83 Carbs Front Carb Overflow down drain tube - not right away

[Evan]

OK, so I have not been on for a while.  Life has been crazy. 

A year ago, I had finished getting the 83 carbs in a good running condition (nice idle, ran really nice -- thanks QBS).  It was starting to get warm (spring in Houston!), but drove to work one day, and it stalls-out pretty bad on a way to work (~13 mile ride early in the morning).  Got it going, rode the rest of the way to work.  Rode home without any issues.

A couple of days later I ride it about 4 miles and park at church in the morning.  After getting home (afternoon), I notice that it is leaking gas out the overflow drain tube.  I think, it was just an overfull tank, hot day, etc.  Next day, it is spilling-out gas as soon as it starts-up.  I didn't have time to deal with it -- started it a few times with the same results over the next few months.

I pulled the carbs off finally on Saturday.  Pulled the tops off the carbs.  Front is wet, rear is dry.  I do a quick clean on the tops (ultrasonic using water).  Set the float levels using Berryman B12 carb cleaner (to clean the bottoms) on the bench.  I may have set the float levels a bit low (rather than too high, ie, 25-30mm).  I capped the T drain on the front carb, and ran 2 tubes, so that I could tell if it is the front carb or the rear carb.  I get it going (needed to swap an oil filled starter, but I already had a rebuilt ready to go).  Runs pretty rough, but starts to go OK after a while.

I take it for a 1/2 mile ride to get some new gas.  Stalls like crazy.  No bottom-end or mid-range.  Put in a couple of gallons of premium.  Get it home again (3 more stalls).  Idle it in the garage, and it not doing so well (hunting).  That was Saturday.

I come home today from work, fire it up.  Still not running good, AND the front carb overflow is spilling-out.  But I do need to get it inspected.  Get 1/2 a mile, stalls 3 times, no bottom end or mid-range.  I turn around and bring it home.

What do y'all think it is?  I am thinking the front float gets "fuel-logged" and then it overfills.  That is all that I can think of.

Any other ideas?

That 91 Miata that someone posted at work is looking like a much better "mistress" right about now!

Thanks,
Evan

[fret not]

Overflowing means too much fuel in the carb, which could be dirt or rust in the float valve letting fuel by.  Do you have a fuel filter inline?  What condition is the interior of the tank?  Are all the diaphragms in the fuel pump/ regulator/ recirculation system in good condition?  Make sure the fuel lines are clear of foreign matter.

[Lucky]

fuel out the overflow means one (or more) of 5 things:
--needle & seat are leaking (front, rear or both?)
--Petcock is leaking
--return path is restricted (goes back to petcock)
--drain screw o-rings are shot
--float levels need adjustment.  you can safely drop them by 3mm.  the overflow tubes i have measured vary in hight by 2-3mm, some were so low that the bowls would overflow with the correct float setting...

--Lucky

[Evan]

Thanks Fret Nut & Lucky for the responses.  Yes to inline fuel filter.  Yes to clean tank.  The fuel pump seems to work well when I use my "test" tank (which has a place for the fuel to recirculate).

Lucky, I don't think the drain screw o-rings would cause fuel to run down the drain tubes (would run out the side of the carb though).  The float needle & seat were both just ultrasonically cleaned, and seem OK.

I left the front float overnight in a bowl of gas to see if it would sink -- but seems unchanged this morning.

I think a blockage on the fuel pump-to-tank return line might be the real culprit.

Any thoughts on capping the return inlet on the tank petcock and having the fuel return line run into a T fitting with the fuel inlet (up stream of the inline fuel filter)?  I would think that would be a modification that someone might have done to make 83 carbs work with an 82 tank....

-Evan

[Lucky]

i've done that mod, it seems to work.

i'm pretty sure if you crack the bowl drains fuel will come out the overflow tubes, but i might be wrong, i don't really know much about these carbs....

[QBS]

Blocking the return line has never caused my '83 any operational issues of any kind.  Evan, contact me.  We need to get together.