Holley Bowl vent fog/vapor

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Tackweld

Tackweld

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After replacing the leaking oil pressure fitting on the 360 block, I of course had to start it up and test my pipe fittin' skills. As the mill was idling, I catch a glimpse of this "fog" coming up and out the vent, then getting sucked down the carb. So.....Is this normal?? I'd appreciate some feedback on this, Thanks

Short YT Vid [ame]http://youtu.be/mAMcRmIyyqg[/ame]

I'm rank novice on Holley's- this is a 750dp. I've had others dp's and vacuum sec's in the past, just don't recall seeing this...
Did get that oil leak stifled though...
Jeff
 
That's interesting Jeff.....I've never seen it before that I can recall? Something for me to think about though. I'll let you know if I come up with some crazy reason why...
 
Ok i'll take a shot.....A wild guess just to keep the conversation going.

How hot was the engine during that vid? It actually looks like steam. My first thought is excessive moisture in a ethanol blended fuel on top of a 220/230 degree engine?
 
Rick, the engine still pretty cool, in fact when I was done with all of this fooling around (oil fitting business, 3 separate video shoots of the vent & standin' there staring at it for some cyphering time) and shut it down the temp gauge was at ~~150 deg.
 
Tackweld said:
Rick, the engine still pretty cool, in fact when I was done with all of this fooling around (oil fitting business, 3 separate video shoots of the vent & standin' there staring at it for some cyphering time) and shut it down the temp gauge was at ~~150 deg.
Click to expand...

Wow! I hope some others have seen this before? One question I can ask is, does the secondary vent do the same thing?
 
I will check that tomorrow Geo, thanks to you and Rick for your ideas. I am ordering a GOOD glycerin filled fuel prs. gauge to check the Aeromotive Electric pump.
 
With that large a volume of vapor coming out, there has to be air being fed into the carb bowl. The amount of air that could be displaced by fuel coming in is pretty small at idle, and should be close to none anyway.....IF the idle circuits are working normally.

I would be suspecting that the idle circuits are messed up and you are idling on the progressives.....Does the engine respond to changes in the idle mixture screw settings? Idling on just the vapor coming out of the bowl could also do it but it sure seems smooth for that. What are the idle RPM'S? Look down into the carb primary throat and see if the primary throttle plate is properly closed (except for a hair of a crack).

The only other thing I can think of is if somehow an exhaust heat riser is sourcing air into the carb......What kind of fuel pump, regulator, and filter do you have?
 
Going to the shop now to check float level, won't have a good prs. guage installed till afterwork tomorrow. nm9- idle rpm's 1000 in N, no heat riser-M1 Single Plane, I will look down Primary bores, yes it does respond to Idle screws in Pri. Block, however Both Idle screws in Secondary Block have been screwed in to lightly seated since I bought the car, if I start to back them out it will run way to rich..< this is next on my tuning list to fix .
Also RCI fuel cell and Billet Aeromotive fuel filter in trunk (before fuel pump) - I will clean the filter also.
 
Kinda looks/sounds like all of the idle air is through the primary. Have you checked the throttle plate opening balance between primary and secondary? I'll be the secondary is pretty much closed. That would explain the high level of vacuum over the primary airhorn. What model of carb? Does it hesitate at all just off of idle?
 
Tackweld said:
After replacing the leaking oil pressure fitting on the 360 block, I of course had to start it up and test my pipe fittin' skills. As the mill was idling, I catch a glimpse of this "fog" coming up and out the vent, then getting sucked down the carb. So.....Is this normal?? I'd appreciate some feedback on this, Thanks

Short YT Vid http://youtu.be/mAMcRmIyyqg

Jeff
Click to expand...

I have this same exact problem, 'cept its on a F*rd big block 472/Holley 780 vac.sec. in my tow vehicle. The vapor was happening on a fully warmed up engine, after a fairly lengthy hi-way drive. If you plug the primary vent, it kills the engine...sec one does same thing. At the same time, I noticed in the clear-glass fuel filter I run (yes, i know, bad idea) there is lots of bubbles coming up from the fuel pump, which I'm thinking is the verge of vapor-lock...or maybe just a failing fuel pump? This situation doesn't happen with a cold engine.
 
Ah..I found the problem. The fuel filter was almost completely plugged with plastic shavings & junk from when the fuel cell was carelessly installed. This did not happen till now because the tank has less than 2 gallons in it. What is shown on the video is the pump pushing air (cavitating I suppose)into the bowl (and out the vent) along w/just enough gas to run at idle. Now all of us know what it looks like to be running out of gas w/a Holley...Thanks everyone for your help Best Regards Jeff
 
Ah... that was my next question....what is the fuel pump etc., was it making noise, and could it be cavitating...interesting to see the vapors. Is this just a straight in/out pump, or is there a return line?
 
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