Pesky Vacuum Leak

6

66WarPony

Well-known member
Hey guys I have an Aussie 2V head and intake manifold. I suspect a vacuum leak at the intake manifold as I've sprayed copious amounts of starter fluid in all the other possible places, with no change in rpm whatsoever. This is the last place I can think of, even though I can't prove it... any other ideas? Anyone know the torque spec/torque pattern for the intake manifold? I've already checked the following:

1. Vacuum ports on the carb and intake manifold.I
2. All gaskets on the carb plenum, top cover, phenolic spacer, and adapter.
3. All connections on the cold air intake.
4. Vacuum connection on the distributor and vacuum gauge.

Thanks in advance for any guidance... Tim.
 
Hi, If you have a vacuum leak the starter fluid spray should have found it by changing the rpms. I never used starting fluid spray (ether) for that, we use carb cleaner or (old school) propane with a wand that we had as shop equipment many years ago. Any way if you suspect an intake manifold vacuum leak, go over the ports slowly and put the little plastic extension on your spray can to have more control over your spray. One other thing to check is that your vacuum hoses are the correct size. I had a problem with my Mustang where the vacuum advance seemed lazy and what I found was another guy used vacuum hose that did not fit tight enough over the nipple. Good luck
 
If all else fails, find a repair shop with a smoke machine and a experienced, qualified mechanic to operate it.
 
hotroady":z2nig1r6 said:
If all else fails, find a repair shop with a smoke machine and a experienced, qualified mechanic to operate it.
Click to expand...

I tried propane this time, and still nothing. my last resort is to replace the vacuum lines. Anyone have any ideas? Anything out of the ordinary or common causes?
 
66WarPony":1y88h0kr said:
. I suspect a vacuum leak at the intake manifold as I've sprayed copio…
Click to expand...

What makes U think U have a leak?

What symptoms R U concerned about?
 
chad":1czri8t8 said:
66WarPony":1czri8t8 said:
. I suspect a vacuum leak at the intake manifold as I've sprayed copio…
Click to expand...

What makes U think U have a leak?

What symptoms R U concerned about?
Click to expand...

I have a vacuum gauge fluctuation of about 1"/Hg. i was also reading that it may be an ignition problem.
 
i wish i knew the right terms - but - what about that internal bleed or overfloe or what ever it's called in that central part on the top edge (in a kinda triangle)_of the carb? know what i mean? I took ur link to a 4WD Utube or other style tech post on moding the weber to off camber driving.

Sompin goin on there? Seems like the kinda thing involved in this symptom. May B 1 of the holes got blocked of something opened up inappropreatly up there?
 
:unsure: you should do a compression test if you haven't already to see if all the cylinders are with in spec. IE within 10 % of each other. Good luck :nod:
 
Well guys, I think I got it figured out: no vacuum leaks can only mean I have an ignition problem... and guess what? I'm fouling 3 spark plugs. :arg:

Anyone know where to source bronze valve guides for an Aussie 2V Head (the valve stems are 5/16")?
 
Ok, so I finally figured out (after process of elimination) that my problems stem from a lean AFR, not from a vacuum leak. I observed the following conditions and drawn a few tentative conclusions:

1. I have 2 fouled plugs, which aren't fouled enough to prevent them from firing effectively, even marginally. I realized this when I swapped the #1 and #2 plugs with brand new ones, and the problem still persisted.
2. I have eliminated all possibility of any vacuum leaks in the system.
3. I retarded my timing about 2-3" Hg, and the problem of my bubbly exhaust has largely in part been almost eliminated. There is an almost undetectable popping at idle, indicative of a lean AFR, and this idea is reinforced by the that my mixture screws are at 2 turns out on my Weber 38/38.
4. A check of the nose cones on the plugs revealed that only part of the plug was colored chocolate brown, while the rest of the cone remains clean. This tells me that the either the timing is advanced too much, or there is insufficient fuel to burn for the timing.
5. To reinforce this above assertions, it should be known that I tune with a vacuum gauge which has had an intermittent fluctuation of only 1"Hg. I am also running stock 3.56 gears and 31" tires, which is a little high for the tire size, and I rarely see 3000 RPMs.

I've already ordered some 0.47 idle jets and some in-between air corrector jets that I didn't have (185's and 195's). I opted for 47's because 50's are slightly too rich as I have engaged part of the progression circuit by turning the idle screw in further than what is recommended. This is a necessary condition because I noticed on a 200 that I had, that even with the correct idle jets, the motor wouldn't idle anywhere near 750 RPMs. Keeping this in mind, I have come to the conclusion that the smallest idle jet that I can use without exceeding 2 turns out on each mixture screw represent the most ideal conditions at idle. Any further insight or advice is welcome... Tim.
 
Your problem is most likely the PCV needs for the 38/38 carb.

They HATE the stock set up unless its baffeled and surge protected.

/viewtopic.php?f=1&t=73925

The stock DUI advance curve isn't helping. You need a custom rework, with a different advance porting as per the standard GM practice.
 
xctasy":1tipaan4 said:
Your problem is most likely the PCV needs for the 38/38 carb.

They HATE the stock set up unless its baffeled and surge protected.

/viewtopic.php?f=1&t=73925

The stock DUI advance curve isn't helping. You need a custom rework, with a different advance porting as per the standard GM practice.
Click to expand...

The pcv is not connected, it vents to the engine compartment.
 
66WarPony":3hvrpphr said:
xctasy":3hvrpphr said:
Your problem is most likely the PCV needs for the 38/38 carb.

They HATE the stock set up unless its baffeled and surge protected.

/viewtopic.php?f=1&t=73925

The stock DUI advance curve isn't helping. You need a custom rework, with a different advance porting as per the standard GM practice.
Click to expand...

The pcv is not connected, it vents to the engine compartment.
Click to expand...


Thanks. I do make mistakes!

Check your needle and seat and your air bleeds. A 2.5 needle and seat helps, and cleaning out the air correctors and air bleeds helps.

A unlit propane lighter is the conclusive itm for the precence of a vac leak.
 
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