Need Some Help Diagnosing a motor issue....

My dad has a 460 in his street rod '56, and we/he cant figure out why it wont run.  He changed the intake manifold that was on the motor when he bought the car, to a new style, and ever since, it will not run right. The intake that was on the motor was an OLD Edelbrock Street Master 460 intake, it looked to be at least 25 years old, and thats why he replaced it, because it looked like crap. He replaced it with a dual plane Weiand manifold, with standard intake ports, (the old Streetmaster had some awful intake ports, they were like 1/2 the size of a standard 460 intake port). He got everything together, and went to start the car, and it wouldn't start. It kept backfiring though the carb, it turned out that the timing was off from when he removed the dist. we reset the timing, but the problem didn't get any better. The car had a 600 cfm carb on it, which I thought was way too small for a 460, especially with the new manifold, which is much bigger than the old one, so he put an 800 cfm on, and the problem is still no better. The engine has a high idle, like a vacuum leak, but it doesn't have a vacuum leak, and everytime you give it gas, it pops out the carb and dies. We can get the motor to idle down by changing the timing, but then it won't start. Dad had another friend over at his place this morning, and they went ahead and reset the dist again, and put a new cap on it since the one that was on was really old, and its still no better. He is about at his wits end, and I don't know what to tell him, I'm beginning to think there may be an internal issue with the motor, but I don't know.

Sorry for the long story, what else should I advise him to check?? Thanks!

How are you sure that there's no vacuum leak? Manifold to cylinder head vacuum leaks are fairly common to BBF's, and that's the first place I'd look, especially if the problem surfaced right after a manifold swap. The high idle tells me there's too much air getting in from somewhere.

maverick wrote:How are you sure that there's no vacuum leak?  Manifold to cylinder head vacuum leaks are fairly common to BBF's, and that's the first place I'd look, especially if the problem surfaced right after a manifold swap.  The high idle tells me there's too much air getting in from somewhere.

I am almost positive, when dad put the manifold on, he did have an intake gasket slip, so when we first started, it had a very high idle, and there was no way through timing or anything else that could get it to idle down, so I, along with a friend of ours, took the maifold back up, and put another set of intake gaskets in, and made 100% sure that everything was in position correctly. The motor still has a higher idle, but not as bad as it did. So then, we blocked off all of the vac. ports on the manifold with brass plugs, and all of the ports on the carb with rubber nipples, just to see if on of them was leaking, and it wasn't because the issue didnt get any better, even changed the carb baseplate gasket, just to be safe, and its still no better...

If this car doesn't have power brakes, I'm still stuck on the manifold to cylinder head leak. You've checked & plugged everywhere else...and this still sounds like vacuum leak to me. Have you run a test along the gasket area?

maverick wrote:If this car doesn't have power brakes, I'm still stuck on the manifold to cylinder head leak. You've checked & plugged everywhere else...and this still sounds like vacuum leak to me.  Have you run a test along the gasket area?  

The car does have power brakes, I haven't run a test, on that area, becuase i'm not sure of the best way to go about testing it. How do you do it?? Thanks again.

514F-1 wrote:

maverick wrote:If this car doesn't have power brakes, I'm still stuck on the manifold to cylinder head leak. You've checked & plugged everywhere else...and this still sounds like vacuum leak to me.  Have you run a test along the gasket area?  

The car does have power brakes, I haven't run a test, on that area, becuase i'm not sure of the best way to go about testing it. How do you do it?? Thanks again.

unplug your big vacuum line that hooks to the intake and block that vacuum port off and try it if it starts the booster is leaking and needs replaced or hose the hose has a bad leak in it

Mark, your dad may have bought the wrong intake gaskets, they may not line up the same as the old ones, and the old intake may have been milled to match the heads, like maybe a angle cut, or a flat milled job?????? you have my number give me a call

There are numerous ways to check for gasket leaks. Some use carb cleaner or starting fluid. Even oil will make a very temporary seal and improve the way the engine runs for a short time...but it's messy. I use propane from a Bernz-o-matic torch with the diffuser removed. When the vacuum leak sucks in some of whatever you're using, the engine will tell you. Just be careful with any flammable stuff around a running engine.
No change = no leak.

I'm sure lots of guys have their favorite methods.

when I install a intake I have 4 x 4" all thread studs that I use in the corner that hold the gasket in place and let me slide the intake down in place and aligned then remove the stud after installing some bolts

Spray carb cleaner around the ends of the intake and around the intake ports and see if the idle picks up.
Have someone stand by with a fire extinguisher just in case.

Never mind I see someone's already suggested that!

Also,check to make sure the newer intake doesn't have a crack somewhere. It's sucking air somewhere. The popping is a LEAN condition from outside air being sucked in.

Did your dad check Intake fitment before installing it Sometime you need to have the intake trimmed if the heads had been milled to get things to fit right . My guess is that the intake gaskets moved while the intake was getting bolted down and the bottom edge of the ports are sucking crankcase gasses.

Tell your dad if the old intake worked before but is just ugly looking have it sent out and have it polished.


Dan

Thanks for all the help guys, I will let him know when I see him tomorrow. Lots of good things to check. Thanks Again!!

What kind of carb is on it??? I had a old (edel~broke) < on purpose.... one time had wore throttle shafts and it run me crazy like this some new bushings and it was fixed it doesn't take much to make things go nutzzzz

Before you go to too much trouble, pull the hose that runs to the brake booster and plug the port just to rule out a problem there. Also take a good look at that hose while you're at it. I know a guy who replaced an engine once, then found a hole burned in the underside of the booster hose. Not saying you'd go that far but...check the easy stuff first.

Did you double check and make sure there aren't any wires crossed?

DaveMcLain wrote:Did you double check and make sure there aren't any wires crossed?

I was going to suggest the exact same thing.

^^^^^^ plus wire condition, check the wire ends, put on ohm meter on them, check for a stuck float / and level as the carb was replaced, if it sat for a while I would pull the valvecovers and check for broken springs and make sure a valve isn't stuck.

It's that fast idle that won't come down that keeps me thinking "vacuum leak". The carb swap didn't change anything either, so I'm inclined to rule it out.

maverick wrote:It's that fast idle that won't come down that keeps me thinking "vacuum leak".  The carb swap didn't change anything either, so I'm inclined to rule it out.

Or he has to keep it idled way up to keep it running with the crossed wires.

DaveMcLain wrote:

maverick wrote:It's that fast idle that won't come down that keeps me thinking "vacuum leak".  The carb swap didn't change anything either, so I'm inclined to rule it out.

Or he has to keep it idled way up to keep it running with the crossed wires.

True enough. Rechecking the firing order should take about 30 seconds, too.

Hey guys, checked the firing order, its all good. He is going to put his old manifold back on, becuase we are both convinced that it is the issue, he has checked everthing that can be checked, so it's got to be the manifold. Ill Keep everyone posted...thanks again for the help...

Found no leaks?

maverick wrote:Found no leaks?

No, he couldn't find any, can't see any cracks, but i'm wondering if there is one in a spot that we can't see, we will be able to inspect it better with it off. Talked to a guy the other day who just bought a Victor Jr intake for his FE motor and was having the same trouble, turns out it had a couple pinholes in it that he didn't catch, I'm thinking this may be the same thing. I'll keep everyone posted, when i hear from him on what he finds out. Thanks again for the help.