Engine stall, no start, start, losing power, Single Carb Jetting

[Whaanga]

My engine has been running well and is very reliable.

However -

Today, on the way home, the engine stumbled a little and then stalled. This has never happened before. It would crank but no start - I thought perhaps it was flooded and so waited 10 minutes or so - but still no start.

I checked the vacuum lines and connections and saw no evidence of leaks.

The gas gauge was reading low and so I thought perhaps I had run out of gas. My wife came to the rescue and brought down the gas container from the shed and I emptied it into the tank.

I tried the engine again and after two attempts, it started up. I drove toward home and it ran fine but on two occasions, it bucked a little and began to lose power. I pulled over and let it settle and then it came back up to full power. This happened two more times.

For the rest of the way home (about five miles) it did pretty well. However, when I would give it more gas to increase speed, the engine would resist and begin to lose power again until I let up on the gas.

I got home and let the bus sit for a few hours and then tried it again and it started right up.

As I work to correct the problem, what variables do I evaluate? Fuel pump? (The bus came with a chattery electric Fawcett pump), carb needle valve? Fuel filter? Other considerations?

Thank You.
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Late 1973 Bay w/a transplanted 914 Engine

[Angus II]

Hello,
I'd, start at fuel filter(s).

[aeromech]

I agree with the fuel filter. Since it’s close to empty I’d drain the tank and replace the finger strainer that lives up inside the tank outlet. And then the main filter.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Nicholas D]

I had a pretty similar issue with my '71 westy about a month ago, took Aeromech's advice and replaced both in-line fuel filters as well as the finger strainer in the tank and it seems to have solved my problem. He also suggested (and I did) flushing the tank once you remove the old strainer. I just ran a short piece of fuel line into a bucket straight out of the tank and ended up flushing out several chunks of something that shouldn't have been there with a couple gallons of fresh gas.

[mikedjames]

I am going to say carburettor needle valve - the stumble is running rich, the no start is flooding that gets worse the longer you crank as even more fuel leaks through.

Happened to me once, engine stumbled a bit at 30mph in 4th, pulled off the road to drop off my daughter at the railway station. Stopped the engine and it would not start until I stopped trying to start it and left it for half an hour.

I was an hour late for work that day. I kept the engine speed up to stop it flooding again.

The needle valve on the progressive carburettor had a very visible wear ring on it where it was in contact with the seat.

At work, I fitted a slightly less worn valve to get me home.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[Whaanga]

Thanks for your help.

I drained the tank, cleaned the sock screen, flushed the tank with fresh gas and replaced the filter.

I had the tank boiled three years ago so thought I would be in good shape.

You can see from the photo that there was a little bit if debris at the very bottom of the screen.

I also used this cheapo plastic filter to watch the flow and see if there was anything coming through. I saw a couple of little flecks but that was it.



I always enjoy bathing in gas but feel confident the tank is not filled with rust and crud. Will check the carb next. The engine runs rich so am planning to change out the jets.

After doing this work, the engine started up and ran well. Wasn’t able to go for a drive but will get to it ASAP.
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Late 1973 Bay w/a transplanted 914 Engine

[Whaanga]

Am seeking some more input here. In my last post I wrote about the work I did to check the fuel filter, finger sock, etc. We had snow here in Rochester recently so have not driven the bus since to see if my work solved the issue.

The snow is now gone and we have nice weather again so I checked out the bus. It started right up and ran great. I went for a little drive in the neighborhood and within one minute the engine bucked a little and then stalled. It started right up and I turned around and drove home. I let the engine run while in the drive way and there was no stutter or bucking or anything. SO - I went on another neighborhood drive and for the first minute or so - everything was great and then the bucking and stuttering started. And as long as I kept the RPM's down, it would run. But If I gave it some gas, it was hestitate and start to fail.

I got home and again and let the engine run in the driveway. It ran fine as long as the bus was stationary. But as I pulled in the garage it stalled and now won't start. I smell gas so I think it's probably flooded.

This happened a couple of years ago and the issue was the float was out of spec. Once corrected, it has run beautifully...until last week. (I've ordered a new needle valve and new jets for my single Weber carb.)

Why does it run so well when not moving? Why does are there issues as soon as I'm in motion? What other things should be considered as I diagnose this issue?

Thank You
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Late 1973 Bay w/a transplanted 914 Engine

[Abscate]

Lets get those plugs out and have a look at them

If the needle valve is getting gunked, the flow and sloshing would explain the driving conditions but symptom based troubleshooting rarely works
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.ssS!

[Whaanga]

Thanks Steve,

Here’s #2 plug. Looks pretty rich.

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Late 1973 Bay w/a transplanted 914 Engine

[Abscate]

That’s some Good rich black fluff....I think the needle valve probably is the culprit based on how rich that looks.
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.ssS!

[Whaanga]

So - replace and/or clean needle valve plus new plugs too?
_________________
Late 1973 Bay w/a transplanted 914 Engine

[Abscate]

You can just clean those plugs, no need to replace.

That fuel filter seems light on gas, isn’t it usually filled up?
_________________
.ssS!

[Whaanga]

Ok - So I did all of the work on the fuel lines, filters, etc. as chronicled above.

Tonight I tore into the crappy single Weber carb and replaced the needle valve. I also replaced the main jets with ones sized at 135 - the ones that were in there were sized at 137 and 140. I also replaced the secondary idle jet that was rated at 60 with one at rated at 55.

The engine started but was not running at its maximum. I adjusted the mixture screw (which was all the way in) and backed it off a half turn at a time until it ran better. And once it the mixture screw was adjusted, the engine ran nice and smooth.

All seemed good - until - I opened up the throttle and the engine died. This happen again and I discovered that no matter what I did, I cannot get the engine run at high RPM's.


I took things apart again and removed the 135 main jets and reinstalled the original ones - and to my frustration, the behavior was exactly the same!! So now I'm stumped - When it comes to comes to carbs - I'm an idiot so would appreciate any help.

Thank You,

Jeff
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Late 1973 Bay w/a transplanted 914 Engine

[Abscate]

Ok, time to check fuel delivery.

Let’s check the voltage at the fuel pump, compared to battery voltage, first.

Then let’s remove the fuel line at the carb and see how much fuel is being delivered in one minute. Needs to be something like 200 ml per minute or more

At load, the. Carb is in its simplest mode, it’s just a pipe sucking vacuum at good air flow. If it idles well but won’t feed at high flow, that really points to fuel delivery
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.ssS!

[Whaanga]

Thanks Steve -

I've been wanting to replace my chattery fuel pump for a while now. Seems like this is a good time. Does any one have a recommendation for a replacement pump?
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Late 1973 Bay w/a transplanted 914 Engine

[aeromech]

I recommend Carter in-line electric fuel pumps. You'll need to find one that puts out about 4 psi. Then get a Holley fuel pressure regulator. Buy two of these rubber isolators for the mount. Get a fuel pump relay too.

https://www.amazon.com/gp/product/B01CVJ4F9O/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.summitracing.com/parts/hly-12-804

_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Whaanga]

Thanks Aeromech,

Is the wiring harness in your third photo a commercially-sold fuel pump relay?

[/quote]
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Late 1973 Bay w/a transplanted 914 Engine

[aeromech]

Zoom in and you can read the part number. It’s available widely and used on lots of different cars. As far as the wires go you make your own. If you need help just ask.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Whaanga]

[aeromech]

You probably could find a fuel pump relay at your local Autozone/pep boys
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound