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Discussion Starter · #1 ·
Hi guys, I have an issue that I need help with.
I just recently installed some new parts on my engine.
  • Autolite Copper Spark Plugs (gap to .045)
  • Edelbrock Spark Plug Wires
  • MSD Blaster 2 Ignition Coil
  • MSD Pro-Billet Distributor (1 heavy spring + 1 light spring + 25° silver bushing)
The car starts up fine with the choke closed, but idles pretty high 1100 - 1300 rpms. Even when waiting for the car to warm up it idles around the same rpms and doesn't show any sign of deceasing. Anytime I try to open the choke, the engine struggles to stay on and dies almost right away. The timing is currently set at 6 BTDC. Before this, with the stock setup, the car was idling at around 600 - 800 rpms. What could be the issue? Do I need to retune the carb or set my initial timing to something else? Maybe different springs + advance stop bushings need to be used? Any advice would be appreciated!

Here is the engine build list
(302 V8)
  • Eagle 347 Stroker Kit w/ ESP
  • Comp Camshaft, Lifters, Rocker Arms, Push Rods
  • Crane Valve Springs, Retainers, Locks, Stem Seals
  • Bronze Valve Guides
  • Sealed Power Intake Valves
  • ARP Main Studs, Rocker Stud Set
  • Milled Cylinder Heads (Factory)
  • Cloyes Timing Set
  • Engine Rebuilt – Balanced, Ported, Polished
  • Holley 650 CFM Double Pumper
  • Holley Dual Plane Intake Manifold
  • Aluminized Headers
  • Flowmaster Dual Cat-back Exhaust
  • Griffin Aluminum Radiator
  • Cobra Valve Covers
 

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My first thought was the carb, but if it ran fine before this I would suspect the timing. What was the timing at before the new distributor?
Does that distributor have vacuum advance? If so 6* with or without vacuum plugged?
6 degrees does not seem like a lot. You might want to advance it in increments and see if it idles without choke on. Then you can start tuning!
 
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Discussion Starter · #4 ·
Hi guys, thank you for the advice. The timing was set at about 10 BTDC before with the stock distributor. Today I decided to bump it up, the timing is currently set at 10 - 12 BTDC, but the engine is still idling high at 1100 - 1300 rpms. So that didn't fix the issue. I also tried messing around with the mixture screws and idle screw, but can't seem to get the car to idle anywhere under 100 without it shutting off. Is there a correct way to plug the vacuum advance? When I pull the line off to try and plug it the engine shuts off. So not sure about what my total timing is at exactly. I've attached a quick video of the engine idle after setting the correct timing. It's dark now, so I will double check my work again tomorrow.

Engine idle
 

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In light of you trying the timing, I agree with Galaxiex ,that it very well could be a vacuum leak.
 
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Discussion Starter · #7 ·
Engine idle okay now

Hi, here's an update, see video above. It turns out my issue was the distributor vacuum advance line was hooked up to the manifold vacuum source instead of to the timed spark port on the carburetor. My guess is that the new distributor was running way too much advance before. Idle checks out now, but I'm getting backfire from the carburetor and it keeps shooting my PCV hose off. Am I running too lean of a mixture? I am waiting for a vacuum gauge to come in, I'm don't do well tuning by ear.
 

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I would get a timing light and a tach on it and note the advance through the RPM range without vacuum and with vacuum. It could be some heavier springs are necessary to slow the advance curve which would also drop the advance earlier on the way down. Usually like to hear a late-timing grumble through the exhaust on deceleration.

Lots of goodies going on here with cam, intake, carb, ignition, and stroker crank. Each one is a variable that complicates the tune. I noticed your build sheet shows no specs on cam grind. I am sure you know that higher overlap cams reduce vacuum and that stroker cranks may need different spark advance at idle than stock cranks.

I read some articles calling for 12 - 14 degrees on a 347 and the cam grind can allow some fire into the intake if everything else is not tuned correctly.

Your vacuum gauge will help you diagnose and Holley has some good videos on youtube. Keep us posted.
 

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Engine idle okay now

Hi, here's an update, see video above. It turns out my issue was the distributor vacuum advance line was hooked up to the manifold vacuum source instead of to the timed spark port on the carburetor. My guess is that the new distributor was running way too much advance before. Idle checks out now, but I'm getting backfire from the carburetor and it keeps shooting my PCV hose off. Am I running too lean of a mixture? I am waiting for a vacuum gauge to come in, I'm don't do well tuning by ear.
One other thought on this. I worked at a motorcycle shop back in the early 80s when emissions regulations were just hitting the industry. We had a particular bike (1981 Yamaha Virago 750) that would lean misfire and blow the carburetors out of the rubber intake boots - similar to blowing off the PCV hose.

The only cure on these was to drill out the factory installed plugs and do a manual adjustment to the O2 setting - basically richen up the idle mixture. The Holley has a lot of adjustment available to you and you can probably get that dialed in with your vacuum gauge by bringing the throttle plate closed to work with the airscrew adjustment.
 

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hm. so you're saying that right now, if you switched the vacuum advance back to "manifold vacuum", the idle would shoot from 700 up to 1100?
what is your timing set at currently?
 
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