demon dumping fuel ???

[jbaker]

i have a new 750 mighty demon that has been giving me fits. the symtom is
rich at idle and cruise. i have done all of the usual things to resolve it,
powervalve, timing, tranfer slots, 4 corner curb idle, idle feed restrictor
size, idle air bleeds. i will say that it is much better than when i
started. jetting for wide open throttle is good, with good looking plugs.

>
> with that said, it will still soot a new set of plugs, at idle/ cruise.
> what i am finding that concerns me and makes me think the carb has some
sort of internal problem, is this......... there are two vacuum ports
> on the side of the carb. one is a timed port and the other is a direct
vacuum port. the direct one having its source below the butterflies.
specifically, the direct one will fill with raw fuel after being run a few
minutes even at idle. ( im not using either one of the ports for advance
and both are capped off )
>
> there also appears to be some puddling in the base of the intake
manifold also. im thinking the fuel is just leaking from some where and
basically finding a home in the direct vacuum port as coincidence. but is
for sure leaking from somewhere. what is interesting is that i can drive
the car, come home and remove the little cap off the direct port,
> dry the cap out and the port tube, leave it set overnite and it will be
dry the next morning.
> then start the car , run it for two minutes, shut it down, and remove
the cap off the direct port, and it is filled with fuel again. that tells
me that it is leaking when the car is running. its coming from somewhere
and making its way to the intake side of the
> butterflies.
>
> so this is more about a leak, than it is about rich idle and cruise, that
is the symptom, along
> with the raw fuel collecting in places.
>
> what are some of the areas that come to mind for you. documented or
undocumented
>
> thanks jerome baker
> kewanee, illinois
> jbaker@kresscarrier.com

[Tony Radford]

Jerome, I don't think this is typical of the Mighty Demon. I'm running one myself on my Windsor stroker. It was a bit rich initially, but after a few dyno pulls and some additional advance, things are great. I've never had anything but excellent idle and throttle response since day one. Did you order yours set up specifically for your engine?

[jbaker]

thanks tony,

not bought specifically for the setup. purchased as stock out of the box

would you be willing to check your direct vaccum cap for fuel
buildup ?

thanks jerome

[TonyMadrid]

Drop a line to Don Gould. He's the guru of these Demon Carbs. You can reach him through his website at: http://4secondsflat.com/

[jbaker]

thanks,

i have in fact talked to don,
he is thinking it may be collecting there from some reversion going on in the intake. ive put that on my list of possibles, and it makes sense.

i hope to spur some of us to look at our direct vacuum ports and see if its happening to others. that would lead me to think that
we all have an internal leak, or it is just a small collection of fuel
in that port from the fuel airstream going by and is not a problem.

check your ports boys

thanks jerome

[mj_duell]

I had a similar problem with my Mighty Demon. Took a while to work out, but the solution was an easy one. What level are floats set too inside the sight glasses?



--Mike

[jbaker]

one third to one half up the siteglass.
it has been suggested to set them at the very bottom of the siteglass. i plan to do that , but with one concern, that being,
will the carb function in a normal manner overall,
after resetting idle and etc.

thanks for the idea.........it will be tried


If it won't fit, force it. If it breaks, you needed a new one anyway.
now dat sum funystuff ratdare

[mj_duell]

That was my concern at first, but setting the site glasses to the very bottom at operating temp and then retuning the corner screws and idle screws solved my problems. Don't worry about jetting until after the carb is tuned and working well. If the carb is not feeding enough fuel under throttle then ease up the floats 1/4 turn at a time and test drive. If the engine stalls or tries to stall under off throttle or braking, try lowering the floats a little more. I also set me initial idle to 1000 before doing the tap on the accellerator pump trick that Don Gould uses. When I finally got the idle I wanted, I bumped the idle up to 1200. Make sure you have the correct timing set for your motor before doing any carb tuning. That's my .02 cents.

By the way, What engine cid, cam are you running?



--Mike

[Tony Radford]

Jerome, if you haven't done it already, you should provide your engine particulars to the BG tech line and see what configuration code comes back. They usually hit it pretty closely if they have the motor data i.e. CID, cam profile, intake, trans, rear end gear etc. At least you could see how it would have looked had it been configured specifically for your engine.

[jbaker]

413 cid
10.2 compression
248/254 @ .050........110 lobe centers



TONY,
thats not a bad idea to give b/g a shot, to use as a comparison
to where im at now.

thanks guys
jerome

[Gasman]

Whatever you do, don't drive or run your motor long in this condition. I recently had to completely overhaul my motor because the carburetor destroyed the rings. It can happen very fast!

[Back in Black]

Which thankfully soon will be gone in favor of a Holley Pro-Jection Commander 950 EFI.

It's still not perfect but the solution was as follows: I set the floats to no more than 1/2 of the window (a little lower actually) and to install a polyphenolic restrictor plate under the carb. They are available as thin as 1/2"
This was the advice from the tech at Demon. Helped out a lot at idle. Also check your needles/seats (clean them) and have a good fuel filter. (My car was delivered without one and I was never told this.. )


And the final thing which I did first actually: Make sure your fuel presure is correct.. if you have a Holley Blue pump it's putting out 2 x the pressure needed. (My car also was delivered this way
) What you'll need in this case is a Holley fuel regulator. All the above was the combo which helped me.

[Big-Foot]

Jerome - I would advise that you remove the carb and disassemble it completely and blow out all passages in the carb as well as making sure there floats pivot freely when you reassemble. There has been reports of machine shavings inside BG carbs in other forums. If you are having fuel spilling into vacuum ports, the only place I can see it coming in is through a Power Valve, bad or wrong metering block gasket or, potentially, a flaw in the metering block casting.
As was said in another message - you can do irrepairable harm to your engine via cylinder washdown (excess fuel washing oil from the cylinder walls) if you continue to run it this way.

I typically set BG Demon float levels between the bottom and 1/3 up the site glass with 5psi fuel pressure.

[jbaker]

thanks guys,

we seem to be narrowing it down here. i really appreciate
the posts so far.

hey bigfoot.........i see you are running approx. 5 p.s.i for fuel pressure.
i wont argue with that and i am somewhat suspicious about my current setting, though b/g says up to 8 p.s.i. is o.k.
i am currently running a mechanical pump putting out 7 1/2 to 8
p.s.i. with no regulator/bypass

i initially did not have enough pump on the motor, and im inclined to leave the p.s.i. alone.
on the other hand you are not the only one to run less than 6
with a demon. i suppose its not out of the question that maybe
my p.s.i. setting may be lending a hand to the fuel dumping issue

in any case, with input from you all its gonna come down to trying things this weekend.

thanks again fellas
jerome

[Big-Foot]

Hi Jerome,
I work on a fair number of both small and big-inch racing engines and have found that anything over 5PSI for street use is not only over-kill, it causes problems in float stability regardless of engine size.
I would probably think about putting a dead-head regulator into your fuel system and turn the pressure down unless you are going to be running a track-day or drag-strip event which is the only time you will be able to tip into any reserve capacity beyond 5PSI. Even then, I would probably stop at 7PSI.

While I am new to this forum, I've been around for quite a while - let me know how I can help.

[jbaker]

hey bigfoot

thanks for your clarity on fuel p.s.i....... makes complete sense.
i especially like the idea of running a regulator and cranking it
down on the street, and if req'd........crank it up for the track.

you mention a DEADHEAD regulator.........i was looking at a b/g
bypass type regulator, which b/g suggests using with a mechanical pump, running gas. please explain the DEADHEAD
regulator. does it require a line back to tank for residual fuel ?


thanks everybody else so far........will be busy tonite, and will keep us updated on solving the dumping issue.

thanks jerome

[Big-Foot]

Hi Jerome,

A dead-head regulator does not require a return line to the fuel tank/cell. BG may be lumping all mechanical pumps into the same category. There are many racing pumps (belt driven) that must have a bypass line to the fuel tank or the pump will burn up the belt or spit it off.. If your fuel pump is driven off the camshaft eccentric (mounted on the timing chain cover/block) you will be just fine with the cheaper Dead-head regulator.

[jbaker]

sounds good, and thanks.
yes, the pump is cam driven

i presume the deadhead would then plumb in directly between the pump outlet and the carb inlet. this is fine other than i will need to rework my current plumbing from the pump to the carb.
that rework is what got me looking at the bypass style, which i can plumb in off the rear tee at the carb inlet hose. the back end of that tee is now capped.... not disturbing the other plumbing is the only reason that i was looking at this as an option. granted i would have the added expense of more plumbing and the more expensive regulator/bypass. did you have a brand of regulator in mind ? im running -8 line size now, and would prefer to keep the port sizes as large as possible on a deadhead style, if i went that route.

i think you are right on as far as b/g grouping the pumps.

i presume using the bypass style will be fine , funtionally ?

in any case thanks for the cost effective opinion

[Big-Foot]

Hi Jerome,


You can use any of the Holley, Mallory, et al, regulators out there. I seem to install more Holley lately, but either company makes a good unit.
Yes, you would plumb the regulator inbetween the fuel pump output and the carb inlet.

I would make sure you pull that carb apart and check for shrapnel inside as well as for problems with the gaskets. I'm really concerned about the volume of fuel you have in your vacuum passages.

[jbaker]

thanks randy,
will be setting the floats lower to nite as a first step.
then irregardless. the carb is coming apart..

thanks a bunch and will keep updating for everyones reference