engine and drivetrain Puddled Fuel In Intake Manifold, Normal?

[Gil. H.]

This past Sunday I took off my 32/36 sync-link kitted carb to clean jets, etc. When I pulled off the carb I noticed a puddle of gas just below the carb in the intake manifold. Wasn't a lot, all absorbed with 1 paper towel, but I wasn't expecting to see puddling gas. There is a small depression in the standard intake manifold. This normal?

Thanks in advance.

[mike472]

This has been bugging me too. I have the sync link and I have checked the float level and rebuilt the carb replacing the check valve in the process not once but twice just to make sure I didn't get a bad one. I put a rubber plug in the vent hole, replaced the mechanical fuel pump in case it was leaking but all to no avail. The puddle keeps coming back. My mileage has been crappy even though the car runs great. After it's warm and I shut down for about half an hour it seems to take a while to start and "clear it's throat" and get running smooth again. Then it runs nice and smooth. There seems to be some residual pressure in the line when I take the fuel hose off the between the carb and fuel pump. I thought that maybe after sitting with pressure in the line it might be forcing its way past the check valve and dumping out the vent hole or into the throat of the carb somehow.

What the hell am I missing here?

[bmwfan]

I had gas flowing out of all of the air intakes on Mikuni 44's after replacing my old electric pump. Mikuni's call for max psi of 4.9, the new pump was rated max 5psi, airtex e84070. I placed a filter king pressure regulator and set it to 3.5psi. Now dry as can be.

[mike472]

I can see that with a non stock electric fuel pump but a stock fuel pump should not be able to overwhelm the check valve feeding the bowl in a 32/26. The only thing I can think of is somehow the float level is still wrong. I know lots of 02's had a return line taking unused fuel back to the tank but would the absence of that cause a leak like this?

[Gil. H.]

I'm going to pull the carb again this weekend and clean the bottom, accelerator pump passages, missed that a couple of weeks ago. I'll also check fuel pressure before pulling it off as well. I've got this PITA hesitation in first gear that's driving me nuts, bogs down then "catches", minimal in other gears. Will check for puddling again. Will also check timing, coil, wires, and float level.

g.

[Mikesmalaga72]

IMHO..Please excuse nerdy explanation lol...  I would surmise that when fuel vapors floating in that hot environment when cooled the vapors perhaps condense into a form of fuel/water liquid. Appears the "dimple" may have been intended for that very purpose, A "sump" if you will to either evap into emission system or atmosphere..    

Edited October 11, 2013 by Mikes 02

[bmwfan]

I would also look at the plugs to see if you are running rich or lean.

In my quest to fix the bogging down between first and second, mine would bogg under normal acceleration but kick but with hard acceleration, I found I was running lean. I think it was partly due to clogging of the air passages as adjusting pilot/ air screws made little difference in idle. I sprayed cleaner in any passage I found. This did help as was able to sync carbs afterward. Also reset timming many times. To find a sweet spot. Now running great under any acceleration. My plugs are now a light tan in color when rechecked after a road trip. They were white before, as in to lean. Also gone is the popping back through the carbs which is a symptom of running lean.

[Gil. H.]

IMHO..Please excuse nerdy explanation lol...  I would surmise that when fuel vapors floating in that hot environment when cooled the vapors perhaps condense into a form of fuel/water liquid. Appears the "dimple" may have been intended for that very purpose, A "sump" if you will to either evap into emission system or atmosphere..    

That kinda makes sense. Hadn't thought about a sump for condensed gas vapors......

[jimk]

Here is my explanation.

The intake manifold gets hot water from the water neck to the intake and back to the pump whether it is warm weather or cold.  Shut down in hot weather and the manifold gives off the heat.  If the fuel level in the carb bowl is a bit high, the fuel perculates into the carb throat and it puddles in the intake.

This can be seen if just after shutdown in hot weather, pull off the air filter cover and watch and wait to see the fuel perculate.

When I was still on carbs, I stopped this hot flooding by installing one of the small heater valves in the hose between the water neck and the intake.  I would close the valve with a cable pull about 30 seconds before turning into the driveway and no hot shut off fuel smell or hard restart.

If you simply lower the bowl level, that causes other lean conditions, so that ain't the answer.

p.s. The water heat is needed to avoid carb iciing and poor fuel vaporization even in hot weather.  It takes heat to vaporize fuel (called heat of vaporization).

Edited October 12, 2013 by jimk

[mike472]

Jim

 

This sort of makes sense.  I tried tweaking the float level and you were right in that it causes others problem like a nice flat spot when the fuel level is to low in the bowl.  I cant believe this is the norm.  It wont happen with the stock Solex 2 barrel.  How come?  Different internal passages that prevent this percolation?   I feel like trying to bypass that manifold heating circuit somehow if thats the problem.  The accelerator pump area is dry as a bone so I know its not coming from there.   Duel setups do just fine with no manifold heat so I don't think it would hurt things.  Right now it sucks starting the car hot.  It always has to clear that flooded fuel out of the manifold and I'm sure thats causing my causing my starting problems.  When cold the car kicks off instantly.

 

I resisted putting megasquirt on this car too but the 318i manifold is under the bench just in case.

[KFunk]

Edit: nevermind, I was thinking you meant somewhere else.

Edited October 14, 2013 by KFunk

[mike472]

Found the answer and I missed it the first time around..... Leaking accelerator pump diaphragm. It didn't look wet at first but after a hot shut down I watched underneath the AP lever and slowly but surely gas start leaking down the lever of the AP and dripping into the depression on top of the manifold. I had replaced diaphragm during the rebuild but somehow it must have had a hole or the paper gasket on the AP was not sealing correctly because some of the residue from the last gasket that was on there was messing up the sealing surfaces. This time I gave both sides a more thorough cleaning with scotchbrite. Presto, no more puddle and better gas mileage. Also no Inka bonfire!

I am sure this is the cause of 99.9% of intake manifold gas puddles.

[Gil. H.]

Was finally able to get to the carb this past weekend, again. Cleaned out the idle jets well, checked the timing and adjusted the main mixture All seems good now. The "bog" going into 1st is gone and revving pretty smooth. While researching I found CD's guide about plugging up a port, haven' done it, but since it's running so good, don't know if I really need to? I need to get a o2 sensor to really get the carb dialed in.