View Full Version : Engine loses power after launch

10-01-2012, 03:57 AM
I'm running a Vega with a 750 h.p. small block with a 1090 Demon carb (96 jets). I use a trans brake, and come out at about 4500 rpm. When the car hooks well, and the front wheels come up, the motor will lose power instantaneously, then regain it....sometimes twice. I have a vent tube from breather to breather on the carb, and the float levels are where they should be. The car is going 9.50's @ 143, but I'm sure I could be in the very low 9's, if this problem goes away. There is really no loss of power or misfiring after the initial launch. Any suggestions?

10-01-2012, 04:44 AM
sounds like you need jet extensions in the rear of the carb :wink:

10-01-2012, 06:06 AM
sounds like you need jet extensions in the rear of the carb :wink:x2

10-01-2012, 09:03 AM
Already has them.....thanks anyway.

10-01-2012, 09:23 AM
Possibly a partially clogged fuel filter or weak fuel pump. What size fuel lines?

10-01-2012, 10:39 AM
Fuel lines are 10 AN......pump and filter are new...MagnaFuel pump w/ Aeromotive filter. I'm in the process of checking the fuel flow at the carb. That should tell me something. Also.....the regulator is new (Aeromotive). Fuel pressure gauge stays at 7.5 lbs.

10-01-2012, 04:01 PM
Might want to check your fuel pickup in the tank....

10-01-2012, 04:59 PM
Fuel isn't coming out of the air vent and going down into the engine is it :?:

10-01-2012, 05:09 PM
Are you running a power valve in the rear?

10-02-2012, 03:59 AM
Are you running a power valve in the rear?

that was gonna be my next question too ...... :wink:

10-02-2012, 04:14 AM
The carb is a Demon 1090 Dominator, and yes it has a primary power valve (6.5) and secondary (plugged) according to the specs. I pulled up on the Demon site. I know less than nothing about power valves.

10-02-2012, 11:42 AM
What is your vacuum at idle?

10-02-2012, 02:13 PM
What is your vacuum at idle?
In gear.

10-03-2012, 11:05 AM
What is your vacuum at idle?
In gear.
Joe - if you're thinking what I'm thinking, the PV is cracking open.

10-03-2012, 04:24 PM
A 6.5 power valve sounds high to me for a 700 hp NA small block. but That should cause a rich low speed problem not what he has described.
Vent tube spill over and rear power valve installed in a hard leaving car sound like probable cause for symptoms described but sounds like he has the covered.

10-04-2012, 03:34 AM
I haven't had the chance to get an accurate vacuum measurement yet....just too busy at work. I hope to do it today. I have a feeling the power valve is the culprit, based on some of the input here. Thanks.

12-13-2012, 10:05 AM
Check your coil for a crack. I had the same problem during launch.

12-29-2012, 07:22 AM
Not trying to be a prick, but are you absolutely sure (you've checked) that the jet extensions are in the rear, not the front? Been there, done that.....also check to see if you have a starter cable or other wire that might contact the header during launch. Haven't done that, but I've seen it....


07-08-2013, 06:03 AM
Try replacing parts in the ignition system. Could be a loose wire.

07-08-2013, 04:33 PM
Had a friend who fought this type of deal.

Ended up being a lose wire in the steering column that was shutting off power to the MSD box for a second.