Burst of air from engine during crank+hesitations at high speeds

[HULK60]

Hey all,

Like the title says, whenever I'm cranking up my fj60 (with recently rebuilt engine) I'm hearing a burst of air coming from the engine. Also, when the engine is warm and I'm anywhere about 2000 rpm, the engine starts stuttering/hesitating causing the whole truck to jerk back and forth. It almost feels like momentary losses of power so I went with a new clutch but that didn't fix it. Vacuum problems? Any help would be great.

Thanks!

Zac

 

[SteveH]

Does it run smoothly at 2000 and 3000 RPM under no load? Big jerky sensations sound like ignition issues - are plugs/wires/cap/rotor all reasonably new?

 

[HULK60]

Does it run smoothly at 2000 and 3000 RPM under no load? Big jerky sensations sound like ignition issues - are plugs/wires/cap/rotor all reasonably new?

Yes, under no load it doesn't quit out like it does under load. Also yes plugs/wires/ and caps are all new.

 

[mwebfj60]

Is this a problem that just started, or been doing it since the rebuild? Any work done recently besides clutch? 2F? Desmogged or smog legal? More details bud.

 

[BlackCat]

If it's backfiring through the carb that means it's probably running lean. That can also cause your issues under load. Vacuum leaks can cause this, among other things.

 

[HULK60]

Is this a problem that just started, or been doing it since the rebuild? Any work done recently besides clutch? 2F? Desmogged or smog legal? More details bud.

Smog legal and no recent engine work. It's only been happening since the rebuild. Totally stock 2F.

If it's backfiring through the carb that means it's probably running lean. That can also cause your issues under load. Vacuum leaks can cause this, among other things.

Carb cap has two uncovered holes that look like they should be plugged. Could this be causing the running "lean"? And what exactly does that mean? Thanks for the info!

 

[Rice]

Simple things first .....
- Put in an earnest search for vacuum leaks. Limit driving until you know there is no vacuum leak ... lean can burn a valve.
- Do a careful check of your ignition wires to be sure none of them cross each other allowing for cross-spark. Also be sure the wires are not touching anything else that is metal.
- If engine is at idle and you blip the throttle does it cough then? A bad carb accelerator pump can cause this.
- what is ignition timing set at?
- just for kicks check the distributor cap for cracks.

- Once you check those items it will be time to inspect the valve train ....

tell us what you find.

-Rice

 

[BlackCat]

Smog legal and no recent engine work. It's only been happening since the rebuild. Totally stock 2F.



Carb cap has two uncovered holes that look like they should be plugged. Could this be causing the running "lean"? And what exactly does that mean? Thanks for the info!

Running lean means it's not getting enough fuel. When air passes into the engine after the carburetor, or in fuel injection after the mass airflow meter, it's not metered. This means the truck doesn't know it's there, and is only supplying the amount of fuel it thinks is needed for the charge of air it knows is present. X amount of air means it gets X amount of fuel, so when air is sneaking in through some sort of leak, there isn't enough fuel. In carburetors, this almost always results in carb backfires, hesitation, surging, lack of power, etc.

 

[HULK60]

Running lean means it's not getting enough fuel. When air passes into the engine after the carburetor, or in fuel injection after the mass airflow meter, it's not metered. This means the truck doesn't know it's there, and is only supplying the amount of fuel it thinks is needed for the charge of air it knows is present. X amount of air means it gets X amount of fuel, so when air is sneaking in through some sort of leak, there isn't enough fuel. In carburetors, this almost always results in carb backfires, hesitation, surging, lack of power, etc.

Thank you BlackCat, what you described is exactly what I feel behind the wheel! I'll be taking it to my local guy tomorrow. Hopefully no damage to a valve!

 

[Landpimp]

could also be the EGR going bad