350 Chevy Engine Stutter @ 3,600 to 4,000rpm

[Baprace]

Have you checked the air bleeds ? I use choke cleaner to spray into the upper air bleeds next to the choke horn, second have the needles and seat been changed lately, perhaps on a rebuild ? The needle & seat may be too small if a cheap rebuild kit was used, then pull the fuel bowls off and make sure the jets are not getting plugged by debris, last make sure there are NO filters in the fuel bowls behind the inlet fittings, just use inline filters.

[user-23911]

You haven't mentioned plug gaps.
To me it sounds like a typical misfire which happens as you're approaching peak torque.
When that happens it's usually because there isn't enough spark energy to light the air fuel mixture at whatever the plug gap and engine load are.


There's several options, plug gap too wide.
Insufficient spark energy.
AFR wrong.


Going over those, reducing the plug gap often fixes it, but without knowing the cause.......the easiest thing to try initially.
If the AFR is wrong, too lean it'll knock too causing damage.
If it's too rich, well you'll see it on the plugs, (they'll be black).
As you probably will if it's too lean....white
As you also will if the gap is too big.

The plugs should always be the very first thing you look at.

[benno318]

im from australia so we dont have them readily available here - but dont taylor's leads have a bad reputation for doing weird things, misfires, mysterious massive power loss and such??

pretty simple to swap with a known good cap/lead assembly??

[Brian73]

Hello,

I just logged back onto the sight and was amazed with all the suggestions. MUCH APPRECIATED!!!!

Holy crap, I never entertained the thought about the gap's in the plugs being to large. New plugs were installed at the end of last season, but I cant remember the gap....Sucks getting old....LOL. I will check the plugs first and then zero in on the HEI with a replacement in hand to swap out. Hopefully, one of those two will be the culprits.

I will 100% let you guy's know what the outcome is.
HAVE AN AWESOME WEEKEND EVERYONE!!!!!

Cheers
Brian

[77cruiser]

Will it pull higher than 4000?

[Tuner]

What kind of car is this? If there is a ballast resistor or resistor primary wire the HEI can not function correctly. A HEI must have full battery voltage and power supply should be with 10 or (minimum) 12 ga. wire. If it is an GM car that originally had points ignition the ignition switch may be inadequate or damaged. If the car has questionable wiring you can power the HEI direct from the battery with a 30 Amp relay and turn the relay on and off with the ignition switch.

[Ron E]

Hi,

I've even offered copious amounts of beer.....

Brian

You have to give them the beer first. Then ask.

[ProPower engines]

This sounds like a common mild stock build and as suggested before un hook the secondaries and see if that changes the issue. Most times a marine carb is a vac sec. type thus allowing the engine to only take so much fuel and since the d.pump will open all 4 barrels it may be just too much carb and not enough prop as it too big to allow the engine to rev higher.
I see this every week guys put a 750 carb on where a 600 was and get a BIG BOGG and lower RPM's and speed cause it falls on its face too rich.

Do the carb test and let us know if that was the issue. You may need a progressive sec. opening set up to fix it if you are stuck with the carb you have.

[MarkR]

Rotor out of phase? A friend said cut a decent size window in an older cap and see where the rotor is hitting the contact point. I went through 3 distrubuors and entually dropped in a good one and 7000 it went

[cjperformance]

Put a vac gauge on it, see if it corresponds to a given vac #. I have had plenty that pull the PV shut prior to sec opening and stutter/miss.
If you cant be bugged checking vac simply put a higher #pv in and retry. Ie if its say 6.5"hg now , try an 8.5 or 10.5"hg PV.

[Brian73]

HI, Guy's

I wasn't able to get up to my boat last weekend. My plan was to attack the issue this weekend, but the weather report is calling for a 100% chance of rain all weekend (Damn). I have a brand new Distributor, vacuum gauge and all tools ready to go, just need some clear weather.

Once I get up and start the trouble shooting process, i will keep everyone informed.

Much Appreciated!!!
Brian

[rebelrouser]

I have had two things that were hard to find that caused an issue like you have. One is sometimes you get a magnetic pick up wound with the wrong polarity, and it will act just like you describe. the other is a defective condenser in the HEI, its only there for noise control, but if its bad it causes the same issue. Now swapping another HEI unit will cure the issue, but I always wanted to know why swapping an HEI unit fixed the problem. And with all the good advice you got, I will add, nothing helps diagnose an ignition system like a good ignition scope, and knowing how to read it. A skill and equipment most guys don't have anymore, but if you can find somebody who can hook up a scope, it checks a lot of things real fast. Good scope guy can pick out bad wires, plugs, coil, rotor, cap, low compression, timing chain stretch, loose bushings in distributor, just to name a few.

[miniv8]

Any chance it could be impeller related? either resonance or cavitation that hits and passes?

I'd start by closing up the plug gaps and have a jet kit handy for the intermediate air bleeds

[BadSS]

Was it running OK before and started running badly after a spark plug change? If it was running OK before, unless you bought them and changed the plugs yourself and know for sure they're the right spark plugs, then it could be they used the older short reach tapered spark plugs (.460") instead of the longer reach (.708") tapered plugs for the newer Vortec heads.

[Brian73]

Hello, Everyone

She Is Finally Fixed........YIPPIE!!!!!!

I installed a new distributor over the holiday weekend and she ran absolutely fantastic, no bobbles, farts or hesitations from idle to 5,300. After some minor adjustments i had really crisp throttle response and manors all the way thought the power band. It was a blast to be running correctly and scaring the crap out of myself again....LOL

Thank you again for all your great suggestions, its pretty cool to have a board full of such knowledgeable people whom are willing to share and help out the rest of us.

Cheers
Brian