Changed intake, now motor won't run right!

['70 C/10 SS500]

This isn't Chevy motor related, but general motor knowledge should help me. On my Cadillac 500 motor, I changed intake manifolds from the stock NO-rise intake to an Edelbrock 2115 Performer intake manifold. The motor was running fine before the swap, but now it doesn't want to run right. It wouldn't idle at all until I turned the idle speed up quite a bit. I have the stock '76 Caddy Q-Jet carb on it. After turning up the idle speed and playing a bit with the timing, I got it to idle somewhat ok, but it is running really rough. In park I can't rev up the motor too fast or it JUST sucks air, sounds like the motor isn't even firing. If I rev it up slow, it'll rev all the way to WOT without any hiccups. With the air cleaner off, when I cover the top of the carb with my hand, the rpm jumps up and revs faster. Does this sound like a lean condition? I tried adjusting the mixture a bit, but either it wasn't helping, or I didn't go far enough.

I've checked the seal all the way around the intake, everything looks good, no leaks or anything suspicious. I torqued the manifold per Edelbrock specs and brought them up with my torque wrench. After spending 4 hours tonight, neither my Dad, freind or myself could get it to run right. Again, before the swap the motor ran nice and smooth, idled great and really wasn't having any problems at all. One other thing though, before I set the idle speed way high to get it to keep running, ( this is after I turned it up SOME, but not quite WAY HIGH yet) it would idle ok but slowly it would get slower and slower until it would eventually die about 1 - 1.5 minutes later. If I revved it up a bit, it would save it from dying, but would again slowly work its way down to dying. I personally think it's running lean, if so, is this something that I'd want to try to solve with the mixture, or is this a jetting problem/solution? I'm not too savvy with carbs and tuning, so this stuff is still a bit over my head.

Please respond if you have any ideas, thanks!

[GMC AMI]

I run a caddy 500 in my 82 Gmc.It sounds like a vac. problem.Get
a Manifold Vacume gauge and test the engine vac.A small leak or a unpluged vac.line.Try a spray bottle with soapy water and spray
around gasket area when motor is running.You should be able to spot bubbling if sucking by new gasket. Let me know or e-mail
and I might be able to help,I used to build and race drag cars.
Good luck,Mike Files

['70 C/10 SS500]

Thanks Mike, I'll try that! Actually, we were going to do that, but the only squirt bottle we had was filled with amonia. I'll either get a new one for water or have to empty and clean that one. Either way, it's going to be checked. Thanks!

[Longhorn Man]

soapy water won't make bubbles, at least, you wouldn't be able to see the bubbles since it would suck the water in and the bubles would be inside the engine.
Try a can of carb cleaner, sprayed around all vac lines and the intake. When the RPM chainges, (sometimes up, sometimes down) then you have found a vac leak right where you are spraying at.
What kind of intake manifold gasket did you use? Did you use the factory steel shim, if so did you bend it at all upon removal? Did you use some sealant, did you use aftermarket gaskets?

[ts71281]

Sounds like you got the distributor installed a tooth off. You're too retarded (no pun intended) Check your timing, pull #1 plug and put your finger over the hole and check for TDC. Take the distributor cap off and make sure the rotor is pointing to #1 plug wire. Also make sure all your wires are installed in the correct firing order or that when you put the wires on the cap that you didn't attach them all 1 spot too far back or forward. The problem sounds like it's in your ignition timing. Try it again!


Joe

[GMC AMI]

A caddy 500 does not need to pull dist. to change intake. There for I do not think this will help this guy. Have you ever rebuilt a caddy engine,I have and it's in my 3/4 ton GMC,out pull any stock
chevy engine. Check out engine specs. The only motor with more
torque is a 455 70 Buick engine.This motor in 80 vette body
ran 95mph in 1/8 mile drag strip 7.4 secs. with stock 308 gears.
I am not knocking chevy's I love them. Mike

[Clancy68]

another fun one that can make motors run kinda funn is a leak in the intake gasket from the lifter valley side, it sucks some oil in to the mix making things even more fun. sounds like your on your way to figuring this out, but you might want to take a look at all of your spark plugs while your in there. that will tell you a ton :if its lean, if its ruch, if your getting oil in there somehow and so on.

--Scott

[Rdrdave]

Sounds like vac. leak. The carb cleaner trick will find it. Squirt in one inch increments so you know where you're at. Check the back of the carb, the carb gasket, all vac lines, vac fittings on manifold, especially the rear since you really can't see that area when putting the manifold on, all around manifold you will definitely hear the difference when it changes. Good Luck. I'd like to see some picks of that caddy in there too if you don't mind.

[68speedalert]

just a thought, the intake isn't just a "square bore" carb mount is it?

Steve

[canadianchevy72]

I think all performer manifolds are spreadbore and have holes for a squarebore carb anyhow.

[GMC AMI]

The old method of soapy water spray mix is an old trick but it still
can show the solution sucking in and you can see the action of
vac. pulling in the motor .On a caddy intake, real flat you will see if you have a leaking intake with soapy mix.Do not knock old ways
until you have tried for yourself.The carb. cleaner is another way
if you want to spend money! More people have soapy spray bottles around than carb.cleaner,just trying to help.

[Longhorn Man]

Sorry mike, i wasn't trying to diss you, it just doesn't make any sence to me.
I'll have to try it, and you are 100% correct on bottle of soapy water verses carb cleaner...and free is always cool.

['70 C/10 SS500]

I've been trying to reply to this post all day long but just couldn't muster it until now, off work. Busy day! Thanks all for your input.

Andy, I used paper? gaskets, the kind recommended for this intake. The stock valley pan/metal gasket is out. I used a liberal (hiss) slathering of Gaskachinch on both sides of the paper gaskets, and used Permatex #2 non-hardening form-a-gasket for the front and rear seals.

The distributor wasn't touched, as with plugs wires, or anything else for that matter. Simply swapped intakes and then put on the carb.

I should take a look at the plugs, haven't done that since I get her back on the road from the motor swap.

As far as the intake being square vs. spread bore, its spread bore, but DOESN'T have 4 individual holes for the separate bbls, just one big hole. I still wonder if that may have something to do with this problem because on the bottom of the carb there are a few "channels" or trenches you might say, that link very small (? vacuum/fuel ?) holes together. The stock manifold has metal just under these in the form of the flat machined surface for the base of the carb to sit on. The stock intake does have 4 individual holes, so its all flat everywhere else other than for the throttle blades. This flat surface in a sense creates a tunnel now out of those channels for "stuff" to go through.

I'm going to use both carb cleaner, for the combustion/fuel properties, to help look for leaks, and also soapy water to look for bubbles and what not as well. Hopefully it'll be something that can be fixed without having to pull the manifold back off for.

I'll keep you posted. Here's a pic of the motor in the truck

[GMC AMI]

I really hate to see you go through all this trouble on such a sweet caddy 500.I know you are trying to take advise from every
one at the same time,step one should be an automotive VAC.
Gauge.They are not that expensive and you will know from gauge
if engine is running in the proper range.No more guessing games
and will head you the right way to enjoying that fine motor like only a caddy swapper can truely appreciate. Big Block GM's Rule!
Intakes are mosty dual or single plain.The diff. being single plane
more for wide open acceleration.Most stock are dual plane.Getting
rid of stock and going to allum. saves a lot of weight and should
perform excellent Good luck,stay away from 69-472 caddy unless
you want to run very high octane,too much compression for today's cheapened fuel mix they pass off as gasoline.

['70 C/10 SS500]

I did put a vacuum gauge on the motor to see what was going on. I disconnected the vacuum advance hose from the v.a. pot and inserted the gauge in the end of the hose. The gauge was reading "late valve timing." If I retartded the timing it would gain vacuum, and loose if advanced. However, when I retarded it, it was much rougher and wanted to die easier. I messed with the timing but ultimately left it pretty much the same as before I started.

I wanted to work on the truck tonight, but have a few rifles begging me to clean/neutralize the corrosive salts eating away at thier barrels. 48 hours have passed since shooting and they have got to get cleaned TONIGHT!

[tom hand]

Originally posted by '70 C/10 SS500




As far as the intake being square vs. spread bore, its spread bore, but DOESN'T have 4 individual holes for the separate bbls, just one big hole. I still wonder if that may have something to do with this problem because on the bottom of the carb there are a few "channels" or trenches you might say, that link very small (? vacuum/fuel ?) holes together. The stock manifold has metal just under these in the form of the flat machined surface for the base of the carb to sit on. The stock intake does have 4 individual holes, so its all flat everywhere else other than for the throttle blades. This flat surface in a sense creates a tunnel now out of those channels for "stuff" to go through.

I believe that is your problem....that is an older q-jet set-up...they only made them a couple of years. The bottom of the carb was cast iron and the exhaust from the heat riser actually ran thru the "trench" I don't believe that carb would ever seal on a performer intake. When you check for vacuum leaks I'm sure you will find a huge one at the carb gasket. I think a newer carb is in your future

[GMC AMI]

There is a thin metal gasket that can seal up this carb. I have the
same quadrabog,nickname,and am surprised that after all his
hard work and money that he would keep old rochester.There is a lot other better choices,I have even ran a 600 Holley on my 500
caddy,ran super but could handle a much larger one.I have to ask myself if he is running the electric anti-diesel solenoid that carb.
uses originally.This unit bumps the throttle up when ign. switch
is on. If the gasket is leaking under carb. you can feel the hot air
being forced out with motor running by just placing your hand
near carb. base drivers side.I have had a gasket burn out on this
same caddy carb.I then had to go back to old thin metal gasket
that came stock on one of the caddy carbs.Problem was then solved.

['70 C/10 SS500]

Mike Files, I don't have anything electrical hooked up to the carb. The choke is manual and all non-mechanical items have been removed. As far as the carb gasket, it is a brand new one that I put on when I took the carb off the stock manifold to put on the new one. Only one week old, and about 3 hours of run time (intermittenly) while trying to tune the motor.

[68speedalert]

Tom Hand, good call on the unusual carb. What really messes them up is if you don't use the metal spacer, with the factory manifol, it will seal on the outside yet suck exhaust into the intake. Flat WON"T idle at all.

Check for an internal vacuum leak (in the crankcase). Remove the pcv valve and plug, somehow, the hole in the valve cover. Remove and plug the crankcase vent the same way. Remove the dipstick. Put your NEW vacuum gauge on the dipstick tube. Start the engine. If you see full vacuum on the gauge, your gasket didn't seal on the lower edge.

Steve

[GMC AMI]

c-10, I think you should pay a qualified mechanic to help you. I realize you are a little over your head here.The vac. gauge told
you ,you have a maj. vac. leak! That is what the late ign. timing
means.You did not change or move any timing components by just changing manifold.I am not knocking your effort,you did a great job on detailing.That caddy carb is designed to use the
soleniod I wrote about.Without it the carb. will never idle correctly.I know from working on caddy motors.This will be last words of advise from me on this thread. If you do not vent this
motor properly,You will develope a NEG. crankcase pressure and
engine will not run smoothly.1st fix the Vac. leak!Good luck and
Happy motoring!

['70 C/10 SS500]

Ok, I hate to admit it, but I have to fess up. Once again, I have proven that I am a jack-ass! Just like EVERYONE thought, (myself included) it was a vacuum leak. On the back of the intake, there is a threaded through-hole that I apparently missed. I thought I looked at ALL the holes and came to the conclusion that they were blind holes back when I was getting ready to do the swap. Guess I didn't actually look at EVERY one! Dumb-@#&! So, I threw in a plug and now she's running great. I still need to do a bit of tuning to get her right, basically to fix all the monkeying that I did to things trying to kill, err..., I mean diagnose the patient!

One thing though, Mike, this solenoid that you refer to, are you sure that it is 1. necessary, and 2. that it came on stock '76 Caddy Coupe Devilles? (I know, all Caddys in '76 had the same motor but...) I've never had the motor diesel on me when I turn it off, it snaps to death right now! You seam pretty adamant about it, yet this is the first time I've ever even heard of one. (That doesn't mean that my motor didn't have it to begin with though, because when I got the motor, one of the first things I did was to get rid of anything and everything I felt wasn't necessary.) Tell me a little bit more about it like its physical description and such.

[GMC AMI]

Mr. 500,I am glad you fixed your prob. The solenoids job was to kick throttle up when key is on,up on shut down of key the sol.
will let throttle drop Idle to assist in a smoother shut off,no running after.The sol. is made to be used on stock man. not the one you are using.I was not totally clear about the idle comment,
Sorry,Caddy engines with stock man. need sol.Not the nice one
you have.You have very good compression.If you do not set idle speed to high you should have no problem without it.What I meant about idle comment ,I left out (down),Idle down when key is turned off.The vac. port that was open,usually for automatic
trans.vac. It has been since High school since I have typed
anything,28 years ago.Sometimes hard for an old guy like me to type with clarity.Great job,life is the best teacher!Love your effort. Mike