Cruising miss (lean)

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branded209

branded209

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Motor is a 360 with 340 race heads from edelbrock, edelbrock flat plain intake 750 proform. I've jetted up the front and back to 76/82 respectively. Replaced my powervalve, and cleaned the idle nipples up top and also moved the timing around. As well as putting a new coil, plugs, wires cap and rotor on it. It will accelerate but when coming to cruising speed at a level rpm and speed it feels like it's missing lean missing. And the plugs aren't dark enough still whitish.
 
Can't really go by plug color with unleaded gas.

I'd be checking my ignition. Same ting happened to me once and I had a wire that would touch a header only while I was going down the road. Another time I was getting surging at low constant RPM. That was the junk MPP dizzy that has an advance rate that is way too fast.

I'd also be considering the total timing including that damned vacuum advance.
 
I agree on the timing as well. I had the same problem. Plug the vacuum advance and see if it still does it.
 
The problem with the timing iDea is a few months ago it ran perfectly, and I hadn't changed the timing. It started doing this resently. I will try plugging the advance off later today after it stops being 112 outside :/
 
branded209 said:
It is vacuum advance and the timing it at 30 total I be leave. I can know it exactly because I was moving it forward and back little bits to try and fix the issue.
Click to expand...

You should know your timing for sure and 30 deg total sounds a little low to me.
 
I have similar issue with Quick Fuel 1050. Secondaries are hanging open only occasionally. Dunno if there's a flat spot on the throttle shaft or what. Maybe check yours?
 
I had a similar problem on my built 318 - miss at high rpm cruise only. Turned out to be a loose connector one side of the ballast resistor. Drove me nuts because I thought it was a carb problem.
 
I'll check the balast, I will check for flat spots also. With the timing, I do not have a light I used my uncles and haven't reset it recently. Thank you for the input guys I will be going through them after work and letting you know if anything works
 
Well, firstly, When cruising or at light throttle accelerating, The engine will want mega-timing; anywhere from 40 to 50 degrees, or more; yes more.
And secondly. the MJs have nothing to do with the cruise fueling unless they are plugged solidly shut!.
>Cruise fueling is handled by the fuel level, the transfer slots and the idle-mixture screws. Cruise fueling is mixed with air from the IAB(IdleAirBleeds) entering the main-wells and emulsifying the fuel that is on it's way to the low-speed delivery ports. It is further smashed into a fine mist by air sneaking past the throttle valves, which you control with the gas pedal.
If the IABs are not emulsifying the fuel, then the fuel drops may become too big to burn in the only-partially air-filled chambers. The fuel just can't find oxygen to react with.
So
the first place to go is the IABs. Then the T-port sync. Then the timing. Later, after this is fixed,you may wish to revisit your MJs. IMO 76s are too big for a typical street cam.

On a different note;
Why did you choose the open-chamber 340 heads for your 360?
 
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I had the same problem with my slant (4 barrel and headers). Turns out the orange box was bad. I put a 6al in it and it really woke up and runs perfect now.
 
AJ/FormS said:
Well, firstly, When cruising or at light throttle accelerating, The engine will want mega-timing; anywhere from 40 to 50 degrees, or more; yes more.
And secondly. the MJs have nothing to do with the cruise fueling unless they are plugged solidly shut!.
No, cruise fueling is handled by the fuel level, the transfer slots and the idle-mixture screws. Cruise fueling is mixed with air from the IAB entering the main wells and emulsifying the fuel that is on it's way to the low-speed delivery ports. It is further smashed into i fine mist by air sneaking past the throttle valves, which you control with the gas pedal.
If the IABs are not emulsifying the fuel, then the fuel drops may become too big to burn in the only-partially air-filled chambers. The fuel just can't find oxygen to react with.
So
the first place to go is the IABs. Then the T-port sync. Then the timing. Later, after this is fixed,you may wish to revisit your MJs. IMO 76s are too big for a typical street cam.

On a different note;
Why did you choose the open-chamber 340 heads for your 360?
Click to expand...
Everything you just said....is in another language
 
If you have installed a 6AL and it solved the issue, there is a bad? reason for that. The MSD is a multi strike with up to 15 strikes per revolution,below 3000rpm, IIRC. If your low-speed circuit is very lean, these Multi-Strikes can relight the fire as the fuel finally finds oxygen as the piston is rising on the compression stroke, and squeezing everything together. That means the power pulse may peak at some point past it's optimum point, and will therefore not be as strong as it could be. This recovers the unburned fuel that would have gone into the exhaust, but almost obviously it will take more fuel to cruise than it should have,due to the softer/longer power pulses. So the net effect may be no wins no losses as to fuel consumption. But theoretically, this is a band-aid for poor fuel atomization, and there may remain significant improvements. There is no substitute for proper atomization and a proper AFR, and a proper chamber. In an efficient chamber with a proper tune,a multi-strike is not a requirement but rather,a luxury.
Once past 3000rpm, the MSD reverts back to single strike, and the output amps of these may in fact be less than an breakerless/electronically-controlled, induction coil system. And power delivery does not usually begin until after 3000 rpm.
But it's true that an MSD can help overcome/solve, a low-speed fuel problem. It's just not the way I roll.
 
Maybe his orange box or the ballast had an issue. The MSD alone let him get rid of the junk ballast resistor, have a rev limiter and simplify underhood wiring. It is a superior ignition. I'm not disregarding that his carb may have been the cause or one of the causes of his problem but if it runs right now and has a decent AFR he should probably let well enough be.


AJ/FormS said:
If you have installed a 6AL and it solved the issue, there is a bad? reason for that. The MSD is a multi strike with up to 15 strikes per revolution,below 3000rpm, IIRC. If your low-speed circuit is very lean, these Multi-Strikes can relight the fire as the fuel finally finds oxygen as the piston is rising on the compression stroke, and squeezing everything together. That means the power pulse may peak at some point past it's optimum point, and will therefore not be as strong as it could be. This recovers the unburned fuel that would have gone into the exhaust, but almost obviously it will take more fuel to cruise than it should have,due to the softer/longer power pulses. So the net effect may be no wins no losses as to fuel consumption. But theoretically, this is a band-aid for poor fuel atomization, and there may remain significant improvements. There is no substitute for proper atomization and a proper AFR, and a proper chamber. In an efficient chamber with a proper tune,a multi-strike is not a requirement but rather,a luxury.
Once past 3000rpm, the MSD reverts back to single strike, and the output amps of these may in fact be less than an breakerless/electronically-controlled, induction coil system. And power delivery does not usually begin until after 3000 rpm.
But it's true that an MSD can help overcome/solve, a low-speed fuel problem. It's just not the way I roll.
Click to expand...
 
AJ/FormS said:
If you have installed a 6AL and it solved the issue, there is a bad? reason for that. The MSD is a multi strike with up to 15 strikes per revolution,below 3000rpm, IIRC. If your low-speed circuit is very lean, these Multi-Strikes can relight the fire as the fuel finally finds oxygen as the piston is rising on the compression stroke, and squeezing everything together. That means the power pulse may peak at some point past it's optimum point, and will therefore not be as strong as it could be. This recovers the unburned fuel that would have gone into the exhaust, but almost obviously it will take more fuel to cruise than it should have,due to the softer/longer power pulses. So the net effect may be no wins no losses as to fuel consumption. But theoretically, this is a band-aid for poor fuel atomization, and there may remain significant improvements. There is no substitute for proper atomization and a proper AFR, and a proper chamber. In an efficient chamber with a proper tune,a multi-strike is not a requirement but rather,a luxury.
Once past 3000rpm, the MSD reverts back to single strike, and the output amps of these may in fact be less than an breakerless/electronically-controlled, induction coil system. And power delivery does not usually begin until after 3000 rpm.
But it's true that an MSD can help overcome/solve, a low-speed fuel problem. It's just not the way I roll.
Click to expand...
Or you are over reacting since my car ran fine before and just recently started the stumble. I changed my ignition controll module and it works. The carb will be rejected and timing dialed in later
 
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