I just purchased a offy quad intake manifold (#5416). I also purchased a rebuilt Holley 390 to go with it. It's going on my stock 250 that was just rebuilt. Other than header pipes, it is completely stock.
I just finished installing it with the primaries inboard and it runs terrible. Soo, I decided to switch it around and put the primaries outboard. It still runs rough. It won't even idle without some help. Question: what's the proper orientation for these four barrels?
According to the instructions that came with the offy manifold, the primaries are supposed to be inboard (toward the valve cover). It also mentions that no jetting changes need be made with this setup. Does anyone else have this setup and could give me some help? I've tried various idle mixture settings with no help. The vacuum ports were all hooked up to various items. I know it's not electronic because it was working great with the one barrel rochester just a few days ago.
Check out the post "holley 390 on 250" on 7-30-2003. Many answers for you are there in that post.
Clyde
I have run a 600 holley On my offey when I had it And all this was on a bone stock 250 and I never had any problems. Maybe somewhere along the line maybe you have a Vacum leak???? weather it be intake to head?? or carb to intake?? Or there maybe a problem with the idle circit on the carb. I know you said it was rebuilt But you just never know. }[oooooo]
Ps One thing that can never be seen is a Tiny bit of trash in the metering block When being rebuilt If all the orfices were Not checked closely (with air Or fluid of some kind It can be over looked. I have gotten carbs from people Say Oh I just had the carb rebuilt But it still won't Idle right Or at ALL. One of the first things I check OR Even Replace is the metering block And check the idle circit hole In the throat of the carb.
But check for vacum leaks Before you think about The carb it self being a problem.
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NovaMan/Twisted6/Larry
I'm not alone!!! i was just going to post the same question. over the weekend i finally got my clifford intake and headers in my nova... 250 w/ 194 head. holley 390, but it won't idle right. starts and runs at 1600 rpm, but any adjustment to get it lower and it either dies, or becomes very inconsistent reving to 1600 then dropping to around 1000 then back up .... put it in gear at any speed and it just dies. ran perfect w/ monojet before the swap. i'm at a loss.
bucky
I have a Holley 390 on my 261 Chevy, runs real nice with the stock 52 main jets on a heated intake.Are you guys running the #8007 model carb? There are several 390 models and some are designed for use on small 4 cylinder engines.The idle restrictions in the primary metering block are smaller than the 8007 model, low speed performance is too lean unless you enlarge the idle restrictions.Your carbs appear to have the symptomns of vacuum leaks .
I have run 4bbl carbs in several positions on my 261, seemed to run the same no matter what. I like to run the carb rotated 90 degrees from the V-8 position, primaries outboard, easier to hook up the cable linkage.
Bucky, that is exactly the problem I'm facing. I tried different idle mixture settings but that didn't help. If it's a vacuum leak I sure can't find it. I may have to take the carb off and do what Larry is suggesting and check the idle circuit. It is a used carb so there's no telling what the previous owner did to it.
Thanks to everyone who responded to my post. Lots of great ideas!
If you're not familar with Holley's I suggest you buy Jeff Williams book on rebuilding Holley carbs.You can find it on Half.Com for less than 10 bucks.Then read the book well and rebuild the carb yourself.Holleys are very easy to work on, it all comes apart and you can really see what's going on.Almost all Holley problems come from the last guy who worked it.Out of the box a Holley will perform well on any engine within the carbs limits.Any stock 390 Holley should start up and run ok on any mild street engine, no matter the number of cylinders, it may have flat spots and need tuning if it's the wrong model , but it won't have the symptoms you describe.I'm assuming you sprayed carb cleaner or something similar around the carb base and intake manifold to head area while the engine was running to check for leaks.So your carb adjustments or interal adjustments are way off.
hello....Interesting.....from what i see is a pattern that seems to relate to idling...here is the Holley suggestion- screw both idle screws in -clockwise-until they stop....then screw out each idle screw 2 and half turns- this is how Holley sends their carbs from the factory...this works in Most cases-especially if you had a carb that worked well and you ONLY changed the carb and you had idling problems-yes you need to check the vac lines-make sure you are running vac line from distributor to vac line located on same side of carb as sec spring housing and on fuel block opposite main fuel inlet.....
If I am correct, both these guys Changed intake manifolds in addition to the Carburetor. The problems Sound like a leaking intake gasket and is hard to detect on the late inlines because they usally leak on the bottom side. The 235-261 had steel rings to help with the alignment but,not so on the late motors. Use a FelPro #MS9786 which is a one piece gasket. be sure to in a new gasket(Incl.) between the Intake and exhaust manifolds. I personally like to put a very thin coat of permatex #2( non-harding)on both side of the gasket at the Intake ports only.
"DO NOT USE SILICONE"!! If you use Silicone the gas will desolve it and you will have a leak. BE sure to leave the 4 bolts between the manifolds started but loose until the intake and exhaust are installed on the head. If you're using Fentons or aftermarket headers you won't have to worry about this. Maybe this will help-Paul
[This message has been edited by paulweldit (edited 12-13-2003).]
I use the Copper RTV all the time on my intake/header Gasket And Race fuel Does not hurt it. And Niether does Reg street Gas. Also One other thing to look at on the Offey Is the extra bolt holes (for the linkage Or a Vac. Line) Make sure the threads are also sealed. And that you are not getting a Vac. leak there. I know You said You went from The stock Intake & carb settup To The Offey
Hope this also Helps To find You problem.
}[oooooo]
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NovaMan/Twisted6/Larry
Something to check which happened to me only once:
New headers, new intake being mounted on 292.
Apparently the intake flanges and header flanges had been both made just a bit over size.
The fit seemed snug getting all the bolts started but what I didn't see was that as I tightened up the bolts the center runner of the intake(cyl 3 & 4) had actually moved away from the head leaving about a .030" by 2" vacuum leak.(on the underside where I didn't see it)
Talk about lean! I actually got it to start and watched as the paint started burning off two header tubes!
After I got it shut off is when I found the leak. Certainly wasn't going to hear it sucking air. You hear nothing else running a 292 with open headers, not then, and not for a few minutes after! ; )
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Pete Geurds
64 Malibu SS
64 Chevelle 2dr wagon
64 Malibu 4 dr sedan
Thanks to everyone that replied to my post!! Great ideas from everyone.
It sounds like I need to get a new fel pro gasket and use some Permatex #2 or copper rtv with it. I didn't realize you shouldn't reuse the gasket when installing a new intake manifold. My fel pro gasket on there now is only a month old but I've taken off the manifold several times and re-tightened it. Sooo, I suppose I've crushed the gasket so much that it won't seal properly. Shows you how much I know about manifold gaskets.
One other question: After I install the new gasket and use the coppper rtv or Perm#2 is there a way that I can check to see if it is still leaking at the mating surface? I believe I saw someone mention spraying WD-40 on it. What would that do, rev up the engine (if it was leaking) since it's a petroleum product?
All the WD40 does is make a temperary seal Just like useing soapy water . and yes the rpms should go up if there is a leak. Once The motor is at Oper. Temp. Shut it down let it cool The retighten the whole system (intake & exhaust) And then you should be good to go. Hope this helps. }[oooooo]
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NovaMan/Twisted6/Larry
Hey guys-im new here, so go easy on me!
Ive got a 70 chevy with a 250 3spd that has idle and acceleration problems. The idle never gets smooth and the truck stumbles on acceleration unless i open the choke. The timing is correct and ive checked for vacuum leaks - found one, capped it and put in a new pcv and hose. I have no idea what to do! could one of you guys send me your old rochesters?haha
I may have one or two laying around I know one is a NEW Rebuilt carb. Email me if you can't get or find one & need it. hope this helps }[oooooo]
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NovaMan/Twisted6/Larry