My Demon has some demons... This is the third Mighty Demon 750 I have received from BG, and for once this one has actually worked pretty well. The first two insisted on draining the fuel bowls into the motor when it was turned off...

A strange things has been happening when I accelerate hard and let off the gas. When I go back into the throttle there is nothing there, its as if the motor has loaded up and died. I can pump it an nothing. It takes a couple moments to come back and then it runs fine. No real part throttle or idle problems, just when you accelerate hard.

What it felt like to me was the that the pump shot was dry.
So why the motor is still hot I figured I would go check it out.
I started the car and it was idling fine and I moved the primary throttle blades and there was no pump shot, it took 5 or more pumps to get any fuel to come out, and I noticed when the throttle blade returns there is still fuel seeping out from the squirter.
The primary pump shot seemed really weak for some reason as well.

The secondary pump shot was a strong squirt and looked to be working fine. I pump the secondaries a few times to make sure they are working, and when I let off the throttle the squirter just kept squirting fuel into the secondaries. After that there was no pump shot for a couple movements of the secondary throttle shaft.

What the hell is going on here, I have never seen this before.

Some suggestions would be helpful as I am at a loss as to what is going on here.

Thanks!

 

almost sounds like the bowls are going dry with no pump shot. but the fuel trickling out has me puzzled. fuel percolation maybe?

What caused the carb to previously empty the bowls into the motor overnight?

 

The bowls are full, it was doing this at idle... The carb was not hot to the touch. I think the accelerator pumps may be shot or something is plugged.

The previous carb was a mystery, BG never gave me a reason why it would do that...

 

What kind of cam are you running? Dont know if it would matter... but a huge vacuum leak does about the same thing, makes you wonder if the cam doesnt have the vacuum to run that carb?

Hows your valve lash?

 

The cam is a XR280R solid roller. I have 12-13" of steady vacuum at idle, plenty of vacuum.

Valve lash is good, was set and checked a few days ago.

 

Sound like the diaphram in the pump is going bad. Why it would run on is a mystery. Adjustment too tight maybe?

 

I know this sounds crazy, but I think it's your fuel pump...

Now, before you dismiss this idea, consider the following:

1. If the problems were isolated to ONE carb, then I'd say your carb had a flaw... But you're on #3, and STILL having various issues... If you were on your third Holley #3310-4, I'd say to send them back, and get a BG. Frankly speaking, while the BG carbs may occasionally have an issue that needs correction, I refuse to believe that 3 of them all have the same problem... It's not the carb, it is another fuel-related issue.

2. You're getting unwanted fuel-flow from your squirters.

3. When coming off of high RPMs and load, the fuel demand suddenly drops, but the flow of fuel into the bowls continues to stay at a high rate... You try to pump the carb to force the engine to run, but it only dumps in MORE fuel, making an already-rich condition worse...

So the question is, are you running a high-volume fuel pump? Max pressure of the fuel supply should be 6-8 pounds, and NO more... What is your line pressure???

Do you have a fuel filter between the carb and the fuel pump? Have you checked it for any blockages???

Did you use teflon tape to seal the line fittings? A common mistake (and one I've done TWICE) is to have little bits of teflon get into the fuel system and clog the metering blocks...

My honest opinion is that your fuel pump is delivering too much pressure, pushing the needles off of the seats and drowning your engine (when running on the road)... As to the other symptoms, I'd wonder if there's a blockage in your metering blocks...

I hope I was able to help...

Eric

 

Eric: Maybe I didn't say it very clearly, the problem isn't the same for all three carbs, the earlier problem was different. This just started happening to the carb that has been working OK for some time now.

The fuel pump I am running is a Mallory Comp 110 electric pump, a very well built piece and I don't think it is the issue. If I was running out of fuel it would go lean as I keep accelerating, I can keep into it past 100 and it will keep pulling. Fuel pressure is set at 6.5lbs. I did not use any teflon tape on any fittings, I am using the Russel sealant. The fuel filter was checked and is clean from debris.

I will try a few things and report back if I find it, the diaphram may be damaged for one reason or another so I will check and replace it if I need to.

The needle and seat may be sticking open and when I let off it is feasible that the motor is loading up.

I'm not done with it, but I am eyeballing a Dominator..

Thanks!

 

When I initially installed the 383, if I got on it hard then off, as the RPM's decreased, the car would stall. Pumping the gas would breifly help, holding it wide open would also, but I could not do that very long.
Naturally restarting was difficult.

It turns out that at high RPM, fuel was gushing up out of the fuel vent tubes becuase there was some trash stuck in the float valves. It took a few times for this to happen before I figured it out.

Also, changing to an electric pump helped solve some starvation issues I was having due to a bent pump pushrod.

 

How's your gas tank and lines? Any rust or corrosion or water? Sounds like maybe something is getting in the needle or float assembly. I had some similar issues and it turned out my tank had decided to start delivering a bunch of rust with the fuel.

 

holleys use check valves. sounds like yours is stuck. but, i don't have a demon book/carb.
maybe lars will chime in

 

i didn't see you mention what the float levels were doing? does it stay consistently in the same spot....

 

I hate to say this... but most of the people I have know to use a DEMON have problems with them right out of the BOX. On the other hand the HOLLEY is much more user friendly...even though demon stole the design from HOLLEY...

As far as your problem... is sounds fuel related. Check your fuel line...make sure you are not losing pressure there... open the sight holes on the carb when you are on level ground...Your float level should allow fuel to just trickle from the sight hole....if the float is stuck it will use the fuel in the bowl and then cut off.... if you line is kinked or losing pressure it will not be able to keep up with demand.

 

The squirters should shoot at even the tiniest movement. My Demon didn't squirt right. From the factory someone had installed the pink squirt cam in the wrong position. You want no slop in the pump linkage and the cam has to make instant pump arm travel

 

Thanks everyone, I went out last night to go over everything and I think I got it fixed.

The gas tank is perfectly clean, no debris, rust, nothing.
Also, the float bowls are consistent, no changes in level when running.

I checked the linkage and found the secondary accelerator pump was bottoming out at WOT and even before then. It took a fair bit of adjustment to set it so it did not bind. This is strange because I just checked this when the carb was off the car and there was no binding, I had the .020" of movement after the throttle shafts were fully open.

I am unsure as to why that would of changed, but it did. I also removed the squirters and found a small piece of red gasket in the secondary squirter. I cleaned both of them out and after I readjusted the accelerator pumps it is not doing it anymore.

Thanks!

 

good Job!

 

Boy, if that isn't a load of

I've worked on more Holley carbs than I can count... New ones, old ones, rebuilds, tuning, etc... My favorite is the old 3310-0 or -1. Later carbs (remember the 4010/4011 "modular" design, for example?) suck, BAD. A variety of quality-control issues, that make them unreliable, and miserable to tune...

If you're using an old-style 1850, then yeah, they DO work ok out of the box... But anything more sophisticated than that, and BG carbs make the Holleys look like what they are: garbage.

Check your patent laws, before you make such claims. The patent for the old Holley technology long-ago ran out, making it public domain technology...

You or I, if we had the technical know-how, could utilize the old Holley technology, and if we found a new way to improve the atomization of the fuel, or achieve some other new process to otherwise improve performance, we could patent it...

Just like BG did.

 

Good job on fixing your Demon's demons, VTDRMS. I'm sorry to hear about you having problems with the first two. That really is unusual. Hopefully, now that you fixed it, it will be a good carb for you. They have always treated me very well. This would probably be a good spot to mention that a return style fuel pressure regulator is a fantastic addition to any performance fuel system. I have solved a ton of fuel system problems by installing a good return style regulator and fuel lines of the size recommended by the manufacturer of the fuel pump. Although somewhat biased toward fuel injection, Aeromotive's website has a bunch of good material on fuel system design.

 

I figured a link might help but don't know how to post it. Anyway...go to www.aeromotiveinc.com. Look for the tech help tab, click on it and go to tech bulletin #801.

 

If you recall, the first design BG carbs were essentially a visual knock-off of Holley's design. Holley took BG to court and thus the BG fuel bowls were re-designed to make the carb look something close to, but not identical to Holley's design.

And while BG's carburetors across all lines are superior to Holley's popular lines as far as components, BG has some quality issues that they have yet to come to grips with. Holley isn't perfect but they're a lot closer to a functional out of the box product than BG is. Not completely unexpected given that BG is, for the most part, a start-up company with a great product but is having difficulty some manufacturing issues. One real benefit of BG entering the carb manufacturing business is that they have forced Holley to step up to the plate as far as moving their product line along.