vacuum lines

[hensonjd]

I have a stock qjet sitting on a stock 454. I see three vacuum lines to hook up. One leaves the distributer, one is between the carb and the distributer, and the other leaves the driverside valve cover. Where do these three lines go and I guess I will just plug the other three. I just had a qjet rebuilt someone had a qjet replacement edelbrock on their and their vacuum ports are completely different. A good pic would help. thanks guys

[Corts60]

The line from your distrubutor will go to either a ported or manifold source on your carb depending on what you want. Ported means that at idle, the port does not draw a vacuum, but just off idle it will. Manifold means it pulls vacuum all of the time except for wide open throttle, at which point the entire engine pulls no vacuum.

I personally prefer manifold vacuum source to my distributer because it advances the timing just a bit that makes for good idling and fast responses.

As for the line from the valve cover, that is your pcv and needs to go to the big bottom port on the front of the carb. That is how the engine draws out fumes from the crankcase.

And the third one? I'm not sure which one you mean, but if it is the brake booster line, it goes to a large port on the bottom back side of the carb.

Hope this makes sense to ya.

[hensonjd]

well i have hooked it up to every different port and i cant figure out what is wrong, but after putting on this rebuilt qjet i cant even get it to idle. It sounds like it is back firing through the carb adn running all kinds of rough. I havnt unpugged or messed with any wires. All that has been tampered with is the swithing of the carb. I need some help...

[MadManAndrew]

Screw vacuum lines. We don't need 'em.

Anyway, I'm not that experienced myself, but I'd say your idling problem is probably with the carb itself, not the vacuum lines.
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[motornut]

i got some pics from a 454 truck may help
can't quite make it all out tho

[Corts60]

Originally Posted by hensonjd

well i have hooked it up to every different port and i cant figure out what is wrong, but after putting on this rebuilt qjet i cant even get it to idle. It sounds like it is back firing through the carb adn running all kinds of rough. I havnt unpugged or messed with any wires. All that has been tampered with is the swithing of the carb. I need some help...

Back firing through the carb is a lean fuel mixture condition. It won't idle because you have a major vacuum leak some where. Check your carb base gasket and double check that all of your lines are not cracked.

I would plug all of the ports on the carb and run the engine. If it idles, one or more of your lines are either cracked or whatever they are serving have an issue. You can check those one by one.

If it does not idle after that, I would buy a can of starting fluid and, with the engine running (might need someone to help you out if it won't idle), spray the starting fluid around the base of the carb/gasket area. If the engine revs up on it's own, there is a leak. Fix the leak and you are golden.

Also, make sure your idle/air mixture screws are both 1.5 turns out from bottom to start with. Go from there and good luck.

-Cort

[motornut]

starting fluid might start a fire with a back fire
use wd40 or a carb cleaner

was it doing the same before?
sending unit ok?

[hensonjd]

No, before I had gotten this qjet and had it rebuilt, It would crank and run but you could tell the carb was flooding and having issues it was an edelbrock bolt on replacement. But now that ive changed to this other carb I cant even get it to start. Which port should be for the vacuum advance?

[hensonjd]

What do you mean by 1.5 turns out. And could i have over tightened it and messed up the gasket? And my timing shouldnt be off bad enough to keep it from running should it?

[hensonjd]

ok got a bunch of the vacuum caps from napa and i got it to where it will run now. I am still get a little bit of back firing through the exhaust how do I tue this thing. I am not real familier with carb tuning so please be patient and walk me through this...

[motornut]

do you know if it is a BB454 stock carb or maybe a SB350?
any part numbers?pics?
ported i believe is drivers side on the front over the idle screw
any idea if the cam has been changed?
turn the idle screws in (just seat them) back out 1.5 turns

[hensonjd]

It is the original 454 cam. So i screw them in till they touch and then back them out one and a half turns. it had a crane cam towing cam put in it.

[motornut]

Originally Posted by hensonjd

It is the original 454 cam. So i screw them in till they touch and then back them out one and a half turns. it had a crane cam towing cam put in it.

i think you ment original carb?
yes to the screws
ah that might be part of the prob can you find out the type
the timing dosn't stay factory after a cam change

[Corts60]

OK, maybe tell us everything that has been changed since the last time the engine ran well.

[hensonjd]

Ok. I was going to change my carb for a rebuilt qjet. So i put it on and I couldnt get it too run it was back firing through the carb. So now that I capped off all of the excess vacuum ports I can get it to start and run but I am getting a slight back fire through the mufflers and it isnt running quite right. So i loosened out on the distributer and have tried to adjust it by hand and cant get it right. So how do i get it timed right and is that what is causing the slight backfiring.

[Corts60]

Yes, timing is causing the issue. Do you have a timing light?

If so, hook that bad boy up and set your timing to around 6-8 degrees. That should take care of the backfiring issue. Then move on back to the carb problem.

[hensonjd]

well i guess if i take care of that the carb should be fine. Key word being should. The only vacuum line i needed was the to the distributer and the one to the valve cover and i got the rest capped. So i guess i am going to get to learn how to use a timeing light. Never done that before. Is 6 to 8 going to work with the towing cam.

[LONGHAIR]

Originally Posted by Corts60

The line from your distrubutor will go to either a ported or manifold source on your carb depending on what you want.

It is not about what you want, it has to be plugged into the fitting that is required by the calibration of the distributor itself. You cannot "just plug it in wherever you feel like". Most of the factory HEI distributors were originally intended (and calibrated) to run with ported vacuum, as such they have more centrifugal advance built into them. Simply connecting one of these to a full vacuum source will probably cause pinging issues.
I am a huge advocate of using full vacuum, but not on totally stock factory HEIs.

Originally Posted by MadManAndrew

Screw vacuum lines. We don't need 'em.

Anyway, I'm not that experienced myself, but I'd say your idling problem is probably with the carb itself, not the vacuum lines.
Posted via Mobile Device

'Nuff said....not experienced

Originally Posted by hensonjd

So i loosened out on the distributer and have tried to adjust it by hand and cant get it right. So how do i get it timed right and is that what is causing the slight backfiring.

This is just making the problem worse. If the timing was ok before you changed the carburetor, nothing changed in that area. Adjusting "by hand" or "by ear" is never going to be right, but it should not have been "messed with" at all. Changing a carburetor and having problems......is a carburetor problem. Whether it's a tuning thing or just a vacuum leak, don't go looking at things that were not disturbed by the install.

[hensonjd]

Yea the funny thing is it was one of those I can feel my self messing up moments when i started jacking with it but hey it already happened so now I am where I am.

[Corts60]

Thank you Longhair for pointing out every one's mistakes.

Hens-

Timing is very easy to accomplish. And, as far as my experience goes, a towing cam is profiled to provide more torque and I don't see any reason 6-8 degrees of timing wouldn't get er done. If you feel the need, you can probably go up to as much as 10 degrees, but pay attention to pinging and dieseling. And, of course, everyone feels differently about how timing should be accomplished and avid "by the bookers" will correct me. For your case, just time the bastard and get your truck back on the road. It will still run, and well.

[LONGHAIR]

There is more than enough mis-information about timing to get most guys into trouble. We don't need to keep reinforcing it.
It seems like a very simple thing, yet we know that even the factory boys screwed it up quite well. Much of the early emissions era thinking was flawed.
The real complexity comes from the fact that "testing" the actual advance curve is rather difficult. Knowing what you have, and where you need to be, are key in this matter. You cannot just drop in any distributor that "fits" and expect it to be correct.
Since the change to computers and fuel injection was quite some time ago, distributor machines are few and far between. This wouldn't be a huge issue if the factory units were "correct" in the first place....but most are not.
It is far more complicated than jus tsetting the initial timing, with a light, another thing that many don't "bother with".