SOLVED - stuttering/bogging at higher RPMs

[superbenk]

Finally fixed my problems today after 4hrs in the 95 deg sun! Turned out my dwell wasn't holding steady at the higher RPMs. The running theory is that as the RPMs increased, the points would bounce over the lobes causing the dwell to change and the ignition to miss. Experimented with some slight gap changes, re-timed & now my stuttering & bogging is gone! Need to fiddle with the idle adjustment on the carb yet, but things seem pretty great at higher RPMs now.

Lots changed on the motor that probably didn't need it, but at least it's set to go another 30 years now

 

[smarks]

Re: SOLVED - stuttering/bogging at higher RPMs

Just curious, but have you ever considered Electronic ignition? Pros and cons to both... just talkin here

Steve

 

[joenapier]

Re: SOLVED - stuttering/bogging at higher RPMs

Superbenk, did your engine bog down right away at high RPM's, or did it run for a moment fine and then sputter?

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

smarks, I've considered it, but I'm thinking a new(er) boat sounds a whole lot more appealing . I'm about done dumping money into this 30 yr old OMC.

It would run fine for a bit after having sat (ie, it'd run ok just after launching it), then start bogging. It'd be somewhat sporadic and could be either really bad or just occasional misses. Took it out this morning and did 25 for about 8 miles up the lake with only minor misses, but on the way home I was concerned it wasn't going to make it because it was so bad.

Haven't done an extended run yet, but the loop I did was extremely promising!!!

 

[smarks]

Re: SOLVED - stuttering/bogging at higher RPMs

The reason I asked about the Electronic Ignition is that I had some issues with a boat I purchased last fall similar to yours.

What I did was do a complete tune, plugs,condensor, rotor, cap, wires, coil and I swaped the points for Pertonix Electronic Ignition. Performance improved alot. I had some surging problems but that turned out to be fuel related.

I'm know how to set points but there a pain on a v6, I keep a set just in case but as of yet have had no problems w/the E/I.

Regards

Steve

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

What did the conversion cost? I have a 4 cyl, not 6 (probably why the problem was so noticeable).

 

[smarks]

Re: SOLVED - stuttering/bogging at higher RPMs

I believe it was $189 for everything, E/I conversion, High output Coil and wires.

Also included were the components and wiring diagram to modify the shift assist switch.

Overtons sells them but with out the mod

http://www.overtons.com/modperl/pro...ines_with_Delco_breaker_point_ignition_system

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

I guess I lied - got about 5 miles out of it and it started running worse than before at all RPMs! I'm so very sick of this boat. Guess I'm looking at a mechanic next. Hard to find one that will touch OMC stuff even though this is obviously just motor related.

 

[smarks]

Re: SOLVED - stuttering/bogging at higher RPMs

Once you get it squared away you'll be ok and no payment I assume

It's hard for me to justify payments on something I use a half dozen times a year. I'm disabled and can't launch by myself or I would probable use more.

Let me know what you find out

Steve

 

[Howard Sterndrive]

Re: SOLVED - stuttering/bogging at higher RPMs

sounds like the coil might be dying

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

Ya, no payments - it was a "free" boat that's only cost me $3k so far . Stupid old crap!

Howard, I hope not, it's brand new (put it on just before our vacation this week along with new wires, fuel pump & water separator).

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

Spoke to mechanic at the marina down the road and he said he could work on it so long as it's just engine work and not outdrive (told me he wouldn't touch the Stringer drive), but he said there was no way he could get to it before we leave Saturday

Kind of giving up on boating this vacation which sucks considering we're in a cottage right on the water

 

[6meter]

Re: SOLVED - stuttering/bogging at higher RPMs

I've had to replace 2 coils in the last 2 years. They had two different symptoms.

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

I've had to replace 2 coils in the last 2 years. They had two different symptoms.

Pretty sure the coil is fine. It's brand new (like I said, put it on just before vacation this week, so this is the first time out with it) and it tested out ok at home. That being said, I'll be testing it again just to be sure.

The sputtering and coughing at all speeds now (after mucking with dwell & timing) leads me to believe something isn't timed right or the carb is mucked up. I tried adjusting the idle screws at the carb, but I wasn't able to improve the idle at all. Adjusting to either side of where they're at just caused it to run rougher or conk out, so I think idle is set ok at the carb.

Took the top off the carb & the bowl was nearly full, so I'm pretty sure the float is working properly & when I pump the gas it squirts a nice pair of jets, so I think the accelerator is ok. Fuel pump is brand new (again, just before vacation), fuel sample is perfectly clean (no water separation AT ALL - dumped 21 micron filter into a jar & replaced it with a 10 micron just for kicks).

I had it idling really nice this morning then took it out for a spin again. Ran nice for about 1 minute then started bogging again and I had to limp it back to dock. After that the idle was a mess again. Checked dwell & timing & both were spot on. Fiddled with carb idle screws again and once again couldn't improve idle, only make it worse in either direction. Yanked plugs & they all looked good (light carbon, but no discoloration or soot, etc.).

Unfortunately I don't have a fuel pressure gauge or compression tester, only multimeter, dwell meter & timing light (and wrenches, of course).

 

[smarks]

Re: SOLVED - stuttering/bogging at higher RPMs

Might be time for a fresh carb: goto:

http://www.flyingfishcarburetors.com

They did mine right thru the mail, carb was all adjusted when I received it. All I had to do was install and start

Steve

 

[Howard Sterndrive]

Re: SOLVED - stuttering/bogging at higher RPMs

might want to check that the resistance wire (ballast resistor) is doing it's thing and dropping voltage to the coil + side with key on

try disconnecting the tach and going for a spin too

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

might want to check that the resistance wire (ballast resistor) is doing it's thing and dropping voltage to the coil + side with key on

try disconnecting the tach and going for a spin too

Had that thought too. Need to hunt down where that's located. Went through and tested everything else elecrical this afternoon but it's flipping hot out there & I have navy blue carpet! Got it back to idling nicely, but it's still sputtering and bogging at speed . Leaning toward fuel again & will check when I can get my hands on a gauge.

What's the likelihood of compression issues given the symptoms I described & the fact the plugs look clean? I don't have a compression gauge either (yet).

 

[joenapier]

Re: SOLVED - stuttering/bogging at higher RPMs

Ben,
I've been watching your post with interest as I have a similar issue with my Mercruiser 260. (Coincidently, I have a 1977 Arabian. I like your walk-thru windshield as launching a runabout is a bit more tricky climbing around the outside. I also dig you "navy" top / bimini.)

http://picasaweb.google.com/joenapier/1977CenturyArabian#

I take it out and it will bog down at WOT after 30-45 seconds. After that it keeps getting worse and worse, not wanting to run even at the lower RPMs for a shorter and shorter amount of time. It also getshard to keep running as I shift into gear. Last time I had to limp back to the dock running at 1000 rpms and dying every 100 yards. Temp is fine.

Now, I am going back in my maintenance records and seeing if something else I did caused this. I reset the timing for the first time in April. Curiously, I found it 10 ATDC! I adjusted it back to 8BTDC and it did idle smoother and seemed to run smoother. But, I'm not sure if the bogging started then too. I need to check this again.

I've replaced the fuel pump, thinking that the bowl was going dry during high gas demand. I replaced the fuel / water separator. The filter has a through-rate of 80 gal/hr which is mre than any engine can swallow.

I rebuilt the Quadrajet carb and spend a lot of time adjusting and adjusting with no satisfying "dialed" in feedback, as if I were approaching an optimum setting. I rode in the back while my sone drove to watch the carb operate.

I heard that the gas tank relief valve can get clogged and create a vacuum in the tank. That was not an issue. (Maybe you should check this?).

I'm rechecking timing and checking the three fuel lines between the tank, filter, and pump for clogging (but that would not explain it getting worse during the test drive).

 

[superbenk]

Re: SOLVED - stuttering/bogging at higher RPMs

I've actually been holding off posting again because I think I reLly did fix it now & didn't want to jinx myself

I pulled the anti-siphon valve off and replaced it with a straight through NPT fitting from an air compressor and it cleared up instantly! I also tried to fill up the tank yesterday with fuel and had a horrible time with the gas coming back out the fill tube, so I'm wondering if the root o my problem was a vacuum in the tank. I put a check ball valve on the vent tube awhile ago to keep in from spitting out the vent everytime I filled it or towed it down the road (it would slosh out). Now I'm concerned the vent is getting plugged somehow.

We actually took the boat out for tubing yesterday for a couple of hours without any issues, so I'm getting confident that it's fixed finally! Never though i'd see the day this thing would run right! If it starts doing it again, I'm going to loosen the tank fill cap and see I that helps. If it does, tank vacuum is obviously my problem. I'll be putting a new anti-siphon on too.