460 idles like it has a vacumn leak but cant find one

[junkyardjeff]

I bought this 77 F150 with a 460 to use while I am working on my 66 F250,when I got it the PO adapted a Qjet to it and with the adapter and the factory carb spacer it idled like crap and ran like crap.  I found a correct adapter to go from the motorcraft spreadbore to a regular holley and it runs alot better but it idles like it has a vacumn leak,I sprayed everything with carb cleaner and blocked off all vacumn ports and still the same so I hooked up a vacumn gauge and it reads 20 so I dont think there is a leak.  It even smells lean but I have a holley 600 on it and could it be a too small of a carb for that large of motor,the carb idled good on a 302 but not on this motor,all the plugs are burning the same and I have not done a cxompresion test but what am I forgetting.  Jeff

[enjenjo]

Check the timing. I believe a 460 used ported vacuum.

[Crosley.In.AZ]

Internal crack of the intake manny fold possible??

[wayne petty]

wow.....   vacuum leak... you said that you found the proper adaptor to go to a square bore.... did you get a picture of it...

what did you get it off of?  did is have an egr valve on the back end?

did you test the egr valve for leaks... through the needle and seat...

sometimes they do leak....


which gasket did you use between the manifold and adaptor..

and between the adaptor and the carb?

there are a ton of options for manifold to adaptor gaskets...

some will work... some will leak internaly..

i know that you checked all of this...  but  i thought i would ask....

i have also had problems... with corrosion between the exhaust and intake passages in the factory ford adaptors.... sometimes just the dividers....

can you get me the casting number off the adaptor...  i think i want one for the 76 ford econoline E250/460 that i drive...


one other thing... since the engine runs on the idle transition ports up past 2200 rpms or so , or until the airflow part the booster venturi's is enough to take over... it still helps.. ... you might have to pull the plugs and drill the idle feed restrictors a bit at a time...  they might be sized for a 302.. and the 460 is just too  much motor for it...


edit.... i just remembered.. you ordered the transadapt adaptor... that we talked about before....

[junkyardjeff]

I got the adapter from Summit and it replaces the factory spacer with the EGR valve so I know thats not the problem,I hooked up, the vacumn gauge and it reads almost 20 so I dont think there is any leaks in the intake plus I plugged off all the vacumn lines so it must be the carb.  I would stick on my AFB but I loaned it out but I am thinking the carb must be too small or some problems with the idle curcuit,the carb works fine above idle and like I said before it seemed to idle fine on a 302 but the secondary needle valve had some issues so I pulled it off the 302 but repaired it before sticking it on the 460.  Jeff

[enjenjo]

Insanity is repeating the same action, expecting a different result. You changed the carb once, and the idle was still bad. Try something else.

Sounds like the vacuum is ok, so look at timing. the distributor may have sticky advance weights, and staying advanced. Or they may be stuck retarded. Get a timing light on it, and see what you have. Heck, some ford distributors have no advance at all, they need an external module for advance.

[junkyardjeff]

I have set the base timing but I dont know if the balancer is correct as I had a couple slip,I think it idled a little better with the other carb but it was a Qjet and it had a adapter on top of the original carb spacer and the adapter was open in the middle and it did not have any power and a six cylinder would of beat it.  Now it runs great above idle with plenty of power but not much on the idle side,due to the mileage being unknown I wonder about the timing chain.   Jeff