Working on the carbs on my 750 K8 and I knew that I needed to raise the needles a bit, but on the SOHC4 750, in 1978, the needles are not adjustable. By doing some searching, I found that many people just said to shim the needles up a bit. BUT, despite the amount of searching I did, I could not find an example anywhere of how to actually do this. Not being scared, I figured I would dive in and document so that others might share in this.
First of all, can this be done with the carbs still on the bike? Yes. It's far more of a pain in the butt than taking them off, so I took them off.
First thing to do is to take off the tops of the carbs:
With the 78 PD carbs, you will need to remove the set screw that holds the upper arm to the throttle arm (the actual part that twists).
As you can see on the other three carbs, the adjustment portions (for carb syncing) are not effected by this, and the set screw screws right into the twisting rod. In theory, the sync of the carbs will not be effected.
Doing each carb one by one is the best way to do this. Less parts flying all over the place. First, lets take a look inside and see what we're dealing with:
All kinds of fun little pieces. What we need to concern ourselves with most is the big arm in the middle, and circlip and the little plastic washer. You will want to remove the circlip and the washer so that the middle arm can be slid off to the side and be removed.
With the parts off and this arm out of the way, we are free to pull the whole slide assembly out.
Make sure you still have all the pieces.
There are two screws that hold the next piece in place This part holds the needles in place with a small spring. Simply remove both screws (don't loose them, they are small) and pull the part out of the slide. The needle can then be removed.
The washers I used, I simply bought at the hardware store, in the metric section. M2.5 Flat Washers.
Each washer is about the space that would sit in between each section on an adjustable needle. This leads to even greater fine tuning if you really wanted to go that far. I only wanted to raise the needle "one position," so I placed on two washers (one for a spacer, the other for where the new clip position should be.
One Washer:
Two washers
Reassembly, as they say in most manuals, is reverse of removal.
I hope this helps someone down the road. You can also search around and find needles from a '77 750, but since they are no longer available from Honda, sometimes it is best to work with what you have.
-Bob
KB02