4.3 gl backfires/lean pop intermittenly

[crustysack]

I have an 01 glastron with a 4.3gl, I replaced the block and heads with a re manufactured engine. Ran fine for about 40 hours. Now when giving it gas while underway it will start popping. I can punch it out of the hole and it will rev right up to 4400, will not pop until 15 or 20 seconds. I can ride around at idle to 3200 rpm no problem, but when I go to give it more gas it will pop. Also if I turn sharply at 3200 rpm it will pop. So far replaced plugs,wires,ditributor cap and rotor, ignition module, fuel filter,fuel pump. Gas tank was completely drained and flushed, pick up tube is clean. new fuel hose. Carb has been rebuilt and upped the jets from 70 to 73 since we thought it was a fuel starvation issue. Carb boat float is set properly, fuel pump runs continuously at 9 lbs the whole time thru all rpms.Timing was done with the shunt and is correctly advanced through all rpms I am out of ideas. Any suggestions would be appreciated

 

[alldodge]

fuel pump runs continuously at 9 lbs

Being a GL (carb motor) and 9 psi, it should be flooding. Most all carbs are unable to take more then 7 psi max

Take the boat out and when it starts popping slow quickly without allowing a lot of water to rush into the stern. Like turn hard and slow down. Pull a couple plugs and see what they look like

What elevation are you running at?

 

[boatlife123456]

the fuel pump should run between 9 and 13, it runs fine and the float is enough to stop the flow, so its not flooding, running at sea level, last plugs I pulled were lean

 

[alldodge]

the fuel pump should run between 9 and 13, it runs fine and the float is enough to stop the flow, so its not flooding, running at sea level, last plugs I pulled were lean

Now that's a bunch of bull, and if you have any spec which indicates that produce it

 

[boatlife123456]

I just looked at the Volvo penta workshop manual and I was erroneously reading 9-13 psi for the injected models, so my pressure should be between 5.75-7psi( per maunal) Tune-up Specifications =Engine Firing Order3.0 GS .................................................. .................................................. ........1-3-4-24.3 GL, GS, Gi .................................................. ........................................1-6-5-4-3-25.0 / 5.8 FL, Fi, FSi .................................................. ..............................1-3-7-2-6-5-4-85.7 / 7.4 / 8.2 GL, GI, GSi .................................................. ....................1-8-4-3-6-5-7-2Fuel Filters3.0 GS .................................................. ...............................................P/N 3855104-0 IAll Other ModelsP/N 3851218-2IFuel Pump PressureAll Carbureted Models .................................................. ..........40 - 48 kPa (5.75 - 7 psi)All Fuel Injected .................................................. ..............Low 13,8 - 27,6 kPa (2-4 psi)4.3 / 5.7 Gi .................................................. .................High 62,0 - 89,8 kPa (9-13 psi)5.0 / 5.8 Fi, FSi .................................................. ...........High 214 - 269 kPa (31-39 psi)7.4 Gi, GSi .................................................. ..................High 214 - 269 kPa (31-39 psi)For

So the pump is to much pressure?? we hooked up a snap on pressure gauge, made a new fuel line from top of pump to carb with a T in it for the gauge and the pump ran continuously at 9psi. This is a brand new fuel pump from Quantum Fuel systems that was described as fuel pump that replaces Volvo#3858261. This pump was a direct bolt in with the proper pigtail receptor.
So you think TO MUCH pressure will cause this pop?
Seems there is no adjustment for the pressure on this pump should I just install an inline regulator between pump and carb and adjust it down?
It seems like to much pressure should cause problems across the rpm range, or (guessing here) when the carb is demanding more fuel and the float opens up the high fuel pressure is forcing fuel down the carbs causing the backfire??
and when I turn the float is opening causing the same issue?
I hope this is the fix, I'm about ready to scuttle this boat.
Again all help is appreciated.

 

[alldodge]

The thread is for crustyshack and my comment was to check the plugs to see if the popping is from detonation, maybe a valve sticking or burn back from to much fuel

Would need to know which GL serial number to verify which pump should be used

I am finding that VP uses a 4.9 to 8.5 psi at idle pump so far as spec

 

[boatlife123456]

crustysack and boatlife 123456 are both me, sorry for confusion but I had trouble logging in and created a new account, The volvo tag reads 4.3gl-c serial#4012096833.
Last year I had same problem with the old block and when I put a new fuel pump on it fixed it. Boat was running fine until I over heated the block (short story raw water intakes got installed backwards) thus the new block and heads.

 

[boatlife123456]

here is a pic of the plug from #3 cylinder this plug was brand new yesterday

 

[alldodge]

ok thanks
Looks like the pump is the right one but most all carbs won't use a pump over 7 psi even holley. So long as its not leaking then no harm.

Being a 2001 at least the rockers are torque and forget

This is why I would like to know what the plugs look like. If they look good and not white, then its not lean. Then would need to see if its a timing issue or cross tracking in like the distributor

 

[boatlife123456]

I thought timing was the initial issue, maybe it backed off after initial setting. So I went out and without the light advanced the timing by hand until the popping went away. got it to the point of running up to 3200 rpm smoothly in a straight line. But could not eliminate the popping when the boat comes under load -when turning or giving it more throttle above 3200rpm. So I ordered the shunt and set the timing according to the info I got off of iboat, Timing is spot on all the way thru. New distributor cap,rotor,ignition module,coil, wires and plugs.

 

[boatlife123456]

Ok so i went out and pulled all the plugs, 1,5,2 and 6 are grayish, 3 and 4 are brown

 

[bruceb58]

You are likely getting a misfire from that #3 spark plug. Can't see #4 very well but maybe from that one too.

You could get that from using a fuel treatment that contains a lot of oil like Seafoam but then I would expect all of them to look like that.

I am wondering if you are getting excessive oil consumption on that cylinder.

 

[alldodge]

The last one is white like real lean. Normally would expect to see all plugs look for the most part the same with a carb. Some look ok, but that last one is white. Wonder if the valve job was not done right

 

[boatlife123456]

That would be a real bummer since I bought a reman from Marine Engines inc. Comes with a warranty but really dont want to pull the whole motor again. Why would the popping only occur at those specific times though. If the valve job was not correct wouldnt that happen constantly?

 

[alldodge]

Marine Engines inc

Not saying anything bad, but they have changed names a few times

Thinking maybe 2 possibilities
Being a 2001 you should have vortec heads and block. The vortec will have rockers which are torqued to spec and done. If there not vortec heads then rockers have to be adjusted

Bad valve job and valve is leaking

Do a compression and leak down test

 

[boatlife123456]

did vacuum test and it runs at 17 at idle with a sligh fluctuation in pressure, less than 1", did acceleration test and it went to 2 then 25 then settled at 17. Side question, on the timing chart I got off of iboats it says " initial-- 1° 600rpm--18° whats the difference between initial and idle..
Ok break out the compression tester next

 

[alldodge]

Initial would be base timing, where its set
Idle is base timing disconnected and its just idling

 

[boatlife123456]

base timing is just the distributor sitting in the correct positon?
explain that to me like Im 5
base timing disconnected with the shunt?

 

[alldodge]

Is this a if Pete and Repete was sitting on the fence thing?

 

[boatlife123456]

no pardon my stupidity, so I set the base timing at 1 with the shunt connected and then remove the shunt and the timing should be 18 at idle and then advance automatically through the rpm range? If so then why cant you set the timing to any one of those values at any set rpm. ie why cant I just set the timing at 21 degrees at 1000rpm