Vacuum leak thoughts...

ecohen2

ecohen2

True Classic
I have come to the conclusion that vacuum leaks on the fuel injected X1/9 are really sinister.... Earlier this month I went through my car doing the annual check-up on it and found a couple of interesting leaks. One of them was caused by a new silicon vacuum line that got soft when it got hot and most likely was leaking. What is sinister about vacuum leaks is they often occur over time and slowly but surely degrade the performance.. So immediately after fixing the leaks the following symptoms went away...

* Inconsistent idle speed and idle hunt during warm-up period
* Poor throttle response
* Bigger than normal throttle drop when you turn on the headlights or not holding an idle
* Engine running hot during extended periods of 60mph or over
* Lots of popping noises when you lift on the throttle

There really are not that many hoses, but making sure the line going from the intake manifold to the distributor and the connections off of the main rubber intake hose are super important..

Just some random thoughts on a cold, raining Thursday morning....

Ed
 
Excellent advice. It’s always about going back to the basics when you have a problem. Ensure the baseline is correct and it will be much easier to solve other problems, if they ever actually existed as other problems as you point out.

Nice work and a good lesson for us all.
 
Well, carbs don't need any vacuum lines to perform correctly, Just block the vacuum line port on the carb (if it even has one), set the timing at 10 degrees at idle (even on a vac advance dizzy) and off you go.
 
Funny you should post this because I have come to the conclusion that I have a vacuum leak somewhere but I can't trace it. My car starts instantly and idles great for about 15 seconds and then it dies unless I keep a foot on the throttle. Then it runs erratically. If I keep my foot steady on the throttle, the RPMs will oscillate up and down.
 
@Huey that sounds way too familiar... Have you tried spraying some starter fluid in the general area of the suspected hoses while the engine is running but still cold? There are a couple of culprits that are hard to detect if you have found no leaking hoses... Down on the back side of the engine is the Auxiliary Air Device which can go bad and behaves like an air leak. Another is a faulty cold start valve that either doesn't work at all or continues to dribble gas once the engine has started.. The last one I know of is the screw on top of the intake manifold along with the components on the side of it that people have seen leak air.

My two big leaks were the line from the vacuum advance to the underside of the intake manifold and the line from a T connector to the drivers side of the intake manifold.

Good luck!

Ed
 
Believe it or not the dipstick seal is also a source of "false air," which is really the term we should be using for an L-Jet era car. "False air" is air that is being consumed by the engine without first being accounted for by the Air Flow Meter or other design elements.
 
Huey said:
Funny you should post this because I have come to the conclusion that I have a vacuum leak somewhere but I can't trace it. My car starts instantly and idles great for about 15 seconds and then it dies unless I keep a foot on the throttle. Then it runs erratically. If I keep my foot steady on the throttle, the RPMs will oscillate up and down.
Click to expand...
I've experienced similar problems. Turned out I had the rubber air intake line split in one or two places. I've had them split where they mount to the intake plenum/AFM and at the crankcase vent hose. It's easy to crack that hose at the crankcase vent connection if you're not careful.
 
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