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Hi All,

I have a 2.2 HP carb GLH omni and it's been running fine the last few weeks. I noticed a couple days ago a loud hissing coming from somewhere behind the carb. I've traced out all the vac lines and they all seem to be fine. I also sprayed them with soapy water and the hissing didn't change pitch at all. It's pretty loud and noticeable from inside the car. Around the same time as I noticed the hissing, the car started to run like crap. It's always been bad, I need to rebuild the carb, but this is now especially bad. It idles too high once warmed up and too low when it first starts to the point where it wants to stall all the time. There's also a pretty consistent miss from one of the cylinders. Anyway, I've been messing with the carb and adjusting it but I also noticed it seems to be backfiring or something. When I drive down a hill in a low gear, like in 3rd, I noticed there's pretty loud pops coming from the exhaust.

I know this is a lot. I was mainly hoping for some advice on the hissing. Any ideas what it could be?

Thanks!
 

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Been along time for me and a carbed Chrysler but...

Brake Cleaner and Water are both Non-Flammable so if they hit a vacuum leak they should yield the same result, the engine rpm's should slow down.
We used to use carb cleaner (and I still do) and the rpm's would increase when you hit the vacuum leak but that is a bit dangerous as carb cleaner is flammable.

1)Does this vehicle use a spacer under the carb?
2)Can you physically move the carb by hand?
3)What happens when you place your hand over the mouth of the carb, does the engine stall or continue running?
With a vacuum leak the engine will continue to run (depending on the size of the leak)
4)How is the PCV system/hoses?
 

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Just as NAJ said, does the carb move any?

Make sure that the carb & its isolator are tight on the intake manifold.

Also, is the brake booster vacuum line alright? It connects on the back of the carb. There's also an one way valve that's connected by 2 hoses from the back to the side of the carb...
 

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Thank you all for your suggestions. I will check tomorrow afternoon and post back! I appreciate the help.
 

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Discussion Starter #6
Been along time for me and a carbed Chrysler but...

Brake Cleaner and Water are both Non-Flammable so if they hit a vacuum leak they should yield the same result, the engine rpm's should slow down.
We used to use carb cleaner (and I still do) and the rpm's would increase when you hit the vacuum leak but that is a bit dangerous as carb cleaner is flammable.

1)Does this vehicle use a spacer under the carb?
2)Can you physically move the carb by hand?
3)What happens when you place your hand over the mouth of the carb, does the engine stall or continue running?
With a vacuum leak the engine will continue to run (depending on the size of the leak)
4)How is the PCV system/hoses?
There is a spacer, yes. I cannot move the carb though. It was loose for a long time however a few weeks ago I discovered that and tightened it down.
The engine does keep running when I put my hand over the carb. It does still after a little while, however its running for longer than it should be if it didnt have a large vacuum leak.
The PCV system seems okay. I shook the valve and it still rattles. But when I pull the valve out while the car is running, I don't hear a change in the hissing.

Also, John, the brake booster vacuum line looks good. But I cannot find the valve you are talking about that connects the back to the side?

Thank you!
 

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There is a spacer, yes. I cannot move the carb though. It was loose for a long time however a few weeks ago I discovered that and tightened it down.
The engine does keep running when I put my hand over the carb. It does still after a little while, however its running for longer than it should be if it didnt have a large vacuum leak.
The PCV system seems okay. I shook the valve and it still rattles. But when I pull the valve out while the car is running, I don't hear a change in the hissing.

Also, John, the brake booster vacuum line looks good. But I cannot find the valve you are talking about that connects the back to the side?
Thank you!
You said you tightened down the carb. Did this include tightening down the isolator that sits on the intake manifold?

Below is a pic of my carb after it was rebuilt. To the right of the carb you'll see a white valve between 2 right angle hoses. This comes off the back of the carb and attaches to the intake manifold for vacuum. However, my carb is a 5220 and most likely you have a 6520 so I'm not sure whether a 6520 has this vacuum assy. Check on top of your intake manifold, driver's side, to see if there is an inlet tube or not.

Another thing to check, if your carb is not too dirty, is the air bowl (top part). These can become warped from over-tightening the air filter assembly on top of the carb. This would definitely cause a hissing sound. :frown2: Look on top of the carb and you'll see 5 Phillip's head screws. Try tightening these. However unfortunately this won't cure any warpage. The warpage occurs where the cleaner assy mount bolt is by the vacuum or solenoid kicker. If you can find the seam between the air bowl & fuel bowl try putting your finger there while the engine is running.

Does your car have AC? If so maybe one of the control vacuum lines came loose or failed. These would be under the dash. Throwing this out because you said you can hear the hiss inside the car. Unless you have a snake under there!:surprise:

See if any of this helps. If not, we'll figure it out!
 

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1)The engine does keep running when I put my hand over the carb. It does still after a little while, however its running for longer than it should be if it didn't have a large vacuum leak.

2)The PCV system seems okay. I shook the valve and it still rattles. But when I pull the valve out while the car is running, I don't hear a change in the hissing.

3)the brake booster vacuum line looks good
1)You are correct, if you cover the throat of the carb and the engine continues to then you do have a large vacuum leak.

2)Are the PCV Hoses/Grommets OK and not cracked/collapsed?

3)The brake booster itself could be at fault, you will need to disconnect and plug the vacuum line from the booster to see if there is any change.

If you cannot find an obvious leak you will need to disconnect and plug the vacuum line from all devices receiving vacuum to eliminate each as the cause.
If that does not produce a change then you know your issue is carb/carb mounting or intake manifold related.
 
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