Vacuum

[GKM007]

Finally got around to purchasing a vacuum gauge to tune my carb. I have just been tuning it from ear since doing my duraspark. I was surprised how close I got it by ear. It is a nice steady 16 with only a hair fluctuation up or down on the gauge. I cannot get it read any higher.

Looking at some vacuum gauge reading info, looks like I might have worn out rings? Can complain to hard though considering it has 260k.

It leaks from about every seal it has and I am pretty sure they are all original. I am wondering, am I losing vaccum from leaky seals? If I replace them will I get better readings?

It is on my list to get a complete seal kit from the local part store as she leaks about a quart per fill up! Thank fully its not my daily, oil gets expensive!

 

[RonD]

Engine vacuum is created by the down stroke of the pistons when intake valves are open, and the air flow restriction at the throttle plate.
When you open the throttle vacuum drops, when you close it vacuum goes up.
Low compression(worn rings or valves) doesn't allow piston to pull in as much air from the intake, so vacuum would be lower.
Intake valves not opening and closing fully or at the right time can lower vacuum.

Most 4cyl, V6 and V8 engines will have 18-22" of vacuum at idle, that's at Sea level to 2,000ft.
That's at about 650rpm, the higher the rpm the less vacuum.

Vacuum leaks release vacuum pressure so throttle plate no longer has full control.
You can remove 1 vacuum hose at a time and plug that port, to see if there is a leak on the hose/device.
Power brake booster can leak vacuum.

Vacuum can also decrease if air can't exit the cylinders completely, plugged up exhaust prevents all the air from leaving a cylinder so not as much new air can be pulled in.

 

[kimcrwbr1]

Are you still using the stock carb? Is the PCV valve new? Is the vacuum port on the back of the egr spacer connected to the carbon cannister, it goes to the metal tube with two solenoids. Its hard to see and the hose gets old and cracked. You can just cap it off. What I did was put a inline restrictor so it pulls a constant slow vacuum to the carb bowl and carbon cannister. I dont like gas fumes under the hood.

 

[GKM007]

Carb is a 2150 non feedback
PCV has about 1k miles
Carbon canister is not hooked up anymore except for what I believe might be a gas tank return line?

Let me think a minute. Going off memory vacuums are as follows

PCV / back of manifold
Dizzy / front of carb
brake booster / vac tree
breather on drivers side / back of carb plate

I cannot think of anymore vacuums I have plugged in? All other sources have been capped off definitely do not have any vacuum leaks. I might have something capped off that should be hooked up somewhere though?

 

[kimcrwbr1]

Did you use the carb spacer felpro 60529
http://www.ebay.com/itm/Carburetor-...ash=item23625f1298:g:AyIAAOSwnLdWtIQ5&vxp=mtr
Surface the base of the carb and install the new spacer and put a new gasket between the spacer and the carb. Do not over tighten the carb down snug is all thats necessary. After a complete warm up snug it down again after the engine fully cools down. Those phenolic gaskets are crap and will eventually leak as the 2.8 runs hotter than most motors.

 

[kimcrwbr1]

The vacuum port I missed is under the brake booster hose pointing straight back toward the firewall. Real easy to miss.

 

[GKM007]

I'll have to check the brake booster.

I'll try snugging down the carb a little more, I have not touched the bolts since it was bolted down.

I did use that spacer (60529) and it came with gaskets glued to both sides. I did also get a gaskets from the rebuild company that was thinner and more of a fiberous material.

Looks exactly like this one.

 

[kimcrwbr1]

Did you put a block off plate for the egr and use the proper egr gasket?

 

[kimcrwbr1]

Another issue I had was the pointer for ignition timing had been bent and was off about 5 degrees. Make sure base timing is exactly 10 DBTDC and then adjust the idle air needles for the highest possible vacuum pressure probably 3-3 1/2 turns out. I also found #42 jets work real good for upper end performance is that a 1.08 venturi carb?

 

[GKM007]

Yea I made my own block off plate by cutting off the base of the EGR unit and RTVing a piece of thin aluminum sheet in between, its ugly but it works.

Timing is correct at 10D BTDC.

Unsure what jets I have in it, I forgot to look when I had the top off checking the bowl level. I can only assume whats in there is 1.08.

All things I have done are pointing as correct. My low vacuum seem more like a slightly tired engine than a missed step somewhere.

 

[kimcrwbr1]

If you can get 17hg at engine idle you will be lucky. Take a length of vacuum tube and stick one end in your ear and search around with the other end all over the top of the motor. The closer you get to a vacuum leak the louder the hissing will be. You can do the same for exhaust leaks to isolate a leak. Another commonly missed leak is for the choke thermostat. The 2150 and 2100 carbs had the preheater tube and it pulled vacuum through the choke housing make sure the cap fits tight and that the fitting for the preheater tube is plugged. it points down at a 45 degree angle toward the firewall. If it still has the flare fitting just get a cap for it or pull the fitting and put a plug in the hole.

Be careful of moving parts when checking for leaks.

 

[kimcrwbr1]

Yea I made my own block off plate by cutting off the base of the EGR unit and RTVing a piece of thin aluminum sheet in between, its ugly but it works.

Timing is correct at 10D BTDC.

Unsure what jets I have in it, I forgot to look when I had the top off checking the bowl level. I can only assume whats in there is 1.08.

All things I have done are pointing as correct. My low vacuum seem more like a slightly tired engine than a missed step somewhere.

http://www.ebay.com/itm/EGR-BLOCK-O...ash=item4ae0f54e3f:g:kjAAAOSwaNBUeXwU&vxp=mtr
Get or make a proper block off plate and use the high temp gasket for the egr. RTV has no place anywhere on a engine in my humble opinion. If it is not leaking it will!