‘74 1.8L L-Jetronic Cold Start Low Idle, Mystery solved! Options

[Van B]

Ok fellas, here’s the run down Aux Air Regulator (AAR) and Cold Start Valve (CSV)/injector both work fine. Many of you have also been keeping up with my high idle issue that we figured out.

But yet, when the car is cold, i.e. room temp, I don’t get the high idle I should on start-up. Instead she cranks a bit and then lumbers to life. Idle lopes around 700-800rpm and then smooths out as it warms.

In all other aspects of operation, the engine seems to be pretty happy.

Thoughts? Experience? (IMG:style_emoticons/default/confused24.gif)

-Van

See post #419 on page 14 for a synopsis of the outcome.

[wonkipop]

good stuff.

the late cap'n krusty had red hot tips.
often i just do a search here to find his methods.



i found some other stuff from the cap'n re the endless discussions about dist vac hookups on 914 1.8s.

the cap'n was firm in his view that all 1.8s came with the two vac hose hook up.
one to advance side of dist vac box and one to retard side.

he also had the best simplest explanation for how it works (the retard side at idle that is).

attached is the screen grab.




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but i also did some searching around in the factory manual.
and maybe got to the bottom of it.

lists two different distributors for 1.8
i definitely have the one underlined and its definitely a two port/two hose connection.
which i have still intact and original. so its never been altered and is still the way the factory says it should be (and the way the cap'n said it should be).




another page on manual.
casts light on 75s.
they have the single port (retard only) distributor.
and if the pollution gear is still hooked up on a 75, the port that faces to the rear of the throttle body and is hooked up to vac advance on distributor of a 74, is hooked up to the EGR valve on the 75.




there is a good section in the factory manual with a cross section and explanation of the vacuum advance/retard distributor.
its worth a read if you want to get your head around it.
i won't try it ends up being a complicated discussion if past threads i have discovered are anything to go by.

suffice to say at idle, only the retard line is working because the other port is closed off by the throttle plate. so only the smaller back section of the vac can is activated. retarding the timing. cap'n krusty explains how snapping the throttle open to take off instantly de-retards the timing at that point and you get a smooth take off.

and when the throttle is part open at cruise both ports work off a vacuum.
but the advance port operates a bigger vacuum chamber which overcomes the smaller vacuum chamber (called the retard). net effect of both working against each other is the bigger chamber advances the whole unit under vacuum.

there is other stuff going on of course, but thats the distributor under influence of mechanical weights. the vacuum bits are really working at idle and at part throttle cruise to do two things. lower emissions at idle and to increase fuel economy at cruise.
very 1970s. fuel crisis/pollution crisis.