Engine Issue 427/425

[Joe R.]

Re: Engine Issue 427/425

I don't have technical knowledge to answer if vacuum is the manifold or "ported". I took the vacuum reading from outlet on throttle plate in correct 4150 Holley carb. where you would connect hose from distributor. Consistently getting 7 in. reading at idle.

Walter,

Are you teeing in between the carb and distributor? What camshaft is installed? How many RPMs?

Joe

[John P.]

Re: Engine Issue 427/425

Hello Walter, What is your base engine timing set at? Did you set the timing with the distributor vacuum advance disconnected and idle speed lower than mechanical advance begins? Are you running direct manifold vacuum to the distributor or ported ? Does the engine run better if you advance the timing by manually turning the distributor? If so, check past posts from Duke and other members converting to direct manifold vacuum versus ported. This also involves changing the vacuum advance unit on the distributor to a lower vacuum signal unit ( B26 unit). These engines need additional advance at lower speeds to increase efficiency also resulting in cooler operation. Also, make sure you check total advance at speed after any modification. and verify that your timing marker and damper mark are correct.

[Greg W.]

Re: Engine Issue 427/425

Walter, If you put two differant carbs on the car with no change, may not be the carb. Had the same rough running on my 427/390 annd it turned to be the voltage regulator.The coil was braking down and not burning the gas. Just an eazy check with a volt meter. Rev it up see how high the volts go. Greg

[Oliver S.]

Re: Engine Issue 427/425

Timing chain set correctly? I heard a similar story couple of years a ago. They tried everything to no avail ... before they found the incorrectly installed tc.
Oliver

[Walter R.]

Re: Engine Issue 427/425

Car had been running fine so that would rule out timing chain.

[Walter R.]

Re: Engine Issue 427/425

I replaced complete TI ignition system with ponints distributor. No change. I checked voltage from alternator and it is OK

[Walter R.]

Re: Engine Issue 427/425

The engine was running fine and problem came up. I checked timing and it was spot on to mark when engine was running OK.

[John P.]

Re: Engine Issue 427/425

Walter, Plug all vacuum lines, adjust idle speed to about 1000RPM and check engine vacuum with a vacuum gauge connected to a port on the intake manifold, not the carburetor. Especially block off vacuum to the power brake booster if so equipped. What is your reading?

[John P.]

Re: Engine Issue 427/425

Walter, Also make sure that reading is steady. If it fluctuates rapidly, it indicated an internal problem such as a possible broken valve spring effecting intake port velocity.

[Walter R.]

Re: Engine Issue 427/425

I don't have power brakes and there is no port directly on intake that I can pull vacuum readings. Only port available is coming from throttle plate that goes to distributor and there is line that goes from carb to choke. This connection on carb itself. No other connections that I am aware of.

[Todd H.]

Re: Engine Issue 427/425

I assume the cap and rotor were replaced when the distributor was rebuilt? Are they still in perfect condition?

I recently put new spark plug wires on my '57 racer. I took my ohm meter along, and I couldn't believe how crappy most of the new wires were. Finally found 1 decent set at NAPA. Since yours was running fine with your wires, and the engine has so few miles on it, they should be fine, but testing them is very simple.

[John P.]

Re: Engine Issue 427/425

Walter, If you have a stock manifold, there is a port directly behind the carburetor that would have supplied the power brake booster. Without power brakes, this port would be plugged. You can also take a vacuum reading from the hose connected to the choke pull-off. This is also the hose many install a T fitting into to supply the distributor vacuum advance. With todays reformulated gas, engine idle speed and stability are effected. I chased a similar problem on a 67 427/435 that was corrected by converting to manifold vacuum with the addition of the lower signal advance unit. This idle instability creates timing fluctuations as well as carburetor power valve issues. Again a vacuum gauge is an excellent engine diagnostic tool.

[Duke W.]

Re: Engine Issue 427/425

I don't have power brakes and there is no port directly on intake that I can pull vacuum readings. Only port available is coming from throttle plate that goes to distributor and there is line that goes from carb to choke. This connection on carb itself. No other connections that I am aware of.

As has been stated previously, tee into the choke vacuum break hose. Report vacuum at idle speed. You should also convert to full time vacuum advance. This has been discussed, including the benefits, numerous times.

IF THE CAM IS OE, the OE 360 12 VAC is okay to use. What is installed? The above assumes an OE equivalent cam. If idle vacuum is not about 14" at 900, the cam is likely non-OE, and you will have to choose a VAC using the Two-Inch Rule.

Duke

[Walter R.]

Re: Engine Issue 427/425

After checking everything possible I replaced plug wires which had less than 5000 miles, cleaned and dried plugs and changed oil again as gas had gotten into base pan. Engine now running OK. Hopefully end of story.