Moparts
Can't get 340 to idle down
Posted By: Limabean70
Can't get 340 to idle down - 01/20/12 10:29 PM
so I bought a 340 longblock from a guy off craigslist who said it was a runner. he kept the intake, carb, and distributor for himself and I still have mine that I took off my 318 about a month ago so I know they are fine. now when I put the motor in i cant get it to idle under 1500 rpm no matter what i do. ive changed the timing a bunch and no change. i know everything is good as i had it running on my 318 so it has to be something in the longblock. i also tried a diff carb and no change. so what in the longblock will make it so i cant get it to idle down? just wondering how far im going to have to tear into this motor and how much this is going to cost me. thanks and love the site!
Posted By: 70Cuda383
Re: Can't get 340 to idle down - 01/20/12 10:37 PM
what do you mean by "won't idle" what cam is in it?
can you physically not get the RPM down, even if you turn the idle speed screw all the way in?
is there a vacuum leak somewhere?
I don't know of anything in the long block that will make RPM stay up.
it's got to be in the cam timing, spark timing, or carb setting I would think.
Posted By: BSB67
Re: Can't get 340 to idle down - 01/20/12 10:37 PM
Is it possible that the intake is not sealing against the head? End rail pins or too thick end rail gasket could keep it from sealing
Posted By: cudarroger
Re: Can't get 340 to idle down - 01/20/12 10:39 PM
Sounds like it could be intake gasket leak. You said everything else has been run before but now you have your intake on different heads. Could be mating surface.Are you sure the heads were not resurfaced?
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 10:46 PM
i dont know if the heads were resurfaced. the seller said he degreed the cam in at 106. i checked the cylinder pressure numbers and they were all right around 160 psi on my gage. i just know the intake, carb, and distr were all running fine on my motor before and theyre not working on this motor so it has to be the longblock. im just looking for ideas before i take it out of the car cuz my place sux to work on cars so i need to know what im dealing with before i get started. plus with school I dont have unlimited time.
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 10:47 PM
70Cuda, to answer your question i tried playing with the carb as much as possible with all the adjustments and it still wont idle below 1500 rpm. all the ports on the carb are plugged up with little rubber nipples.
Posted By: RobX4406
Re: Can't get 340 to idle down - 01/20/12 10:51 PM
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 10:55 PM
At 1500 rpm is the idle still choppy? Cause if not the problem is elsewhere.. If the cam timing where wrong but the cam still mild it would idle down to some extent.. What your describing sounds like it's carb/ignition/vacuum leak related... Something happened between removal & reinstallation...
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 10:55 PM
Quote:
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
its an edlbrock torker and edlbrock carb. like i said this combo worked before so it has to be the longblock. i know you guys know more than me so if I have to take it back to the guy or try to get him to pay for some fixes i need to know what to say to him.
Posted By: DAYCLONA
Re: Can't get 340 to idle down - 01/20/12 11:00 PM
I had this problem one time before,...turned out to be a piece of gasket mat'l from the carb baseplate that got stuck on the SECONDARY throttle blade holding it open ever so slightly, just a tinny, tiny, winnie little bit! that the idle would never go down no matter how far you backed the idle screw off or OUT!...take the carb off and check to make sure the shaft blades are sealing front and rear completely.....
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:03 PM
Quote:
I had this problem one time before,...turned out to be a piece of gasket mat'l from the carb baseplate that got stuck on the SECONDARY throttle blade holding it open ever so slightly, just a tinny, tiny, winnie little bit! that the idle would never go down no matter how far you backed the idle screw off or OUT!...take the carb off and check to make sure the shaft blades are sealing front and rear completely.....
thanx, i cant right now cuz im on vacation in portland, or (rain sux) but I did have a friend helping me tune it who's a lot more experienced than I am and he said the carb was closing all the way. hes also the one that said it has to be the longblock cuz the intake and carb were working fine on my other motor.
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 11:09 PM
Quote:
Quote:
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
its an edlbrock torker and edlbrock carb. like i said this combo worked before so it has to be the longblock. i know you guys know more than me so if I have to take it back to the guy or try to get him to pay for some fixes i need to know what to say to him.
You bought a motor on C/L & you think your gonna get the seller to pay to fix it.. 
Never mind that it's not gonna be a problem with the long block.... Find someone with more experience than your friend...
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:13 PM
Quote:
Quote:
Quote:
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
its an edlbrock torker and edlbrock carb. like i said this combo worked before so it has to be the longblock. i know you guys know more than me so if I have to take it back to the guy or try to get him to pay for some fixes i need to know what to say to him.
You bought a motor on C/L & you think your gonna get the seller to pay to fix it.. Never mind that it's not gonna be a problem with the long block.... Find someone with more experience than your friend...
why cant it be the longblock? my intake and carb were working fine before so it has to be the longblock right?
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:14 PM
oh, and the cam is a comp cams xe274h, he said it should idle at about 950 to 1000
Posted By: RobX4406
Re: Can't get 340 to idle down - 01/20/12 11:15 PM
How long has the carb been stagnant. If it was sitting, was it completely drained and blown out of ALL fuel...
Sure can be the carb in that case.
Posted By: stumpy
Re: Can't get 340 to idle down - 01/20/12 11:17 PM
Because there is nothing in the long block assembly that can cause that problem. If it won't idle down it's a carb intake or linkage problem.
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:19 PM
Quote:
Because there is nothing in the long block assembly that can cause that problem. If it won't idle down it's a carb intake or linkage problem.
are you sure? im not disputing you but the score is tied right now 1 to 1 lol my buddy says it is the longblock and you say it isnt
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 11:21 PM
Quote:
Quote:
Quote:
Quote:
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
its an edlbrock torker and edlbrock carb. like i said this combo worked before so it has to be the longblock. i know you guys know more than me so if I have to take it back to the guy or try to get him to pay for some fixes i need to know what to say to him.
You bought a motor on C/L & you think your gonna get the seller to pay to fix it.. Never mind that it's not gonna be a problem with the long block.... Find someone with more experience than your friend...
why cant it be the longblock? my intake and carb were working fine before so it has to be the longblock right?
Because the long block is a mechanical device, if it has compression which you've verified it's gonna run, the cam timing could effect that but it would cause a choppy race car sort of idle... Thats not what your describing... You have a carb/ignition/vacuum leak issue...
You might try talking to the guy that sold you the engine, he might have the tuning skills to help you if your cool about it.. You call him up & expect him to give you money back & he'll tell you where you can go....
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 11:23 PM
Quote:
Quote:
Because there is nothing in the long block assembly that can cause that problem. If it won't idle down it's a carb intake or linkage problem.
are you sure? im not disputing you but the score is tied right now 1 to 1 lol my buddy says it is the longblock and you say it isnt
You say 1 to 1 but we have allot more than one guy here saying look again... Your buddy is wrong...
Posted By: stumpy
Re: Can't get 340 to idle down - 01/20/12 11:24 PM
I've been a mechanic for 45 years and have built engines for that long.There is nothing in a long block that can cause a high idle problem. BTW it's more like 8 moparts guys aginst your buddy.
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 11:25 PM
Careful, Stumpy's gonna get Grumpy... Like Me...
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:27 PM
Quote:
I've been a mechanic for 45 years and have built engines for that long.There is nothing in a long block that can cause a high idle problem. BTW it's more like 8 moparts guys aginst your buddy.
lol sorry, I got lost in the count as I was reading things. i guess i'll take an 8:1 vote any day
Posted By: stumpy
Re: Can't get 340 to idle down - 01/20/12 11:31 PM
You need to ask the guy you bought the motor from if the heads have been cut and if so by how much.
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/20/12 11:37 PM
thanks for all your help.
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/20/12 11:40 PM
If you have a stick shift you can drive it but an auto dropping it in gear can be hard on parts....
Posted By: mcmopars
Re: Can't get 340 to idle down - 01/20/12 11:41 PM
Quote:
I've been a mechanic for 45 years and have built engines for that long.There is nothing in a long block that can cause a high idle problem. BTW it's more like 8 moparts guys aginst your buddy.
yuuuuuuuuuup
Posted By: Challenger 1
Re: Can't get 340 to idle down - 01/21/12 12:02 AM
Quote:
Quote:
Quote:
Carb/intake combo?
Some carbs have linkage interference issues on certain intake manifold creating a vacuum leak.
its an edlbrock torker and edlbrock carb. like i said this combo worked before so it has to be the longblock. i know you guys know more than me so if I have to take it back to the guy or try to get him to pay for some fixes i need to know what to say to him.
You bought a motor on C/L & you think your gonna get the seller to pay to fix it.. Never mind that it's not gonna be a problem with the long block.... Find someone with more experience than your friend...
This post is far as I read.
Yea as soon as I read where you blamed the "long block" I knew you needed a better helper.
How could the block and heads be at fault as long as the cam is in right? I'll bet you don't have enough intial timing, I'll bet that has been suggested already. Your in the right place to learn.
Posted By: Dodgem
Re: Can't get 340 to idle down - 01/21/12 01:01 AM
You have a huge vacuum leak somewhere. you sure the big plug is on the back or front of the carb??
Spray Brake clean around the carb base then around the intake when the RPM picks up you have found your vacuum leak.
It could be under the intake if it is not sealing on the under side of the ports no good way to spray that like on a big block.
Pull the intake bolts a little tighter to see if it changes. could well be the end rail gaskets are holding intake up from sealing right. did you put those centering plastic things on the end rail gaskets may be helping to hold intake up.
BUT it is right there at the intake and carb area. If the carb is not being held open by a to tight throttle cable or other it's getting air somewhere else.
Pull the throttle cable and kick down off carb for now to make sure they are not holding carb part way open!
It's right there you will find it!
Long block cannot feed it the air to run up!! another vote.
It's carb held part open, intake to head seal, carb to intake seal or a big plug of intake or carb like where power brakes or PVC go.
Posted By: Dodgem
Re: Can't get 340 to idle down - 01/21/12 01:03 AM
Intake ports 318 to 340 are different sizes check later for matching and proper 340/360 intake gasket set!
Posted By: GTX MATT
Re: Can't get 340 to idle down - 01/21/12 01:12 AM
Another one on the its not the long block side here! Intake manifold is probably leaking. Either its not torqued correctly, gaskets are no good, goobered up too much rtv around a port or something, it wont line up correctly, etc.
You did use new gaskets, right?
Did you take the carb off of the manifold or did you swing the entire thing as a unit? Check to make sure that you did not disturb the choke.
PCV port plugged in or blocked? That's an easy one to miss because its in the back. Maybe old dry rotted vacuum caps that you disturbed when you swing the manifold and carb?
Posted By: RobX4406
Re: Can't get 340 to idle down - 01/21/12 03:31 AM
When the intake was installed, did you note the spacing of intake to head?
Place intake on engine, no gaskets and slide it to one side, measure distance using feelers from manifold face to head face. If it more than about .060-.080 you may need thicker intake gaskets. No matter how much you tighten the intake, up to cracking it, it will not seal.
Do the simple stuff first to rule that out. Vacuum leak under/around carb, linkage hanging up would be my first check.
Set timing to about 15* BTDC and leave it. Recheck it if you get the idle down because you're probably already into the mechanical curve at 1500 rpm. My guess it's gonna want about 20* BTDC to run well at idle.
Posted By: MRHWS
Re: Can't get 340 to idle down - 01/22/12 03:25 AM
Quote:
When the intake was installed, did you note the spacing of intake to head?
Place intake on engine, no gaskets and slide it to one side, measure distance using feelers from manifold face to head face. If it more than about .060-.080 you may need thicker intake gaskets. No matter how much you tighten the intake, up to cracking it, it will not seal.
Do the simple stuff first to rule that out. Vacuum leak under/around carb, linkage hanging up would be my first check.
Set timing to about 15* BTDC and leave it. Recheck it if you get the idle down because you're probably already into the mechanical curve at 1500 rpm. My guess it's gonna want about 20* BTDC to run well at idle.
That's my guess. Something's bass ackward.
Posted By: calrobb2000
Re: Can't get 340 to idle down - 01/22/12 06:29 AM
hi
2 things come to mind here ,
you should have removed the roll pins front and rear of block deck so they do not hold manifold up and not let it seal to heads . if you did manifold should still hae clearance under front and rear of deck when installed with gaskets or a no seal condition will happen in port area . this would be due to head milling .
look in distributor for too light of springs or maby one broken , not bringing timing down at idle causing a hi idle condition !
Posted By: roe
Re: Can't get 340 to idle down - 01/22/12 07:13 AM
I had something similar when I first dropped in my 360, I had the freaking throttle cable set too tight. Check the small stuff like that, and the vacuum caps, vacuum hoses. Do you have power brakes? I had the plastic cap that goes into the booster crack before, that'll give you a nice vacuum leak. How well is your intake sealing? Did you do the spray test yet around the intake sealing area yet?
roe
Posted By: jeff57
Re: Can't get 340 to idle down - 01/23/12 06:16 PM
not to step on toes or become a stat, you have a vac leak probaly intake to head. take it off and start over.check gasket alignment and port size. don't make it harder that it has to be dude,its just nuts and bolts
jeff57
Posted By: bboogieart
Re: Can't get 340 to idle down - 01/23/12 06:34 PM
I notice we are not hearing back from the O.P. anymore.
Hmmm.
Not the long block, means he did something wrong. Didn't want to hear that. Maybe his freind didn't want to tell him, either. We all make mistakes. I hope he comes back, and I hope he gets it fixed. As said, this is a great place to learn. I myself have had the same problem, and it was a poor seal between intake and heads.
Posted By: 1_WILD_RT
Re: Can't get 340 to idle down - 01/23/12 06:34 PM
O/P hasn't posted since friday, I wonder if they got the engine torn down yet....
Posted By: Secret Chimp
Re: Can't get 340 to idle down - 01/23/12 08:44 PM
Murphy valve in the coolant heater crossover banjo port was sticking and sucking air past the gnome ignitors, I'll bet you money.
Posted By: Challenger 1
Re: Can't get 340 to idle down - 01/23/12 08:49 PM
Quote:
Murphy valve in the coolant heater crossover banjo port was sticking and sucking air past the gnome ignitors, I'll bet you money.
That's it!! Why didn't I think of that???
Posted By: Dodgem
Re: Can't get 340 to idle down - 01/23/12 09:16 PM
He said he was away on holidays?
Posted By: Limabean70
Re: Can't get 340 to idle down - 01/23/12 11:34 PM
Quote:
He said he was away on holidays?
thats right, i cant work on it till i get home. just wanted to thank you guys for all your help though.
Posted By: Ramrod39
Re: Can't get 340 to idle down - 01/24/12 05:33 AM
Quote:
Murphy valve in the coolant heater crossover banjo port was sticking and sucking air past the gnome ignitors, I'll bet you money.
Only if he wasn't running the anti-rupture gnome ignitor tips and who does that anymore?
Posted By: 70Cuda383
Re: Can't get 340 to idle down - 01/24/12 02:16 PM
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He said he was away on holidays?
thats right, i cant work on it till i get home. just wanted to thank you guys for all your help though.
That's what were here for. remember, the only dumb question is the one you DON'T ask that causes you to destroy your engine or car!
such as this one! had you not asked the question here, and just followed your buddy's advice, you would have pulled the engine out and torn it all down for no reason! but since you asked, you now know that it's all in the "top end" i.e. vacuum leak, timing issue, etc.
Posted By: Moparnut426
Re: Can't get 340 to idle down - 01/24/12 02:43 PM
The basic engine is a simple air pump, That thing is getting un adjusted air somewhere causing the idle to stay high. Also causing a lean condition most likely. All the carburetor is is an air fuel metering device. and the intake dispurses that air fuel mix evenly through out the engine, any air entering the engine in any other way is a LEAK, and causing a high idle, unless you have the timming all jacked up.
More than likely an air leak.
Which has already been stated.
I have had a stuck pcv valve do this,and have had a brake booster check valve/gromet do this.
I have also had the small 318 port size tin gaskets leake with a 360 port size intake,from under the intake,burning oil/smoke showed up right away.
had a carb not torqued down give fits for a couple days,went to R&R it and found the nuts loose
I wager vac leak but I have also had to reset carb settings/adjustments when swaping from engine to engine.
get a vac gauge and timeing light on it and check for leaks