QuestionQUESTION: Hi, it's Jon with the 76 Midget (1275 motor in it). I adjusted the timing, also
did a valve lash on the motor. I turned my efforts to the carbs. I equalized
the "hiss" best I could with maintaining the idle at just a hair below 1000rpm
(as per tach). I then removed the pistons to see if moving jet adjusting bolt
(think it was counter-clock wize) to the top would lift the jet seats up.
Interesting, it looked like there was no movement. I did, however, notice a
slight change in the run of the motor by moving the bolt then
downwards...As I backed then 3 full turns aroung and then re-adjusted the
"hiss" with idle screw. The car ran for a quick shot in first across the road
what seemed better. Could however be the timing and the valve lash (if the
adjusting bolt is really doing nothing!
I hae twin su's...Funny, the drivers side carb has a spring loaded needle and
the one closest to the nose does not move.
Suggestions...? I would assume they are Hs2's...
JGP
ANSWER: The timing and the valve clearance must be set first because the adjustment of the jets is done by the response when the spring loaded pin is lifted on each carb.
The hiss must be set by the idle stop screws not by any jet adjustment. When you adjust the 5/8" "Nut" upward (lean) you may have to reach under the carb and lift the jet up to meet the adjusting nut. When you adjust it down it will push it down. If you are looking for movement by looking in at the top of the jet you will not be able to see how far it is moved by only 3 flats but it did move it.
If you have one piston with a spring loaded needle and one with a fixed needle, you have two different year model carbs or different year piston and top pot. Each piston is a machine fit to it's top pot and must never be switched with another.
Lifting the front piston by the spring pin is supposed to give you the result of a slow running two cylinder engine. It it speeds up your other carb is too rich and if it dies you either didn't get the hiss correct or the other carb is too lean.
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard, can my jets be seized...they don't seem to move in either direction.
The spring does, but not the "seat" of the jet. What I mean by the seat is
looking down into the "hole" with the pistons removed. The brass piece with
the hole in it I assume is the piece that does up and down. Here is the
wackiest part...when you move the adjusting bolt, there is a change in the
engine's tune--even though the seat is not moving. I have moved fully up
and down with the adjusting bolt to confirm it is not moving.
Suggestions to unseize?
I suck. JGP
ANSWER: Jon, The jet is the center brass tube that the needle goes into and when you adjust the 5/8" NUT on the bottom, it moves the jet up and down but not very much. When the bottom nut is run all the way up the brass jet should be flush with the bridge of the carb. When you run the adjusting nut all the way down it will only drop the jet down about 1/8 of an inch but when you pull the choke it should go down about 1/4 inch. This is providing you do have the two SU carbs used on the 1275cc Midget engine. On the bottom of the carbs you should see a lever on each that have a pull spring on one end and a clevis pin connecting the lever to the jet and on the other end of the lever is where the choke cable is attached. Just above the clevis pin on the jet is a 5/8" hex nut that has a coil spring above it. If this is not what you see on each of your carbs then you don't have the SU carbs that came on the 1275cc Midget engines in the US.
Howard
---------- FOLLOW-UP ----------
QUESTION: Yes, they most certainly are su's..that brass tube, is not moving up within the carb to the seat at the top. Last night, I adjusted down, it pulled the jet down--but would not pull back up. The jets are down about 1/4 inch--poss a 1/2 inch. The choke linkage is not pulled down, nor is the cable now attached. I disconnected the levers attached to the bottom of the jet (the plastic bottom bit with the fuel line in) and tryed pulling the jet lower to see if seized and I could free. The jet did drop lower--but still will not go back up. So, now I can see about about a half inch of the jet tube protruding from the bottom of the adjusting bolt when it is adjusted up. So. It is possibiliy pulled lower then its normal limit. I think I may need to remove the whole jet to correct? Poss the jet locking bolt and remove to refit? Could the tube be poss bent a bit and that is why it will not go up? OR could the choke within the carb be actually seized? You cannot force it up either from the bottom.
JGP
AnswerThere should be a flat plate rod attached to the plastic part of the jet and it is supposed to be spring loaded to lift up on the jet. Sometimes the jet is stiff so try lifting the jet back up. The adjusting nut never lifts the jet it just allows the lever to lift the jet up when you adjust the nut upwards. The adjusting nut can only push the jet down.
Howard
