71 Fast Back Recommissioning

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 12:19pm

The reason the brass fellas were fitted are because the cut offs got to an age and they failed. When it failed your car wouldn't start. They did have a small screw in the end, if you wound the screw it opens the valve to get your running. But obviously you loose the cut off function so the engine may run on. By the time these failed the cars were very old and parts were hard to come by. People didn't want to pay the big bucks for the replacement parts if they could be found. So "fixes" like the one seen on your carbs were used.
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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 12:21pm

broady_6 wrote:
11th May 2019 - 12:16pm
When you rebuilt the carbs, did you take that brass bit out?

Wiring wise, extend the wire from the choke around to the cut off solenoid when you fit them.

Yeah these will fit https://www.vwheritage.com/058129413e-i ... c-vw-spare
I don't think they are the correct ones - they may fit, read the entirety of the posts in that earlier thread, different jet sizes
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 12:26pm

Ive used one in the past, it will fit. even if the jet its wrong. Theyre removable, so the correct jet can be fitted.

Ive got a few correct type 3 ones, I am willing to loan them out (but theyre not for sale) if you want to try them before you buy some?
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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 12:32pm

Anyway back to a previous point, if you didn't take the brass bits out. I bet your problem is dirt in there. Take them out, clean it all out and it should run just fine. You may just find its difficult to turn it off
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JackReddick
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 12:38pm

broady_6 wrote:
11th May 2019 - 12:32pm
Anyway back to a previous point, if you didn't take the brass bits out. I bet your problem is dirt in there. Take them out, clean it all out and it should run just fine. You may just find its difficult to turn it off
Ok mate i’ll grab some carb cleaner when i go shopping and clean it out and see what happens 👍

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 12:42pm

If you have access to compressed air, it would be good to take the carb to bits again. With that brass bit out and then blow through all the parts of the idle circuit. Im pleased weve found a smoking gun :D

If you do need to borrow the proper cut offs ping me a message and ill can sort out a loan
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 3:21pm

Afternoon update time-

I’ve cleaned out the left carb (including all jets) and set both carbs back to “default” ie volume control screw out 1.5 turns and idle control set to just touch plus half a turn.
The right carb sounds much more throaty, the left carb seems quite lazy and if i disconnect the carb linkage and just rev the left carb it backfires a bit.
Also when i turn it off, there is smoke from the right carb if you open it up but not the left, sounds like maybe the left side still isn’t firing?

Anyone got any ideas?

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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 3:26pm

What did you do with the brass screw that is in the solenoid hole ?
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 3:27pm

Although it "sounds" like it is, is it actually? Always check the exhaust branches for heat. That will tell you what's firing and what's not.

Is it running better? It sounds rather like the idle or main circuit is still blocked on the left carb. When you take the carb top off, is the bowl full of fuel?

Out of interest what was behind the brass nut?
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 3:38pm

937carrera wrote:
11th May 2019 - 3:26pm
What did you do with the brass screw that is in the solenoid hole ?
I blew that out with the carb cleaner and refitted it. I tightened it all the way in, i’m not sure if that is correct?

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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 3:41pm

broady_6 wrote:
11th May 2019 - 3:27pm
Although it "sounds" like it is, is it actually? Always check the exhaust branches for heat. That will tell you what's firing and what's not.

Is it running better? It sounds rather like the idle or main circuit is still blocked on the left carb. When you take the carb top off, is the bowl full of fuel?

Out of interest what was behind the brass nut?
Yep the bowl is full of fuel. It’s not a nut, it looks like the bottom half of the solenoid minus the solenoid.
Basically the right half of this-
https://www.dellorto.co.uk/shop/other-c ... -solenoid/

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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 3:43pm

I would take it out again and see if it is interfering with the flow of fuel. If it could be, then shorten it or don't screw it in so far and run a test.

As well as the exhaust heat check, repeat the pulling of the spark plug test you did earlier.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 3:45pm

JackReddick wrote:
11th May 2019 - 3:41pm
It’s not a nut, it looks like the bottom half of the solenoid minus the solenoid.
Basically the right half of this-
https://www.dellorto.co.uk/shop/other-c ... -solenoid/
That being the case then it probably is obstructing the fuel flow. I would expect that the solenoid will pull the obstruction out of the way, is that right Broady ?
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

JackReddick
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 4:01pm

937carrera wrote:
11th May 2019 - 3:43pm
I would take it out again and see if it is interfering with the flow of fuel. If it could be, then shorten it or don't screw it in so far and run a test.

As well as the exhaust heat check, repeat the pulling of the spark plug test you did earlier.
If i check the exhaust, 1 and 2 are hot, 3 in the tiniest bit warm, and 4 is stone cold

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 4:08pm

Yeah, the off position is the plunger is "inside" the carb, and the running position when the solenoid is engergised is pulled out of the carb.

Just had a play with one to see if I can video how it works for you. But its too small to catch on a camera phone

If it is a chopped up end of the proper thing then it will be in the off position. Thus stopping your idle circuit from providing any fuel. I think the best thing you can do it PM me your address and I will loan you my spare pair to fit and see if it gets you running. If it does then you know its worth spending the money on a new pair
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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 4:10pm

So you probably still have a carb problem.

Thinking about the solenoid, and comments about jet sizes, it probably works the opposite way round, plunger in one position with fuel passing through the nozzles / jest when running, voltage off the plunger extends further exposing a shaft with no holes so the fuel flow is cut off. I was more thinking of a diesel cut off valve. Broady can educate further (ignore this looks like I was correct first time)

Another test for you. but better done when the engine is cold. Pull the king lead and try to start the car. Then whip the plugs out and see how wet they are. If number 4 is bone dry and 1/2 are wet, then that confirms a fuel issue.

Is the fuel pump delivering fuel to the left hand carb ?
Last edited by 937carrera on 11th May 2019 - 4:12pm, edited 1 time in total.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

JackReddick
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 4:11pm

broady_6 wrote:
11th May 2019 - 4:08pm
Yeah, the off position is the pilunger is "inside" the carb, and the running position when the solenoid is engergised is pulled out of the carb.

Just had a play with one to see if I can video how it works for you. But its too small to catch on a camera phone

If it is a chopped up end of the proper thing then it will be in the off position. Thus stopping your idle circuit from providing any fuel. I think the best thing you can do it PM me your address and I will loan you my spare pair to fit and see if it gets you running. If it does then you know its worth spending the money on a new pair
Thanks mate i’ll PM you in a bit.

What i find weird is the other carb is set up in exactly the same way yet both cylinders appear to be firing ok

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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 4:13pm

JackReddick wrote:
11th May 2019 - 4:11pm
What i find weird is the other carb is set up in exactly the same way yet both cylinders appear to be firing ok
That's the bit I have been scratching my head on. Are the brass bits the same both sides ? Take them both out and put a photo up
Last edited by 937carrera on 11th May 2019 - 4:14pm, edited 1 time in total.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 4:13pm

Yeah, he says the float bowl is full of fuel. A very wise man once tought me. When in search of a problem, fix all know faults before you go looking for more. We know the idle cut off system isnt right. So I would be correcting that before going any further. Ive saved myself hours with that principal in the past, and wasted many more by ignoring it :lol: :lol:
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 4:15pm

I will put money on the fact that both cut of jets still have the plungers inside. When they were "modified" someone tried to secure the plungers into the "run" postion. But as its a dodgy mod, eventually one as returned to the "off" position and stuck there.

If youve got time on your hands you can aways swap the two jets over and see if 1 and 2 stop running
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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 4:41pm

I think I've got it now.

The external bit we can see remains fixed. The plunger rod extends from the electrical part through to the section on the inside of the carb with the holes and slides back and forth internally. Default position is extended by a spring, which blocks the jet/port off, solenoid engages and withdraws the internal rod which exposes the idle jet/port to flow.

I would examine the solenoid in a number of orientations and see if it remains open at all times, or can become obstructed.

Learning through other peoples bodges, probably done with good intention at the time.
Last edited by 937carrera on 11th May 2019 - 4:42pm, edited 1 time in total.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

JackReddick
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 4:42pm

So below are the two “solenoids”
I’ve now swapped them round and still no difference to the running.
3 and 4 branches are still cold and i can still disconnect the ht leads making zero difference to the running
Image

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broady_6
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Re: 71 Fast Back Recommissioning

Post by broady_6 » 11th May 2019 - 4:45pm

Yeah correct description of how it works.

Did you test the plugs for a spark on the block as described earlier?

Youve got compression, if youve got a spark, then youre missing fuel.

There will be a blockage in the carb somewhere. Welcome to post it up to me and ill ultrasonicaly clean it. Or I can post you down a carb with a solenoid for you to play around with.
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937carrera
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Re: 71 Fast Back Recommissioning

Post by 937carrera » 11th May 2019 - 4:49pm

Well, that's that theory out of the window then. They do look different at the end though. Did you check that the ports were open to allow fuel to flow on both ?

Back to the wet spark plug test, or

Is it possible to swap carbs over. I know you'll need to block the balance pipe connections off and omit the throttle connections, but if it starts and idles with problems on 1 and 2 you know it's a carb issue.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

JackReddick
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Re: 71 Fast Back Recommissioning

Post by JackReddick » 11th May 2019 - 5:05pm

broady_6 wrote:
11th May 2019 - 4:45pm
Yeah correct description of how it works.

Did you test the plugs for a spark on the block as described earlier?

Youve got compression, if youve got a spark, then youre missing fuel.

There will be a blockage in the carb somewhere. Welcome to post it up to me and ill ultrasonicaly clean it. Or I can post you down a carb with a solenoid for you to play around with.
There’s nobody about to crank it over for me whilst i earth the plug so i can’t test it on the block at the minute. When i remove the ht leads from the dizzy for three and 4 i can see sparks/an arc if you hold the leads close enough, obviously this doesn’t mean there isn’t a problem. Admittedly i’ve swapped the leads and plugs around from 1 and 2 to 3 and 4 (then relocated on the dizzy) but it’s still the same symptoms.

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