Backfire .........POP ???

[blownbbf]

We are having problems with a 406 small block Chevy. It has a 420 mega blower, victor jr heads, small roller, twin holley 650's dps.
Even after it has heat in the motor..... when you spike the throttle its giving a lean backfire POP. eek! It has 15 deg initial with a total of 34.The power valves have been removed and jetted up 5 or so.
We are thinking of going to 50cc acc pumps? Could the problem maybe be the squirters being too small or maybe does it need a more aggressive cam on the linkage for the acc pumps?
Any suggestions?
ps What do you think of the size of the carbs being used? 750's would probably be a better choice ehh? I wonder how much power we could pick up with extra 200+cfm?
Thanks in advance

[Hotcrusader76]

Are they HP650's or #4777 650cfm's?

[blownbbf]

4777... Help !!

[Ian]

Now I am the first to admit that I do not know much, but it could be that you need a more aggressive cam on your acc pump. Are the carbs brand new?

[Hotcrusader76]

Could you also please fill us in more with the engine specs? Fuel pump type? Fuel filter's condition? Fuel line size? Etc.
[ January 21, 2003, 04:48 PM: Message edited by: Hotcrusader76 ]

[Craig]

Start with bigger shooters, then you can dial it in with a Holley pump cam kit. I spent a lot of time dialing in my big heavy Buick Gran Sport at the drags. I were running slicks so when you stand on it from off idle, you instantly get that lean condition. Once I started getting it dialed in, it had a great 1.5 60' times, and this is just a street car. You're should be on the right track with it being lean condition, but also make sure you're running enough adavnce in the ignition.
[ January 21, 2003, 04:51 PM: Message edited by: Craig ]

[Hotcrusader76]

Most likely you have the stock little red 240 cam which pumps out approx ~18cc of fuel for every 10 or so pumps (average). Going to position number two with that cam should give you another 2cc's of shot.
Now if you bought the lighter red cam 330 (3 possible positions), you could jump to a total 30cc shot or 37.5cc (pos.2)all with keeping the 30cc pump mechanism.
Otherwise you can foot the bill and get a 50cc conversion for all four corners. A waste in my eyes for that application. Then your dealing with the turd brown cams. Way more shot than you need right now.
Just look into purchaseing some 330 cams I think they are commonly called the pink ones. I do carry these cams and could have them shipped out tomorrow if ya like. Send me an email.
~Ty

[GofastRacer]

OH well, here goes all my stars!!..... :rolleyes:
The simple cure!.. wink
http://free.***boat.net/ubb/Avatars/Forum_Graphic_Depot/Toilet.JPG

[Craig]

The Flying Toilet Bowl? :D
Supposed to be good full throttle, but have heard verying degrees of success with idle and part throttle charcteristics?

[blownbbf]

I think we have the pink ones already,with a 28 squirter. Should we go bigger with squirt?
Also can a person change just one acc pump on each carb, or do you need to do all four?
Thank you
Rick

[blownbbf]

Its a 9.2 cr, 232,236 dur .540 lift. Blower is undriven 15%.Elavation on a good day is 4500 and for the dial in its just pump gas.
The holley book says 8 pounds (cough)with 400 ci and 15% undriven..... does anybody here agree with that?
[ January 21, 2003, 08:08 PM: Message edited by: blownbbf ]

[Badboat1]

I think you need more inital timing in it first off and 28 squirts no way enough 35 should be close and 25 degrees inital timing would be good and limit it more for full advance.
Badboat1

[GofastRacer]

Craig:
The Flying Toilet Bowl? :D
Supposed to be good full throttle, but have heard verying degrees of success with idle and part throttle charcteristics? Hmmm, a friend of mine has one on his Nova on alcohol, once in a while he takes it out on the street and you'd never know the difference except for the throttle response, it's one of the easiest systems to set up!.. :cool:

[Infomaniac]

GofastRacer:
Craig:
The Flying Toilet Bowl? :D
Supposed to be good full throttle, but have heard verying degrees of success with idle and part throttle charcteristics? Hmmm, a friend of mine has one on his Nova on alcohol, once in a while he takes it out on the street and you'd never know the difference except for the throttle response, it's one of the easiest systems to set up!.. :cool: I have never used one but I do not see it being any different than any other injection system. Nothing short of bad ass.

[GofastRacer]

You got that right, I think it's the spool in the barrel valve that makes it so driveable, it has a very gradual ramp that makes the transition from idle to WOT very smooth!... :cool:

[Fiat48]

Badboat1:
I think you need more inital timing in it first off and 28 squirts no way enough 35 should be close and 25 degrees inital timing would be good and limit it more for full advance.
Badboat1 I was thinking the same thing. More initial timing might solve that hesitation with no other changes.
If it were me, I'd lock the distributor. Start it at 34 degrees. No advance to worry about.

[Tee]

I had this problem with my old motor. The fix for me was that I had the idle screws in too far. Backed them all out another 1/2 turn and the problem went away. I was running twin 650 #4777's also.