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how do I put cv carbs on a head made for slide carbs?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Background:
I thought I was being clever in finding an easy way to remove valve shims. I was tired of my home made tappet depressor working only half the time, so I thought of this: Turn the crank until the cam is pressing down on the tappet, shove a screw driver in the keep the tappet where it is, and turn the crank until the the cam is pointing the other way (where it should be when you do this using the correct method). The tappet is depressed nicely, and the shim comes out easily. I did this for intake valves on #3 and 4. When I put the bike back together, guess which cylinders don't work? (I ignored the snapping noises...:() I know the error of my ways, at least.

Anyway, I took the head off to find #3 and 4 intake valves not closing. I decided to let the shop fix them, as I didn't feel like messing with the valves myself. Anyway, they told me that new parts would be expensive, so I found a parts head on ebay. This was a 79 gs550 head, my bike is an 82. I figured it would work because the part numbers for the valves were the same. I brought both heads to the shop, and told them to get me one good head from them. When I came back, they told me that my original 82 head was cracked (damn those noises...), so they rebuilt the 79 head. That's fine and dandy, so yesterday I'm back in my garage, expecting to ride by the end of the day.

As I'm almost ready to put the head back on, I notice that the carb boots are different (the rest of the head looks perfectly compatible). This is when I realized that the 79 model still had slide carbs, and my 82 had cv.

My question:
How can I match the two up? The cv carbs have larger mouths, and won't fit on the slide carb boots. The difference in diameter is about 6mm. The cv boots won't bolt on because they're too big and their bolt holes are too far apart.

I thought of maybe cutting new holes for the bolts in the cv boots so they can bolt up. Are there any better solutions?
 
The only solution I see is to find a set of slide carbs that are the size intended to mate to the 79 head. As a rough comparison, the flow of a 26mm VM slide carb is about the same as the flow of a 32mm CV carb, so you will not be able to match up carb diameters on a 1 to 1 basis if you are going to change from CV to VM or vice versa. You could make custom induction boots that will accept 32 mm CV carbs and neck down to fit 26mm intakes and intake volume will remain the same, but velocity will increase, so you will have to figure out how to rejet them for the correct mixtures. Overall, I think it is a simpler and more realistic choice to buy the carbs that were designed to fit the 79 head.

Earl
 
The carbs have to be off a 550 - the spacing is very close and the throttle hookup is between carbs 3 & 4.
 
Use radiator hose (from a car) and cut 4 equal lengths to use as boots. Use radiator hose clamps instead of the suzuki clamps and it'll squish that radiator hose down on the carbs nicely. They are hard to fit the first time, but after they take a "set" to their surroundings they come off and go on just fine. This is what drag racers have been doing for years to fit those monster lectron carbs on their bikes.... If nothing else this will get you on the road till you find different carbs.

BTW, I have been using rad. hose for 2 years now without any failures and I ride to work every day, year round
 
Thanks for all the help.

HiSPL said:
Use radiator hose (from a car) and cut 4 equal lengths to use as boots. Use radiator hose clamps instead of the suzuki clamps and it'll squish that radiator hose down on the carbs nicely. They are hard to fit the first time, but after they take a "set" to their surroundings they come off and go on just fine. This is what drag racers have been doing for years to fit those monster lectron carbs on their bikes.... If nothing else this will get you on the road till you find different carbs.

BTW, I have been using rad. hose for 2 years now without any failures and I ride to work every day, year round
Click to expand...

This is interesting. How do you attach the hose to the head though?

I was also thinking the same what Earl was saying. I figured that if the valves are the same size, the intakes have to narrow down to the same width anyway. Also, it's still the same volume of air going through the carb, and since the carb is still the same size, the velocity of the air in the carb should still be the same, right?

I don't really want to buy the older carbs because of potential problems with the air box not fitting, the linkages being wrong, or anything else that decides to pop up.
 
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