Testing for Vac leaks on intake system

Ask and give advice here
User avatar
Tony Z
Donor
Donor
Posts: 14992
Joined: Wed Sep 14, 2005 8:33 am
What model do you have?: 2.3L 69; 1302; P/Van
Location: Klipheuwel (near Durbanville), Cape Town or working at sea
Has thanked: 191 times
Been thanked: 487 times
South Africa

Testing for Vac leaks on intake system

Post by Tony Z »

I have posted this a few times in the past, so decided to do a "how-to" so it can be saved for future reference......

To test for a Vacuum leak, go thru the following and you should come right.

Buy some quick start. This comes in a spray can
Start the engine, in Neutral and hand-brake on.
Open the engine lid.
with engine running spray a tiny amount into the air filter. You will hear the engine change revs, sound, whatever, it will do something. Take a note of how it changed, you will be looking for something similar soon.
Now at each joint, rubber and gasket spray a bit of quick start around it. You can be a bit more liberal here than at the air filter. If you have a vac leak, the quick start will get sucked in and you will hear the engine sound change.
Check for more leaks.
Once you have found and noted any leaks, go back to them. Spray quick start again to check if you got it right.
Spray again, this time a lot less - this makes 100% sure you are not feeding the carbs indirectly with quick start.
Be 100% sure you are feeding the leak and not the air filter with quick start.
Repair
Test by doing the same.

Good luck


A lean engine often has decent flat spots and a very warm exhaust. Also the temp of the exhaust gas will he higher than usual.
On a near stock engine, a rule of thumb is to hold you hand about 20cm from the exit of the exhaust pipe. The gas should be warm. If it feels hot, then you have an issue (timing, lean mixture, dead or unthreading plugs....).
Another rule of thumb is that if you suspect the carb being the culprit, then you probably suspect wrong. Make sure everything else is right first cause the carb is often the last item to give issues.


ZeroAxe
Drive Train
Posts: 3004
Joined: Tue Feb 21, 2006 12:07 am
What model do you have?: FUmobile
Location: It doesn't matter.
Been thanked: 1 time

Re: Testing for Vac leaks on intake system

Post by ZeroAxe »

Tony Z wrote:cause the carb is often the last item to give issues.
Unless the brass bushing on the bottom shaft is worn out oval.
VW Enthusiast
ImageImageImageImage
Rusty
Oil Stain
Posts: 147
Joined: Sat Mar 04, 2006 1:14 pm
What model do you have?: 1600TP Willys
Location: Hondeklipbaai

Re: Testing for Vac leaks on intake system

Post by Rusty »

Thanks TZ - that's very informative. Now how about telling me (us) how to tell when the carb is running lean or rich & which way to turn those screws on a 34 pict 3 to change the situation.

:hangloose:
Rust NEVER sleeps
User avatar
Tony Z
Donor
Donor
Posts: 14992
Joined: Wed Sep 14, 2005 8:33 am
What model do you have?: 2.3L 69; 1302; P/Van
Location: Klipheuwel (near Durbanville), Cape Town or working at sea
Has thanked: 191 times
Been thanked: 487 times
South Africa

Re: Testing for Vac leaks on intake system

Post by Tony Z »

thats another topic altogether.... post a question in the advice section and you will get most of your answers
bonolo
Oil Stain
Posts: 117
Joined: Thu May 03, 2007 1:48 pm
Location: Rustenburg,RSA
Been thanked: 1 time

Re: Testing for Vac leaks on intake system

Post by bonolo »

Can a carburator cleaner be used as a substitute if I dont have a quick start spray ?
User avatar
Tony Z
Donor
Donor
Posts: 14992
Joined: Wed Sep 14, 2005 8:33 am
What model do you have?: 2.3L 69; 1302; P/Van
Location: Klipheuwel (near Durbanville), Cape Town or working at sea
Has thanked: 191 times
Been thanked: 487 times
South Africa

Re: Testing for Vac leaks on intake system

Post by Tony Z »

probably, you could prob use deodorant if you wanted, but it wont be as easy to tell the difference and I have no idea how the engine will like it.
Quick start is a fuel (Ether I think), anything else isnt, they just happen to burn too.
User avatar
subie
Drip
Posts: 25
Joined: Sun Dec 28, 2008 5:57 am
What model do you have?: Kango beachbuggy
Location: Velddrif

Re: Testing for Vac leaks on intake system

Post by subie »

I really like this piece of advice.
It always bemuse me when I see the oke's from the "rev right motors brigade" furiously
attack the carb first when there is any problem.
As an AC rookie I would think if you run with a working air and fuel filter and know your carb and intake system is airtight then there should be nothing that can un-adjust itself realistically.
Bliksem die engels is swaar!! :lol:

subie

Another rule of thumb is that if you suspect the carb being the culprit, then you probably suspect wrong. Make sure everything else is right first cause the carb is often the last item to give issues[/b





[quote="Tony Z"]I have posted this a few times in the past, so decided to do a "how-to" so it can be saved for future reference......

To test for a Vacuum leak, go thru the following and you should come right.

Buy some quick start. This comes in a spray can
Start the engine, in Neutral and hand-brake on.
Open the engine lid.
with engine running spray a tiny amount into the air filter. You will hear the engine change revs, sound, whatever, it will do something. Take a note of how it changed, you will be looking for something similar soon.
Now at each joint, rubber and gasket spray a bit of quick start around it. You can be a bit more liberal here than at the air filter. If you have a vac leak, the quick start will get sucked in and you will hear the engine sound change.
Check for more leaks.
Once you have found and noted any leaks, go back to them. Spray quick start again to check if you got it right.
Spray again, this time a lot less - this makes 100% sure you are not feeding the carbs indirectly with quick start.
Be 100% sure you are feeding the leak and not the air filter with quick start.
Repair
Test by doing the same.

Good luck


A lean engine often has decent flat spots and a very warm exhaust. Also the temp of the exhaust gas will he higher than usual.
On a near stock engine, a rule of thumb is to hold you hand about 20cm from the exit of the exhaust pipe. The gas should be warm. If it feels hot, then you have an issue (timing, lean mixture, dead or unthreading plugs....).
Another rule of thumb is that if you suspect the carb being the culprit, then you probably suspect wrong. Make sure everything else is right first cause the carb is often the last item to give issues.[/quote]
TonyE
Oil Pump
Posts: 255
Joined: Wed Oct 29, 2008 9:10 pm
What model do you have?: 1976
Location: Uitenhage
Been thanked: 1 time

Re: Testing for Vac leaks on intake system

Post by TonyE »

Another way to test for air leaks is to turn the air screw on the carb close , if it still idles it getting air from somewhere else.( A leak)
User avatar
bugspray
Floorpan
Posts: 3468
Joined: Thu Jun 26, 2008 4:18 pm
What model do you have?: 71 Westy + 74beetle
Facebook: http://m.facebook.com/profile.php?r0d306f00&refid=7
Location: Pretoria- beetle / Benoni - Bus
Has thanked: 24 times
Been thanked: 16 times
South Africa

Re: Testing for Vac leaks on intake system

Post by bugspray »

bump. will try this out as im told that this could be a problem to my car not startin... oh and free bump for the peeps that missed this.
Image
More than meets the eye!
sacem
Drip
Posts: 4
Joined: Wed Nov 03, 2010 8:12 pm
What model do you have?: Dune buggy
Facebook: none

Re: Testing for Vac leaks on intake system

Post by sacem »

Excelent advice specially if you are running non stock multiple carburetores
SACEM
User avatar
John Alves
Crankshaft
Posts: 791
Joined: Thu Jan 31, 2008 1:06 pm
What model do you have?: 58Ghia 68bug68buggy
Location: Cape Town
Has thanked: 3 times
Been thanked: 48 times
South Africa

Re: Testing for Vac leaks on intake system

Post by John Alves »

I have fuel leaking from the intake rubbers, but the motor runs fine.
Could this be the start of a vac leak?
No sense being pessimistic. It wouldn't work anyway.

1958 1600 TP Karmann Ghia
1968 1600 TP Beamish buggy
1968 1500 SP Beetle
User avatar
John Alves
Crankshaft
Posts: 791
Joined: Thu Jan 31, 2008 1:06 pm
What model do you have?: 58Ghia 68bug68buggy
Location: Cape Town
Has thanked: 3 times
Been thanked: 48 times
South Africa

Re: Testing for Vac leaks on intake system

Post by John Alves »

Tony Z wrote: you could prob use deodorant if you wanted, .
Doom also works, but that kills bugs dead
No sense being pessimistic. It wouldn't work anyway.

1958 1600 TP Karmann Ghia
1968 1600 TP Beamish buggy
1968 1500 SP Beetle
User avatar
Tony Z
Donor
Donor
Posts: 14992
Joined: Wed Sep 14, 2005 8:33 am
What model do you have?: 2.3L 69; 1302; P/Van
Location: Klipheuwel (near Durbanville), Cape Town or working at sea
Has thanked: 191 times
Been thanked: 487 times
South Africa

Re: Testing for Vac leaks on intake system

Post by Tony Z »

John Alves wrote:I have fuel leaking from the intake rubbers, but the motor runs fine.
Could this be the start of a vac leak?
My guess is you already know the answer, which is why you are asking....
My guess is that when the engine is warm, the rubbers work fine, but if they are cold, there is a slight vac leak. Check for leaks at idle just after starting the engine on a cold morning.
User avatar
John Alves
Crankshaft
Posts: 791
Joined: Thu Jan 31, 2008 1:06 pm
What model do you have?: 58Ghia 68bug68buggy
Location: Cape Town
Has thanked: 3 times
Been thanked: 48 times
South Africa

Re: Testing for Vac leaks on intake system

Post by John Alves »

Thanks, I will try that
No sense being pessimistic. It wouldn't work anyway.

1958 1600 TP Karmann Ghia
1968 1600 TP Beamish buggy
1968 1500 SP Beetle
User avatar
fig
Bus Driver
Posts: 12214
Joined: Fri Jan 20, 2006 10:08 pm
What model do you have?: Type 2
Facebook: https://www.facebook.com/groups/258896479219/
Location: Where life is cheap and death is free
Has thanked: 287 times
Been thanked: 321 times
Contact:
South Africa

Re: Testing for Vac leaks on intake system

Post by fig »

If fuel is leaking out then air is definitely leaking in. I think you may be surprised at the performance boost once you've fixed the leaks and retuned your carb.
fig
Kaapse Kombi Kult

"Whether you think you can or whether you think you can't, you're right." -- Henry Ford
Post Reply