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Discussion in 'The Garage' started by down4thakrown, Aug 6, 2005.
is it suppose to be higher? or hold the vaccuum in gear?
then when i put it back in park the rpms dont go back up to 1000 but, stay at about 4-500rpms?? and they wont go up unless i throttle it up to 1000 or over then drops to where it was before in park.
it'll move in gear but, wont stay running unless foot is on the pedal
when i shut if off when its running at 500rpms and its still in park. then i start it up it will still idle at 500rpms until i rev it past 1000rpms then it will stay above 1000 until i put it in gear again.
Are you running a new carb by chance?
yep just got it today. and i still cant get the thing to idle in gear.
Is it by chance a 600 cfm Edelbrock preformer?
nope holley rebuilt q/j
New manafold or new gaskets then??
new manifold,new engine, new cam, new q/j, new tranny, new power brake booster & master cylinder, unilite distributor.
i tried the idle screws at 1.5,2,2.5 turns out and it didnt seem to change it at all.
Ok. Sorry to lead you on like this but I recently put a new manafold and carb on mine and it did sorta the same thing. I think the motor was a old worn 305 and the carb was a 600 edelbrock prefomer, and a edelbrock preformer manafold. I never tuned my carb but it did the same thing with the idle though. I never checked any vacume presures though. I would say though that the drop in rpm is what is causing the vacume drop. I am also have very little knowledge on this subject.
I have heard of people on here having goofy thinks happen with manafold gaskets on here. Maybe this is one of those things?
Also the motor developed a slight knock not to lond after I put the carb and manafold on and then eventualy took a dump after about 2000 miles or so. But I am hoping that that was just the old warn out motor.
It sounds like one of three things to me:
First is that your timing may be way off. Having it too retarded / advanced can cause terrible vaccum numbers. Check it with a light, and set it to about 12 degrees BTDC, you typically wanna run the most timing you can, for the most power. If you get a noise that sounds a bit like shaking a marble in a tin can when you accelerate, or go up a hill, your engine is detonating (the fuel mixture is firing off on its own before the spark is suppost to happen, its extremely hard on an engine, and should be avoided as best as possible) If you get detonation, you'll wanna back the timing off a degree or two.
The second thing could be a big vaccum leak somewhere. Seeing as you have a new carb, make sure that you hooked everything up correctly, and that you didn't leave any ports open, or miss a port somewhere. Take a can of carb cleaner and spray it around the base of the carb (with the air cleaner on, otherwise it just sucks the spray right in and may be a bit missleaking, err, missleading ) and along the intake gaskets, if your RPMs ever increase, your leak will be in that general area. Oh yeah, make sure to check that your brake booster, cruise control, or vaccum operated heater controls (if so equipped) are not leaking. They are often overlooked when there is a big vaccum leak.
The other thing it may be is a poor mixture. Try putting the mixture screws all the way in, and backing them out about 2.5 turns each (being careful not to tighten them too much, you can damage them). If it idles good that way, set your idle to about 650 rpm or so, and slowly back off / turn in each mixture screw one at a time until you get your best vaccum. Then it'll be in a fair good tune (you basically are aiming for your best vaccum at an idle, the reason why it runs so well when you put your foot into it is that the carb moves over to using it's jetting above a certain RPM)
As far as the high idle thing goes, thats controlled by choke stuff (wether it be hot air, electric, or spring) basically, most people give the truck a pump before they fire it up, which sets the carb into high idle mode. You then start the truck, and it'll idle at about 1000 rpm or so. When the choke is closed, it'll hold the carb in high idle mode until the choke opens up, usually while you are on the go. Then when you come to the next stop light or whatever, it'll suddenly be low idling. If you sit there and wait for the choke to open up while idling, it'll remain in high idle until you give the pedal a quick tap, then it'll lower the idle (normally when you accelerate, you release the kickdown without even knowing it)
Quite a nice system to have if you ask me I always gave my truck two pumps before I fired it up while it was still carbed, and the high idle was a big help in the winter (engine never liked idling low when it was cold out)
Now I have a TPI setup, and the computer takes care of all of this stuff for me
Edit -- I should mention that idling at 550 rpm isn't always a good idea either. If you have an older engine, the oil pump may not be able to produce enough pressure at that RPM to keep your engine oiled, and it can also lead to lower vaccum numbers. 650 - 750 rpm in drive is a fairly good number. No reason why you cannot idle your engine at about 850 rpm in park, though that lope it makes at 550 rpm truely sounds quite cool
yea that was probably do to an old motor. a new carb and intake shouldn't kill a motor off unless it was on its last leg.
it idles smooth at 8* advanced. i did the carb cleaner thing and theres no big changes in the idle. its real responsive when i press the gas when its in park. doesnt miss or studder or anything. just when i put it in gear it drops to 4-500rpms. then when i put it back in park it wont go back up unless i rev it past 1000rpms then it will hold it. even if i shut it off it still idles at 4-500 until i rev it up. i think its a vacuum leak. if i where to un hook the vacuum line that goes to the tranny and put it in gear will the idle still drop, or would this be a bad idea.
Unhooking the vac line to the tranny wouldn't make a difference in it. Thats only there to help the tranny decide on shift points
That issue with the carb dropping way down in rpms -- When it does that next, go and turn up the idle screw a bit, see if that makes any difference
what if it does or doesnt? i cant go do it right now it has goten to late. but it will be one of the first things i do tomarrow. i really want to get this thing running being that i only have to do is put the seats and a rack or bed on the back and its done. this is soooo aggravating.
yeah, this is why I spent a bunch of money to go EFI. Carbs are a pain in the butt as far as I am concerned :P The best you can do is fiddle with it until you get it to run fairly decently, then just don't touch it after that, lol Though, I must say it sounds like a low idle type issue, esspecially if it has good throttle response and such. What are the vac numbers like at about 800 rpm or so? The optimum is about 20 inches of merc on a stock engine. Mine usually hung around 18 - 19 or so, but I am a fair bit up as far as elevation goes, so I assume that was about as good as it gets up here.
there at 10" when in park and 0 when in gear. and thats at 1000-1100 rpms.
Hmmmm always wondered about the "holly" rebuilt qjets.
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