run on question

[stock1970]

what causes run on?
run on = when turning off the engine keeps running for a few seconds..
is it timing.. currently set at 7.. or is it carb to lean, or to rich.. or is it just bad gas?

351w, 2barrel carb, 76 bronco

 

[wildbill]

Can be carbon in the cylinder's timming. You should ck the timming and if it still doing it I would use water get motor up to temp run about a qt. of water into the carb. by running about 2000 rpm and use the water to pull it down to about 1200 rpm Dont kill it not good. Dont get by the tail pipe as if it is carbon it will be hot comeing out. This works very good on carbon good luck. Bill %) ;D

 

[stock1970]

the engine is new and was just put in last week end.. so i dont think it would be that..
the intake and carb are used, the plugs are new, dist new, cap and wires are used..

 

[ugly74]

what compression ratio is your engine?

I've had engines that had compression ratios in the 11-1 range that would sit there forever, dieseling after the key was off. the solution? put it in gear and dump the clutch while standing on the brake;D %)

 

[stock1970]

compression is not very high.. 8.5 to 1 ..

i will mess with the timing a little when i get home.

 

[Explorer]

This is a shot in the dark, but the first time I wired in a Duraspark somehow I still had a few volts at the coil with the key off and it would do that. But I agree with checking the timing.

 

[ja840a]

you can check the carb too since it is used, sometimes the floats don't close the gas supply all the way and it will just sit there and drip gas down into the intake for a few and it will run by dieseling... you have to have two people though, one to shut it off the other to have flash light to see look down the carb...

 

[carmi]

I would check your carb first. Often if your idle speed is adjusted to high it will lead to run on. More importantly, if your idle screw is adjusted to high, but the idle mixture screws are set to rich (to compensate for the high idle and lower the rpm) then you have a very rich condition where the engine will continue to burn all the excess fuel. It could also be that your float is not adjusted right, as mentioned above. Does the exhaust smell very rich?

 

[DCrews]

Mine did the same thing last week.Filled up with 93 oct hasent done it sence.

 

[bronconate]

Timing is to advanced, check into that a little more. That has always been my expierence/solution with what you are dealing with.

 

[barronj]

me too, me too

Do lower compression engines favor less timing?

I have a fresh 9:1 aluminum headed 351, dieseling anytime it's warm. Timing is set around 12*. Exhaust smells rich, to the point that the warden always complains I smell of gas anytime I've driven it.

I have an intake leak that I'm going to fix this weekend, I guess I'll try backing off the timing & resetting the Ebrock carb.

I'm also running too cool. I run cooler than 170 most of the time. I'm putting in a 190/195 (whatever it takes ) thermostat this weekend as well.

 

[12-Pack Jeff]

What temperature does the engine run at? When I got my bronco after driving it for a while it would run at 210-220 degrees and had a 195 thermostat.. I put a 160 thermostat in it and on the street it runs about 170 and does not diesel anymore when I shut it off unless it gets to 210+. I could have also backed the timing down but this is a better solution for my preference. I would double check your timing also, make sure that your 0 marks are lined up together so you get a true reading of your timing measurement

 

[Steve83]

Run-on is caused by 2 things:
1) throttle stop too far open
2) hot spots in the combustion chambers

Eliminate either one & it'll stop.

 

[DirtDonk]

Agree with that. Most Broncos came stock with an "anti-dieseling" solenoid at the carb linkage. I think it was also called a curb-idle(?) solenoid and maybe a few other things as well. You actually set your normal hot idle by adjusting the solenoid. When the key was turned off, the solenoid released the throttle lever so the blades would close down even farther. Thus reducing the tendency for an engine to try to keep running on the little amount of fuel that would normally try to keep entering the engine.

Although not absolutely required, they sure help in situations like this. Might not hurt to add one to your new carb setup.

What's your idle speed? Is the choke fully open when warmed up?
Until you get it fixed, if you have an auto tranny, stop the engine while still in gear. If a manual tranny, keep it in gear and use the clutch to drag the idle down a bit while you turn the key off.

Paul

 

[oldiron]

Are you running an electric fan?