Engine break in idle fluxuations-any ideas?

jim_howard_pdx · 10-13-2002, 11:33 AM

Well my engine is back together.

The new engine is a .30 over 351 block. New main and rod bearings. Crank was ground .20 mains .30 rods. New rings. New bronze guides. 16 new Ferrea Stainless Steel Valves, new valve locks.

The new cam is 296/396 duration 236/246 @ .050 lift. Lift is .496 intake, .519 exhaust.

My Holley 750 is jetted 72 on the mains and 76 on the secondaries.

Upon fire up, the engine ran with slight missing. Random missing. We tuned the idle circuit and ran the cam in at 2200 RPM for 20 minutes. During that time, the car would run steady for a while, then after a few minutes it would reduce rpm slightly, then increase slightly, then steady for a while, then do the reduce and increase over again.

Oil pressure remains very good, the engine was running on the hot side while breaking in the new cam, but this engine always runs on the hot side without air movement through the radiator.

Any ideas on the break in RPM fluxuation?

I plan to do a compression check this morning, and check each plug.

My wires should be ok, but I will check each one. The random missing is really bugging me.

Would a lean or rich mixture account for the RPM fluxuation?

PKRWUD · 10-13-2002, 03:28 PM

An unstable mixture could cause that. It's too bad you didn't have a vacuum gauge hooked up during break-in. I would attach one for the near future, and use it to help diagnose any irregularities. Note the vacuum gauge actions as soon as you notice anything odd, or a fluctuation in the idle.

Take care,
~Chris

10-13-2002, 11:33 AM	#1
jim_howard_pdx Registered Member Join Date: Apr 2002 Location: Portland Oregon Posts: 247	Engine break in idle fluxuations-any ideas? Well my engine is back together. The new engine is a .30 over 351 block. New main and rod bearings. Crank was ground .20 mains .30 rods. New rings. New bronze guides. 16 new Ferrea Stainless Steel Valves, new valve locks. The new cam is 296/396 duration 236/246 @ .050 lift. Lift is .496 intake, .519 exhaust. My Holley 750 is jetted 72 on the mains and 76 on the secondaries. Upon fire up, the engine ran with slight missing. Random missing. We tuned the idle circuit and ran the cam in at 2200 RPM for 20 minutes. During that time, the car would run steady for a while, then after a few minutes it would reduce rpm slightly, then increase slightly, then steady for a while, then do the reduce and increase over again. Oil pressure remains very good, the engine was running on the hot side while breaking in the new cam, but this engine always runs on the hot side without air movement through the radiator. Any ideas on the break in RPM fluxuation? I plan to do a compression check this morning, and check each plug. My wires should be ok, but I will check each one. The random missing is really bugging me. Would a lean or rich mixture account for the RPM fluxuation? __________________ 1966 Customized for daily street and highway domination. 358 Windsor running 425 HP C-4 Auto and 3.25 Posi

10-13-2002, 03:28 PM	#2
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	An unstable mixture could cause that. It's too bad you didn't have a vacuum gauge hooked up during break-in. I would attach one for the near future, and use it to help diagnose any irregularities. Note the vacuum gauge actions as soon as you notice anything odd, or a fluctuation in the idle. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
1968 engine numbers, 289 or 302?	andybud	Classic Mustangs	5	09-11-2003 12:14 PM
Popping sound @ Idle when engine cold, any ideas??	jetuomi	Windsor Power	10	05-31-2001 12:40 PM
Need help with idle	oldman	Windsor Power	8	05-30-2001 12:50 AM
Need Engine compartment dress up pics and ideas..	SKYWLKR	Windsor Power	5	04-27-2001 08:36 AM
Engine Idle Surge	RMARIANI	Windsor Power	12	02-01-2001 09:38 AM