Sputter - Pop - Fart - Go like Heck and Back

[cjflanagan]

All right guys- Need advise on an 89 Mercruiser 350 Magnum Alpha One, Rockchester 4bbl. Complete top end rebuild over the winter. Now have 160 psi all around, new head gasket, heads plained and pocket ported, 3 angle valve job, new valves, 16 new springs, all new gaskets, valve lash adjusted correctly, new coil, wires, plugs, Cap & Rotor, and ignition pick up. Timing adjusted well, new water separator, oil filter. All electrical grounds and wiring checked. New dual 850 amp deep cells with isolator on cranking battery. New remote oil reservoir. New gimble bearing. Fresh tank of regular gas.<br /><br />Engine starts and idles perfectly. Hole shot is very good, and time to plain is 50% faster than before. Top end speed up 10 miles per hour from last season. The boat is tight, responsive to the throttle, charging well, great oil pressure, running at about 140 degrees. Sounds clear and crisp...no clatter, knocks, or taps. <br /><br />However after about 10 - 20 minutes, it starts just a tiny bit of sputter - which will then lead to a miss - and finally to an all out popping and farting event through the carb with a loss of power. If I throttle back it works itself out and if I'm patient she will eventually come back around and go like heck again. For a while that is, then it will do it again, then run good, then do it and again. She never dies (bless her heart). So here's what I think. I do not think it's electrical because I have verified and double checked all my connections and all my components are new. I think it's fuel related (don't you?). So I checked the vent tube, it's OK. I have not checked the fuel pump (mechanical), the carb (not rebuilt but worked when I strarted), or anti-siphon valve, because I do not know how to approach and isolate this. Wife wants me to take it in, I can't do it guys, I've come to far on my own to have a wrench take it over the finish line. Teach me how to diagnose and isolate a fuel problem.<br /><br />BP

 

[tim10034]

Re: Sputter - Pop - Fart - Go like Heck and Back

thanks for the reply in my post....i will try to help u with what little knowledge i have... first i would check the gas cap , i would open up the gas cap and run it to see if u get enough air sucking in the vent at the cap. to check the anti syphon valve u could do two things..one is to disconnect it and run another connection without a vavle....or some ppl put a primer bulb on fuel line before the fuel filter.and if u see it collapse then u have an obstruction before bulb..sometimes there is a screen on the pickup line inside the gas tank that could be dirty, i hope this helps....

 

[Boomyal]

Re: Sputter - Pop - Fart - Go like Heck and Back

Ditto on the tank vacuum possibility or it could also be the fuel pump dying. I had one that died a slow death and acted similar. It would idle fine and then at speed start acting up. Started out intermittently then quit in the middle of the channel. luckily I had a new one on board.

 

[DJ]

Re: Sputter - Pop - Fart - Go like Heck and Back

Are you running the original ignition coil?<br /><br />The mods you made may have made firing the plugs a little more difficult.<br /><br />If the coil overheats, it will act that way.

 

[Bondo]

Re: Sputter - Pop - Fart - Go like Heck and Back

I think it's fuel related (don't you?).

Yep.......<br />Could be All of the above......<br />a pressure gauge, rigged to the Carb. Inlet, Should read 5/6psi.... No Less than 4psi....<br />Pull the Filter,+ dump it into a pan,+ inspect for debris......<br />To by-pass the tank, Hook-up a portable tank to the fuel filter inlet......<br />It Could be $hit in the Carb, But I Doubt it.....<br />It Seems to be Up-stream from there.......<br />DJ could also be right... It's easy enough to test... Swap out the Coil, Just to eliminate it.....

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

B- I had a new accel coil in there. Yesterday I took it out and put the original back in just to be sure. Didn't make a difference. T- When it was going down the lake I undid the fuel cap to see if that made a difference - nope. DJ - What modifications have I made that would require a coil upgrade. My efforts are to restore to new not modify.<br /><br />B- my dad has a pressure/vacuum gage that I think would work well for your test. It's a Penske that he bought at Sears when I was a boy. When he passed away I inherited all his tools. Anyway, would I connect it to the inlet where the clear plastic hose from the fuel pump goes? Or, are you saying to rig something into the main fuel line like a "Y" and measure off that? <br /><br />I will check the screen and filter.<br /><br />Are you saying to rig a test tank that bypasses the fuel pump? What does it do gravity feed?<br /><br />In my original post I said the timing was done right. I'm beginning to question myself on this. When I hooked my timing gun on it, it just didn't make any sense to me. The marker on the flywheel seemed to be out about 30 degrees. When I got the line in the indicator it ran like crap. I think the Mark IV ignition was throwing things off. So...I basically ran the motor up to about 2500 rpm on the trailer, but with the boat in the lake and in gear to simulate load. Turned the distributer till it started to lean out and then brought her back a couple degrees. Is this ok? If not, how do I set the timing with a Mark IV and a gun? I know lean timing can cause excessive heat and possible pre-ignition?

 

[merc 140 pontoon]

Re: Sputter - Pop - Fart - Go like Heck and Back

Well, the title of your post made me think you were writing about me last weekend--the diagnosis there was microbrew and pickled eggs, but you probably don't really care about that.<br /><br />I'll tell you my ignition story. It may not apply to your Mark IV, but then again it might, so I'll tell it anyway. My Merc 140 I/O acted just like you describe. The hired gun couldn't find it. Of course, he never took it out on the lake, he just ran it on muffs. After a lot (lot, lot, lot) of trouble-shooting and soul searching, I finally got a tip on a forum like this and found the problem.<br /><br />I have a Pertronix Ignitor "electronic" ignition module. It sits inside the distributor cap and replaces the condensor and points. It needs power, so one red wire runs out of the cap to a power source. Well, turns out a different hired gun wired the Ignitor wrong. He picked up the power at the coil positive post (CPP). As you may know, the CPP only sees 12V during cranking, from the crank assist wire direct from the starter to the coil. Once started, the CPP voltage drops to maybe 9V, supposedly to save the points (or, chicken and eggwise, to allow there to be a boost applied during starting in the first place). Anyway, the Ignitor instructions clearly say to pick up power at a full 12V switchable power source--which the CPP is NOT. The reason this is important, as I found out, is that the ballast resistance in the circuit can incrase with age. My engine does not have a ballast resistor (or two) on the transom. It has the infamous "resistor wire" built into the harness. As that harness ages, the resistor wire can deteriorate. In my case, like many I'm told, the resistor wire will be OK when the engine is cool, but after 10 or 20 or 30 minutes of running, the rsistance increases and causes problems downstream (speaking electrically, of course). I was able to confirm this by tracking the CPP voltage as the engine compartment heated up. Then, in my case, the voltage would drop to 8V, then 7.5V, then 7V, and BAM, the Pertronix Ignitor circuit would SHUT DOWN. But it wouldn't just shut down... it would sometimes come back online, then go down, then back on, then down, ..., then up, then down for good--meaning 60 to 90 minutes cooldown with the hatch open before she'd run again.<br /><br />As you can imagine, this was a bear to identify until someone pointed me right to it. By then, I'd checked just about everything else. On top of all this, I also had a cooling problem which was later fouond to be some very, very old impeller pieces inside the water pocket in the driveshaft housing. The point here is that the two problems together made it almost impossible for me to diagnose either one. I finally decided I was going to solve it or else, and after 2 or 3 months of heads down effort (weekends and many weeknights), I finally solved the two problems.<br /><br />I don't know if your Mark IV is even susceptible to this, but if I were you, I'd confirm that the voltage downstream of the ballast resistor (before the coil) is steady during that 20 minute run period.<br /><br />Good luck in any case.<br /><br />M140P

 

[Bondo]

Re: Sputter - Pop - Fart - Go like Heck and Back

Anyway, would I connect it to the inlet where the clear plastic hose from the fuel pump goes? Or, are you saying to rig something into the main fuel line like a "Y" and measure off that?

The clear plastic line is Just a Vent to allow gas to go to the Carb., rather than the Bilge, In case of a Diaphram Rupture....<br />You need to know the Fuel Pressure, At the Carb. Inlet...... Yes, "T" it(Main Fuel Line) off, to Check it.....<br />

Are you saying to rig a test tank that bypasses the fuel pump? What does it do gravity feed?

No,<br />Hook it up to Either the Fuel Filter Inlet, Or the Fuel Pump Inlet.... You're trying to by-pass your Tank,+ It's related fittings,+ lines.....<br />

In my original post I said the timing was done right. I'm beginning to question myself on this.

Ya, Me Too........<br />Initial Timing Should be 8* at idle.......<br />

...I basically ran the motor up to about 2500 rpm on the trailer,

That's Another No-No...... You should Never get much more than Idle, on the Muffs.......<br />

Mark IV ignition was throwing things off.

It Shouldn't.......<br /><br />How Fast a motor will SCREAM, with No Load, has Nothing to do with What it'll do under Load......<br /><br />Good Luck,+ Keep us Posted............

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

B- you missread my post look again. No stinkin Muffs. Lake Dude! The trailer was in the lake! Just kidding I appreciate the help. Merc 140 - This is a great post. I can see how this would be tricky to chase down. In figure 1 My ignition module looks like #7. Two of the wires in #8 go to the coil and the other two go to the distributor & ignition pick up (#11 in figure 2). Are you saying nothing in the #8 harness should go to the cpp?

It has the infamous "resistor wire" built into the harness

is this #8?<br /><br />Figure 1<br />

<br /><br />Figure 2<br /><br />

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

I hooked a voltage meter to my dash with Velcro. I attached the positive side to the positive terminal on the coil. I attached the negative side to the bolt on the thermostat cover. <br /><br />Next, I went out on the lake. At the start,the voltage was about 12.5. Sure as sugar, 20 minutes into the experiment the sputter and farting started. The voltage never dropped. If I throttle back to idle, it runs fine. The second I give it gas on comes the problem. I open the fuel cap to vent the tank, no help. <br /><br />While the problem is happening if I open the throttle wider, the problem gets worse and there are back fires through the carb. If I throttle back the problem goes away. <br /><br />Sometimes while the problem is happening, it will snap out of it for a second or two, and the boat lurched forward with great strength for a few seconds.<br /><br />Tomorrow, I'm going the fuel route Bondo recommended. But I'm curious as to how fuel and temperature can be related.

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

I guess I'm just talking to myself here...

 

[Preston]

Re: Sputter - Pop - Fart - Go like Heck and Back

I would definetely put a pressue gauge inline before the carb. It really sounds like fuel starvtion. More likely than not you have got a weak fuel pump.

 

[Boomyal]

Re: Sputter - Pop - Fart - Go like Heck and Back

Ditto to Preston. Get that inline fuel guage between fuel pump and carb. Have someone else aboard to watch it when the motor starts to act up.

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

fuel pump on the way. Will update next weekend.

 

[seamegr]

Re: Sputter - Pop - Fart - Go like Heck and Back

BP, make sure that you are not getting fuel vapour lock. This happens when the fuel gets heated up in the fuel lines or the tank. It boils and evaporates in the line and the fuel pump can't pump vapour. The fuel can also boil away in the carb but I think that is much less likely. Make sure you don't have the lines too close to a source of heat.<br /><br />Up here in the frozen north we have winter gas and summer gas. Winter gas evaporates at a lower temp and using it in the summer can cause problems.<br /><br />If the fuel pump is the same mounting as a SB Chevy in a car, be careful when installing the new pump. You have to make sure the fuel pump push rod is in the right position. <br /><br />The pressure gauge that has been suggested will be your best tool to find your problem. <br /><br />Greg<br /><br />PS, I love the subject line, LOL when it says taking you back to...

 

[cjflanagan]

Re: Sputter - Pop - Fart - Go like Heck and Back

No go on the vapor lock theory. I checked that out long before I came to the board. Fuel line is nice and cool to the touch.

 

[outboardguy]

Re: Sputter - Pop - Fart - Go like Heck and Back

Vapor lock can occur with or without heat.You could try and tee in a vacuum line between the fuel pump and the tank. You should see no more than 2 inches of mercury vacuum.If you see more then you have a restriction in the tank or fuel line.

 

[merc 140 pontoon]

Re: Sputter - Pop - Fart - Go like Heck and Back

BP212 -<br /><br />Sorry for the delay in replying. Your voltmeter experiment sounds well done, and seems to have eliminated the voltage drop possibility.<br /><br />I had thought about a an exhaust obstruction (failed shutters), but I don't see how that would take 20 minutes to show up.<br /><br />So now it's back to basics--you have to have fuel and spark. I don't know about OMC manuals, but Mercury published procedures for checking these. You can easily check that you're getting spark out of the coil wire, and then you can easily check if you're getting spark from the plugs. There are also published procedures for checking fuel flow rate, but with a hot engine, the fuel pressure gauge and vacuum gauge are a better idea. Whatever you do, follow the procedures for your equipment.<br /><br />Are you sure you don't have something in your fuel tank that's blocking the fuel outlet? I had a fuel can rubber hose fall into a fuel tank once. It was a bear to get out, but I didn't want it shutting down the flow at the wrong time.<br /><br />You said the electrical components are new. Did you keep the old ones as spares? Maybe you can swap them back in one at a time. Perhaps your distributor cap or plug wires have a defect that opens with engine compartment warmth. I doubt it, but once you rule out low fuel flow, you've got to be creative.<br /><br />Are you sure the ground from the engine to the battery is clean and secure?<br /><br />Is the new tank of fresh gas from your normal, reliable source?<br /><br />That's all I can think of. Good luck.<br /><br />M140P

 

[Sammy805]

Re: Sputter - Pop - Fart - Go like Heck and Back

I had similiar problem as you have last year with my 350 magnum with 480 hours. Had the head re worked with new intake valves, valve springs, and decked. Assembled it and checked compression and all cylinders were around 180 dry. I can not wait till this summer.<br /><br />My problem was weak valve springs causing the valves to float at wot, and it would not recover unless I brought the boat to idle. But before I found the problem, I replaced the fuel pump, rebuilt carb, replaced fuel line, anti syphon valve, plugs, wires, cap and rotor.<br /><br />I know that you have replaced alot, but have you looked into the ignition module and the possibility of the cam being off time with the crank?<br /><br />1. Ignition modules are known to break down with heat, so after running 20 minutes it may start to mess with your total timing, which would cause missing at upper rpms.<br /> <br />2. You said that with the timing light and the engine running good, the timing mark was way off. If the cam was out of time with the crank the mark would be off. Did your problems just sort of develop out of no where? If so, this could be the problem.<br /><br />High hour engine always run the possibilty of jumping time because the chains start to wear. <br /><br />This is just my 2 cents, and I hope that you find the problem, so you can have a good summer of boating.

 

[LubeDude]

Re: Sputter - Pop - Fart - Go like Heck and Back

Sometimes these things are a pain in the Bu*t to find and sometimes its something easy. Have you checked to see if your Carb is tightened down tight, this can cause the problems you are experienceing after warm up. You may have to change the gasket! Just another thought.