High idle after installing carb spacer

[gizmoduck81]

Hi all,

Short version: I installed a 0.5" carb spacer, no other changes, and I can't get it to idle below 2500.

Long version: 1963 GMC with a 454 out of a 1988 Suburban. Edelbrock 1411 750cfm carb, Edelbrock Performer RPM intake, and "RV" cam from prior owner. I'm assuming the heads are stock, but I haven't checked. It was running great, fast idle at 1500 and normal idle in D at about 650-700. I was having problems with vapor lock, so decided to try installing a 4-hole spacer to see if it helps. I didn't adjust anything and put everything back as it was. Turn the key and it climbs to about 2500 rpms. The throttle isn't stuck, I don't detect a vacuum leak anywhere, adjusting the fast idle screw does nothing.

Any ideas?

Thanks,

Ryan

[TJ's Chevy]

Take the carb spacer out and see if that fixes it.

[Captainfab]

If you don't have a vacuum leak, that spacer is somehow holding the throttle open a little. Have you tried disconnecting the throttle linkage? You could also try, removing both the carb and spacer from the engine and then bolt the two together and see if you can see anything.

[Kenfuzed]

The fast idle linkage may be hanging up. Otherwise it sounds like a vacuum leak.

[gizmoduck81]

Originally Posted by Captainfab

If you don't have a vacuum leak, that spacer is somehow holding the throttle open a little. Have you tried disconnecting the throttle linkage? You could also try, removing both the carb and spacer from the engine and then bolt the two together and see if you can see anything.

I did disconnect the throttle linkage and manually tried kicking it off fast idle, but nothing changed. I inspected to ensure everything was moving freely when both were installed on the intake, but I haven't removed to inspect. I'll try that this weekend to see if I'm missing something.

Thanks for the help!

[gizmoduck81]

Originally Posted by Kenfuzed

The fast idle linkage may be hanging up. Otherwise it sounds like a vacuum leak.

I tried taking it off fast idle, but no change. There doesn't seem to be any issue with the fast idle cam or linkage when I move them. I'll look again for a leak this weekend.

Thanks!

[Raked 64]

Spray carb cleaner or wd40 around base of carb and intake. When engine changes RPM, you will have found your vacuum leak location.

[storm9c1]

My vote is also a vacuum leak. Did you use new gaskets on both sides of the spacer? And did you scrape off any old gasket? Paper gaskets get indented with the carb and intake outline patterns. Reusing them with a spacer may not seal properly.

[gizmoduck81]

Originally Posted by storm9c1

My vote is also a vacuum leak. Did you use new gaskets on both sides of the spacer? And did you scrape off any old gasket? Paper gaskets get indented with the carb and intake outline patterns. Reusing them with a spacer may not seal properly.

I did use the new gaskets provided, top and bottom of spacer. However, you made me realize that I didn't scrape the old one off completely. I didn't have a razor with me so I just removed what I could of the old gasket by hand (no huge chunks left, but small bits). It wasn't perfect, so that's probably the issue. I can't hear any obvious vacuum leak, but it's sounding like this might be the problem (haven't had time to test by spraying area with carb cleaner/wd40). I'll remove, scrape off properly and test it out. Unfortunately I won't be able to until Sunday most likely.

Thanks!

[Kenfuzed]

Vacuum leaks like that will often go undetectable by ear. We often test for vacuum leaks on motorcycles by using a propane torch (unlit of course) and wave the tip around areas that could exhibit a leak. Works the same as with using WD-40 or carb cleaner, a change in RPM will occur when the gas finds its way into the leaking area, but without any mess from a spray.

[Captainfab]

When you reconnected your vacuum lines, could you have possibly connected your vacuum advance to manifold vacuum when it was connected to ported vacuum previously? That would increase the idle speed.

[prostreetC-10]

Just throwing my hat into the ring. Complete guess since I am not standing there but is there anyway that a throttle blade can be hanging up on the inside of the spacer or gasket? The spacer holes are usually large enough to support an 850 1.75 plate but if you somehow used too small of a 4 hole gasket, the throttle blades can get hung up on the inside of the holes. IF you are using an open plenum base gasket or more than one gasket, it is easy to tighten them down enough to where they will bow. Is this a phenolic spacer?

[prostreetC-10]

Originally Posted by Captainfab

When you reconnected your vacuum lines, could you have possibly connected your vacuum advance to manifold vacuum when it was connected to ported vacuum previously? That would increase the idle speed.

This happens all the time. On an Eddy, they look the same and easy to mix up.

[storm9c1]

Originally Posted by prostreetC-10

This happens all the time. On an Eddy, they look the same and easy to mix up.

Agreed. But adjusting the idle stop screw should tune that out. Based on his initial explanation, it sounds like he ran out of travel on the screw, which would indicate a vacuum leak or blades caught/stuck open.

[Marv D]

Curious,, was it an open or a 4hole spacer?

And what made you think it was going to offer any improvement on what sounds like a very stock motor

[gizmoduck81]

Originally Posted by Captainfab

When you reconnected your vacuum lines, could you have possibly connected your vacuum advance to manifold vacuum when it was connected to ported vacuum previously? That would increase the idle speed.

I hooked it back up to ported. I keep the manifold side capped. Left side goes to distributor, middle to PCV, right is capped. The rear port is hooked to my booster. All new rubber, as well.

[gizmoduck81]

Originally Posted by Marv D

Curious,, was it an open or a 4hole spacer?

And what made you think it was going to offer any improvement on what sounds like a very stock motor

It's a four-hole phenolic spacer. The original gasket was open, though. The only improvement I was hoping for is solving for percolation.

This all started because about a week ago I drove home from work in 85 degree weather, about 40 minutes, and stopped at the store. I was in the store for about 15 minutes and when I started it back up it was hard to start and then acted like it wasn't getting gas at idle. Fuel pressure was down to 4 from the normal 5.5 - 6 and I couldn't see gas in the glass fuel filter. However, there was fuel trying to sputter/gurgle in from the pump. This led me to believe things heated up quite a bit after I shut everything down since the fuel wasn't moving and there was no air cooling things down. My fuel hose is close if not resting on my heater hoses. So, to nip everything in the bud I installed some insulation on the hose and the spacer (just to be extra safe). At some point I'll re-plumb the fuel line.

This weekend I removed the spacer and re-installed the open gasket and everything returned to normal. I ordered Edelbrock 9266 (divided square bore heat insulator gasket) and will install that when I have time.

[luvbowties]

Originally Posted by gizmoduck81

It's a four-hole phenolic spacer. The original gasket was open, though. The only improvement I was hoping for is solving for percolation.

This all started because about a week ago I drove home from work in 85 degree weather, about 40 minutes, and stopped at the store. I was in the store for about 15 minutes and when I started it back up it was hard to start and then acted like it wasn't getting gas at idle. Fuel pressure was down to 4 from the normal 5.5 - 6 and I couldn't see gas in the glass fuel filter. However, there was fuel trying to sputter/gurgle in from the pump. This led me to believe things heated up quite a bit after I shut everything down since the fuel wasn't moving and there was no air cooling things down. My fuel hose is close if not resting on my heater hoses. So, to nip everything in the bud I installed some insulation on the hose and the spacer (just to be extra safe). At some point I'll re-plumb the fuel line.

This weekend I removed the spacer and re-installed the open gasket and everything returned to normal. I ordered Edelbrock 9266 (divided square bore heat insulator gasket) and will install that when I have time.

Maybe not to deal w/your present problem, but I 'read' in various articles that Edelbrocks like lower pump pressure than the 5.5-6psi you mentioned.
Sam

[Marshy]

Couple of questions...
What distributor do you have?
What is your initial timing?
What is the total mechanical timing advance and at what rpm?
What it the max advance added from the vacuum?
Did you try the suggestion of 10* initial timing and hooking the advance to the manifold vac??
Do you use a fuel regulator with a return line?

[dave`12]

I'm no expert, but rerouting and insulating the fuel line might be your best option. I had a problem with vapor lock once and that solved it.

[Kenfuzed]

I'm not a fan of using ported vacuum for the distributor advance, EVER. Ported vacuum was introduced for use when car makers were attempting to satisfy the EPA prior to the catalytic converter days, and only advances timing after the throttle opens. Using that method results in a hotter and rougher lean idle, and trying to set timing to correct the idle can lead to a serious ping under load. Manifold vaccum allows for cooling during idle by advancing timing only when the throttle blades are closed.

Personally I have always set my timing at around 3500 rpm (34-36*) and allow the manifold vacuum to take care of the idle. My distributor can is attached to the manifold vacuum on my Edelbrock. Even on my aggressively cammed truck the lope is smooth and consistent and it starts quickly whether hot or cold.

Disclaimer: Some may disagree with the above but this works for me every time so not looking to relaunch an argument over the "best" way to set timing... YMMV

[storm9c1]

Originally Posted by Kenfuzed

I'm not a fan of using ported vacuum for the distributor advance, EVER. Ported vacuum was introduced for use when car makers were attempting to satisfy the EPA prior to the catalytic converter days, and only advances timing after the throttle opens. Using that method results in a hotter and rougher lean idle, and trying to set timing to correct the idle can lead to a serious ping under load. Manifold vaccum allows for cooling during idle by advancing timing only when the throttle blades are closed.

Personally I have always set my timing at around 3500 rpm (34-36*) and allow the manifold vacuum to take care of the idle. My distributor can is attached to the manifold vacuum on my Edelbrock. Even on my aggressively cammed truck the lope is smooth and consistent and it starts quickly whether hot or cold.

Disclaimer: Some may disagree with the above but this works for me every time so not looking to relaunch an argument over the "best" way to set timing... YMMV

Some my disagree, but I fully agree! Ported vacuum is an emissions control and it causes more problems than its worth.

But also keep in mind that on a stock engine, switching from one to the other often needs some retuning. The vacuum advance curve needs checked to make sure it's not pulling in too much timing (8-10 degrees is ideal, 12 is probably max). Sometimes it also needs a distributor recurve with the mechanical advance. I always recommend resetting the idle mixture screws with a vacuum gauge after making this change. Just switching without a retune usually gives undesired results and steers people away, claiming it made the engine run worse.

[Marshy]

Originally Posted by storm9c1

Some my disagree, but I fully agree! Ported vacuum is an emissions control and it causes more problems than its worth.

But also keep in mind that on a stock engine, switching from one to the other often needs some retuning. The vacuum advance curve needs checked to make sure it's not pulling in too much timing (8-10 degrees is ideal, 12 is probably max). Sometimes it also needs a distributor recurve with the mechanical advance. I always recommend resetting the idle mixture screws with a vacuum gauge after making this change. Just switching without a retune usually gives undesired results and steers people away, claiming it made the engine run worse.

I followed your advice and it made mine run a lot better. Hence my questions above to the OP.

[fleetsidelarry]

Originally Posted by gizmoduck81

I ordered Edelbrock 9266 (divided square bore heat insulator gasket) and will install that when I have time.

gizmoduck, that's the same gasket I use. I bought one but before I ever put in on I learned this: IF you're experiencing the common Edelbrock percolation, try changing your starting routine. I think the heat percolation causes the gas from the bowls to pool in the manifold, and if you try to start in the normal fashion with your foot off the gas it acts like it's "flooded" (especially if you pumped the pedal a couple of times).

what I learned to do was: 1. don't pump the pedal at all, and 2. hold the pedal about 1/3 to 1/2 open (or wide open if need be, like you would start a flooded engine), 3. start.

Doing this when hot, mine fires up without undo cranking, often almost immediately

[Kenfuzed]

Originally Posted by fleetsidelarry

gizmoduck, that's the same gasket I use. I bought one but before I ever put in on I learned this: IF you're experiencing the common Edelbrock percolation, try changing your starting routine. I think the heat percolation causes the gas from the bowls to pool in the manifold, and if you try to start in the normal fashion with your foot off the gas it acts like it's "flooded" (especially if you pumped the pedal a couple of times).

what I learned to do was: 1. don't pump the pedal at all, and 2. hold the pedal about 1/3 to 1/2 open (or wide open if need be, like you would start a flooded engine), 3. start.

Doing this when hot, mine fires up without undo cranking, often almost immediately

This is a great tip and its easy to forget that a carbureted engine can be a little finicky compared to the more modern fuel injected vehicles we have all become accustom to. Cracking the throttle open slightly during a hot start without pumping excess fuel also avoids setting the automatic choke and provides the added air to the starting mixture to fire up easier than a flooded/choked condition. This works with both the Edelbrock and many other carburetors when percolation is suspected.

Of course I always like having a phenolic spacer in there just for an added measure on these 95+ summer days while sitting in traffic.