truck runs like crap after reving it up

[79bonanza]

ok i got a 78 k10 with a inline 6 250 with a monojet 1 barrel on it. i rebuilt the carb and replaced the intake and exhaust gaskets and did a egr delete on it.

the problem now is after i rev it up it, it wants to stay rev'd up and come back down no matter how closed the butter flies are. after awhile it starts to come back down but then it has a bad miss and wont idle and you cant touch the gas or it back fires and stalls out.

im thinking i have like a rediculous vacuum leak somewhere because when you close the choke it revs up instead of idling down like it should because its not getting any air right.

so would that be right could i have a vacuum leak really bad and make it pull more fuel threw the carb after i rev it up?

 

[Fordum]

Well, it can't run without air. if the butterfly is closed, it should slow down. If not, its getting air from somewhere.
I would take a hard look at your egr delete. That is a good source of a vacuum leak if its not plugged all the way.

I would make sure that the butterfly is closing all the way, it would not have to stick open much.

You have checked the fast idle cam on the choke right?

 

[79bonanza]

yea my choke stuff is all back where it was befor i rebuilt the carb, it didnt do this befor so i dont think the choke would be messing with it now.

would a vacuum leak only show up once the engine is reved up tho i mean it should always be leaking right

 

[Fordum]

would a vacuum leak only show up once the engine is reved up tho i mean it should always be leaking right

If it was a solid leak, like a line off or something like that yes, it would leak all the time.
But, you could be sucking in a gasket that is not quite in position.
When you rev it up, the gasket gets pulled in and lets in air. Then, as the flow slows down, it slowly moves back into position.

There are a couple of ways to find it, you can use a smoke generator to fill the system with smoke to see where it leaks out.
But that requires some kind of smoke delivery system.

Or you can do the WD40/propane/brake kleen test.
With the engine idling, spray one of the three around the gaskets and fittings. Just don't get it in the intake of the carb.

If you hit a vacuum leak, the engine will change speeds.

I have good luck with a propane torch unlit.

But, I am real suspicious of the carb. Have a nonstaining fire extingouser handy, take the breather off, rev it up, and look down the throat of the carb as it is running away to make sure the butterfly is all the way closed.

I would wear goggles, or better yet use a mirror, in case it blew back through the carb.

Also, don't forget, open throttle is when the vacuum signal used to go to the egr valve to open it.
Might want to check and see if you have a vacuum line in the wrong position.

 

[Fordum]

Not sure how, but this was a duplicate post, so I deleted it.

 

[diesel4me]

If it only started doing this after the carb was rebuilt,it might be that the top bowl gasket was replaced with one that has a passage bolcked that should be open,or vise versa--often rebuilding kits come with more than one gasket and it has to match the original perfectly...I had one carb drive me coo-coo when I rebuilt it and used the "matching" gasket--only problem was who ever rebuilt it before me used the wrong gasket and I assumed it was the correct one--had to tear the carb down again and try the other gasket,and that fixed it...

I would also suggest if it statred doing this right after "deleting" the EGR valve that its probably getting exhaust re-circulated still,which is a vacuum leak,only worse,because it contains unburned fuel,which might be why it keeps racing for awhile after revving it up...I usually leave the EGR valve on the engine and just unplug it,rather than make a block off plate..just be sure it closes fully ..