VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 1935 207 vacuum readings

I recently picked up a 1935 QC with a 207 in it. When I got it, went through it ( Points, condenser, plugs, timing, compression test ( all good and equal) ). Tried to adjust the W1. The low speed adjustment has no effect screwed all the way in or out 3 turns. I decided to rebuild the carb and when I finished, the low speed mixture screw still does nothing. I decided to run a vacuum test ( manifold vacuum) and found that the vacuum gauge fluctuates rhythmically between 5 and 18. The engine starts and runs good ( I may hear a little misfire occasionally) Not sure what to make of all this. I’ve looked at some charts out there but not sure where to go from here. Would doing a leak down test tell me anything? Maybe I should try to adjust the valves? Leave it alone ? Thoughts?

You probably have a valve sticking You can pour some ATF through the carb. throat with the engiine running at a fast ide or squirt some on the valve stems.

Good call on the sticking valves. I put some sea foam down the carb and in short time the vacuum reading stayed pretty steady at 18. Cyl leak down test was great. Nothing leaking from any cylinder. 60 psi was enough to make it hard to keep the piston on TDC. I did find one other thing I need to look into. All plugs are black. Not really wet but a velvety looking black. It was enough to have me check the dwell and find it near 20. I adjusted the points to get the dwell to 30. Adjusted the timing by ear to Reduce the misfire I could hear lost to minimal. The low speed adjustment on the carburetor still does nothing.

I dont know if GM had dwell settings at that stage but my literature indicates 30 to 36 degree dwell as an average for most 6 cylinder engines and I generally used 34 to 36 as this gives the coil time to fully charge.
Tony

Hi Tony,

The dwell angle range you noted is well within specs for any 6 cylinder engine.

In a 6 cylinder engine the maximum dwell is 60 degrees. This means that the points are always closed. The coil works best when the saturation time (when current is flowing through it) is about 2/3 of the total cycle. So 2/3 of 60 is 40.

If you set a new set of points at 36 degrees dwell it should go to about 38 or 39 degrees after the initial wear of the rubbing block.

Remember that the timing needs to be reset after you change the dwell or point gap.

If throttle shaft is worn you could be sucking air in around the shaft, may need to have bushing installed. With it running spray a little B-12 at the shaft and see if it speeds up. Best of luck and be careful not to set the place on fire!

Thanks for all the replies! I will bump the dwell up to around 36. Somewhere someone told me to try spraying any areas where there could be vaccum leaks with mapp gas and see if the idle picks up. I did that all around the carburetor, intake gaskets… Did not find any change in idle speed. That mixture screw has never done anything before I rebuilt the carburetor or after. There is some hesitation in the engine when I accelerate quickly from idle. Having the choke partially on helps that problem. I am not an expert in rebuilding these carbs so I could have something wrong. I may have to find an appropriate replacement for the carburetor to try

You might want to PM Chipper or Dean Echols about the W1 carb. Those can be pretty tricky to rebuild correctly. There are lots of internal passages and plugs that make it difficult to cleaned completely.

One point I would check is to remove the idle screw completely and look at the taper on the tip. If someone seated it too tightly that will cut a groove into the taper. It will never adjust correctly with that groove.

Plugging the idle mixture circuit on a W-1 is not frequent but can happen. If plugged and air pressure will not clear the blockage it is necessary to remove the passage plugs, clean out with drill bit or wire, install new plugs. Normally it is carbon plugging so carburetor cleaner will not remove it.

I didn't have much luck with modern carburetor cleaner on the idle circuit of my W-1.
It's pretty anemic compared to what we used to be able to get.

An old service manual I have said to use lacquer thinner so I tried that.
It actually worked much better.

I pulled out the idle screw, the plug next to it, and the idle jet, and squirted lacquer thinner through the passages using one of those old squirt cans like lighter fluid used to come in.
Used LOTS of air directed through every hole I could, paying attention to the air bleed hole near the top of the bore inside the cast body, and the 2 ports near the throttle plate.
Alternate squirting lacquer thinner and blasting with air until you think you've got it clean.

Soak the idle jet in the thinner and blow it clean, but DO NOT use a wire or anything else but air to clean the small holes in it.
There should be a thin tapered sealing washer under the head of the idle jet. Don't re-install the jet without it, or the inside end of the tube won't seal properly afterwards.

I managed to open up an idle circuit using the above method without having to resort to removing those domed brass plugs.
Hope this helps.

All good advice. The Carburetor Shop has excellent kits and information. Here are the W-1 instructions from their site;

https://www.thecarburetorshop.com/Carter_W1_service.pdf

Dave