Done several searches and come up empty on this question.

When the car sits over night, the float bowls bleed down. Car starts fine, but seems to smoke because of it for the first bit of startup.

Car runs great, no real issues to be had as far as the carb goes. Recent rebuild.

Thanks carb guys!
-P

 

There is mention of his float bowls mysteriously draining and the cause of the problem was found to be a stuck/faulty fuel vent check thingy. (It's the weird lil useless object just forward of the tank and mounted on the top under the car....)

Go dig up his thread to see a picture of this thing...
https://www.rx7club.com/build-threads-293/project-resurrection-running-log-770184/page6/

look about 80% down the page and you will see the valve he took out of the car and cut in half.



Hope that helps.

 

I still get this happening on occasion. Replacing that valve helped, but did not completely eliminate the problem.

Seems to be related in some way to the vent system, or possibly a combination of the vent system and the vacuum power valve system, but thus far, it's unresolved.

But my thread can at least tell you what I've tried thus far.

 

I know that if the float bowl vent solenoid is not hooked up (or not functioning) then the carb will fill with fuel in the secondary barrels after shutdown. I would assume that that gas would be coming from the float bowls, so it would therefore stand to reason that it could leave them empty. Might be worth checking out.

The FBVS is located on the driver's side of the front of the carb, right by the alternator. It will have a single wire coming from it, which should be connected to a switched 12 volt source.








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I've checked the bowl vent extensively on mine; no detectable malfunction. Doesn't mean that it could not be bad in Twilight's case, though.

 

The vent solenoid is removed. It shorted out and almost caught the car on fire! That's when I rebuilt the carb and put my SA intake on. Right now I have the vent line nipple hooked into the pcv system before the pcv valve, tied into the vent on the oil fill tower..


The richer noid bit in your post makes sense. Did you try pulled the spring to make it stiffer in hopes of sealing better? You say yours is nearly flooded when trying to start again. I don't seem to have any starting issues. Just the smoke. Rob from Pineapple said if the carb bleeds down it will cause smoke at startup.

 

I call it "nearly flooding" because it produces fuel smoke on start. Once or twice it has been difficult to start but that went away some time ago.

Bowl drain produces excess smoke at start both by having excess fuel in the chambers, resulting in incomplete combustion, and because the fuel washes the oily film off of the inside of the chambers. Or so I have read.

 

Is that like mine sometimes where it sounds like its running on 1 rotor till it warms up?

 

^ 88 Mine does the same thing.

It'll feel exactly like it's running on one rotor until you feather the rpms up to at least 1K and then it'll stay smoothed out.

It'll only happen if the car sits for more then a day and it does smoke upon start up. I never associated it with leaky bowls though...? I always thought the one rotor feeling was the ignition being in need of attention and the smoke on start up was my motor internally being in need of attention as well.

 

Yep, that's what it felt like; needed WOT cranking to start, huge belch of smoke, then ragged operation for 30-40 seconds which self-cleared as things dried out.

Haven't had that problem for over a year. Still not enitely sure what made it go away.

 

Hmmmm only my back bowl did not hold level since yesterday... could that explain the one rotor feeling..???

 

If the vent is stuck open could the fuel be evaporating rather than bleeding out??? Just throwing out ideas

 

The back bowl is the only one which feeds the accelerator pump, and the vacuum power valve system.

My typical symptom has always been the rear bowl dropping much more than the front.

If you get the car up to temp, then shut it down, and monitor the bowl levels repeatedly over time (hours to a day or more), you will actually see the rear bowl level rise as fuel in the jets and bleeds bleed back into the bowl, then slowly drop over extended time. Some of that drop is evap into the charcoal canister, and some goes down the carb throat into the engine.

How much it drops after any given shutdown seems to correspond directly to how much smoke you'll get on start up, and how difficult it may be to start.

One possibility that I've talked over with Sterling is that if the rear bowl level rises too much, the VPV system collects the overflow and drains it into the engine. But that behavior should be constant.

The front bowl doesn't react nearly as much nor as rapidly.

 

Today I shut down my fuel pump while the car was running idle to use up all the fuel in the bowls until she stalled. Next start up I would like to see how much if she still smokes.

I don't have trouble starting her at all since Sterling did my rebuild, smokefest or not. It catches by about the second crank everytime so far.

 

Good to know that it is not just me. The guy I bought the car warned me that the engine might need to be rebuilt soon due to the smoking, but I took a chance and bought it anyway.

 

It's still something worth solving, as excess fuel is known to shorten seal life - - due to the flushing action it has on the oil film inside the chambers.

Besides, it's annoying.

 

So I started her up after running the bowls dry and letting her sit for 24 hours, no smoke at all.

So what's the downside to running the bowls empty until the culprit is figured out here..?? Gaskets drying out can be one thing, but I've been starting the car while it's currently off the road every other day at least.

 

^^^^^^^^^^^^^^^^^^^^^^

Bout the only thing you could do would be run Pre-Mix.

I'm suprised the carb guru's haven't figured this one out.

I'm thinking about rebuilting the spare I have and see if it still does it.

 

So now my carbs acting like it's overfueling at constant light load speeds. Say 30mph and slower. You can head the unburnt fuel burn in the pipes. Freeway speeds or heavier load and it goes away.

I wonder if I take the carb off an fill the bowls, if I could see where it's draining.