It came with 750 carbs that the previous owner thought would work. Given what I have read here (http://forums.sohc4.net/index.php?topic=108792.msg1218564#msg1218564), elsewhere, and from advice from people who know more than me; it seems the best option is to find a set of stock carbs.
It is proving quite difficult find them, however; also, the head, valves, and cam are all worn. Within tolerances, but enough that I am interested in looking at other heads. So, here are some alternative setups I have heard about; has anyone had experience with them?
- 79/80 head and carbs
- 81 head and 79/80 carbs
- 81 head and 82 carbs
- 550 head and carbs
- 550 head and 650 carbs
Any insight is much appreciated.
With a bike in a box. You never know for certain what you actually have to work with. Lets start out by confirming what you have. The 81-82 650 used the CV vacuum slide carb. The carb spacing on the head was changed to fit those carbs. The CV carb head can be identified easily by looking at the bottom 2 fins on the intake side. Those fins will be cut back towards the head. The earlier 79-80 mechanical carb head will have the fins running the full length. Most any used head that you will find is going to need work. So unless the cam saddles are damaged, or the fins are broken. There is really no need to replace the head. The valve guides are replaceable, and the valve seats can be re-cut.
The 550 heads will not work on the 650 due to the high dome pistons. You would have the pistons beating against the head the first time you tried to turn it over. Combine this with the smaller valves, and restricted ports of the 550 head. It would not make a good choice for a replacement on the 650.
650 cams are getting hard to find at any kind of a decent price. If yours is still in useable condition. You will want to use it. The only other option is to have a cam hard welded, and reground. This can be done through either megacycle, or web camshafts. If you go the regrind route. Try finding a good 550 cam core to have welded up. This will give you the option of choosing from the performance grinds available for the 550. The draw back to using the 550 cam is that you will also need to use the 550 tach drive gear, and tach along with the cam. The 550 is a different ratio from the 650.
The stock carbs for the 81 650 were the VB44A. These have the pressed in pilot jet. It is common to swap in the VB44C carbs from the 82 650. The 82 carbs will have the screw in pilot jets, and make cleaning the carbs easier. Using the 750 carbs was common on the earlier mechanical carb heads. I am not sure if the vacuum carbs from the DOHC 750 will fit on the later heads.
This leaves your options as.
Keep the stock 81-82 head with the 82 VB44C carbs.
Change to the 79-80 head with the mechanical carbs. Possible 750 carb upgrade.
