Can't get it tuned right

[Moon's74]

This thing is driving me crazy...or maybe it's just too late.

302/470TA/performer/MSD/stock dizzy

Engine idles fine, but loads up, sputters, at higher rpms. Basically, no power.

Replaced power valve and jets on carb.

Back 4 spark plugs are very black, front 4 plugs are light brown...just right. What gives?

I can't seen to get the timing correct. I've read that vacuum advance should be on manifold vacuum (ie full time)? Wait a minute, I've also read that it should be on the timed spark advance on the carb? Which one is it?

Also, with no vacuum to the dizzy my timing is way advanced, like 40 degrees. Checked the harmonic balancer position with #1 at TDC of compression stroke, sits right a 0 on the pointer. Start it up and the timing light shows 40 degrees advanced.

Checked the vacuum diaphram on the dizzy, it works correctly.

Tried to retard the timing and it loads up really bad and will not run.

With timing at the advanced, original, position I revved up the engine and it advanced even more...without the vacuum connected. No change with the vacuum connected to the timed port on the carb.

Where should the transmission get it's vaccum from? Tranny and PCV are on bottom front of carb, back port is plugged for lack of brake booster.

My apologies for the long post, but I'm baffled.
What am I missing? Thanks.

 

[broncnaz]

Sounds like the mechanical advance may be stuck in the advance position. Might want to just replace the dist. or try fixing it your self its a bit of a PITA but its basically free. If you pull the cap off the dist can you turn the rotor any?
Get that fixed then see how it drives.
You might want to check the float levels on the carb and make sure all the screws are tight sounds like you may have a flooding issue if the back plugs are black although most manifolds dont feed just the back half of the engine. What manifold are you running?

 

[Moon's74]

I'm running a performer 289.

I've adjusted the floats, idle screws, and choke.

I can turn the rotor CCW about 5 degrees and it springs back. It won't turn in the CW direction. Does this mean it's bad, or is that normal?

Where should the vacuum to the dizzy be plugged into?

 

[oleguy74]

make sure you don't have a broken spring on centrifigal adv.ccw and springs back is good.put it to ported(timmed)vac.trans and pcv are full manifold vac.

 

[broncnaz]

5 degrees sounds a little low. but at least it moves so thats a good sign. Still as oleguy said soemthing could be broken.
I dont think your flooding as that manifold should be a 180 degree so that kinda rules that out for the back plugs.

Dist vacuum should be hooked to the port on the side of the carb thats above the idle mixture screw.

For your high speed running it could be either the secondaries are opening to early and to much or they are not opening and your running out of airflow. But then again I've had timing do that same exact thing.

Put your engine back on TDC and check to see make sure the rotor is pointing to the #1 position on the dist cap. Maybe the rotor is out of phase. could be a broken roll pin on the dist gear.
Do you have good plug wires? Did you just install the MSD or did this problem just pop up? Maybe the MSD is bad they do tend to fail more often than other setups.

 

[cobradoc]

Mechanical advance is stuck.Vacuum for the tranny needs to be direct manifold vacuum,not ported.

 

[av bronco]

After you check your mech. advance set your timing with the vacuum advance disconnected, then connect to ported vacuum, then if it dont run right its got other probs.

 

[DirtDonk]

Engine idles fine, but loads up, sputters, at higher rpms. Basically, no power.

Not surprising at all, if initial timing is set at 40° and you're still getting mechanical and vacuum advance!!!!! You're basically just running out of power because the pistons are still coming up when the flame-front hits the the top.

Replaced power valve and jets on carb.

To what? Same size and rating, or different?

Back 4 spark plugs are very black, front 4 plugs are light brown...just right. What gives?

Can't tell yet. Get the dizzy in order and then move on to the carb if you still have uneven plug readings.

I can't seen to get the timing correct. I've read that vacuum advance should be on manifold vacuum (ie full time)? Wait a minute, I've also read that it should be on the timed spark advance on the carb? Which one is it?

In the case of your Bronco, like the others have said, it should be timed, or "ported" spark vacuum.
Some cars are spec'ed to run full vacuum, and other smog vehicles run it, but through so many controls that it's not quite straight vacuum either.

Also, with no vacuum to the dizzy my timing is way advanced, like 40 degrees. Checked the harmonic balancer position with #1 at TDC of compression stroke, sits right a 0 on the pointer. Start it up and the timing light shows 40 degrees advanced.

Sumpin's not smellin' right.
What timing light are you using first of all? If it has a dial-back feature, check to make sure it's at zero.
What's your firing order? Have you double-triple-quadruple checked the order of the wires and where the number-1 wire is in relation to the rotor at TDC?
That was mentioned too, but it's worth repeating.
And the "out-of-phase" comment is worth digging deeper into if you can't find anything obviously wrong.
And last, but not least, are you sure you're hooking the timing light pickup to the number-1 plug wire? Don't go by the distributor order unless you know it's exactly right. Follow the wire from the cylinder itself to make sure.
I know that's basic stuff, but since we're not there to look over your shoulder and utter snide remarks at you in person, we get to have fun here while you're sweating under the hood.

Checked the vacuum diaphram on the dizzy, it works correctly.

If it's still hooked up when you're checking your timing, that's why you're at 40 degrees. If it's hooked to a timed port, it won't do that unless your carb plates are not in the correct position.

Tried to retard the timing and it loads up really bad and will not run.

Gotta check into this, but get the dizzy inspected first, disconnect the vacuum, then try again. It may be just as simple as the idle adjusted to low so when you start to retard the timing, the engine just wants to stall and it sounds like it's loading up.
Next time you try to retard the timing so something more normal, keep one hand on the throttle and see if you can keep it running. If not, on to step 39.

With timing at the advanced, original, position I revved up the engine and it advanced even more...without the vacuum connected. No change with the vacuum connected to the timed port on the carb.

No change in timing, or in the way it acts when revved up?
There should be little or no change in timing when the hose is hooked to timed vacuum since there is little to no vacuum signal in the port while the throttle blades are closed.

Where should the transmission get it's vaccum from? Tranny and PCV are on bottom front of carb, back port is plugged for lack of brake booster.

PCV is on the large 3/8" port on the front (or back if you prefer). I thought the Holleys had the PCV port on the side? Are the T/A's set up different?
The trans would normally be hooked to an intake manifold vacuum source near the back of the manifold. I don't see why it couldn't be hooked to a small port on the carb, at full manifold vacuum, but they aren't "normally" hooked to the carb. They're typically hooked to a vacuum "tree" type connector near the back of the manifold, along with brake boosters too, sometimes.
Maybe someone who knows more about that can chime in and tell you if it's a problem to have it hooked to the carb.

Paul

 

[DirtDonk]

And as someone else asked, did this just start or has it been an on-going issue?
You just buy it like this or did you install the carb and manifold?

Thanks

Paul

 

[stock1970]

if it only acts up when you are trying to give it gas, then i would make sure there is no gasket leaks on carb to intake and intake to block.. just my .01 ..

 

[blubuckaroo]

#1 is cylinder is the one on the passenger side front. I'm not trying to be offensive but a lot of Chevy guys make that mistake.

 

[Moon's74]

I've double-quadruple checked the firing order and hand over handed the wire to the right plug.

I replaced the intake and carb. Hasn't run right since. It was sitting in the garage for a while before I installed everything. Probably got moved a time or two. I marked the dizzy position both on the dizzy by the block and at the number one cylinder position from the rotor to the dizzy body before I took it out...with the #1 piston at TDC on power stroke. Stabbed it back to same position.

The timing light is not a dial-back and was connected to the correct plug wire, see first comment.

I reset the #1 cylinder to TDC on power stroke, the timing pointer was at 0 on harmonic balancer and the rotor was pointed to where the #1 cylinder is on the dizzy cap. I then, once again, removed the dizzy and re-stabbed it...I know it was moot with everything pointing in the correct place, but I wanted to check a tooth off in either direction...neither lined up to numero uno on the dizzy cap. Stabbed it back in correctly. No change in status.

I did mess with the carb at first. Changed the power valve to a 45, no change, back to stock 25. Changed primary jets to 58. Changed black secondary spring to silver, looser spring, no change, back to black...that's when I started messing with the dizzy and got frustrated.

BTW, I totally understand the no brainer questions and I don't get my panties in a bunch over them. Any and all help is greatly appreciated.

I'm leaning towards bad dizzy. Are we missing anything?

 

[Moon's74]

With respect to new dizzy. Steel gear or iron gear, which one is mandatory. My understanding is that early models, like mine, can use either gear, but late model 5.0's REQUIRE a steel gear only. Is this correct and can I buy one with a steel gear?

 

[cobradoc]

Steel gear is fine.Are you running a Duraspark?If so does the box have the potting melted out of it?If it does replace it.6.5 should be the stock PV.Make sure the transfer slots on the secondaries are not uncovered.IE the throttle plates are closed.Floats should be set so fuel just dribbles out if you rock the truck.Base timing should be 10 to 14.

 

[broncnaz]

I'm not sure about running a steel gear on a cast cam. I'd go with the cast gear. I dont think you can buy a duraspark dist with a steel gear anyways.

next two questions what color are your spark plugs? Do you have a vacuum guage and what is your vacuum at idle? is it steady?

If the transfer slots in the secondaries were uncovered his idle speed would be way high. Doesnt sound like he has any idle issues.

 

[cobradoc]

They only have to be exposed 30 to 35 thou to jack his world up.

 

[broncnaz]

Yes but that usually results in a very high idle to the point adjusting the mixture screws doesnt even make a differance.

 

[cobradoc]

I'm not the one that needs help here.

 

[Moon's74]

Out of town last 2 days. I appreciate all the input. Back at it today. Hopefully we'll find a smokin gun. Thanks again to all.