The Stovebolt Site Forums The Shop Area Engine Shop spark plugs for a 235

Mike it is possible the diaphragm in your carburetor is leaking. I've written about this a few times and have showed people how I fix it. In basic terms, there is always vacuum present at the bottom of the diaphragm. That is by design and Carter used that variable vacuum to make the metering rod go up and down as needed (as Jerry mentions above). If the diaphragm is leaking what will happen is two things: raw gas will be sucked past it (the diaphragm) and right into your intake manifold and also there won't be the proper vacuum to make your metering rod work correctly. The lack of vacuum will cause the small part of the rod to be in the up position and that will make things run richer. Not to bore you but when vacuum is high, the diaphragm is sucked downward and this causes the fat part of your metering rod to enter the main jet. When vacuum is less, the diaphragm is not sucked down and the spring pulls the metering rod upward causing the small part of your metering rod to be in the main jet...giving your engine a richer mixture (which would be needed going up a hill for example). The "bonnet" that sits atop your diaphragm rod gets distorted when somebody over-tightens it and the use of the gasket shown in the image below will make things worse. What happens is the corners of the bonnet get pulled down leaving a gap between them. You can see I have shown one side of this one was warped .006 and the other side was warped .008".

To fix it, you'll need to get a nice flat piece of wood and use a drill bit of about 1 1/4 inch diameter to make a hole as you see I've done in the first image below. Then cut a hole out of a small piece of 320 grit sandpaper and 600 grit sandpaper. Then set the sandpaper on the wood piece (start with 320 grit) and rotate your bonnet piece back and forth until it is nice and smooth and all the warpage has been removed. Then follow with the 600 grit paper to smooth it even more. It should look like the second image below. Please don't re-use that gasket if one was in the kit you got.

This is just one possibility. While you have your carburetor apart please check the float settings too. An incorrect float setting can cause a rich-running condition. Hope this helps.