TheSamba.com :: View topic - 71 square w/ PDSIT carbs starving under load

Thu Jun 02, 2016 10:55 pm

So, I am completely beside myself. I have a 71 square with carbs. I bought it from po who resurrected it after sitting nearly 30 years. I had to change the fuel filters (2) several times due to crap in the tank. No biggie. It ran great until a few months ago. I was having issues with it backfiring and sputtering on the way home after work and parked it for a while.
Found carbon build up in the cap, changed it and got it running again only to drive off and have it die a block out. Went through fuel system, changing out all rubber including filler neck and vents. Same thing. New fuel pump and an external hard line after that. Same thing. Rebuilt carbs. Same thing. Electric fuel pump. Same thing, but 1/2 block further. I'm flummoxed.
Can anyone offer any suggestions?

Thu Jun 02, 2016 11:12 pm

Always be sure to eliminate the ignition system as the source of issues before moving on to the fuel system. Bad condenser? Weak coil? Platinum spark plugs?

I've seen a bad condenser mimic fuel delivery issues like a mockingbird.

I see you are in Eugene. I'm in Thurston/ Springtucky.

Fri Jun 03, 2016 6:33 am

Tram,
Thank you for the reply. I put in a new condensor and points when I changed the cap and rotor. Thought about checking the coil. Maybe I'll grab another condensor too. Can't remember what plugs. I should just change them to anyway.
I am in Eugene! About as far South East as you can go. Are you going to Woodburn?

Fri Jun 03, 2016 11:16 am

kayazvws wrote: Tram,
Thank you for the reply. I put in a new condensor and points when I changed the cap and rotor. Thought about checking the coil. Maybe I'll grab another condensor too. Can't remember what plugs. I should just change them to anyway.
I am in Eugene! About as far South East as you can go. Are you going to Woodburn?

No shows for me this year... too much work!

Keep us posted on your progress. Are you getting your parts from Zack at Springfield German?

Fri Jun 03, 2016 11:39 pm

Update...
I replaced the condensor and the coil. Made it to the top of the hill and back down. Going for a second run and it konks out. Same issue as before. Gets to a hot enough temp and acts as if it's starving. Each time I start it after initial run, it idles fine but nothing under load unless I let it sit for a couple minutes. Almost like it's reloading the fuel lines. Then it will go for a few seconds. :(

Sat Jun 04, 2016 6:45 am

Better drive your beater to Woodburn today & get your VW running better for next year. See you there with the Type 3 contingent.

Sat Jun 04, 2016 3:21 pm

where are the fuel lines routed?
are they sitting on the block at all?

sounds like the fuel is getting too hot and you are vapour locking

Fri Jun 10, 2016 9:00 am

Not vaporlocking. All lines are up off the block and routed as they were when it was running good.
Just bought a pair of carbs to rebuild. Hopefully this does the trick.

Thanks for all of the suggestions everyone.

Sun Jun 12, 2016 11:04 pm

How did you go with this issue?
I was experiencing exactly the same symptoms on my 73 squareback. My solex carburetors were rebuild by the PO, and it had new fuel lines installed and an inline filter. Same problem as you - it would start and idle fine, but run rough after a couple of minutes of driving.

I had stripped, cleaned and reassembled the carbs 3 or 4 times with no change. I had also replaced the fuel filter and flushed out the fuel lines with no improvement.

Eventually, with the help of my brother, we found that there was a flake of rust in the float needle valve which feeds fuel into the float chamber which was restricting the flow of fuel, so it would idle fine, but run rough after a couple of minutes driving as the float chamber was emptied and the restricted flow of fuel from the needle valve couldn't keep up with the flow required.

I had checked the needle valves out a couple of times before, but the flake of rust was only dislodge after a very thorough flush.

After cleaning it out and reassembling, we put it all back together and haven't had the problem since.