Calling Carburetor Experts

rfarkash wrote: The plugs that have been in the last 3 years are the 203's gapped at .032 - boat ran/run's fine with these. I put in NEW 24's gapped at .035" and had the stutter issue. Put the OLD 203's back in to diagnose and problem went away so I am assuming the new 24's are at fault.

This would've certainly been some nice to know info at the start of the thread.

rfarkash wrote:     Am definitely going to be doing points, rotor, cap etc this year. Since I've had the boat (3 years) have put on only 50 hours so I don't think that's excessive in term or plug or dizzy maintenance.

Just a guess here but my thinking is the larger gap of the new plugs is making some other part of the ignition (which is marginal at best) not be able to provide the spark needed to make that extra jump reliably. Another possibility is one of the new plugs is bad. That can and does happen too, albeit very rarely. However, a definite possibility.

.035" is the right gap and unless you have some other head on there that you've failed to tell us about, the 24 is the right plug. I have no idea why the 203 plugs are in there but I'm admittedly more of a Chevy guy so if I'm wrong on the plug, someone else I'm sure will correct me.

50 hours in three years, while not a lot, isn't justification for ignoring the ignition. There must've been some reason you changed the plugs in the first place. I would still change the cap and rotor at the very minimum. The points might very well be OK and just confirming the the contact surface is clean, the gap is correct and the timing is spot on will be sufficient but you need to check that. Personally, I would just change them and be done with it. Also verify the plug wiring is good.

rfarkash wrote: And the answer is...... Ignition. Put the old Autolite 203 plugs back in and problem is gone - runs like a champ. So it wasn't anything fuel related. Now my question is the plugs that are in and work are 203's gapped at around .032". I thought a standard 351w was supposed to use Autolite 24's gapped at .035"? Thx Ron

I won't say I told you so....LOL.

Let me see if I got this right. You've been running the Autolite 24's for three years and everything has been fine until now. How many hours have you put on these plugs over the past three years and not had a problem? So WTF makes you think that those are now all of the sudden the wrong plugs?

You had a plug go bad on you!!!! It happens. Hence, the reason that your first plan of attack is doing a tune up that should include new plugs, points, condenser, cap, rotor and timing at minimum and check/inspect the wires as suggested.

Get a set of new 24's gapped at .035" and you should be good to go again.

I would highly suggest you also do the rest of the ignition system or you're going to be having additional issues before too much longer. They've all been in service for three years and how many hours?

I'm sure that Pete will argue that logic but it's what I would do if it was mine.

Never heard of points that didn't have a ballast resistor. I would put one in.

You have a different problem than the OP. You have an off idle stumble.

Look at the accelerator pump nozzles in the carb and make sure that you're getting a good shot of fuel as soon as you move the throttle. Verify that the accelerator pump cam lever is adjusted to have no slop in it when it sitting at idle.
You should also make sure that the idle mixture screws are adjusted for the highest idle RPM or the highest vacuum when the boat is warmed, idling and in gear so you have to do this on the water.
You make sure it setup like this and your off idle stumble will disappear.

The secondarys will never open until you have it loaded and running at speed.
As far as the coil does this stuill have the points or EI conversion?

OK - sounds like either the carb or ignition. Plugs are new this year and gapped to .035" and wires are in good shape as far as I can tell but will resistance check. Will double check timing and points ca and rotor. Will also do the carb cleaner test. I'm certainly no expert, but with it starting, running at high and low fine, I'm suspicious of the carb which is what led me to ask the question. But ignition tune up certainly can't hurt.
Thx
Ron

Well, I'm certainly no expert, but the fact that it starts easily and idles fine and has no miss at upper rpm suggests to me that the ignition system is fine. The rpm band that you describe is exactly where the carb moves from the idle circuit to the mid range, and then beyond that to WOT. The carb may just need a disassembly and good cleaning. It acts as though there is a clogged vacuum passage internally. If you get a can of carb spray, with the engine running at 2500+, spray carb spray into carb. Keep it running. After it stabilizes, get it back to 3K+ rpm, and using your hands, cover the carb, starving it for air, until it almost dies (but don't let it), then quickly remove your hands. The incoming air will actually go supersonic, and can dislodge dirt particles. repeat this a couple times and see if it improves. If not, It may need a teardown. Hope that helps.

How old are the plug wires? Maybe one is starting to break down,you could ohm them out to check

1989 SN with 351w, 1.23 tranny and 4160 carb. Starts up on first crank, idles solid and steady. If slowly cruising anywhere from headway speed up till around 15mph (tach under 2000), engine feels like its missing or loping - kind of like stuttering. Accelerates just fine (maybe a bit of hesitation), and butter smooth at anything over 2000rpm.
From looking through the forums I think it may be something with the primary jets, but I really don't know my way around carbs. If not the carb, could it be the points/ignition? Haven't really messed with them in the past 3 years, but assume if it was ignition related would be worse at high speed/loads?
So how do I go about diagnosing and fixing?
Thanks
Ron