Throwing in the towel

[sschefer]

Re: Throwing in the towel

Wanted to add that Ive used 2 different rebuilt carbs with same results.

Sorry must have had a posting collision LOL. I'd be on those heads then. Don, it's doesn't sound like an outdrive problem to me but ya never know and it's certainly something that needs to be eliminated from the equation.

 

[CobiaXL]

Re: Throwing in the towel

Have you had the outdrive off ? Looked for restrictions in the exhaust, like broken shutters or something?

Outdrive has been removed and resealed.But never looked thru exhaust,Heading to shop now to check it out.

 

[CobiaXL]

Re: Throwing in the towel

I'd have to go with Don S on this one. A sand hole in the casting is the typical culprit. Over time the fuel flushes a tiny piece of grit out of the hole it was plugging and the carb goes south on you.

The other possibility is in the heads. Weak valve springs or pitted valves/seats will cause these symptoms also. At higher RPM's the valves will start to float and never fully close. In boats, there is a lot more moisture in the air and after shutting down a hot motor, that moisture will settle in the intake and eventually on the valves. If your motor does not have stainless steel valves you could have pitting at the seats.

Valves can be tested with a vacumm gauge although weak springs won't show up until the higher RPM's. If you're looking to rule out possibilites, I'd pull the heads and have them done by a shop that knows the difference between an automotive and marine head. I'd also think about replacing the carb.

3 different heads with same results.The head that is on now has been completely overhauled,(new valves,seats,seals,springs,rockers and push rods) by a local machine shop that deals with race engines.

 

[Silverbullet555]

Re: Throwing in the towel

P.S. Forgot to add I already did run fuel line straight from 2 different pumps to carb to a can of gas with same results.I will add that My fuel pressure is 5-7lbs till I hit the popping then pressure gets very erratic,jumping back and forth from 3-7 lbs.

This stood out to me and I am no expert, but it sounds like there is an issue in the fuel delivery. Something in the pick up, a collapsing line. I don't know, but based on this quote, I would be looking primarily at fuel delivery unless there is something else that would cause the pressure to become erratic.

Since you have run from different tanks, you can eliminate the tank, but solve your fuel pressure problem and I would think you solve the other issues.

 

[infideltarget]

Re: Throwing in the towel

I must still be missing something here. Popping thru the carb is ignition of gasses inside the intake tract...right? That means that whether it is timing related, or a poor intake valve seat, or whatever...a plug is firing while the intake valve on "X" cylinder is still open. Is there some other way to get fire into the intake that I have somehow overlooked? Maybe too high compression ratio or too low octane causing predetonation before the plug fires? I realize an ultra lean condition can cause issues when running power adders, but that typically is a melted piston dome, and head damage, then a catastrophic failure and one big pop thru the intake. The surging fuel pressure issue could be from when the gasses inside the intake ignite, the pressure inside goes from negative vacuum to a positive pressure, momentarily causing the fuel to push back into the feed lines, resulting in a low pressure reading. Then when the vacuum returns the pressure comes back. If this is happening each time a cylinder fires, it could cause a rhythmic "pulsing" of the fuel pressure high/low/high...etc. He has been through heads, and carbs with the same results. He has overhauled the entire fuel system, and even tried higher pressure electric pumps. Floating valves, from too much lift/duration or weak springs can cause the same issues, but he said the head was gone thru and replaced with the same effect. Back to too large of a cam, or timing advance coming in too rapidly. Springs in distributor were replaced, but are they the right tension? Maybe letting the weights fly too soon or too much? I'm not a marine mechanic by any stretch, but auto engines is another story. Is there THAT much difference in a marine engine? Please...someone tell me what I am missing here too.

 

[CobiaXL]

Re: Throwing in the towel

I must still be missing something here. Popping thru the carb is ignition of gasses inside the intake tract...right? That means that whether it is timing related, or a poor intake valve seat, or whatever...a plug is firing while the intake valve on "X" cylinder is still open. Is there some other way to get fire into the intake that I have somehow overlooked? Maybe too high compression ratio or too low octane causing predetonation before the plug fires? I realize an ultra lean condition can cause issues when running power adders, but that typically is a melted piston dome, and head damage, then a catastrophic failure and one big pop thru the intake. The surging fuel pressure issue could be from when the gasses inside the intake ignite, the pressure inside goes from negative vacuum to a positive pressure, momentarily causing the fuel to push back into the feed lines, resulting in a low pressure reading. Then when the vacuum returns the pressure comes back. If this is happening each time a cylinder fires, it could cause a rhythmic "pulsing" of the fuel pressure high/low/high...etc. He has been through heads, and carbs with the same results. He has overhauled the entire fuel system, and even tried higher pressure electric pumps. Floating valves, from too much lift/duration or weak springs can cause the same issues, but he said the head was gone thru and replaced with the same effect. Back to too large of a cam, or timing advance coming in too rapidly. Springs in distributor were replaced, but are they the right tension? Maybe letting the weights fly too soon or too much? I'm not a marine mechanic by any stretch, but auto engines is another story. Is there THAT much difference in a marine engine? Please...someone tell me what I am missing here too.

Im on same track as you with ignition....At this point im willing to try anything.Almost ready to swap ignition over to MSD..The admiral isnt takingtoo kindly to the 350.00 investment.As for the cam its totally stock.rpmmachine.com is where complete overhaul kit was purchased.
The flapper in exhaust seems to be opening and closing properly.

 

[infideltarget]

Re: Throwing in the towel

I am not familiar with how that engine is set up as far as the timing chain and gears. Is it possible that when they (or you) reassembled it, that it was reassembled with one of the gears off by a tooth on the chain? If this were the case, it could easily cause what you are describing, especially if it was put together with your base timing @TDC actually being BTDC. If this were the case, as soon as your distributor started putting in ANY amount of advance, it would already be too much. This is why I am saying to pull the rocker cover, and watch the valve actualtion in relation to #1 cylinder. You have already tried the distributor adjustment, and it seems you have a handle on that part, so it would seem to me to go back farther. It's really easy to get a timing chain off by one tooth, even for a seasoned professional race engine builder. Before you spend the money on the MSD, go bcak to the basics, and make sure the base timing is correct.

 

[Don S]

Re: Throwing in the towel

Outdrive has been removed and resealed.But never looked thru exhaust,Heading to shop now to check it out.

Look in the outdrive as well.

 

[Raystownboater]

Re: Throwing in the towel

I think a prop change which is basicaly just bogging the engine and not allowing it to rev too fast, is just masking a timing problem.

I completely agree, however, in my case I had everything adjusted properly and it would run like a dream in the driveway. Once I dropped it in the water, and tried to go to full throttle, I would get backfiring through the carb and it would only run at just above idle. The Mercruiser mechanic at the marina is the one that actually suggested a prop change and that fixed the problem.

In my honest opinion, he is too far into this to give up and there is a HUGE knowledge base on this site that will get him back on the water in no time!

 

[fishrdan]

Re: Throwing in the towel

It sounds like a lean condition to me, lean pop through the carb. What height was the float set to, was the power valve replaced when the carbs were rebuilt? Are both of the carbs "marine" carbs, are they both for a 3.0L (140/130HP) were the jets swapped around? Did you go through the fuel system troubleshooting DonS posted?

I'd almost be tempted to rig something up (for testing purposes only) to squirt a bit of additional fuel into the carb when the problem is happening. Rule out or confirm a lean condition. [DISCLAIMER, don't do this unless you realize the concequences, you could blow up yourself and your boat if you mishandle fuel!]

Almost ready to swap ignition over to MSD..

Here's a better ignition, cheaper too Delco Voyager. Though, without further troubleshooting, you'll just be throwing parts at it.

On the distributor, were the correct springs used (IT suggested) and did you check the shaft bushings. If the shaft bushings are worn, dwell and timing will jump all over the place.

 

[Don S]

Re: Throwing in the towel

Let's look at what has been done so far.

2 different carbs, Same Exact Problem

2 different fuel pumps, Same Exact Problem

2 different fuel systems, his tank and remote tank, Same Exact Problem

2 different distributors, even swapped out distributor from another running boat. Same Exact Problem

2 different long blocks, Same Exact Problem

cap rotor and wires replaced Same Exact Problem

Props, even if over propped, will not cause a popping from the carb. Low rpm yes, but not popping through the carb.

So what is common with the 2 ????? The exhaust system being plugged up could be one possibility.
If it was timing, I doubt both distributors would have the exact same problem.

Was the vibration dampner from the old engine used on the new engine? If so, could the outer ring moved and throwing the timing way off? If different dampners, throw that idea out the window as well.

Test run the boat with the ESA module disconnected. Have plenty of room, you may not get it out of gear without stopping and hooking the ESA module back up.

One other on the water test, run a jumper wire from the battery + terminal to the coil + terminal and see what happens.

 

[infideltarget]

Re: Throwing in the towel

Check this out...same problem, bad cam.

http://www.riverracer.net/forums/archive/index.php/t-75550.html



3: Backfires Through Carburetor (From Mikuni Corporation website)

Common Causes:

Ignition: The engine's faulty ignition can contribute to backfiring through the carburetor.
Cam design: Long duration cams with early opening intake valves can contribute to backfiring.
Intake manifold air leak: A lean condition due to an intake manifold air leak can cause backfiring.
Carburetor jetting: An overly-lean low-speed circuit, non-functioning accelerator pump or clogged pilot jet can contribute to backfiring.

(Backfiring, defined)

When starting an engine, timing that is too advanced will fire the spark plug before the intake valve is closed. The flame front will travel back in to the intake manifold, igniting all of that air and fuel as well. The resulting explosion then travels out of the carburetor and air cleaner. A common air filter will allow the gases to escape, but will block the flame front. On many small marine engines, no air filter is used, but a screen is placed over the intake of the carburetor as a flame arrestor to prevent these flames from escaping the intake, and potentially igniting fuel, or fuel vapors in the enclosed sump or bilge of the boat and causing a fire or explosion. Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously.



Here's another one...

http://www.carkb.com/Uwe/Forum.aspx...does-vacuum-leak-causes-backfire-through-carb

And yet one more...

http://forums.corral.net/forums/5-0-5-8-engine-tech/877054-popping-through-carb.html


The only reason I have not agreed with the lean carb issue is that you have already tried more than two carbs, and have redone the entire fuel system. Vacuum leaks could still be a culprit, and as I have said, timing (be it from the chain, all the way to the dist). Like the other s have said...throw a crapload of fuel in it, and if it stops...its a lean condition. If it blows up, it was timing.

 

[CobiaXL]

Re: Throwing in the towel

I am not familiar with how that engine is set up as far as the timing chain and gears. Is it possible that when they (or you) reassembled it, that it was reassembled with one of the gears off by a tooth on the chain? If this were the case, it could easily cause what you are describing, especially if it was put together with your base timing @TDC actually being BTDC. If this were the case, as soon as your distributor started putting in ANY amount of advance, it would already be too much. This is why I am saying to pull the rocker cover, and watch the valve actualtion in relation to #1 cylinder. You have already tried the distributor adjustment, and it seems you have a handle on that part, so it would seem to me to go back farther. It's really easy to get a timing chain off by one tooth, even for a seasoned professional race engine builder. Before you spend the money on the MSD, go bcak to the basics, and make sure the base timing is correct.

The engine had same exact issues before rebuild but i always pull rocker cover to set BASE timing,I don't believe marks unless I put them there.

 

[CobiaXL]

Re: Throwing in the towel

Look in the outdrive as well.

Looks clear as far as the eye can see...Also ran a snake thru it and feel no obstructions.

 

[infideltarget]

Re: Throwing in the towel

The engine had same exact issues before rebuild but i always pull rocker cover to set BASE timing,I don't believe marks unless I put them there.

Roger that. Check this one off the list. You are POSITIVE the chain was put on correctly?

 

[CobiaXL]

Re: Throwing in the towel

Let's look at what has been done so far.

2 different carbs, Same Exact Problem

2 different fuel pumps, Same Exact Problem

2 different fuel systems, his tank and remote tank, Same Exact Problem

2 different distributors, even swapped out distributor from another running boat. Same Exact Problem

2 different long blocks, Same Exact Problem

cap rotor and wires replaced Same Exact Problem

Props, even if over propped, will not cause a popping from the carb. Low rpm yes, but not popping through the carb.

So what is common with the 2 ????? The exhaust system being plugged up could be one possibility.
If it was timing, I doubt both distributors would have the exact same problem.

Was the vibration dampner from the old engine used on the new engine? If so, could the outer ring moved and throwing the timing way off? If different dampners, throw that idea out the window as well.

Test run the boat with the ESA module disconnected. Have plenty of room, you may not get it out of gear without stopping and hooking the ESA module back up.

One other on the water test, run a jumper wire from the battery + terminal to the coil + terminal and see what happens.

One of the first things that was unhooked was the esa..Same damper was used but like i said earlier posts,marks or notches mean nothing to me unless i put them there.I ran a wire straight from battery + to coil + to maybe eliminate entire ignition wiring,no change.

 

[CobiaXL]

Re: Throwing in the towel

Roger that. Check this one off the list. You are POSITIVE the chain was put on correctly?

No chain,timing gears with notch aligned correctly.

 

[infideltarget]

Re: Throwing in the towel

No chain,timing gears with notch aligned correctly.

Few more checked off the list. Roger that.

You read the links I posted? Did you re-use your old cam with the rebuild? Re-use the old intake manifold? ( Possible bad sealing surface if re-used.)

 

[CobiaXL]

Re: Throwing in the towel

Check this out...same problem, bad cam.

http://www.riverracer.net/forums/archive/index.php/t-75550.html


same issues when I first purchased boat with stock engine.Engine in boat now is almost entire differ setup,only things the same from stock boat to now is fuel tank,thermostat housing,and, alternator and distributor.
3: Backfires Through Carburetor (From Mikuni Corporation website)

Common Causes:

Ignition: The engine's faulty ignition can contribute to backfiring through the carburetor.
Cam design: Long duration cams with early opening intake valves can contribute to backfiring.
Intake manifold air leak: A lean condition due to an intake manifold air leak can cause backfiring.
Carburetor jetting: An overly-lean low-speed circuit, non-functioning accelerator pump or clogged pilot jet can contribute to backfiring.

(Backfiring, defined)

When starting an engine, timing that is too advanced will fire the spark plug before the intake valve is closed. The flame front will travel back in to the intake manifold, igniting all of that air and fuel as well. The resulting explosion then travels out of the carburetor and air cleaner. A common air filter will allow the gases to escape, but will block the flame front. On many small marine engines, no air filter is used, but a screen is placed over the intake of the carburetor as a flame arrestor to prevent these flames from escaping the intake, and potentially igniting fuel, or fuel vapors in the enclosed sump or bilge of the boat and causing a fire or explosion. Improperly adjusted carburetors that create a lean condition during acceleration can cause the air fuel mixture to burn so slowly, that combustion is still taking place during the exhaust stroke, and even when the intake valve opens. The flame front can then travel up the intake and cause a backfire. In this situation it is conceivable that there is a backfire occurring in the intake manifold and exhaust manifold simultaneously.



Here's another one...

http://www.carkb.com/Uwe/Forum.aspx...does-vacuum-leak-causes-backfire-through-carb

And yet one more...

http://forums.corral.net/forums/5-0-5-8-engine-tech/877054-popping-through-carb.html


The only reason I have not agreed with the lean carb issue is that you have already tried more than two carbs, and have redone the entire fuel system. Vacuum leaks could still be a culprit, and as I have said, timing (be it from the chain, all the way to the dist). Like the other s have said...throw a crapload of fuel in it, and if it stops...its a lean condition. If it blows up, it was timing.

same issues when I first purchased boat with stock engine.Engine in boat now is almost entire differ setup,only things the same from stock boat to now is fuel tank,thermostat housing,and, alternator and distributor.

 

[infideltarget]

Re: Throwing in the towel

same issues when I first purchased boat with stock engine.Engine in boat now is almost entire differ setup,only things the same from stock boat to now is fuel tank,thermostat housing,and, alternator and distributor.

Possible voodoo curse placed upon you or the boat?