carb adjustments for Mosler CB-40 on a Mini Max

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

karmarepair

Well-Known Member
HBA Supporter
Joined
Jan 13, 2011
Messages
382
Location
United States
Propane or butane will also work for finding intake leaks.

And a recent post in FlyCorvair was about troubleshooting an engine down on power at full throttle. To make a long story short, the cam timing was off. Camshaft vs crankshaft was at least one tooth out. I don't know of any way to check this short of cracking the case, but better mechanics than I might be able to figure it out. Fixing it WILL require cracking the case if that is indeed the problem. Here is the thread in question, the answer is way down in the comments WW Flycorvair : “Question for my mechanics, and my mechanics only, cone heads

"I stuck my finger in the oil filler hole, put my finger on the intake rocker, and watched for 21 degrees btdc when the rocker flinched. It was wrong by one tooth, confirmed by taking 5th bearing off." You could do something similar with a 1/2 VW, and I think Bob Hoover has post about cams that has the opening and closing cam timing of a stock VW cam. On a Corvair, one tooth was worth about 7 degrees of cam timing, I'd have to check the VW Tech manual to find out how many teeth in a VW cam gear to see what that number would be. In this Corvair mystery, the cam gear itself was mis-marked.
 

Kim Brown

Member
Joined
Jan 13, 2020
Messages
22
Running after the valve work on one side was not noticeably different, started a little easier, actually felt like more compression, not sure of static rpm as we are now getting discrepancies with a Tiny Tach and an expensive light reading tach. We are still running lean and have not found significant air leaks using starter fluid rather than dw-40, may have one small one, working on it tomorrow.
 

Kim Brown

Member
Joined
Jan 13, 2020
Messages
22
We leak tested everything we could find using starter fluid rather than wd-40, found nothing out of the ordinary. Plugs are definitely coming out white, lean, lean, lean, valve work got rid of the temperature variation from one side to the other but lean is still there. Have done many variations of carb adjustment, to no avail.(new zenith from Hummel) Have not done compression check but it starts well now and runs up in the high 2000s, having difficulty with tach readings so not exactly sure on rpms, any lean explanations out there that any one can think of? Thanks for your help
 

Marc W

Well-Known Member
Joined
Mar 31, 2017
Messages
678
Location
Colorado
The new Zenith carb on my VW had a problem which caused me to take it apart. It was full of aluminum shavings! I have no idea how they got there. Disgruntled employee? Anyway you need to see what's going on inside that carb.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,851
Location
CT, USA
The new Zenith carb on my VW had a problem which caused me to take it apart. It was full of aluminum shavings! I have no idea how they got there. Disgruntled employee? Anyway you need to see what's going on inside that carb.
Something in the carb wouldn't explain the difference between cylinders.

You might swap the ignition sides, just to rule that out. Depending on the magneto you may or may not have to retime it.
 
Top