As many of you are aware ive redone the top end on a 5.0 mustang, switched to carb. Have everything back together, its getting gas, timing is close i believe. As soon as the engine starts the rpms try to jump to 5k and im forced to cut it off. Any ideas?

Carb is a used 670, cant see any binding in the linkages. Supposedly a fairly new carb so it shouldnt be too junked up.

Vacuum leak?
Electical? Brand new electrically controlled advance distributor. Mallory Max Fire.

12/3/2009 8:14:47 PM

Quote :

"Vacuum leak?"

[Edited on December 3, 2009 at 8:26 PM. Reason : s]

12/3/2009 8:26:08 PM

oh noes

12/3/2009 9:07:40 PM

Pull the jet and see if it's sticking open.

My ATV does this when I crank it after it's been sitting for a long time. A couple of throttle blips usually makes it taper down. I'm usually cranking it on starter fluid if it's sat for that long though, so I'm sure that has something to do with it.

12/3/2009 9:28:35 PM

if the needle stuck open on a holley 670 it would start and run a couple seconds, then geyser fuel out of the bowl vent(s)

12/3/2009 11:12:40 PM

Same thing happened on one of my jet skis...spent 3 days trying to figure out the problem...turns out I didn't bolt down the carb tight enough

Check that you've got all the seals tight. A long shot but my be the issue.

[Edited on December 4, 2009 at 1:32 AM. Reason : the]

12/4/2009 1:31:45 AM

brotherman has an intake leak, and he knows it I bet, he just does not want to have to go back and re-do all his pretty work... it has been a long while but it is still such a very familiar feeling

[Edited on December 4, 2009 at 3:17 AM. Reason : vac leak, or REALLY fubar'd throttle linkage :busted:]

12/4/2009 3:16:45 AM

^unfortunately i think your right.

the front and rear of the intake manifold dont have a gasket just rtv, thinking i might go back and use some cork with some rtv

12/4/2009 6:20:36 AM

your leak is more likely the carb base, a leak around the valley is less likely to be entering the intake ports.

Have you checked to make sure the primary and secondary butterflies are nominally closed and working properly? You do have the right fuel pump on there right? (although you would just flood it, instead of the engine running away)

12/4/2009 7:18:51 AM

Quote :

" he just does not want to have to go back and re-do all his pretty work... it has been a long while but it is still such a very familiar feeling "

I hate that feeling so much.

12/4/2009 12:04:45 PM

^^good point about the intake ports

12/4/2009 12:46:32 PM

^^ Thats how we learn.

12/4/2009 7:23:01 PM

got it running and idling this evening. of course it would be the dumbest little thing.

pulled the carb to make sure i had all vacuum lines plugged - check
checked the floats to make sure they werent sticking - check
retorqued all the intake manifold bolts - check (some had loosened quite a bit actually)
reinstalled carb - check

then as im putting the throttle cable back on i noticed that its not allowing the throttle to close completely!

hook everything back up, start it, damn near perfect. funny how that works. ill post some vids when I get a chance to tune it Sunday.

12/4/2009 8:39:52 PM

12/4/2009 8:50:57 PM

why the tall valve covers?

12/5/2009 12:59:44 AM

have to clear the studs and rollers, stockers wont fit.

12/5/2009 7:37:16 AM