454 help please!

[Guest OldSkoolBus]

Hello All!

 

First post, so please bear with me as a noob.  

 

I have a 1936 Wayne School bus that has been fully restored.  I am having an issue (electrical/timing/carb?) that I was hoping to get some input on from someone with more engine knowledge than myself.  While I consider myself to be a "Car Guy", I am far from an "Engine Guy"

 

So here is the issue:

 

On initial (cold) start, everything is fine.  Bus runs like a champ!  this seems to be only after sitting for a few days or at least overnight.  

 

I drive the bus for 20-30 min, then kill the engine.  Almost without fail, when restarting, it seems to be a "Hard" start. does not turn over smoothly but will always start eventually (2-3 seconds of cranking).  Upon starting, the bus runs horribly.  I can usually get it home, but it runs as if the plugs are fouled or timing is off.   Vehicle backfires and sputters.  If given full throttle, it will still accelerate, but reluctantly.

 

After the "Hard start" issue I let the bus sit overnight, and the next morning she fires up and runs perfect....drive for 20-30 min...shut it down...restart...same issue.

 

Side note:  I can drive the bus for hours on the initial start without any issues, it is only on the restart that I have the issue.

 

Engine is a 454 with Twin Holley 4bbl

 

Any thoughts?

 

Pic below:

 

 

Edited July 20, 2016 by OldSkoolBus
more info (see edit history)

[JACK M]

That is a weird problem. Especially with being able to run for long periods with no problems.

I would suggest that you get it to act up then run some spark tests (good hot spark on all cylinders) and fuel tests (pressure to the carbs).

Also make sure that the fuel line from the pump to the carbs is not in a hot place causing a vapor lock which is more common on hot days.

We are seeing some odd coil and condenser failures lately, even with new parts. So swapping out some ignition parts may yield some success.

 

The HAMB lends itself more to modified vehicles than this site but there are many of us that will be interested in what you eventually find as we as mechanics are interested in some of the maladies that people run across.

I hope that what ever you find you will update here.

 

Very cool bus by the way !!

 

[carbking]

Purely guessing:

 

The 454 is going to create a LOT more heat in the exhaust than the original engine.

 

Don't know where your fuel tank is located, but if using the original tank, and the exhaust is anywhere in close proximity to the tank; the tank vent (often through a hole in the cap) may not be able to keep up with rising pressure from the heat once the engine is turned off. Two much pressure in the tank will cause the carb bowls to run too full and create an overrich mixture, which could cause your symptoms.

 

Easy to check. Before attempting a hot restart; carefully remove the gas cap. If it tries to remove your arm, or you hear a loud "whooosh", you might play with the tank vent.

 

Truly an interesting problem. Really a good looking bus.

 

Jon.

[60FlatTop]

You need to thoroughly check every function of your timing. Check the vacuum advance, some modifiers don't think they are needed. Be sure that both the vacuum and mechanical advance mechanisms don't stick in their advanced position when the engine is shut off. Sticky ones will sometimes creep back overnight but not in a few minutes.

That's a starting point, could be the end point too.

Bernie

[Guest GT52]

If the engine has aftermarket electronic ignition components, like a Pertronix unit or an MSD box/coil, I would start there.  Those units are notorious for a whole host of odd heat-related "failures", including what you're describing.  If you have an OE coil and points to drop in there temporarily that would be a good test.  If you're already running points, I'd replace the coil and see what happens.  It sounds a lot like a heat-soak issue after you shut the engine off hot, and there is little air movement under the hood.

[intimeold]

454

 

I have had some experience with big block Chevy and Ford 429/460 engines. In non modified cars, street rods and campers.

 

Those engines in stock form,  generate tons of heat; then if they are modified, which even makes the heat problem worse.

 

Some cases we had luck. making a heat shield; and fitting it between the starter and block.  That is NO easy feat. Not much clearance there.

 

Always use a thermostat. Something like a  160 degree.

 

And always use a fan shroud, that actually surrounds the fan.

 

Some people have had luck, by adding a Water Wetter.  You can Google that.  I did have a 1958 Chevy 348 Tri-Power, that I used something like that and it did help.

 

I think the ignition timing has already been discussed. And check the advance too.

 

Looking at your machine, we can rule out rust and scale in the engine, by the way a nice machine you have there.

 

Of course make sure the radiator is designed for an engine that large.  I'll go back to that fan shroud, You have to use a good one; with a good fan too.

 

Take the starter to a starter rebuild shop; and have them check it.

 

It could be a combination of the above suggestions.

 

Good Luck

 

intimeold

 

 

[padgett]

Sure sounds like fuel boiling in the line. If using a mechanical pump is it fitted with a return line to keep the gas circulating (originally used on GM cars with AC). Where is the gas tank ? Does the fuel line from the tank run near the exhaust pipe (back in the early 70s A-body station wagons had the fuel tank in the driver's side rear quarter. They were not available with dual exhausts, all pipes ran down the passenger side).

[Mark Shaw]

I agree with Padgett, you probably need to install a bypass tee at the carb to allow fuel to circulate back to the tank rather than sit in the hot engine compartment waiting to be metered by the carb float valve.  Electric fuel pumps can help by increasing pressure to reduce boiling, but a continuous flow of cool fuel from the tank should eliminate any possibility for fuel starvation related to vapor lock.