mev

Gentlemen,

My '74 has a 400 cu small block with HEI ignition. (It came with it.) The engine was rebuilt by a reputable builder. But he probably followed my directions instead of doing what was right. Anyway here's some particulars and the problem(s).

Idles at 780 RPM
Compression: 250 psi each cylinder
Holly carb w operating electric choke
HEI ignition is _now_ on a separate +12V source.
AC Delco 45T plugs w 0.045" gap
Timing 10 BTDC
Before adding separate 12V source, plugs are black indicating rich a mixture.
In an unsuccessful attempt to solve the problems I:
1) adjusted valve lash while running.
2) leaned the mixture 1/4 turn (both sides)

Problems:

1) If the engine doesn't start on the first attempt, exhaust gas exits the carburetor and fuel exits the Holly's vents. This occurs with a pfffft not a BANG.

2) The car backfires (with pops not BANGS) from the (right hand) tailpipe.

3) In my uninformed opinion, the engine smells like it's burning rich.

Since exhaust gas is exiting the carb I assumed that the lash was keeping an intake partially open. Adjusting the lash didn't eliminate this symptom.

To fix the black plugs and stop the tailpipe's popping I leaned the mixture 1/4 turn on the new Holly carb. I haven't check the plugs but the tailpipe still pops.

So now I'm guessing I told the builder to use the old hydraulic lifters and one of them is bad.

Thanks for any help

Mark Valenti
tiomev@hotmail.com

cv67

Could very well be a lobe pull the intake
Do rockers start getting "loose" once they are adjusted meaning with some run time?
HEI should have 12 volts runing to it that sounds fine far as I know

mev

When I did the lash adjustment (while running) I thought the rockers were tight. I backed off _at least_ a full turn on all of them before they would start ticking. After zero lash I gave them a half turn, a quarter at a time. I haven't checked since. But I will.

Thanks for the reply.

74modified

It could be a number of things. First of all fuel should not be coming out of the vents no matter what else is happening. - Fuel pressure too high, float setting too high, or bad/dirty needle seats.

63mako

You have a wiped cam if you put used hydraulic lifters on a new flat tappet hydraulic cam. NO DOUBT! Really bad place to try and save $80.

Mike Ward

Could be a couple crossed plug wires.

garygnu

do a compression check .maybe the distributor is off a tooth or 2 .maybe a bad valve not seating .if the valves were set wrong a valve could be hanging open a little .saw a way to check for a bad cam lobe .put a bright line or spot on the push rods .rotate the crank with the plugs removed .if the line or dot rotates the lobe mite still be good .or set a dial indicator on each rocker and measure for lobe lift.what intake do you have ?some intakes had a hole from the plenum into the passage connect to the exhaust ports .if you have a intake like this tap the hole and plug it .

63mako

http://www.cranecams.com/bulletins_listview.php?s_id=4

mev

I forgot to mention a compression check showed 250 psi on each cylinder

mev

The cam is the original cam also. Does that change your opinion? (About the cam not about being stupid/cheap.)

Thanks

mev

Hahaha. That was an earlier problem that got fixed.

diehrd

That sounds 100% dead on . I would lean towards float level to high.

Check that stuff and post back..

mev

I will. Thanks for the second.

mev

Thanks

roadblock69

Since it has spit back through the carb, you may also want to check the condition of the power valves. That could also cause fuel to burp out of the vent tubes.

keithl1967

what made you adjust the valves (I assume it is a hydraulic cam)? If you overtightened one, you could have wiped a cam lobe (or bent a pushrod, etc).

As far as re-using the cam and lifters--that is generally OK (but not recommended), but you MUST NOT mix up the lifters--ie, they must go back on the EXACT lobe they came off of, otherwise you are asking for trouble, because the wear patterns will not match...

Is there "popping" through the carb also?

Duane4238

Something else to check, here. (I know from experience) Make sure your Holley carb accelerator pump arm (arms if double pumper) are adjusted correctly. If too tight, they will drip gas while at idle and when you shut down. Check how to adjust in a holley performance book.
Duane

mev

Because the exhaust vented through the carb and because gasoline exited the carb throat and vents, when the engine didn't start immediately, I concluded that an intake valve was not closing 100%. If so, adjusting the lash could have solved this problem.

The lifters are hydraulic.

Although I didn't record the number of turns to loosen and tighten the rockers, I'm certain they are not tighter than before.

We used a Sharpie felt tip and numbered the lifters when we pulled them. They should be in the same locations.

There are two different backfire noises when running: a distinct pop at the tailpipe, and a muffled pop of no discernible, origin even with the air cleaner removed. To answer the question, the carb does not pop.

Thanks

63mako

If the cam was swapped and lifters matched with the lobes they came off of your probably fine. I misunderstood, thinking you used a new cam and used lifters. If compression is #250 across the board and uniform your cam lobes are likely fine as are your rings and valves. If your positive your valves are set correctly your looking at ignition or fuel. Most times it is ignition, start there always. If your plugs, wires, cap and rotor, points and condenser are all good then distributor timing and advance curve are next. Make sure your shaft bushings are tight, centrifugal and vacuum advance is working, advance plate and weights moving freely and Vacuum can diaphragm is good. Set up your timing curve properly following Lars papers. You will have to email him @ V8FastCars@MSN.com to get the most recent version. Once this is done, then and only then address carb issues. All the ignition stuff needs to be right and done no matter what so start there as 90% of perceived carb issues are really ignition related. If the car was running right with that carb at some point with a sudden rich condition likely a dirt, needle, seat issue or saturated float.

mev

I will

Thanks