Mechanics

LOPING IDLE

1986 Nissan Truck • 4 cylinder 4WD Manual • 273 miles

I hav a 1986 Nissan 720 Pickup, Z24 motor, carburated, 4wd, 5 speed. I have been having this problem for quite some time but I can correct it by just reving the engine and letting it drop back to idle. It only happens after the enging is warmed up. While driving, if I take it out of gear to break it will drop to idle then idle will raise a bit then it start loping. If I rev the engine a couple times then let it drop to idle again it will idle fine with out a hitch. If im downshifting while stopping and engine breaking it will start loping maby 50% of the time while just taking it out of gear and not engine breaking it happens maybe 70% of the time. I dont have any loss of power or hesitation while accelerating or any other type of performance loss. It will also start loping if I just start up the truck and let the choke kick in and let it warm up just sitting in the driveway, after it gets to operating temp and the choke kicks off is when it stars to lope. I rev it once and it idles fine, but this truck has done that sence I can remember when my dad drove it. So I dont know what it could be. The carb freshly rebuilt maybe 1000 miles ago so I dont think its that. Just put a brand new air filter so I know is getting plenty of air. The only thing I can think of would be the EGR valve possibly or something in the inner workings of the enging witch im dreading sence this it my daily driver. Please help. Thank you.
Avatar
Hoffert88
February 3, 2012.



REBUILT DOES NOT NECESSARILY MEAN "RIGHT"

HAVE YOU TWEAKED THE MIX SCREWS ANY SINCE THE REBUILD--DO YOU KNOW HOW TO DO IT WITH A VACUUM GAUGE OR A TACH/ DWELL METER?

HOW BOUT CHOKE AND HIGH IDLE, ARE THEY ADJUSTED RIGHT? DO THEY MOVE FREELY?

VACUUM LINES HOOKED UP CORRECTLY?

IMMA JEEP CJ KINDA GUY, I KNOW LITTLE ABOUT YOUR CARB OR THE SET-UP.

IS IT STILL ORIGINAL OR HAS STUFF BEEN ELIMINATED OR MODIFIED?

LOOK AT THIS--IT'S FROM BEFORE THIS SITE WAS REMODELED--SOME THINGS LIKE "QUOTES" DID NOT TRANSFER OVER WELL, THIS MAY HELP YOU IN "TRANSLATING" STUFF TO MAKE SENSE

http://www.2carpros.com/questions/jeep-wrangler-1988-jeep-wrangler-engine-issues-when-braking

RETURN WITH A SMILE

THE MEDIC


Tiny
CJ MEDEVAC
Feb 3, 2012.
I know it doesn't necessarily mean right. But after the rebuild I had it smoged, it didn't pass (due to a clogged air filter that I mistakenly over looked, read my other post for more info) and had everything checked by another third party tech. He checked the fuel flow everything was spot on, the choke operates as normal as I have known it to be. I think it could be the choke just by the way it sounds but that's what I'm trying to figure out. All hoses are good and hooked up right. The smog shop had messed with them cause they thought they were causing the problem (last time i'll ever go there) and totally fugged it. Had that fixed by the same 3rd party tech. The high idle is just the second barrel valve right? If so iv never heard it called that but yes its adjusted right and opens up when it needs to. Nothing has been modded (yet). The choke is really the only thing I can really think of at this point but haven checked it yet. What's the best way to go about doing that?


Tiny
Hoffert88
Feb 9, 2012.
COULD YOUR FLOAT BE SET TOO HIGH?

OR

NEEDLE AND SEAT DEFORMED OR DAMAGED ALLOWING FUEL IN CONSTANTLY?

DRIVING MIGHT KEEP IT LOWER, WHILE IT'S S. UCKING DOWN THE FUEL.

THEN AT IDLE, FUEL LEVEL RISES AND GETS HIGHER THAN THE VENTURIS

TO SET UP THE SCENARIO (MY THOUGHTS)---FUEL LEVEL TOO LOW FOR SOME REASON, RUNS BUT NOT GOOD----THEN AT IDLE, RISES TO CORRECT LEVEL, RUNS REAL GOOD!----UNTIL FUEL LEVEL IS TOO HIGH, THEN IT BASICALLY STARTS FLOODING, TOO MUCH FUEL INTO THE CYLINDERS. HOW EVER THIS CARB OF YOURS, USES A POWER VALVE (OR EQUIVLENT). MAYBE IT'S ADJUSTED WRONG OR BLOWN (A BACKFIRE CAN BLOW THEM ON SOME CARBS)

I LOOKED AT AUTOZONE AND ADVANCE AUTO FOR YOUR CARB--IT IS NOT IN EITHER. I'M SORTA GOOD ON SIMPLE CAR THEORY, SUCH AS WITH MY TWO JEEPS A '77 AND A '46

I LIKE TO BE "IN COMMAND", RULE OUT COMPLICATED LINKAGES, SO I HAVE MANUAL CHOKES ON BOTH OF MINE.I DECIDE IF IT NEEDS CHOKIN' OR NOT. IF IT WILL DRIVE WELL WHEN I TURN OPEN THE BUTTERFLY. IF NOT I MAY CRACK IT SHUT SOME, TILL I'M AT FULL OPERATING TEMP.

IN FACT TO MAKE MY '77 EZer TO TUNE, GET BETTER MILEAGE, POWER WHEN I DEMAND IT.

I INSTALLED A 4 BBL OFFENHAUSER INTAKE ON MY 258 INLINE 6 CYLINDER. I THEN MOUNTED A HOLLEY 390 CFM CARB ON IT.

TUNING IT WAS DIFFICULT FOR ME AT FIRST, I COULD NOT "READ THE PLUGS" WORTH A CRAP, WHEN I SHUT HIM DOWN COASTED TO THE SIDE OF THE ROAD TO PERFORM A "PLUG CUT" TO DETERMINE WHAT SIZE JETS TO USE.

I FINALLY FOUND THAT I COULD INSTALL A OXYGEN SENSOR CLOSE TO MY HEADERS, AND USE IT TO RUN A AIR/ FUEL RATIO GAUGE.

THE GAUGE DISPLAYS IN LEDS. LEAN, STOICH (JUST RIGHT), AND RICH.

IT FLUCTUATES AS YOU DRIVE UNDER DIFFERENT CONDITIONS. FLAT ROAD AT 55 MPH IS WHAT I SELECTED MY BEST JETTING FOR. MY "IN DASH" VACUUM GAUGE ALONG WITH MY AIR/ FUEL GAUGE HELPED ME SELECT A "POWER VALVE" TO TWEAK IT ALL TOGETHER.

THE NEWER BELLS AND WHISTLES ALONG WITH SMOG CRAP BLOWS MY MIND! I'M SORRY I CANNOT HELP MORE.

EVEN W/ SIMPLE CARBS, I HAVE FOUND THAT THERE ARE FEW WHO TALK THE TALK AND WALK THE WALK. MOSTLY "JUST TALK" AND COBBLE THE REST OF IT UP. I DO MY OWN WORK, BUT I DO ASK THOSE WHO "SUPPOSEDLY KNOW", FOR INFORMATION, I'M PRETTY GOOD AT "CENSORING OUT" THE "WANNA BE'S" MIS-INFORMATION, I DO READ ABOUT MY OWN SYSTEMS, AND TRY HARD TO FIGURE STUFF OUT "CORRECTLY" ON MY OWN. I DO NOT LIKE "I THINK", I WANT THEM TO BACK UP THEIR ADVISE WITH FACT--THAT CAN BE FOUND IN PICS OR TEXT---PROVEN.

IF YOU CAN ELIMINATE SMOG STUFF (NOT CHECKED IN YOUR AREA) MAYBE AN AFTERMARKET SIMPLE TYPE CARB MIGHT DO YOU BETTER. I HOPE I'M NOT WASTING YOUR TIME.

LET ME KNOW HOW IT'S GOING

THE MEDIC


Tiny
CJ MEDEVAC
Feb 9, 2012.