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Old 07-08-2008, 08:11 AM
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Chevy 305U how to measure vacuum

Hello guys,
I read in Haynes book that measuring vacuum on manifold would give useful info about engine status.
I have 78 Monte Carlo with 305 U engine with Rochester 2bbl carburetor. I bought the car some months ago and do not know anything about it. The car was not driven for the last 10 years. It was very hard to start the engine and it was running uneven. I changed spark plugs, wires, adjust timing and idle speed, overhauled carburetor. Now the engine starts immediately and runs at 500 rpm The problem is that it smokes a lot when cold, white smoke like oil smoke then the smoke reduces but it is still more than it should be, I think.
So, according to the book I can get some info about the problem by measuring the vacuum on manifold but I do not know where to connect vacuum gauge
I will really appreciate your help pointing me where I should connect the vacuum gauge.
Thank you very much.
Ivaylo

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Old 07-08-2008, 12:51 PM
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There should be a Vacuum port right behind the carb Possibly a "T" that is the best spot to get a accurate reading.

Sounds like you idle is a bit low .

Check the EPA sticker to see what the proper RPM setting is.



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Old 07-08-2008, 01:54 PM
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More than likely needs the valve stem seals renewing after all that time without running, they could have hardened.
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Old 07-08-2008, 05:49 PM
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Oil smoke is blue. Coolant is white. Check your coolant level to see if it goes down. It could be a blown head gasket, intake gasket, cracked head or block allowing coolant to enter a cylinder. This would show up as white steam when started.
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Old 07-08-2008, 09:13 PM
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Not sure of the weather conditions in Bulgaria, but any where it is Cold/Cool out & there is humidity there will be some steam action from condensation in the exhaust system .

This is why the newer cars have gone to a stainless alloy where as the older cars with a straight up steel pipe will rot out faster if not used, in a humid environment.

But as the above post stated check the coolant check your spark plugs for coolant .

If its not consuming any then it should be nothing to worry about.





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Old 07-09-2008, 03:27 AM
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Quote:
Originally Posted by Rob Keller
There should be a Vacuum port right behind the carb Possibly a "T" that is the best spot to get a accurate reading.

Sounds like you idle is a bit low .

Check the EPA sticker to see what the proper RPM setting is.



R
Hi Rob Keller,
Thanks for your replay.
Do you mean the hose that goes from bottom of carb to top of it? It is on the back of the carb.

The idle is 500 rpm according to the label on the engine compartment and 600 with conditioner on.
Best regards,
Ivo
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Old 07-09-2008, 03:49 AM
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Hi guys,
Thanks for your replays.
The smoke is definitely oil one it smells like burnt oil
I also have Trabant, it has two-stroke engine and I know the burnt oil smell

The weather in Bulgaria is rather hot... south east Europe... now about 30-35 C day time

Unfortunately I broke the transmission , so I have not driven the car long enough to see if it consumes oil and coolant .
Thank you for your help
Ivo
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Old 07-09-2008, 05:10 AM
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Hows the compression @ WOT? What do you mean by running uneven? That plus white smoke = head gasket . Coolant will have a sweet smell. Do you have a compressor? If so close the coolant system and put compressed air in the over flow hose next to the radiator cap. This will pressurize the coolant system. See if you have leaks. You can also pull the plugs and wait till psi is gone then crank the engine to see if coolant squirts out one of the cylinders.

If it hasnt been runnning for 10 years then the oil my be ok cause you dont know if they put oil in the cylinders to store it or any kind of history, that is of course you just bought it. Get it running for a while and hold a rev on it like if you where breakin in a cam.

Vacume gauge will tell you condition of valves, timing, exhaust, springs, cam, fuel, but you need to know how to read it. You said you had it running so what did the gauge do when it was running?

If you suspect valve seats one thing that works well is Seafoam. Get the engine to operating temp then pull the brake booster line. Get the engine to 2500 rpm then stick the hose in the seafoam can. As soon as you stick the hose inthe can let off the throttle, and let it stall out. Wait 5 minutes and start enginne and run the rest of the seafoam out of the can. It will smoke for a long time so keep running it to clear out the seafoam.
I have used this on a gm ironduke that was missing and poping under load due to valve seats having to much carbon. After the cleaning it did not miss a beat .

Hope you get it running good. I had a 76 monte with purple honies after the headers and got it to idle at 400rpm it sounded at stop lights. Blap...Blap ,,,Blap.... Blapp.......
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Old 07-09-2008, 01:19 PM
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Quote:
Originally Posted by rack
Hi guys,
Thanks for your replays.
The smoke is definitely oil one it smells like burnt oil
I also have Trabant, it has two-stroke engine and I know the burnt oil smell

The weather in Bulgaria is rather hot... south east Europe... now about 30-35 C day time

Unfortunately I broke the transmission , so I have not driven the car long enough to see if it consumes oil and coolant .
Thank you for your help
Ivo
I went though East Germany a few times and those Trabbies sure made the air blue.
When the wall came down they descended on us in Wolfsburg.
Canīt you install the V8 in the Trabant...............
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Old 07-09-2008, 02:20 PM
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Quote:
Originally Posted by malc
I went though East Germany a few times and those Trabbies sure made the air blue.
When the wall came down they descended on us in Wolfsburg.
Canīt you install the V8 in the Trabant...............

the Trabant is as big as the V8 itself :-)
I will post some pics of it
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Old 07-09-2008, 02:48 PM
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Hi n-gin,
Thanks for your replay.
Unfortunately English is not my native language and I don't know all the terms you use
For example, what is WOT?
I did not measure the compression and vacuum yet. I just got the gauges yesterday. I will do it during the weekend and get back with results
By uneven I meant... like rpm goes up and down, stopping... but there were many problems with timing, broken cable insulation, fuel supply etc...
I install new distributor cap with coil, new cables, new spark plugs, rebuild carb, fix fuel supply and adjust idle rpm and timing. Now the engine starts just half crank and runs stable at 500 rpm but smoking I will take some pics to see what I mean
Thank you very much,
Ivo
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Old 07-09-2008, 11:34 PM
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WOT is wide open throttle.
With a compression tester you see what you have.
How to do it.

Have you checked for vacuum leaks, manifold to heads, carb to manifold etc ?
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Old 07-15-2008, 07:09 AM
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Hello everyone,
I measured the vacuum at T behind the carburator.
The vacuum is 17 in Hg and it is steady, does not go up or down at idle.
I made also test described at Haynes Monte Carlo book, raving the engine, vacuum drops almost to zero, then goes up to approximately 23 in Hg. and then drops to normal
So, I think there is no problem with it or this does not mean anything?
I did not check the compression yet, I did not have assistant available , but i removed the spark plugs and they all were black by carbon. There was not oil or any other liquid...
I also noticed that the oil level is above the full mark on the deep stick. I measured it when the engine was cool. I read in some manual that I should check the oil level when the engine is hot. What is the correct way to check the oil level?
I will be back with more results soon.
Thank you very much.
Ivo
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Old 07-15-2008, 12:31 PM
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In My Humble Opinion {IMHO}

When I want the most accurate reading on a level surface.
I check the dip stick when it is cold & has been parked over night or 12 hours.

This allows time for the oil stuck to the metal inside the motor to drip back to the oil pan.

On a Typical American V~8.

You can figure 1/2 a Quart is stuck to the inside after the motor has been started.





R
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Old 07-21-2008, 06:07 AM
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Hello again,
Finally I measure the compression of my engine.
It is between 110 and 120 psi on different cylinders, engine hot and WOT.
I also changed the oil. It was very dirty with a lot of carbon deposits in it. I put 4 liters of oil in and the oil level is between add and full marks on deep stick. It was overfilled with oil because I drained more than 5 liters from it. Now the engine does not smoke much but I think I have problem with carburetor adjustment.
The problem is that now it is very hard to start the engine when it is cold
When I open chock plate it starts much easier. I think the mixture is very rich as it has very strong gasoline smell. is this connected with idle mixture somehow?
Thanks a lot.
Ivo
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