pull the plugs. Was the cam a flat tappet?how much was spent on blue printing the engine? Pull the top off the carb? change fuel filter?

what have you done so far? compression good? was the engine tuned after installation?

why did you put a mild 350 in where a turbo boxer used to live?

 

I pulled plugs 2 & 4. They looked the same, brand new. The engine was rebuilt by Dave Conway at Propower Engines. $3500 with a flat tappet cam. I removed the valve cover to make sure all the valve were opening. I didn't measure the valve travel. I have looked for vacuum leaks around the intake with carb cleaner, and on the brake booster line. The vacuum gauge is bouncing around all over the place. I checked compression on Cyl 4 it was plenty high.

My next guess was to take the carb off and take it apart, but I've never done that before.

Any other ideas on what to check first?
Cheers
Mike B

Oh, and the V8 has at least twice the power of the original flat 6 in this ,77. And way easier to fix, or so I am told.

 

sounds like you have lost one side of the carb . look down the carb while the engine is at about 2000 - 2500 rpm and see if the fuel flow is even . or do the down and dirty and cross two plug wires and back fire the heck out of it !

 

What is back firing it going to do? And how exactly do I do that?

 

back firing will hopefully knock the dirt out of the jet . cross two plug wires and open and close the throttle several times . DONOT DO THIS A HOLLY CARB !!!

 

cold engine... count the number of fractions of a turn it takes to lightly seat the idle mixture screws from their current position..

then remove them.. with some carb spray and a spray nozzle.. spray into the idle mixture screw holes.. followed by a blast of compressed air. do this 3 times per side.. you might have a clogged idle feed restrictor and that will cut off the fuel to half the carb up thru about 1500 or 1800..

 

Check for intake leaks. Both from the outside and internally. Not sure about your modified engine but usually anything more the 2" of vacuum at the oil dipstick tube means an internal leak.

 

Sounds like a big vacuum leak on one side of the engine given 2,4,6,8 are all in a row. The carb if on a 2 plane intake starving on one side would affect a different cylinder mix that would include 2 cylinders from each side. A single plane intake would have all 8 drawing from a common plenum that would screw up eveybody.

I think the cam loosing all the lobes for one side of the engine is a remote possibility.

A vacuum gage that bounces is a good indicator that there are cylinders not pulling evenly. My first inclination if this is on one side would be the intake isn't sealing up a common area of leakage is along the bottom so a conventional check for leaks may not yield any useful information.

Bogie

 

OK, thanks everybody for the feedback, I got around to looking at it again last weekend. I took the carb apart completely and cleaned all the needles, jets, and passageways with carb cleaner and air, plus adjusted the floats and put it all back together. Put it back on the engine, and it runs exactly the same. So either the carb is still broken or its not the carb.

Next I tried a few things suggested by various people. The symptoms are at idle the header temps are approxiamately 2-700F 4-200F 6-200F 8-200F. And all the odd cylinders are about 550F.

When I rev the engine up to even 2000rpm, cylinders 4, 6 & 8 kick in and it runs more smoothly, and the temps go up on those cylinders.

I put a vacuum gauge on the PCV valve inlet and there was no reading, I think that means there is not a large internal vacuum leak.

I then tried adjusting the idle mix screws, even completely closed, neither idle mix screw would cause the engine to shut down or change rpm. That seems weird??

I took my propane torch with a rubber hose on the end and fed propane all around the intake, bottom of the carb and even in the filter, and there was no change to the idle.

So I'm still stumped, and looking for ideas?
I did get a call from Dave the engine builder who suggested these things to try. Thanks to whomever on here let him know. Much appreciated.

Mike B

 

Back in early summer my sbc did the same thing and I found that The (new) intake gasket had given it up. Altho it was for a sbc it was no big enough to properly cover the intake ports of my aluminum heads. Strangely enough the propane didn't reveal the leak where wd40 did. I'm thinking the cylinders were already so lean the it had nothing to fire the propane and the thicker oil closed off the leak enough to help the cylinder fire. I recall I replaced it with a felpro 1266.

 

Can you tell me where exactly you found the leak? Where to apply the WD40 to make it obvious?

Cheers

 

somebody last week posted a picture.. of how they found their leaking intake manifold gaskets.. they transferred the base plate gasket holes to a piece of metal... drilled and tapped a hole so they could hook up some low pressure air to it... air was found leaking out the crankcase breather openings.. indicating a leak that was not visible.

 

"out the crankcase breather openings" Would that be the valve covers?

 

Thanks for the input. Pulling the intake is not so easy as it requires the engine to come out. Can't clear the distributor in the engine bay as the engine comes in from the bottom. PITA. Hopefully I will have some time over the holidays to get at it.
Cheers and Merry Christmas everyone.
Mike

 

You can feed some propane or acetylene into the valve covers and see if it affects the idle. If it does you have an internal intake leak. A common issue is using intake bolts that are a little to long and they bottom out or worse hit a push rod. This is not something that can happen in all engines but I don't know which off the top of my head. You could try pulling the intake bolts and putting a flat washer under them and re-torquing.
If the heads were milled excessivly or the deck cut a lot it will effect the angle of teh intake to head contact which can also cause internal leakage.