Surging stalling above 30mph

[Grodr625]

Hey guys I am getting ready for a cross country drive in my ‘64 S400 bus with a 318 poly. Engine has been running smooth until lately. Above 30-35 mph the engine feels like it’s about to stall. I get surging where gas pedal reacts and other times where it feels like an auto transmission slipping. The engine is still alive, but barely responds to my input.

I just replaced the coil, points, condensor, and replaced a dry rotted vacuum plug on carburteor. Any ideas on what’s happening here or what else I should check? My initial thoughts are vacuum leak.

I just tried to go above 30, got tons of surging and barely made it to a parking lot where the engine stalled out as I coasted in. After it cools down will run fine until pushed past 30 again.

[MadMC63]

Before or after you changed ignition parts?

[Grodr625]

I replaced the parts trying to eliminate the issue. There is a lot of fuel vapor coming from carburetor making me think its flooding, but also making me wonder if there is a vacuum advance issue or a vacuum leak somewhere. Its hard to check for leaks at speed. Any tips?

[PwrWgnDrvr]

I just tried to go above 30, got tons of surging and barely made it to a parking lot where the engine stalled out as I coasted in. After it cools down will run fine until pushed past 30 again.

Running fine until pushed past 30, then stalls and won't start until it cools down is contradictory.
Obviously, after it stalls and u coast to a stop, you are going less than 30.

[Grodr625]

Vehicle starts normally, idles fine, drives around town nicely. Once I start to push it last about 30, the engine starts to surge and eventually stops responding. You can still tell its barely running and today when the issue repeated itself, I coasted, with engine barely alive but unresponsive to driver input, to a stop where it promptly died.

The engine wont start for a bit after this happens maybe 5 minutes and then it will run right for a few minutes at low speed and begin to hesitate and stall out. Letting the vehicle sit overnight allows it to run fine until pushed to faster steady speed.

Cheers

[wally426ci]

Accelerator pump in the carb maybe?

[PwrWgnDrvr]

Sounds like it is seriously flooded, which is a carb problem. Setting awhile lets the extra gas evaporate so that it will start again. Then the cycle repeats.

[Grodr625]

So after further inspection I see a puddle of oil resting on top of the waterpump and some overspray on fan and drivers side inner fender. Will a leaking intake manifold gasket cause a vacuum leak and an oil leak?

Here are photos of my vacuum hoses coming off the carter bbd. Does everything look routed correctly? There is an unused port at rear of carb that I have plugged.

The vacuum choke has stopped operating (always open) further pressing the vacuum leak as culprit. I am planning to try the ol aerosol spray rpm spike trick to try to find the leak.

The carburetor is a rebuild unit from Autoline with maybe 100 miles on it, but could potentially be a bad or misadjusted float?

I am thinking I might as well replace the intake manifold gasket and go ahead and check my valve lash while I’m messing around with the top end.

[Grodr625]

Accelerator pump in the carb maybe?

I think this is worth checking out! Frustrating to have to open up this rebuild, but I haven’t driven it much in the two years since the carb was purchased.

[MadMC63]

The choke pull-off hose is right. The un-used line connects to the thermal sensor in the air cleaners snorkel. The large line typically attaches to the PVC.

[MadMC63]

The choke pull-off hose is right. The un-used line connects to the thermal sensor at the bottom of the air cleaner housing. The large line typically attaches to the PVC.

[Kaegi]

I bought a rebuilt from that same outfit in canada. they do not know how to rebuild carbs. they didnt have the horseshoe strap that holds the float hinge pin in place installed. float was just bobbing around in there and engine flooding horribly. also have you checked fuel flow and fuel pressure? filter clogged up? weak fuel pump?

[Grodr625]

I bought a rebuilt from that same outfit in canada. they do not know how to rebuild carbs. they didnt have the horseshoe strap that holds the float hinge pin in place installed. float was just bobbing around in there and engine flooding horribly. also have you checked fuel flow and fuel pressure? filter clogged up? weak fuel pump?

Good to know! They do a good job with branding and packaging and I just assumed Canadian was typically better than Chinese. Fuel flow seems high, just by looking at the carb filter, it is completely full, but very clear. I replaced my pre pump and pre carb filters last week. Steady streams of fuel coming spraying inside carb. Fuel pump has about 100 miles on it, stock mechanical unit. Looks like I have some work to do.

[Wildergarten]

Hey guys I am getting ready for a cross country drive in my ‘64 S400 bus with a 318 poly.

I wouldn't, unless I had a spare carburetor, tools, and a couple of filters. What you've got sounds to me like dirt floating in the float bowl occasionally clogging an orifice.

[wally426ci]

Accelerator pump in the carb maybe?

I think this is worth checking out! Frustrating to have to open up this rebuild, but I haven’t driven it much in the two years since the carb was purchased.

Are you heading back toward New Jersey? moving again? best of luck with the trip. I think we can sort this new problem out.

[Grodr625]

Are you heading back toward New Jersey? moving again? best of luck with the trip. I think we can sort this new problem out.

Hi Wally, you are correct. I am packing all my belongings and driving east back to NJ. Bittersweet reverse manifest destiny you could say. This forum has taught me a lot and I appreciate the ability to tap so much experience, thanks team :)

As far as tools, I am bringinging everthing I have. I have two resourceful friends coming for the trip with their respective roadtrip tool essentials.

For the trip we have a 6 ton jack and stands, 4x4 block of wood, 5 foot breaker bar, Budd wheel socket, spare wheel/tire mounted, extra coil, extra fan belts, extra points/condensor, extra fuel pump, spare carb, extra ballast resistor, spare coil of rubber fuel line, full electrical kit, fire extinguisher, fuses, oil, jugs of water, AAA RV premier, and a big ol roll of duct tape. And and the factory service manual, of course!

I have ordered a carb rebuild kit, an intake manifold gasket, and new plugs & wires. Here’s hoping these will do the trick. I’ve been looking up the intake manifold gasket job and it seems pretty straight forward aside from a heavy cast intake to lift off. Main take aways from Trey and others were: use red RTV, ditch the rubber end gaskets, and 30 ft/lbs. I might run a stud front and rear to help drop into place on first shot.

[Grodr625]

Hey guys I am getting ready for a cross country drive in my ‘64 S400 bus with a 318 poly.

I wouldn't, unless I had a spare carburetor, tools, and a couple of filters. What you've got sounds to me like dirt floating in the float bowl occasionally clogging an orifice.

I will be tearing into the carb this weekend if my kit arrives in time. I did let my past filters get too dirty, and could very possibly introduced dirt into the carburetor.

[Wildergarten]

Flat forehead is sign of wisdom grasshopper!

They need bigger emojis for something like this.

[Grodr625]

I got the intake gaskets replaced yesterday and am about to tear into the carburetor. That manifold was pretty darn heavy! Fingers crossed for no leaks. I ran red rtv around all the intake/exhaust and water passages, sprayed metal gaskets on both sides with copper rtv, and then put more rtv on top of metal gaskets around water passages only. Let the rtv tack up and over the course of 3 hours tightened it down incrementally in torque. I ditched the foam gaskets and went with straight bead of rtv front and rear.

You can see in the first photo why I opted for new fasteners. Mickey mouse job by PO for sure.


Fasteners needed- 8 pcs : 3/8-16 x 1-1/4”
8 pcs: 3/8-16 x 2”
16 pcs flat washer (used M10)

[IHWillys]

I experienced similar symptoms many years ago with a '55 Pontiac. It would start fine when cold, run good for a little while but then it would start to surge with the occasional lean pop out the carb, eventually forcing me to the side of the road. Let it sit a bit and it would restart fine and do it all over again. The issue was a partially clogged fuel filter in the inlet of the carb. Some fuel would get past but not enough to maintain normal operation. Thus the above symptoms. The little filter needed cleaned, a regular sized filter between pump and carb, and in the end, a good fuel tank cleaning.

Ken