[T3] Mystery cures...

[Jim Adney]

On 19 Aug 2018 at 3:02, J. Jonik wrote:

> '71 /t-3 Std. A little resistant when starting...but then catches fine, no
> smoke or anything..but then runs sorta rough.   Did clean up of connections,
> timing and all that and it seemed better.  Then same thing...resistant
> starting...took a few key turns etc.  Then rough for a
> while...then...ker-pow....like it cleared it's throat and performed perfectly
> after a little bit of driving.  

"Ker-pow"? Did it actually go bang as you were driving down the 
street? 

A couple of thoughts:

It's possible that it's hard to start because there's air in the line 
after being shut down hot. This is a VERY common problem, but not 
consistent with a "ker-pow". The cure is to add a priming switch that 
you can use to fill the line without wear to the ignition switch, 
battery, and starter.

[I make a $10 kit to add such a switch to any FI Type 3.]

Or it could also be that you have 1 cylinder (#4?) that is having 
trouble firing. That would quickly lead to that cylinder getting 
flooded (filled with excess gas that is too rich to fire.) Once you 
get up to speed and run some air thru that cylinder, that clears it 
out, but the excess fuel has been dumped into the exhaust system, 
where it may eventually get ignited (ker-pow) by hot exhaust gases 
from a cylinder that did fire. You can diagnose this by starting the 
engine and then removing one SP wire from the distributor at a time 
until you find the one that does NOT make the RPM drop. One possible 
cure for this is to fix the bad cylinder. (Check that SP wire to make 
sure the resistance is not infinite.) If it's the #4 SP, take it to a 
place that can fix that plug.

It's also possible that random cylinders are flooding each time. My 
'73 has this problem. I've solved it by installing a special fuel 
pump switch that allows me to turn the pump off while the engine is 
running. I let the pressure run down until all cylinders are firing 
and then turn the pump back on.

[I make a $30 kit with a special 3-way switch that lets you prime the 
system, run it normally, or turn the pump off.]
-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************