Popped through the intake.

[Pmt133]

Problem is different enough that rather than cluttering up my carb thread I figured it best to start a new thread.

So what happened: Ran the boat today after rebuilding the carb. Ran for about 2.5 hours with an hour break in the middle. So out on the water for 3.5 hours total. Upon nearing the ramp I started pushing it a little... nothing crazy, 3600 rpms for maybe a minute or two. Got a single pop through the carb under the spark arrestor. So I backed off to 2800 to investigate. It didn't sound quite right, but wasn't missing. Dad cracked open the dog house and all of a sudden it popped several times like pop corn. I dumped the throttle and idled it the 1/4 mile to the ramp. Seemed fine but I wasn't going to try pushing it any harder.

So when I got home I checked a couple things, pulled the plugs to make sure nothing looked scary, and they're good. No detonation, timing mark on the strap is good, fuel mixture seems about right. Nothing to write home about.

So next I ran a compression test, saw about 160 across the board, so again, nothing abnormal.

Finally I pulled the cap and rotor. Seems like a little scale build up inside and there were these points, not corrosion but a little slag hanging off the tip of one of the electrodes. I plan to pick up a cap and rotor tomorrow as well as plug wires.

I think that is a good place to start. I also have had issues in trucks in the past with the vortec style intake having vacuum leaks... but I wouldn't think it would run so well for so long then all of a sudden mess up. This happened a couple weeks ago too at nearly the same point in the trip... So there is that. I'm not denying that I messed up the carb but... I don't think it would run as well as it did if there were something wrong with what I did... but I am also an idiot and have been wrong many times before.

I'm just looking for input on if this is a good direction to move in for now. Appreciate it.

-Paul

 

[Scott Danforth]

Popping through intake is either running lean, or timing is off

 

[Jmunk]

Sounds like what I used to call a lean sneeze. If the timing is correct you need to go over the carburetor again. When you say carburetor was rebuilt - did you you strip it down completely and verify all passages are clean? Is the float height correct? If your confident the above is correct may need to verify fuel PSI.

 

[Pmt133]

Popping through intake is either running lean, or timing is off

I had double checked timing the other night... per my engine 10 degrees BTDC in base timing. Seemed about there with my dial back so I left it alone. It is a thunder bolt V however. I'm not seeing anything on the plugs that is telling me it's lean but I can be wrong.

Sounds like what I used to call a lean sneeze. If the timing is correct you need to go over the carburetor again. When you say carburetor was rebuilt - did you you strip it down completely and verify all passages are clean? Is the float height correct? If your confident the above is correct may need to verify fuel PSI.

Stripped, wire run through passages that I could get, jetted with compressed air the whole 9. I've done enough and had to fix enough others that I leave nothing unturned. Float height and everything was quadruple checked before I bolted it all together. I can't say I'm 100% sure the carb is perfect... but I am pretty sure everything I did is right. It does have the OE mercruiser electric fuel pump. On the trailer I tested it got ~ 6psi but I suppose I can run it with the gauge on to see if it is maintaining it at speed.

 

[04fxdwgi25]

How old is the fuel? Has the fuel / water separator been changed?
Take a fuel sample and see if there is any water in it.

 

[Pmt133]

Fuel was about 12 hours old. separator is due for a change though... I'll pull it too.

 

[Bondo]

Fuel was about 12 hours old. separator is due for a change though... I'll pull it too.

Ayuh,..... Dump it's contents into a clear vessel, to examine it's contents for anything but clean fresh gasoline,.....

 

[Pmt133]

Ayuh,..... Dump it's contents into a clear vessel, to examine it's contents for anything but clean fresh gasoline,.....

Got an old glass jar just for that. Will do.

I did do a little more detective work and cut open a couple plugs. 5 and 6 were the only ones that looked a little odd. Based on this, I take it back that it isn't a little on the lean side. Also, since it isn't dark out and I can accurately see this... that looks like maybe a little rust on the plug tip... reversion?

 

[Scott Danforth]

You know that plug has the threaded portion missing.....

Regarding rust on the plug, if you have water in the fuel, you get lean popping and rust on plugs

 

[Pmt133]

You know that plug has the threaded portion missing.....

Regarding rust on the plug, if you have water in the fuel, you get lean popping and rust on plugs

When I check fueling, I cut the threads off to read the base of the porcelain... That's how I was taught. The thin grey band at the base indicates a little lean... Should be about double that thickness.

The rust on the plug is only present on #5 and #6... Will be pulling the water separator when I get back home.

 

[Pmt133]

Water separator was immaculate. Let it sit for half an hour and no visible water was present.

 

[flashback]

The slag on the points may be throwing the timing off enough to cause the popping..

 

[Pmt133]

The slag on the points may be throwing the timing off enough to cause the popping..

That's what I am hoping...

 

[Pmt133]

So before I go and do anything else... This is my intention for today...

I plan to double check timing, set it in base mode etc. confirm all that is correct.

Then look at the fuel system. We have some pop up storms blowing through today and I'd rather not get caught out on the water in one. I plan on checking for vacuum leaks first, I can do that in the driveway.

Fuel pressure while at speed as well will have to wait...

The carb itself... I've been thinking about this. The previous owner that sold me the engine said the engine was a remanufactured one as a long block... I am wondering if the camshaft that was installed is no longer the correct match for the induction system if they just tossed in a generic 4.3l cam... If its a multi tooth keyway on the timing set that could've been done wrong as well... The only reason I mention this is that the engine has been a little underwhelming since the repower...

Are we all agreeing that it seems a little lean? I'd love for some things to check beyond what I listed... I just can't really think of anything. I'd love to give a serial number as well, but it was scraped off the engine and honestly... Since it is a reman unit wouldn't be of much help anyway if they changed around a bunch of internals...

 

[Pmt133]

So today, I checked for vacuum leaks, couldn't find anything obvious. New cap and rotor as well as plug wires are in. Rechecked fuel pressure, while running, I am seeing a steady 7 psi with the new separator. I also had to readjust timing by about a degree, so I went through that whole process again....

Bay test tomorrow. My buddy will be out just in case I need a tow. Hopefully not.

 

[Pmt133]

So... I ran up and down the river at a nice 3700 rpms. Boat runs great there, about 31-33 MPH. Everything seemed great... until it didn't. It started missing after about 10 minutes. I dumped the throttle. I can describe only what I hear as basically arcing coming from the distributor/coil area.

Coil is quite hot to the touch given how short the ride is... based on the fact it ran that way with 6psi of fuel pressure best I could tell... I'm comfortable removing fuel system from the equation at this second... I took a recording of the noise best I could that I'm going to attach once I've got it uploaded... but I'm a little confused. Also, I'm getting water between the head and intake flange so I need to pull the intake and replace that gasket too.

Any thoughts?

 

[Pmt133]

Update:

Running back to the ramp I took it easy, 2600 rpms, about a minute in I just started completely losing power/rpm. No pop or back fire just felt like someone dumping throttle... I'm at the ramp, let it idle the rest if the way as it seems fine doing that..

 

[Pmt133]

So basically, it would seem the necessary conditions for this to set are:

• Engine needs to be hot and ran for a bit, muffs won't do, needs to be in water
• needs to be at elevated RPMs for prolonged period

I am thinking I will start by replacing the intake gaskets... While I don't believe it is the issue, I've had a leaking closed cooling cap steam up the distributor and cause similar issues... From there I also plan to ohm out the coil. While I doubt the coil is the problem (I've only ever had 2 fail in my entire life and they were the cheap coil on plug types, not a regular can coil) I can at least confirm it is within spec.

From there, I got nothing. I've also included the link to the video of the arcing so you can hear what I was talking about, although on video it sounds more like a rattle....

 

[Fiberform71]

For me it sounds like the coil is loosing his spark to a ground peace(ticking sounds) is it possible to look at it when it's dark? Maybe you can see where the sparks is ticking over.

 

[Pmt133]

For me it sounds like the coil is loosing his spark to a ground peace(ticking sounds) is it possible to look at it when it's dark? Maybe you can see where the sparks is ticking over.

OF course I couldn't duplicate on the trailer in the dark... So no go there. I lightly misted down the coil with water from a spray bottle... Caused it to run like sh!t and stall several times. Couldn't see any visible arcing. Monday is another day, got 3 days of work for the time being.