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View Full Version : Should I have vacuum on line 28 at the carb?


greentee76
02-21-2008, 07:59 PM
I have searched and searched for the answer to this question and can not find it. It would appear that I should have vacuum where line 28 connects to the carb, but I have been looking at so many vacuum diagrams that I will be having black spaghetti nightmares.
Assuming I am supposed to have vacuum on this port, what should I be checking if I don't?
steveko
02-22-2008, 05:13 PM
I believe it's ported vaccum from the carb.It assist opening the vaccum secondary if that's what you're checking.
swiftymorgan
04-12-2010, 09:59 AM
Same question, is there supposed to be vacuum on line 28?

With the line disconnected from the thermovalve I measure zero vaccum at line 28. I isolated the secondary diaphram and it holds vacuum. I put my vacuum pump right on the carb port and air flows freely.

The main problems are it won't come off fast idle when cold and hard restart in hot weather.
TIA
87 Accord LX
A20A1
04-19-2010, 09:14 AM
it's venturi vacuum not intake manifold vacuum... test the vacuum port on the carb at Wide Open Throttle then you should see vacuum, there isn't much venturi vacuum at idle.

Anywho the venturi vacuum from the carb helps move the secondary diaphragm. You can connect the carb directly to the diaphragm if you want to.
swiftymorgan
04-22-2010, 07:33 AM
Good info, thanks. I already connected directly to the secondary diaphragm and it seemed to make a difference. The thermo valve is always open so I plugged the lines and that seemed to also help
jlebr549
05-27-2010, 04:17 AM
Based on my understanding of the vacuum circuit there will be some small vacuum at high rpm with the breather on the carburetor.
Without the breather installed I don't think you will get any, thats why you will never be able to see the secondary kick in.
jlebr549
05-27-2010, 04:40 AM
The best troubleshooting tool outside of a multimeter for a car is a hand operated vacuum pump.
Having two on hand is even better.
swiftymorgan
05-30-2010, 01:08 PM
The best troubleshooting tool outside of a multimeter for a car is a hand operated vacuum pump.
Having two on hand is even better.

Thanks for the reply. I have a hand vacuum pump and agree it's a great troubleshooting tool.

FOLLOW UP: Switching to ethanol free gas solved all my starting problems, runs like brand new.
A20A1
06-23-2010, 08:01 AM
lucky... we only get E10. :(