78 FJ40 2f idle issues (1 Viewer)

[Relix]

I have a 1978 Fj40 with the 2F engine factory carb, and I'm having trouble ajusting the idle... When I ajust the idle with the air cleaner assembly off I can get the idle to a nice steady 800 rpms using my digital timing light as a tach.... Now after doing that I put the air cleaner assemble back on the engine(being careful not to be in contact with the choke cable) and restart the truck the idle jumps up to 1200-1700rpms....

I thought that was strange so I tested removing the top portion of the air cleaner assembly while the truck was idling and the rpms dropped down to normal, put it back on with the truck idling normal now and the rpms jumped back up....

What gives??? Any and all help will be appreciated...

 

[CruiserMax]

With a clean filter installed correctly you should have a low idle of around 650 or so.

 

[Pin_Head]

Pretty wierd, but just a guess:
It sounds like you have a combination of a vacuum leak and a clogged air filter element. The air filter effectively applies a choke, delivering more fuel along with air supplied by the vacuum leak.

 

[Relix]

Ok changed the air filter, and the the idle is still....How would you recomend searching for a vacuum leak?

 

[fj40charles]

Ok changed the air filter, and the the idle is still....How would you recomend searching for a vacuum leak?

Spray the base of the carb with some carb cleaner while the engine is running... See if the rpms change.