[1991 FJ70 3f] Need help understanding vacuum guage (1 Viewer)

[MalcolmY]

Hi

I connected the Vacuum gauge to one of the two nipple filter directly on the intake manifold (one hose goes to a VSV, the other goes to the distributor side of the engine). I also just changed this small fitting with a brand new OEM part and installed a new PCV valve and a new intake to carb gasket.

The reading fluctuates, or shakes, between 12 and 13. I looked for vacuum leaks, there may be one but I couldn't find it even with a starter spray can. Could this be related to the valves? How exactly? Could the idle mixture screw do this?

Here's a video with clear audio:

 

[nickolai]

you might get more answers in the 40 series or 60 series forum - 2f and 3f are pretty simillar.

Have you checked for vaccuum leaks with carb cleaner?

 

[MalcolmY]

Yes I did check but couldn't find any leaks. I mainly checked around the carb and intake manifold. And the vac advance hose. I don't know where else to check.

 

[ozcrusier]

How does the engine run does it have a dead spot or run lumpy.

 

[jblueridge]

I have seen problems like that on MGBs.
Once it was air leaking in around the throttle shaft.
Another time the twin carbs needed new carb-to-manifold gaskets and correct tightening.

Have you disconnected vac hoses and plugged or capped off sections one at time?

 

[MalcolmY]

How does the engine run does it have a dead spot or run lumpy.

The engine runs smooth no problems at all, no clicking from the valves and I made sure the distributor timing is set about 9 degress.

I have seen problems like that on MGBs.
Once it was air leaking in around the throttle shaft.
Another time the twin carbs needed new carb-to-manifold gaskets and correct tightening.

Have you disconnected vac hoses and plugged or capped off sections one at time?

The weird thing is the three vacuum hoses coming from the carb don't seem to pull any vacuum at all. I disconnected the hoses one by one, replaced all the short ones but nothing changed.

I sprayed near the carb gaskets but didn't notice anything either.

 

[nickolai]

Vac Visual: Quick Guide to Vacuum Gauge Readings

Bottom Right - Carb out of adustment perhaps - maybe some crud in the venturi?

 

[MalcolmY]

Vac Visual: Quick Guide to Vacuum Gauge Readings

Bottom Right - Carb out of adustment perhaps - maybe some crud in the venturi?

I read that link before and other similar pages, they don't seem to cover my problem exactly. I do have an almost steady needle but under the normal expected range (about 14).

What's a venturi (the carb was cleaned last year btw).