Quick timing question
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 877
Likes: 59
From: Minneapolis, MN USA
Quick timing question
Hi all,
I have a 1970 small block. I am noticing that the longer I run the car, after I shut it off, it will "diesel". But say I start it and only drive it for a couple minutes, then shut it off...no diesel. If I drive it longer, I might get a little diesel...and if I drive it even longer, then it will diesel a bit more.
Would this be a symptom of timing or dwell? And if so, do I need to increase/decrease to make it go away?
Thanks!
I have a 1970 small block. I am noticing that the longer I run the car, after I shut it off, it will "diesel". But say I start it and only drive it for a couple minutes, then shut it off...no diesel. If I drive it longer, I might get a little diesel...and if I drive it even longer, then it will diesel a bit more.
Would this be a symptom of timing or dwell? And if so, do I need to increase/decrease to make it go away?
Thanks!
Le Mans Master
Joined: Jul 2000
Posts: 6,663
Likes: 162
From: columbia city in
change gas stations.is the car running hot .what is the idle rpm.I also have ran some seafoam down the carb.you could have carbon build up on the pistons.timing should not have changed if it was right before ,but the dwell could be off anytime.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
Octane
What is the octane rating of the gas you're using, and what is your idle speed? Higher octane and lower idle can stop run on. There's other stuff you can do, if it's an auto, shut it down in drive, then put it in park.
Last edited by SH-60B; Jul 20, 2016 at 08:37 AM.
Thread Starter
Burning Brakes
Joined: Oct 2000
Posts: 877
Likes: 59
From: Minneapolis, MN USA
Hi guys - thanks for the responses.
The gas is a bit old...from last fall. However, I now only use the non-oxy fuel so it has no ethanol in it. I thought this would help protect me from the "old fuel" issues? I believe that fuel is a ~90 octane? It's definitely not 87.
The carb (Holley 650 dp) was totally re-built and put on last spring.
It idles about 800 or so?
The gas is a bit old...from last fall. However, I now only use the non-oxy fuel so it has no ethanol in it. I thought this would help protect me from the "old fuel" issues? I believe that fuel is a ~90 octane? It's definitely not 87.
The carb (Holley 650 dp) was totally re-built and put on last spring.
It idles about 800 or so?
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,213
Likes: 1,173
From: Southlake, TX
Fresh high octane gas, plus seafoam, plus a pull back on timing and you shoudl see a big improvement.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,213
Likes: 1,173
From: Southlake, TX
There are several schools of thought, but here is the way I was taught.
1) read the directions on the Spray can.
2) Work in a well ventilated area
3) bring the engine temp up to normal with air cleaner off.
4) bring idle up slightly by hand or by choke
5) intermittently squirt sea foam spray in the carb until is runs rough and then let it smooth out- do this 8-10 times
6) Squirt the can into the carb until you make the engine die. The engine will run rough, buck, smoke and get squirrely but keep squirting until it dies. When it dies, continue squirting for 5-7 seconds.
7) Let the engine "heat soak" for 10 minuets
8) start the engine and watch the "smoke show"!!
9) drive the car "hard" for a couple of miles, making sure you get the rpms up or the smoke disappears.
10) buy a can of the liquid SF and add it to the gas tank.
I'm not sure if others have suggestions, but that was what I was taught.
It really made a difference with my fuel injector "cone" pattern on my 82 improving my idle noticeably as it got ride of the CFI "Drip".
1) read the directions on the Spray can.
2) Work in a well ventilated area
3) bring the engine temp up to normal with air cleaner off.
4) bring idle up slightly by hand or by choke
5) intermittently squirt sea foam spray in the carb until is runs rough and then let it smooth out- do this 8-10 times
6) Squirt the can into the carb until you make the engine die. The engine will run rough, buck, smoke and get squirrely but keep squirting until it dies. When it dies, continue squirting for 5-7 seconds.
7) Let the engine "heat soak" for 10 minuets
8) start the engine and watch the "smoke show"!!
9) drive the car "hard" for a couple of miles, making sure you get the rpms up or the smoke disappears.
10) buy a can of the liquid SF and add it to the gas tank.
I'm not sure if others have suggestions, but that was what I was taught.
It really made a difference with my fuel injector "cone" pattern on my 82 improving my idle noticeably as it got ride of the CFI "Drip".
Last edited by billschroeder5842; Jul 20, 2016 at 10:18 AM.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,213
Likes: 1,173
From: Southlake, TX
Tech Contributor
Joined: Aug 1999
Posts: 14,356
Likes: 6,328
From: At my Bar drinking and wrenching in Lafayette Colorado
Run-on after shutdown is a function of idle speed and throttle blade opening at shutdown. You need to decrease throttle opening at shutdown to eliminate it. One of the most effective ways to do that is to increase timing at idle (with vacuum advance and/or initial timing) so that the idle speed (throttle opening) can be lowered. Advancing the timing will also cool the combustion temperature to further assist in reducing the problem.
Lars
Last edited by lars; Jul 20, 2016 at 01:12 PM.
Burning Brakes
Joined: Oct 2015
Posts: 781
Likes: 113
Hi all,
I have a 1970 small block. I am noticing that the longer I run the car, after I shut it off, it will "diesel". But say I start it and only drive it for a couple minutes, then shut it off...no diesel. If I drive it longer, I might get a little diesel...and if I drive it even longer, then it will diesel a bit more.
Would this be a symptom of timing or dwell? And if so, do I need to increase/decrease to make it go away?
Thanks!
I have a 1970 small block. I am noticing that the longer I run the car, after I shut it off, it will "diesel". But say I start it and only drive it for a couple minutes, then shut it off...no diesel. If I drive it longer, I might get a little diesel...and if I drive it even longer, then it will diesel a bit more.
Would this be a symptom of timing or dwell? And if so, do I need to increase/decrease to make it go away?
Thanks!
MY 4 barrel Quadrajet is stock other than upgraded float..I run my timing about 16 degrees above TDC,,idle after warm up is 750...
Plugs are gapped at stock .045 and burn clean..wires-dist are newer but stock stuff.
I .. can give you a link to non ethanol station.s in every state..if you cannot find one in MN..Jim
Le Mans Master
Joined: May 2007
Posts: 5,007
Likes: 1,114
From: North tonawanda NY
No one has mentioned it..BUT you should run NON Ethanol gas in your '70..I have headers on my 78 L48.. Run non ethanol 92 octane fuel..
MY 4 barrel Quadrajet is stock other than upgraded float..I run my timing about 16 degrees above TDC,,idle after warm up is 750...
Plugs are gapped at stock .045 and burn clean..wires-dist are newer but stock stuff.
I .. can give you a link to non ethanol station.s in every state..if you cannot find one in MN..Jim
MY 4 barrel Quadrajet is stock other than upgraded float..I run my timing about 16 degrees above TDC,,idle after warm up is 750...
Plugs are gapped at stock .045 and burn clean..wires-dist are newer but stock stuff.
I .. can give you a link to non ethanol station.s in every state..if you cannot find one in MN..Jim
Last edited by augiedoggy; Jul 21, 2016 at 04:09 PM.
Burning Brakes
Joined: Oct 2015
Posts: 781
Likes: 113
Perhaps I missed it but did the OP pull plugs and does he have a carbon build up issue/ The tuneup specs on the OP'S car has been changed some since my '78 L48 350 motor.Jim
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
I had the same issue with my 68 427 (11:1 comp), I now run a 50/50 mix of 91 non-oxy and 110 leaded racing gas. No more dieseling
Yup it's an expensive mix, but worth it. I don't know if it matters for your era of Cylinder Heads but mine needs the Lead.
Yup it's an expensive mix, but worth it. I don't know if it matters for your era of Cylinder Heads but mine needs the Lead.
Burning Brakes
Joined: Oct 2015
Posts: 781
Likes: 113
HMM.. your big block and era it was designed to used gas with lead..is a bit different from the OP..BUT.. I truly believe specially after running old ethanol fuel that the Clear.."E0' ethanol free..FUEL is a good place to start.Maybe also the carb cleaning and fuel filters.Gotta be something about residual fuel in the system when engine is shut downJim
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
HMM.. your big block and era it was designed to used gas with lead..is a bit different from the OP..BUT.. I truly believe specially after running old ethanol fuel that the Clear.."E0' ethanol free..FUEL is a good place to start.Maybe also the carb cleaning and fuel filters.Gotta be something about residual fuel in the system when engine is shut downJim
Burning Brakes
Joined: Jul 2016
Posts: 767
Likes: 74
From: Blaine MN
Hi guys - thanks for the responses.
The gas is a bit old...from last fall. However, I now only use the non-oxy fuel so it has no ethanol in it. I thought this would help protect me from the "old fuel" issues? I believe that fuel is a ~90 octane? It's definitely not 87.
The carb (Holley 650 dp) was totally re-built and put on last spring.
It idles about 800 or so?
The gas is a bit old...from last fall. However, I now only use the non-oxy fuel so it has no ethanol in it. I thought this would help protect me from the "old fuel" issues? I believe that fuel is a ~90 octane? It's definitely not 87.
The carb (Holley 650 dp) was totally re-built and put on last spring.
It idles about 800 or so?
Dave
Le Mans Master
Joined: May 2007
Posts: 5,007
Likes: 1,114
From: North tonawanda NY
HMM.. your big block and era it was designed to used gas with lead..is a bit different from the OP..BUT.. I truly believe specially after running old ethanol fuel that the Clear.."E0' ethanol free..FUEL is a good place to start.Maybe also the carb cleaning and fuel filters.Gotta be something about residual fuel in the system when engine is shut downJim