Trick to clear idle jet? (1 Viewer)

[Southbound]

Pretty sure my idle jet is clogged since, well, my truck won't idle. At all, without major choke action. Started suddenly. Fuel cutoff solenoid is fine. Haven't check much else. This happened a year or two ago and I read a thread on here with a trick to clear the idle jet by doing some procedure which involved some revving, some deceleration, I can't for the life of me remember the details and can't find the thread, but it worked beautifully. Anybody have any idea what I'm referring to? Would like to try that trick if I can find it before digging much deeper into the issue.

 

[salvage60]

I think it's called the "okie tuneup". You rev the engine and then cover the carb with your hand. The idea is to suck any debris through the small holes under a lot of vacuum. From my experience a vacuum leak somewhere is more likely the cause of the idle issue.

 

[mongoose2231]

I had the same problem. Fiddled with the truck for months. Sea foamed it and low and behold. She ran like new, idled like it should. Have someone Rev the engine to 1500 rpm, while you quickly pull the fuel line going to the carb and stick it in a seafoam bottle. Let the engine suck that in and burn it. Make sure to rev the engine or it will die. Then run another bottle of seafoam in your gas tank. Problem solved. Do check all vacuum lines though

 

[Output Shaft]

The okie tune up can work for some clogs. A few years ago my cruiser would start sputtering occasionally on the freeway or driving up any hill. I had to pull off the freeway several times and show the carb who was boss by removing the air cleaner and carb stud, the revving the engine to 3000 rpm or so... Then slamming my hand down on the carb while I let off the gas at the same time. I did that about 8 times and the engine then ran good enough to get home. Took apart the carb later and found a piece of plunger boot floating around inside the float chamber.

An okie tuneup can save your arse

 

[Pin_Head]

A more aggressive approach is to remove the idle mixture screw and idle fuel cut off solenoid, spray their holes with carb cleaner and blow out with compressed air. Repeat.

 

[CaptClose]

I was experiencing the same symptoms. I checked for vacuum leaks using WD40, checked the ICS for the "click" to verify operation and everything checked out fine. Went on to try the "Okie Tune-up" and that didn't seem to help. I finally called @CenTXFJ60 who told me to check the fuel filter... I thought the filter was probably okay because the engine ran fine at higher RPM's with no sputter... But I figured I'd replace it anyway and wouldn't you know it... Problem solved. Thanks Jim!

Note to others reading this thread: Try the obvious things first.

 

[Pin_Head]

It is hard to imagine how a fuel filter could cause a won't idle problem when the truck runs fine otherwise at higher speeds. A clogged filter will restrict fuel flow, but you only need a tiny amount of fuel at idle and you need a lot of fuel at high speed.

 

[CaptClose]

It is hard to imagine how a fuel filter could cause a won't idle problem when the truck runs fine otherwise at higher speeds. A clogged filter will restrict fuel flow, but you only need a tiny amount of fuel at idle and you need a lot of fuel at high speed.

I thought the same thing. However, Jim explained that higher RPM's create more pressure to push fuel through a dirty filter verses the lower pressures at lower RPM's. Maybe there's a sweet spot where the filter is just dirty enough to stall at idle speed, but clean enough to be okay at cruising speed?

Either way, the new filter solved the problem for me when all else failed.

 

[Pin_Head]

The fuel filter is on the suction side.

 

[CaptClose]

The fuel filter is on the suction side.

True... So maybe more pressure to "pull" the fuel through the filter then? I don't know... Maybe someone can explain why or how a new fuel filter would solve this issue? @Output Shaft where are you? Do you have an answer for this riddle?

 

[Pin_Head]

Coincidence.
It happens.

 

[Output Shaft]

Well I don't have an answer, but I like to come up with hair brained theories.
Your supposition sounds correct..

Maybe.....
When the engine is idling at low rpm (with a clean fuel filter), the fuel pump is sucking fuel at a slow rate. A rate that is sufficient to supply the carb with enough fuel, but not with much gusto. The excess, as always gets pumped out the return line back to the tank.

When the engine is running at high rpm and especially at lighter throttle, the fuel pump is pumping way beyond the requirements of the carb, and a lot of fuel is flowing through it.... most of it back out the return line to the tank.

So your, and Jim's guess sounds right. The reason (maybe) the engine was starved of fuel with a dirty fuel filter at idle but not at higher rpm was because the pump didn't have enough umph to pull the fuel past the clogged filter.

 

[CaptClose]

Well I don't have an answer, but I like to come up with hair brained theories.
Your supposition sounds correct..

Maybe.....
When the engine is idling at low rpm (with a clean fuel filter), the fuel pump is sucking fuel at a slow rate. A rate that is sufficient to supply the carb with enough fuel, but not with much gusto. The excess, as always gets pumped out the return line back to the tank.

When the engine is running at high rpm and especially at lighter throttle, the fuel pump is pumping way beyond the requirements of the carb, and a lot of fuel is flowing through it.... most of it back out the return line to the tank.

So your, and Jim's guess sounds right. The reason (maybe) the engine was starved of fuel with a dirty fuel filter at idle but not at higher rpm was because the pump didn't have enough umph to pull the fuel past the clogged filter.

Thanks OS.. This makes sense. Do you think there could also be an issue with my fuel pump as well? Everything now sees to be aces, but you never know...

 

[CenTXFJ60]

Well I don't have an answer, but I like to come up with hair brained theories.
Your supposition sounds correct..

Maybe.....
When the engine is idling at low rpm (with a clean fuel filter), the fuel pump is sucking fuel at a slow rate. A rate that is sufficient to supply the carb with enough fuel, but not with much gusto. The excess, as always gets pumped out the return line back to the tank.

When the engine is running at high rpm and especially at lighter throttle, the fuel pump is pumping way beyond the requirements of the carb, and a lot of fuel is flowing through it.... most of it back out the return line to the tank.

So your, and Jim's guess sounds right. The reason (maybe) the engine was starved of fuel with a dirty fuel filter at idle but not at higher rpm was because the pump didn't have enough umph to pull the fuel past the clogged filter.

OS, I'm by no means a mechanic, but having been stranded due to a bad filter, I always go to that before I dig deeper into the system. You explained it really well. For me, I just tried to figure out what pulls the fuel through the filter and figured it's the vacuum delivered by the mechanical pump. As RPM's increase (Cam rotation), then suction pressure increases. As you stated it makes sense a partially clogged filter may not draw fuel under lower suction. Increase the RPM's and fuel can be forced through. At least until it's completely clogged. If that does not cure the issue my second move would be to remove the fuel intake line, drain the bowl and use compressed air to clear any debri from the bowl. As I told Ryan, better lucky than good . And always keep a spare filter in your ride. Appreciate your feedback above.

 

[CaptClose]

Jim (@CenTXFJ60) is being modest... He's not a mechanic by trade (his day job requires a suit) but this guy has more cruisers than most people have pairs of socks! Haha! His latest build is one of my favorites on Mud.

Anyway... That actually clears things up for me and makes perfect sense now. Thanks again Jim.