the damper. It's used to validate full advance the groove is TDC or 0

Timing tab is standard SBC. The big V is TDC

At 2800 RPM, your total advance should be 32 or 34 (see decal on vanity cover)

Yes, I understand the setting and what the tape is used for.. I just want to make sure I’m reading the setting correctly. I have not seen a label like this on my other boats.

When at 3k rpm the green area of the sticker in dead center of the largest notch on the timing finger, if that makes sense. At idle the bold 8deg line is dead center of the largest notch.

 

[Scott Danforth]

Yes, I understand the setting and what the tape is used for.. I just want to make sure I’m reading the setting correctly. I have not seen a label like this on my other boats.

When at 3k rpm the green area of the sticker in dead center of the largest notch on the timing finger, if that makes sense. At idle the bold 8deg line is dead center of the largest notch.

its a standard timing tape. mostly used on performance engines so you can check timing advance without an advance timing gun

so your timing is good

now check fuel pressure at the carb

 

[Dillon36]

its a standard timing tape. mostly used on performance engines so you can check timing advance without an advance timing gun

so your timing is good

now check fuel pressure at the carb

That's the plan.

Checking the entire fuel delivery system to the carb. pump is brand new so we will see.

 

[Scott Danforth]

if you need to rebuild the carb, I have one or two (hundred). I have also used the same carb on my 468 until going bigger (thread in sig)

 

[Dillon36]

if you need to rebuild the carb, I have one or two (hundred). I have also used the same carb on my 468 until going bigger (thread in sig)

thank you,

This carb has been rebuilt twice by the shop and we have even tried a band new one with no change in performance so I'm guessing its not the carb