Improperly Installed Intake = Engine Revving By Itself? Wtf

[Boss 351]

Hi guys, a friend of mine with a carb'd 5.0L GT asked me for some help. He changed the intake, distributor and installed an MSD box. Car would start, revv up to 4k or whatever by itself then die (no idle)...

I checked the dizzy install, found TDC and all - it was all installed properly. But the intake manifold was missing a bolt (cylinder #4) and wasn't torqued... I'm thinking the intake is leaking air, allowing the engine to "bypass" the carb and revv up until it ran out of fuel? Does that make sense? I'm sure ignition can't cause this symptom...

Thanks

 

[aar0s]

my first guess would be air leaking around the intake gaskets causing it to rev.

 

[NIKwoaC]

Definitely a significant vacuum leak going on.

 

[tannerc91gt]

throw the MSD box away just in case....

but yes, vacuum leak is where I'd start. Id think youd see more of a surge than just a hanging throttle though.

 

[srtthis]

Leave the msd... One step at a time... Do a bunch of changes it might end up doing goofy stuff.

 

[mob]

I would think the car would just run rough and maybe die at idle, but I dont know about just reving to 4k by itself from a vacuum leak. Definitely fix the intake and then go from there. The throttle cable is hooked up to the carb correctly and isn't stuck?

 

[Boss 351]

Yup that's why I posted, it's so weird. There's no way the ignition system can do that to an engine. I'm not entirely sure if it goes up to 4k, just sounds like it (tach is dead). Starts, goes up in revvs and dies. Throttle cable is installed ok.

 

[srtthis]

What kind of carb?

 

[Boss 351]

What kind of carb?

Stock Carb on Weiand intake with EGR spacer installed. Bolt missing on cylinder #5 water area, not properly torqued either... I didn't install the intake but suggested to get the bolt out and re-install with a torque wrench and following the proper tightening pattern...

 

[srtthis]

Sounds to me like the air fuel screws need adjusted... When we were adjusting the new carb on the race car the car would have a run away idle till we got the air fuel screws adjusted right