AirSpeed VW Community Forums

Technical => Engine Tech Forum => Topic started by: kombikruiser on May 14, 2016, 03:25:58 PM

Title: Fastback keeps dying
Post by: kombikruiser on May 14, 2016, 03:25:58 PM
I am having a hell of a time figuring out whats wrong with the ’67 fastback at the moment. Usually pretty good at figuring this stuff out, but this is going on 2 months now and I’m at my wits end. Any suggestions would be welcome.

Everything is stock, aside from upgrades listed below.


- Starts and idles perfectly when cold. Accelerates perfectly, after 1 min warm up, no hesitation or lack of power.
- Loses power after 2-5 km, feels like starving for fuel/running on 2 cylinders . Look at fuel filter beside tranny, 1/2 full (horizontal)

-Remove fuel line from from either carb; SIGNIFICANT SUCTION AND/OR VACUUM FELT BEING RELEASED FROM FUEL LINE?!?!?!? Positive that there is no fuel line blockage ( Turning on ignition with fuel line disconnected results in free flowing fuel, no restrictions, pump(s) is working fine ) Tank Vent is clear.

-remove top of carb, float bowls full
-Install fuel line back onto carb, turn on ignition, car starts ( after a couple seconds) idles fine. Accelerate away normally, symptoms return again, but quicker, after 10-30 seconds.

Let car cool overnight, starts fine, repeats above symptoms.

Steps taken so far:

-New points and condenser, then points changed to Pertronix Electronic Ignition.
-New Flamethrower Coil, New Bosch Blue
-New Distributer Cap and Rotor, stock vacuum Distributer.
-New Ignition Wire set
-New Spark Plugs.
-Timing set to 7.5 as per VW service manual

-Fuel tank removed and cleaned
-Fuel tank vent clear, no blockage
-New gas cap and seal
-Tank filter/strainer replaced.
-90 degree elbow at tank connection cleaned
-3 different electric fuel pumps tried, pump located directly under tank
-All hard fuel lines cleaned well.
-All rubber fuel lines replaced. Fuel filter located beside transmission. At no point is the fuel line higher than the inlet of the carbs. Minimal length of fuel line in engine compartment to prevent fuel from getting hot.
-Dual Carbs cleaned in parts washer, all passages and jets blown out (Rebuilt 8 months ago but went through anyway)

-New Battery
-Oil Bath Filter clean.
-Valves adjusted.
-91 octane supreme Chevron fuel used

I’ve searched samba forums, but cannot seem to figure this one out.

Thank you,
Title: Re: Fastback keeps dying
Post by: BUSDADDY on May 14, 2016, 04:08:45 PM
So you currently have an electric pump?, how is it powered (relay)?
Title: Re: Fastback keeps dying
Post by: kombikruiser on May 14, 2016, 04:17:17 PM
Powered from fuse block, on with ignition. No relay.
Title: Re: Fastback keeps dying
Post by: BUSDADDY on May 14, 2016, 04:30:39 PM
Then I suspect your ignition switch is breaking down when it gets warm. Bring a test lead (the ones with alligator clips on each end) along and jump between a live all the time fuse and an ignition fuse next time it dies, or do it first and see if it doesn't die at all.
Do keep in mind you'll have to pull the wire to shut the car off.

You really should get that fuel pump on a relay so it's not adding load to the ignition switch and doesn't run when the engine's stopped, a rabbit relay that connects to the coil or tach wire is the easiest to install.
Title: Re: Fastback keeps dying
Post by: kombikruiser on May 14, 2016, 04:34:00 PM
Yes, If I keep using the electric pump a relay will be added. I plan on returning the lines to the engine fuel pump as soon as I have this problem resolved.

The ignition was replaced by a brand new ISP type 3 ignition 6 months ago, so I really don't think that's it. I feel like it's fuel related.
Title: Re: Fastback keeps dying
Post by: BUSDADDY on May 14, 2016, 04:39:23 PM
OK, then bring a small squirt bottle of gas along and try a shot down each carb next time it quits, if it runs for a few seconds you've ruled out ignition issues and know it's fuel related.
Don't trust that Pertonix, they do occasionally fail or go intermittant, if you have points maybe install them during the troubleshooting phase of this.
Title: Re: Fastback keeps dying
Post by: kombikruiser on May 14, 2016, 04:46:45 PM
Haha, yea I've had my share of Pertronix failures, although this one is 1 week old out of the box, and I used it to eliminate points and condenser acceleration hiccups,which worked as the car accelerates much better now (when it runs)

When the performance decreases the car will continue to idle. If I keep trying to keep speed up while its dying, it is harder to start after I shut it off with the key. Which makes me think fuel.

Could it be a vacuum advance issue? The distributer is about the only thing I haven't changed.

Drove this car last summer with zero issues, this has all begun since spring.

Thank you for the suggestions Busdaddy.
Title: Re: Fastback keeps dying
Post by: BUSDADDY on May 14, 2016, 05:19:08 PM
Vacuum advance issues will make it kind of sluggish but it'll still keep up on the highway OK and idle fine (unless the retard side is ruptured but then it'll do it all the time, even worse when cold).
So this did the same thing before the Pertronix went in?, or at least very similar?

When it's acting up have you tried removing the gas cap?, any sudden whoosh of suction or pressure?

You may want to try a gravity feed fuel supply from a Jerry can or outboard motor tank in the rear trunk over the engine just to eliminate all the lines and pump. Just make sure you play safe and bungee it down.
Title: Re: Fastback keeps dying
Post by: rustybug61 on July 14, 2016, 09:49:30 PM
vapour lock? I'm kinda having a similar problem. I don't have the answer yet either