carb issue

[leanburn]

i have a 340 mildly done up, i was running a 750 demon and my buddy bought a new 750 holley hp so i put it on to see if there was a difference cause i'm going to buy a 650, i just don't know if it should be a demon or holley. the holley ran fine in the 15 degree weather but today it was 26 degrees and i suddenly have a bog on full pedal take off and when it idles it starts to ''surge'' and smells rich. i pulled a couple of plugs and they look perfect so i changed the back squirter from a 31 to a 25 and theres no difference. float bowels are to the bottom of the hole and ive played with the mixture screws by ear and tried a vacuum gauge so i'm confident they are set right. i'm a two stroke guy and i have expierienced what too lean can do [hence the username] so i'm scared to jet down, is there something else i'm not doing?

[Chryco Psycho]

the problem could be as simple as the carb getting too hot & boiling the fuel , if it is the HP it will have 2 squirters as well so if you are trying to go full throttle at low RPM it may be difficult to get both squirters excatly right but you are on the right track with it

[leanburn]

o.k so ive tried 4 different carbs, a holley 600 vacuum secondaries, holley 650 mechanical, holley 750 mechanical and a 750 demon mechanical. after some tuning on each carb the only problem i have left is i'm dying on top end as if i'm starving for fuel. now after saying that, the demon doesn't seem to die, just the holley's but i havent had the demon on for a while. should i be changing my fuel pump[mechanical] or be looking at something else such as the msd?
oh yeah, other than the top end everything seems not bad.
 i just got home from the track, once the car cools off i'm going to try my demon again, i'll let you guys know if i'm having the same problems with it.

[ntstlgl1970]

Put a fuel pressure gauge on it, and tell us what it reads when it "dies out". That will tell you where to go next

[leanburn]

i will have to get some ''riggin'' on monday, i'll let ya know. got my demon on now, i'll go for a rip in a bit.

[leanburn]

took her for a rip and goes like stink with the demon, screamed through all gears up to 6,000 in 3rd and the holley's were dying at 5,000.
do the demon's have bigger float bowels?

[nivvy]

man you need to stop gambling on carbs or youll go broke....... 

since you have a demon lets go from there..... just dont buy a edelbrock......... 

buy a 30 dollar fuel pressure regulator and a 15 dollar guage man..........
1 thing at a time.........   

we will have that thing screaming.........

[nivvy]

i will have to get some ''riggin'' on monday, i'll let ya know. got my demon on now, i'll go for a rip in a bit.

quit that now.............   

[leanburn]

yup... it was the pump, i happened to have an electric that i was going to put on my dart and never did so i stuffed that on. since i had to use all my fittings for my pump i couldn't hook the gauge back up but screamed her to 6,000 through all gears and seems fine. now back to trying out some different carbs

[Chryco Psycho]

 

[leanburn]

ok so it's confirmed, i tried the holley 750 hp again, before this one died at 4500 in 3rd and now it pulls to 6,000 no problem. i'm still having problems with the accelerator pump. i can't seem to choke it back enough and the demon comes out of the hole no problem. from my understanding these carbs are ''brothers'' but there must be some differences in the accelerator pumps, does anyone know what the differences are?
 the demon had #31 squirters front and back, both cams are in the #1 posistion and the springs are in stock position.
 the holley came with the same setup but i changed the back squirter to a #25 and the back cam to the #2 posistion and tightened the springs [both front and back] until there was no more gain.

[Chryco Psycho]

you want to adjust the spring on the lever until the play is just removed & make sure the pump still has travel @ WOT
 the Pump cam controls the volume of fuel pushed by the acc pump , the squirter controls the speed the fuel is delivered  ,
 so is the Holley Bogging of the line or it is soft responding  bog is to little fuel so you need to increase squirter size , soft is too much fuel
 basically you want to make the squirter as small as possible without causing a bog , & the cam as small as possible as well , squiret will have far more effect on instant bog , cam will have very little effect but can waste a lot of fuel if it continues to squirt long after the bog is covered

[leanburn]

the bog is right out of the hole, if i get on my stall over 2500 it disappears. changing the squiter to a 25 and the cam (pink) to the #2 hole didn't seem to help, but when i tightened the spring it seemed to make a huge difference but still not 100%. by the way i'm doing this to the secondaries cause when i just part throttle it everything is fine. thanks physco.

[Chryco Psycho]

With double pump carbs it can be difficult to tune out the bog when you force it wide open , I would suiggest go the other way with the cam back to #1 position & the Squirter up to 32 or bigger , or just learn to half step & wait a split second to open the secondaries wide

[leanburn]

i'll give that a try and if it doesn't work then i guess i will be buying a demon, i was hopeing for the holley cause all my friends run them so it's easier and cheaper to play around when you can borrow parts instead of buying them just to find out they don't work. although i must say i bolted the demon on, jetted it and never looked back.
 i wish there was someone around here who played with thermoquads, i have one on my dart and love it, throttle response is awsome but in this part of the world people look at you like a cow with a bastard calf when you mention anything but demon or holley.