What people probably do wrong in cleaning them is they may mess with the adjusting screw or not seal them when they put the cover back on. Just take the little cover off and spray it out with some electrical contact cleaner, gently lift the little thermal reed and get under it too. Don't mess with adjusting it. Put the cover back on and seal it with a light coat of RTV silicon. Make sure all of the hoses are tight and not cracked, better yet, replace them if they are old.
They work off of engine vacuum. If there are any air leaks, they won't work correctly. The little reed plate is a bi-metal thermal valve that slightly bends when it senses heat from the cylinder head. When this happens, it acts as a valve and shuts off the vacuum to the choke.
How to Adjust the Auto Choke
I was excited to learn just how to make adjustments to the auto choke. First, you need to determine if your choke is working properly and if not, which end (cold or hot) isn't working properly.
There are two possible symptoms of an auto choke in need of adjustment.
1) The bike is very hard to start when cold but once it gets running, it runs well. This if generally due to the choke not 'closing' properly when cold.
2) The bike starts great, but once warm, it struggles to get to top speed (maybe only 20mph vs 25mph that is normal) which is an indicator that once the bike gets to temp, the chock stays closed and the bike doesn't get enough air. Sometimes removing the air filter resolves the second symptom by giving it more air.
To test your auto choke, remove it from the bike completely. It is always good to do a thorough cleaning before you begin. Remove the cover and make sure the bi-metal can move freely in and out and that the valve is not stuck. If it is, more cleaning is required.
Room Temp Test - When you have the auto choke assembled and off the bike, take note of the valve position by blowing in each tube. First, blue in tube 1 (closest to the bimetal) and see if air flows. This is the additional air from bystarter chamber. As long as it isn't cold (50 degrees F) you should have at least some flow. Same with tube 3 (furthest from bimetal). You should at least have some flow unless it is over 100 degrees F.
Cold Test - Place the choke in the refrigerator for a few hours. This should get it to the perfect temperature that completely blocks off the air from the bystarter chamber. Blow in tube #1 and it should be completely closed off.
Hot Test - Put a lighter on the back side of the auto choke for about 2 mins. This should get it hot enough (115 degrees F) to completely block the flow to the intake pipe from tube #3. blow in tube #3 and it should be closed off.
The picture below shows you how to hold the adjustment rod with a needle nose vice grip. You simply push the bimetal down and slide the vice grip jaws under the adjusting nut and clamp down leaving room for adjusting nut to move up or down. To adjust, you can use a regular needle nose pliers to grab the small adjusting nut on top and turn the direction needed.
- If your Cold Test fails and the choke isn't closing enough. This means the adjusting nut needs to be loosened.
- If you Hot Test fails and the choke isn't fully opening. This means the adjusting nut needs to be tightened.
Once you have made adjustments, go back through the testing procedures again.