mechanical fuel pump, 1974 dual carb bus

[Birdibus]

The word on the internet is that mechanical fuel pumps original to our buses, particularly but not limited to the years 1972, 1973, 1974 dual carb type4 engines, is that when the internal diaphragm fails the crankcase can be flooded with gas. Gas in the oil can cause rapid destruction of the engine. very bad.

I have gas in my oil. There are a couple other possible causes such as stuck choke plates or bad needle valves in the carbs, but since I see leakage at the fuel pump, I am slogging through endless pages of discussions and have learned a few things. Rebuild kits for OG mechanical fuel pumps for dual carbed buses seem to be unavailable as far as I can tell. A consensus seems to be building that rotary pumps are much quieter than electric pumps and are probably more reliable. They cost far less than NOS or rebuilt mechanical pumps. They do not require a pressure regulator. The old fuel pump should be removed and the hole covered with a plate such as the one offered by the Busdepot.

I'm collecting topics to list here since it has taken a lot of time to find some of these discussions. (sorry, they are mostly from another site)

What's wrong with type4 fuel pumps?

source for good fuel line: Pelican Parts

'super quiet' rotary electric pumpMassIV

mech pump replaced

Best electric fuel pumps

Fuel Pump block off plate

A good discussion and links

CB Performance rotary pump

[Birdibus]

This was a nice exercise in researching fuel pumps, but it turns out I don't need one. My problem was a split fuel line at the tee. I didn't know the right place to look so I didn't see it, as I should have.

A few corrections to the above post:
1974 and 1971 buses use 5mm fuel line. The above link is to 7mm fuel line which I understand is for FI engines, so I need to find a source for 5mm.

It is rare for original mechanical fuel pumps to fail in such a way that gas floods the engine. The pump has a vent and tube at the bottom for such emergencies, spilling the gas onto the ground instead of down the pushrod tube. Both the diaphragm would have to break and the vent tube be plugged in order for gas to flow to the crankcase.

Fuel pump failure is a possible, but unlikely cause of gas contaminating the oil. The most likely causes relate to the carburetors. I might have an issue with stuck choke plates, or I might have a needle valve problem. It seems to be an intermittent occurrence. Colin did a little quick fix to free up the right choke plate where it seemed to bind slightly against the case. If it ever pops, bucks, and kicks like it did in March, my assignment is to pull the carb covers and check the choke plate positons. The needle valves used during the rebuild of my carbs are the old ones. Apparently the new needle valves can have problems. Colin says, when first installed, the neoprene in the valve needs to be primed with fuel in a running engine. If not it might not seat properly and allow gas to get past.

[dtrumbo]

I really like buying from this place. They have the hose you need at a good price and you'll have it in one day since they ship the day you order from Phoenix.

http://www.autohausaz.com/search/produc ... er=N203551

[Sluggo]

I really like buying from this place. They have the hose you need at a good price and you'll have it in one day since they ship the day you order from Phoenix.

http://www.autohausaz.com/search/produc ... er=N203551

Autohaus AZ is the best! Great prices. Most of the same stuff you find everywhere else but cheaper. Free shipping on orders over $50 and they ship FAST! Plus (unlike some other companies) they call you when they notice the slightest anomaly in your order or if something is unavailable or back ordered.

Based on your description and without intimate knowledge of your vehicle, your carbs or any mechanical fuel pumps, I'd say needle/seat, bad float (happened in my Beetle with a mechanical pump) or a faulty cut off valve.

[dtrumbo]

Plus (unlike most other companies) they call you when they notice the slightest anomaly in your order or if something is unavailable or back ordered.

They're the best. They called me when a part I really needed was going to be delayed by a day. I always order from them first if possible. I have Bretski to thank for turning me on to them.