'86 SR5 Carb & Choke Quandary

[ARCHINSTL]

OK - bear with me for a minute..............

I was able to fix the no-power-from-1K-to-2K-RPM-problem by installing an unbroken TVSV a while back. However, the engine is dying when the accelerator is touched from idle (800+ RPM) to 2K until it is thoroughly warm. When it starts to die, the options are to immediately goose it above 2K or let it die down to 300 or so, at which point it will self-revive to 800. This, of course, makes immediate driving awkward. When warm, it runs pretty well.

This next may seem dumb, but my only real experience with carbs was with the SU as used on most BritMobiles years ago as well as Volvos in the 50s and 60s. This was pre-smog, of course, and the SU was a very easy carb to comprehend and tune (it also used a manual choke-yeah!). I presume, as the Tercel Owner's Manual states, that when the accelerator is pressed twice, the choke is closed and a fast idle cam is engaged. Well, on my carb that does not happen, whether by the pedal or by moving the throttle quadrant by hand. Nothing seems "broken", per se, but there is just no engagement of a cam or movement of the choke shaft/linkage. So far the starting has been instantaneous, but then the o/s temps have been in the 90s for some time, so it's not exactly "cold" starting.

So - I'm listing what I've done thus far and request an opinion (or two or three or more):

> New (Bosch) plugs and cables
> New Bosch oxygen sensor
> New fuel pump, filter, and all fuel lines inside the engine bay
> New air filter
> New TVSV
> All 40+ vac lines replaced
> All diaphragms checked by "oral vacuum" and they (seem to) work
> HAI device in snorkel reconnected-someone had disengaged the operating rod from the flap
> New manifold-to-snorkel hot air tube
> Totally clogged EGR valve and delivery pipe removed and scoured clean
> Three new lower carb gaskets (last mech did not use gaskets on either side of the heat shield-just sealer).
> All carb pivots, etc. cleaned, but carb not rebuilt
> Did not remove the little fuel window and clean-forgot-not clear what the fuel level is-the window is pretty cloudy
> HCV cleaned/lubed on i/s side of manifolds and seems pretty free-moving
> Idle, fast idle, and TP position checked and (slightly) adjusted, per the FSM

Additionally, has anyone replaced the Aisin regular choke with a manual unit? AZ, et al, have these "universal cable units" for not many $, and it does seem like a simple fix - advice?

Thanks to all - and have a Glorious 4th, as they say...
Tom M.

[TercelFix]

Hello Tom,
I am no pro on your model, but you have a feedback carburetor. The tvsv or Bvsv is basically telling the computer that the engine is now hot. Untill this point, the computer runs the carb as if it were on choke, or rich. Another note, outside temperature will not affect the starting condition of the motor, even if it is 110 degrees outside, the motor is still starting 'cold' or not at normal engine running temperature. The engine will warm up faster if it is warmer outside.

You basically have a primitive fuel injection system, what others would call carburetor fuel injection or CFI. You have no choke and cannot install a manual choke, as far as I know. It is the job of the tvsv to act as the choke. There is a vacuum restriction device inline going from the tvsv to a vacuum switch. This vacuum restriction is to always start on choke even when motor is still warm at least for the first few seconds. Check the vacuum sw with the ignition sw at run but motor not started, then get someone else to start the engine and watch the voltmeter. When the motor is 'hot' the sw will change. Best done with a motor that is already warm.....

Next part, the Electronic air bleed control valve EBCV, I haven't figured out what it does, either adds more air to lean the mixture or more air to raise idle.....

I would recommend you get a service manual, and a vacuum tester, the hand pump and gage type. I do not use mine often, but it can find problems real fast.



rc