Engine run-on problem

Got a SBC 327. Had a 600 CFM Edelbrock on it, but it would bog and ran real rich. Switched to a 500 CFM Edelbrock, now the engine will run-on after I try to shut it off.

Could the timing be too far advanced?? If not what else should I look at as the problem. Never dealt with this before.

Thanks

 

Sounds like timing to me

 

Idle speed too high will do that too.

 

if it did not run on with the 600 and now it does with the 500 did you mess with the timing in between carbs changes? i suspect you have the idle set up and when you shut it off it still gets fuel because the ****erflys are not closed.

 

Thanks guys. I'll first back off the idle speed and see if that fixes it. Then resort to monkeying with the timing. Did not touch the Dizzy when I switched the carbs out.

However when I did set up the timing with the 600 CFM carb I just set it by ear. Driving it around it does not ping or knock, so I have not thought about it again.

 

All of the above could be correct. There is the good possibility that your ****erflys are sticking open from maybe a spacer, a gasket, the intake, or something preventing them from closing all the way. I have seen this run people in mad circles, me included once, to only figure out that was a physical restriction keeping the ****erflys from closing.
Good luck
Wil Sakowski
www.sakowskimotors.com

 

Just went through the same thing with my Edelbrock..Running rich, idled high even with the adjuster screw all the way out....I had the va***n advance from the dist. connected to the wrong va***n line on the front of the carb...switched them, now it idles down and is not running rich...put about 30 miles on it in the last day or so...no problems....hope thats it...good luck...

 

What kind of float is in the new carb? Phenolic? Run on is commonly caused from the carb flooding due to a sinking float. Lotsa black smoke at idle?

Flatman

 

No black smoke. Carb is brand spankin' new.

 

Got my va***n line hooked to the small port on the lower left front of the carb, as you face the carb. That is what I was using before without issue.

 

I've always found run-on to be caused by carbon in the cylinders igniting the fuel charge. Otherwise, with the ignition off, the engine will shut off.
Also known as "Dieseling".

The carburetor isn't causing the problem, just enhancing it.

 

I think your pulling va*** from the wrong port...

 

Make sure the carb is on tight and no vacuum leaks. Oh BTW, what is that knocking sound?

 

Do you have an MSD box on it? If so there's a diode that needs to be there to correct this.

 

Man i love these posts... heres something to think about other than the carbon in the cylinders heating up and causing the engine to keep running for a bit. Alternator feed back and electric fan feed back can keep em running too. The fan will let it run when shut off till the fan stops rotating. Ask me how i know this .... Funny thing was id even driven the car but never shut it off while the fan was kicked in just cause of luck.. If an alternator is feeding back you usually cant shut off the engine unless you pull the coil wire ,battery wire or the hot to the dizzy like on an HEI...
Dave
ps: vacuum is right me thinks from my carb hookup.. that shouldnt make it run on anyway unless agai its too hot in the cylinders causing combustion..

 

If the engine "diesels" when the key is turned off....'generally' it's retarded timing. Advance the timing and turn the idle down, as it will increase when advancing it.....

 

wrong plugs maybe?

 

I'd say the idle speed is too high. Here is a simple test to find out:

With the engine running at 'idle', turn your idle screws all the way in (shutting the fuel to the idle circuit off). If the engine continues to run (it is drawing fuel from the transfer slots or worse, the booster venturis), your throttle plates are too far open (high idle speed).

 

If the choke is closed (only takes a bit) it will cause this also when the engine is at opperating temperature...

 

How would it keep running without spark? You've got a spark / carbon issue here.

 

+1
Dave

 

Diesels don't have plugs.....so when a gas engine continues to run without ELECTRICAL ignition, that's why it's referred to as "dieseling"

I've seen rebuilt engines "diesel" when turned off (also my own cars)....it's "generally" the retarded timing causing the problem, and usually on warmer days....a retarded engine runs hotter in the cylinders, hot enough to the point of keeping the plugs hot enough to keep the engine firing when piston comes up on TDC on compression...of course though, it's not running GOOD, like with ign on...
The engine basically acts like a model airplane glowplug engine.....

 

Yep. If you don't believe it, try shutting your engine off when it's hot while holding the engine speed at about 1500 rpm (don't do it, I'm kidding)...

 

The driver side is the full vac port.

Frank

 

I'll fiddle with the timing. Always thought it was a bit retarded.

 

Thanks GP I'll try switching that around and see if it helps.

 

Thats what I did on mine...BIG difference...hope thats it..

 

Lucky Strike, did you get the problem figured out?

I'm having the same problem with a 292 inline 6. I was going to adjust the timing again (just put in a diff distributor), but last night I realized that my timing light was stolen out of my truck.

 

Not yet. I've gotten distracted by a bike for a while and have not ironed out the run on issue with the truck.