|The MGA With An Attitude
CHOKE ADJUSTMENT on the MGA -- CB-102
It may seem odd that one hole in each choke arm is grossly oversize, but it is real and original. The oversize hole allows some "lost motion" so the fast idle can be actuated before choke begins to com on.
At 01:02 PM 9/29/03 -0400, Steve Merical wrote:
>"I've been preparing my MGA for winter driving. It's my only car now."
Damn! You have my instant attention and respect. I haven't done that since college days, but I do still remember how to do it.
>"I moved the choke cam from position 1 to 2. Perhaps when it gets real cold it will go to position 3. However, in position 2 the idle screw does not engage the cam until the choke is pulled out about 1/2 inch even with the idle screw all the way in.
>In position 1 it engaged it immediately. Is this right or what should I be doing differently? I thought 1 was for hot weather and 3 for cold, maybe I have this backwards."
You may be starting in the middle of the adjustment process rather than at the beginning. And the link position is not a seasonal adjustment, but is there to compensate for long term wear in the moving parts.
Step 1: Adjust the link between the choke arms such that both main jets will start to move at the same time when you pull the choke (synchronization). Be sure the jets return freely upward to rest by spring force only when the choke is released.
Step 2: Adjust the cable length such that the choke knob will pull out about 3/8" before the main jets start to move (pre-travel). Then return the knob to rest position.
Step 3: Back off the fast idle screw to almost zero extension (nearly flush with bottom of arm).
Step 4: Set proper running mixture, then set idle speed, and synchronize the air flow (sets fast idle arm to normal rest height).
Step 5: Set the link on the fast idle cam to whatever position makes the cam as close as possible to the fast idle arm without touching it. Touch the cam gently on top to press it down to eliminate any clearance and backlash in the link (rest position as high as possible without touching the arm). Cam must move freely to return with just a light touch.
Step 6: Adjust fast idle screw to be very close to the cam, but with no interference. It's okay if you can slip a bit of paper in between, or back the screw off 1/8 turn from the point where it touches the cam (working clearance).
When you first start to pull the cable the cam should start to move immediately. When you release the knob/cable back to rest position, the arm and screw should push the cam back down to rest position. If it doesn't, then there is excessive friction at the pivot point of the cam. This is where there is a multi-turn spring washer under the head of a shoulder screw. On mine the shoulder of the screw seems to have dug into the throttle body, effectively shortening the shoulder, so the spring washer squeezes the cam too tightly. Solution is to remove the screw, apply a drop of thread lock adhesive, replace the screw, and screw it in just far enough to apply a small pressure on the spring washer, just to keep the cam from rattling, but to allow it to drop easily by gravity or by the slightest touch from above. Let it set for an hour for the thread lock adhesive to set up.
That should be it. When you start to pull the choke knob the first 3/8" of travel will be for fast idle only. Additional pull will start to lower the jets to richen mixture while increasing the fast idle speed as it goes. Full pull on the knob should lower the jets a LOT for full choke in cold weather, and kick the throttle open a very noticeable step at the same time. When tuning for cold weather, you may want to make a final adjustment immediately after a cold start.
For very cold weather start, pull full choke and hold the throttle down just a quarter inch if it helps to keep it running after it starts. Crank to start and tickle the throttle if necessary to keep it running at a reasonable fast idle speed. As soon as functionally possible, push the choke in about half way and adjust for smooth fast idle. If it gallops it's too much choke. If it stumbles and wants to die it's not enough choke. Then if the fast idle speed is too high with the proper amount of choke, back off the fast idle screw slightly to get the desired fast idle speed.
For milder cool weather, either pull only half choke to start, or pull full choke and be prepared to release it to half choke as soon as it starts.
You should not need to reposition the fast idle cam link seasonally. If you think you need more choke for warm up in cold weather, back off the fast idle screw just a bit so the jets move a little more before getting too much fast idle. That way the choke comes on earlier relative to the idle speed. For summer weather when you don't need much choke to start, give it a little more fast idle adjustment so the idle speed comes up early before it gets too much choke. That little tweak on the fast idle screw should be sufficient for making any seasonal adjustment for choke rise relative to fast idle rise.
Check the next page for additional tips on cold weather starting.