Shunyun
New Convert
Were do I test manifold vacuum on my 225? I have a BBS carb; Ive tried testing at the port that goes to the choke diaphragm but have zero vacuum. Are there any other places?
Manifold vacuum on 225?
- Thread starter Shunyun
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Been so long I don't remember. One port you surely have is the choke pull off. What year is the intake/ carb?
You have a manifold tap for power brakes, etc? Usually there's a "tree" off stuff on there
You have a manifold tap for power brakes, etc? Usually there's a "tree" off stuff on there
We removed a pipe plug from one of our runners in the intake and replaced it with a nipple so we could test for vacuum.
Shunyun
New Convert
I believe it's the original BBS, looks like the one in the manual.
BillGrissom
Well-Known Member
The choke pull-off diaphragm should be connected to full manifold vacuum. If you are measuring nothing, maybe the port is plugged, you have the incorrect carb gasket (needs slots for the vacuum ports in the base), or perhaps your gage doesn't work. If the choke pull-off doesn't work, you will have a tough time starting in the winter and/or it will start then flood.
Shunyun
New Convert
Thanks Bill, that led me down the right path. I took off the carb, attached a hose to the carb port (the one that goes to the choke) then blew and listened for the noise. It was blowing out at the gasket, right near the port. For whatever reason, the gasket is blown right at that spot, so I'm ordering a rebuild kit. Guess I'm lucky, could have been a more mysterious problem.
Thanks again!
Shunyun
New Convert
Just a follow-up... I ordered a rebuild kit and determined that the previous rebuilder had put on the wrong gasket between the top and middle sections of the carb. Following the flow from the choke port, it goes to a channel in the upper portion (about 1/8 circle) and at the other end of that channel it passes to a paired hole on the main section of the carb, ultimately passing down to another channel in the bottom and out to manifold vacuum. The old gasket on it was missing a hole. As to why I heard it when blowing on the choke vacuum port, I can only guess that the previous builder hadn't tightened the carb down enough and air was somehow blowing through the nearest opening, in this case at the near edge where the gasket was thinnest.
Anyway, thanks for your guidance, I wouldn't have found this otherwise!
Anyway, thanks for your guidance, I wouldn't have found this otherwise!
BillGrissom
Well-Known Member
Glad you resolved that. Most of us would have never figured out, which is why a carburetor that doesn't work right is often a continual frustration, plus hard to know if it really is the carb and not a vacuum leak or ignition problem. Easy in theory, but complicated little beasts when you consider all the ports and things that can go wrong. It sounds like the kit they used had multiple gaskets for different applications and they chose the wrong one. The instructions are usually pretty sketchy in those kits.
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