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408 SBC Blower motor backfires?

3K views 23 replies 4 participants last post by  madmike87 
#1 ·
fresh rebuild on 400 sbc. Has the 871 blower, dual Holley 700 or 750 cfm blower carbs cant remember exactly which they are, petronix dist. with second strike. First of all the motor will not start without giving it a little throttle. But when it does get going it runs and sounds really good and wants to go. The other thing is after it starts and I rev it a few times it will idle for about 5 seconds on its own then dies puffing out white smoke and fuel from the carbs. My thoughts are carb adjustments need to be made but I have no idea where to start with them. I think they may be flooding out at idle. I have not messed with any settings on them yet. Would rather consult with those who have first. Or if anyone thinks it could be something else please let me know. Any input would be greatly appreciated. Thanks.
 
#10 ·
no need to start engine to set float levels.
turn on 1 pump,remove site screws(all of them) the level should be just below the threads where you took out the plugs,,,shaking car should allow slight spillage,but only when shaking car,not constant.

what are the regulators set at? 5 ish?
 
#13 ·
will do just waiting for the time to get around to it lol. My guess right now is the float levels are off from all of the research I have done. Also do you think a 2.5 exhaust will do or should I go with the 3 inch? Because right now its so loud I cant start it in my neighbor hood with out risk of cops being called?
 
#19 ·
Wow those are very nicely priced. Ok so I finally got to work on the truck a little bit today. I turned on the fuel pump let the bowls fill up then turned it off. Then I took out the plugs for the sight glass holes and when I did fuel just poured out, like a lot of fuel poured out like they were full to the top. Now granted the engine is at a slight angle back and the plugs are on the back of the carbs so I figured a little bit of fuel would come out. But to me it seemed very excessive. Now my next question is the adjustments for them. Do I take the needle set screw in or out to lower the fuel level inside the bowls. Right now I just need to get them as close as possible until I get the chance to take the carbs off or do the adjustment when they are level.
 
#20 ·
level the car,,,you must have a jack if the car cannot move.
loosen set screw on top of float bowl.
turn nut one full turn clock wise.
rock the car so fuel is below threads
turn on pump
if fuel still comes out,repeat.

final adjustment should be fuel is even(slightly lower) than the threads,,,all 4 bowls

you have adjusted the fuel pressure to 5 ish pounds?
 
#22 ·
Ok adjusted the floats to where they need to be and fuel pressure is right at 5 psi. It stopped backfiring when it dies though. But it only idles for about 7 to 10 seconds. Runs like a top too. But my guess now is idle mixture screws but their is like 8 of them and I have no idea how to get them all in sync. Any Ideas?
 
#23 ·
start with all of them at 1 1/2 turns out from bottom(do not bottom them out tight,be gentle)
make sure the linkage is syncronized. turn the idle screws in 1/2 a turn. Keep the engine running by adding throttle as required until engine warms up.
If this engine is new,I hope it has a roller cam?
 
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