Thread: 1976 S3 Petrol 'Surging/Hopping' Up Hills & 'Cold Start' Question

1. Poor running up hills. Sounds like fuel starvation. Look for an air leak in the suction line from the tank to the pump, or the bottom of the pickup in the tank blocked - and it may only block by sucking up rubbish out of the bottom when the flow increases. Another possibility is ignition issues - I have had what looked like fuel starvation that turned out to be the points had closed up, and other things that give poor ignition could have similar effects. Fuel is sucked from the tank via a drop pipe in the top of the tank. Removing the panel under the driver's seat will show it. Late S3 may have this combined with the fuel sender, but not, I don't think, on the swb.

2. Fuel gauge. The issue, seeing it also affects the temperature gauge, is certainly a wiring issue, most likely an earthing problem.

3. Cold start light. The cold start light is switched by a switch on the cable and by a thermal switch on the top of the cylinder head, held by three screws (I seem to remember this was discontinued in later S3. The cold start with the Zenith is a simple choke, and all the light does is remind you it is still out when the engine warms up.

Hope this helps

Agree with John on fuel starvation
Recently had the same issue. Turned out to be a blob of gunk (highly technical term) that was being pushed into the float valve and slowing the flow only under high throttle operation
Cleaned the float valve chamber and the issue went away

need to look at fuel lines pump ect for surging first.

late ser 3 has a sealed tank for evaporative emmisions so you need to look if the breather is not blocked. I raided an early model and the tank breather filter is in the cap.

mine was surging very bad when cold until I selected low range.its much better since I replaced the spark plugs with a wide heat range type.

Last night it was dreadfull reversing a trailer into the yard in the rain. this is engine mount issue and sliding joint in the rear drive shaft.

my ser 3 the cold start light is a switch on the choke cable earthed and no switch used on the engine.1978.

Thanks guys,

Took a quick look at a couple things when I got home from work.
Looked at the top of the tank but didn't have time to get stuck in. Saw the gobs of sealant and knew I'd be doing some scraping/cleaning and possibly need to drain the tank, then source or make up some new gaskets, so not a job for tonight. At least this clears up how my fuel is fed, looks like it's from that black hose.
426_IMG_20170403_161319.jpg
There's 2 fuel filters (so far), an AC Delco paper element filter mounted to the bulkhead, and the glass bowl on the fuel pump. As you can see in the photo, there's some large objects in the glass bowl, the red-ish bits look like they could be from the sealant used on the fuel sender.

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Time is limited for me, we're fixing up the house to sell, and I can't let a major job on the LR turn it into a dead object sitting in the driveway for much more than a couple days.
While checking things out, I noticed the fuel pump is new.

Originally Posted by Cowboy Don

Thanks guys,
.......
While checking things out, I noticed the fuel pump is new.

Sounds like someone else was trying to fix the problem. The drop pipe into the tank should have a mesh filter on the bottom of it. This may be largely clogged with muck from the tank, lets fuel through until you increase the flow. It may also have one or more pinholes rusted in it - if it is sucking air this won't help either.

Blockages such as this can be found by sucking on the pipe using an oil syringe.

Clean your carby, filters and blow the fuel lines out, then remove the fuel sender from your tank and use a decent hose, about half inch "ID" as a syphon hose, to vacuum your tank out.
Use a torch so you can see into the tank and get any crud out from the corners etc. Keep tipping ten or so litres back in through a good strainer and repeat the process.

Alternatively removing the drain plug gets a lot of crud out, but some may remain in the corners or low spots if your bus is not on even ground.
Good luck.

Cheers, Mick.

Worth commenting on a problem similar the one described I had with a 4 cylinder 1970 LWB I owned in 1975 -76: At close to top speed - 70 mph on speedo it was inclined to surge /hop a bit. The problem became far worse, with it doing the same at about 40 mph after I pulled the (mechanical) fuel lift pump off the motor to replace the diaphragm which had started to leak and reinstalled it. Took me best part of two days to find cause. Anyway, the fuel line from lift pump to carby was nylon or whatever with short bits of steel pipe that had screw fittings on them. In the manufacturing process, the short piece of metal on the fuel pump end apparently had not been "deburred" after cutting. When pushed into the nylon tube, had cut a flap that restricted fuel flow in the process. The process of removing and replacing it from fuel lift pump was enough to disturb this little flap and make it a more effective unintended fuel flow restrictor. Was relatively quick and easy to fix the problem compared with what was involved finding it.

Thanks for the replies, everyone. Hopefully I'll get some time this weekend and start at the source by draining the tank and inspecting it. Reckon I've got some gasket paper so I should be able to get away without ordering parts (for now).

By the way, when priming the fuel pump it had excellent suction, instantly filing the bowl.

Also, thanks for the replies on the 'Cold Start'. I'll check to see if the thermostat is wired in any way to the light. If not, I'll assume, as JDNSW said, that being a Zenith carb the light is simply there to remind me the choke is on.