Holley/Demon Carb stumble

[fishmens67]

The sound quality is not good, but you can see this doesn’t stumble.

This is what I tuned on tonight.

did you tune this engine, no stumble, but a little sluggish. is that a small block Chevy ?

 

[Cudafever]

I took all my Idle and Main air bleeds as well as my main jet kit with me to the track but with the big crowd, that showed up to are small little track, i didn't have time to do more then swap the Demon carb for the Proform.

 

[fishmens67]

race car only? get it to idle and transition off idle cleanly, drive around pits @2k and tune for WOT around 12.8 afr. Put 12" extensions on the headers to get a better sensor read. Get the plugs front to rear as close as you can get. Unleaded pump gas leaves virtually no color even @12.8 Once your in the 12.8 ball park jet up or down for best mph and you are done.

 

[yellow rose]

did you tune this engine, no stumble, but a little sluggish. is that a small block Chevy ?

Yep. It’s a bit sluggish because there is no load on it. I can make it snappy just doing a free Rev, but it will be lean with a load on it.

I’m not a big fan of loading the converter and stomping the throttle trying to hold it. I’ve seen guys kill converters doing that.

And, I’ve had customers kill converters listening to gurus telling them to put the trans brake on and mat the throttle to “see” converter stall. A few of those tests and the converter is junk. The point is to set the tune for greatest stall speed. Ignorant way of doing it, but I watched a video of some YouTube hero doing just that.

 

[Mattax]

Remove it and jet for mph.

Like you’d do before there was such a thing as an A/F gauge to look at.

I got some big disagrees last time I posted that. LOL.
But that really is the goal, best power, and mph is something that actually reflects best power.

I took all my Idle and Main air bleeds as well as my main jet kit with me to the track but with the big crowd, that showed up to are small little track, i didn't have time to do more then swap the Demon carb for the Proform.

That's what eventually motivated me to put the car on a chassis dyno. Track's were busy and crowded. Sometimes I'd get two passes on a T&T. Or we'ld enter and race, but then there wasn't much time between rounds to look at plugs, the slip and make a jet change. And of course there's the whole business of staying in the rounds to further distract the driver (usually me but it didn't matter).

 

[mderoy340]

I use the meter to get close and as a tool to get the curve flat all the way down the track. Ticket/mph is the final tune. Once you are base lined and the curve is flat you can then go up/down depending on DA.

 

[Cudafever]

OK guys, i feel it's time to put a period on this thread. The Demon is as tuned as it's going to ever get with out a 50 cc squirter, and then it is still TOO BIG!!!!
However, i feel that there need to be some facts put out here for any one who reads threw this thread trying to fix a similar Problem.
First the 1.75" Proform base is a good replacement piece for the 850 Mitty Demon, and the smaller main body(designed for the 1.75 butterfly's) will fit with no problems as long as you pay attention to the gasket holes...................BUT/HOW EVER....... THE IDLE AND HIGH SPEED "AIR JET" IN THE MAIN BODY ARE NO WERE NEAR CLOSE ENOUGH TO US WITH THE MITTY DEMON "METERING BLOCKS". Also with the smaller booster/bore you can't just measure the Mitty Demon idle and main air jets and put them in the Proform main body(i never attempted to do this and might have got me closer) But by the time you have got this far with TOO BIG OF A CARBURETOR IN THE FIRST PLACE. I't will be way cheaper to just buy a Proform 750 double pumper and be done with it.
If you have more cube's or are revving it much higher them me......the 850 Proform might be a good idea. Other whys just by a 750.
Remember the the Mitty Demon is actually more like a 950 or 1000 cfm carburetor!!!

Final note if you have one of these carburetor or any Holley based Demon.......good luck!
I found several placed were the finish was not good and the main jets in the metering block had a thread burr just waiting to fall off and cause more problems, the metering slot in the bore of the main body had a sliver of alu just begging to fall in to the idle slot. And who know how much other trash i blow out the three time i rebuilt it.

If you get an opportunity to by one......Don't!
I will be starting a new thread with my 850 Proform after i have got the basic done like timing sweeps and jet/top end sweeps......or maybe i will just be happy with it at that point........

I thank each and every one of you that have helped pull me threw all of this. It has been a journey and i say again, THANK YOU!

 

[yellow rose]

OK guys, i feel it's time to put a period on this thread. The Demon is as tuned as it's going to ever get with out a 50 cc squirter, and then it is still TOO BIG!!!!
However, i feel that there need to be some facts put out here for any one who reads threw this thread trying to fix a similar Problem.
First the 1.75" Proform base is a good replacement piece for the 850 Mitty Demon, and the smaller main body(designed for the 1.75 butterfly's) will fit with no problems as long as you pay attention to the gasket holes...................BUT/HOW EVER....... THE IDLE AND HIGH SPEED "AIR JET" IN THE MAIN BODY ARE NO WERE NEAR CLOSE ENOUGH TO US WITH THE MITTY DEMON "METERING BLOCKS". Also with the smaller booster/bore you can't just measure the Mitty Demon idle and main air jets and put them in the Proform main body(i never attempted to do this and might have got me closer) But by the time you have got this far with TOO BIG OF A CARBURETOR IN THE FIRST PLACE. I't will be way cheaper to just buy a Proform 750 double pumper and be done with it.
If you have more cube's or are revving it much higher them me......the 850 Proform might be a good idea. Other whys just by a 750.
Remember the the Mitty Demon is actually more like a 950 or 1000 cfm carburetor!!!

Final note if you have one of these carburetor or any Holley based Demon.......good luck!
I found several placed were the finish was not good and the main jets in the metering block had a thread burr just waiting to fall off and cause more problems, the metering slot in the bore of the main body had a sliver of alu just begging to fall in to the idle slot. And who know how much other trash i blow out the three time i rebuilt it.

If you get an opportunity to by one......Don't!
I will be starting a new thread with my 850 Proform after i have got the basic done like timing sweeps and jet/top end sweeps......or maybe i will just be happy with it at that point........

I thank each and every one of you that have helped pull me threw all of this. It has been a journey and i say again, THANK YOU!

I’m a bit confused. I watched the video again, and I’m not sure how a 50 cc pump would fix that. You are never out of pump shot. A bigger pump housing won’t make the pump shot last longer if it didn’t run out. And the shot is controlled by the pump cam and the size of the nozzle.

I’ve heard about the 50 cc pump being a upgrade, but I don’t see how this would help I your case.

 

[Cudafever]

Agree about it not fixing the problem, But you can see the front squirted giving up before the back. So if i was to put a 50 cc squirter Pump in, it would be the front and then a larger Squirter.

I had a 1000 cfm Themoquad i tried on my stockesh 340. ran grate if you got moving before you asked the secondary to do there job.

That's the same problem i'm having here with a Demon carb with 1.75 butterfly. This 850 Demon carb, in all reality is a 1000 cfm carb. Trying to work on a 408 that i shift at 5800 rpm just don't work.

My proform 850 is to big as well being i'm at 6600 feet elevation, and a, so called mild 408. that is just to big as well but i can work with it and will still work if i decide to race at a lower elevation.

 

[j par]

.....

I thank each and every one of you that have helped THANK YOU!

Your welcome!.... and if I can be of any further assistance please feel free to ask... ...

 

[yellow rose]

Agree about it not fixing the problem, But you can see the front squirted giving up before the back. So if i was to put a 50 cc squirter Pump in, it would be the front and then a larger Squirter.

I had a 1000 cfm Themoquad i tried on my stockesh 340. ran grate if you got moving before you asked the secondary to do there job.

That's the same problem i'm having here with a Demon carb with 1.75 butterfly. This 850 Demon carb, in all reality is a 1000 cfm carb. Trying to work on a 408 that i shift at 5800 rpm just don't work.

My proform 850 is to big as well being i'm at 6600 feet elevation, and a, so called mild 408. that is just to big as well but i can work with it and will still work if i decide to race at a lower elevation.

Thanks