Plastic floats and XV920 float needles in the 78-79 carbs

[DGXSER]

I have a set of 78-79 carbs that I rebuilt some time ago. I used the XV920 float needles and they had the plastic floats in them already.

Now the question, float height? My first thought is that I should set the height as specified for the carb body. But then I have read to set the float height as specified for the newer carbs with plastic floats (23 +/- .5 mm).

I just tonight finally got these carbs mounted in my bike and running decently well. Took a while to get the idle set properly, and then synched the carbs. The performance from idle to 3-4k is great, nice power, smooth operation. Past about 3-4k I get no power at all, in fact, the bike will not go above 4k period! This suggest to me low main jet mixture, meaning possibly low float level.

Bringing me back to my question, for those who have made this change to the plastic floats in the early carb bodies, what float height has been successful for you?

[bikerphil]

I tuned a set of early carbs with plastic floats before, I set them to 22MM, a tad richer than the stock 23MM. Use the measurement for the type of float, not the type of carb body. I did not have the XV920 float valves which may be taller than the OEM but as long as the float is set to the correct number, it shouldn't matter. The float tang might need to bent a bit further from center to hit the correct number. Good luck, you now have the higher performance carbs on your bike.

[DGXSER]

Thanks Phil, I will have to pull them and check / reset the float height.

My plan was to get these running decent to use to diagnose the other XSives bike I have been working on. Eliminate or confirm the carbs as his issue perhaps. But, if they give me better performance that I can notice, I may stick with these on my bike anyway. I will say that idle screw is a bit of a PITA to get to.

[Yard Dogg]

You could get a tapered rubber plug from Ace, then drill a hole in it and run a tube through it up the side of the carb. I firmly believe in fuel leveling, it's the only way to really know how much is in there. Set it at 2mm from the carb body.

[bikerphil]

Don't forget the mains on those carbs are much bigger than the late carbs, stock is 137.5, I'm sure you know this. On both of my bikes, I have rigged up a remote idle adjuster for that PITA knob.

[DGXSER]

Phil, I do have the 137.5 mains, 42.5 pilot jets. I also put the stock sized air jets in them, I forget the size. All four needles were set to the middle position.

I actually did the rebuild probably a year ago. I think I set the floats to the 25.7 setting though, that could easily be the issue if they should be 22-23mm.

[bikerphil]

Yep, air jets should be 185's, the richer float height should solve your problem.

[DGXSER]

It has been an interesting afternoon so far. I found out so far that my memory is not as good as I had hoped. The floats were at 23 mm, I tried lowering them and it did not help any. So I did a throttle chop test, the plugs were black as black can be. So I raised the floats up to 24 mm, same thing, I got it up to about 4500 RPM, but still, plugs were black as black can be.

So I look at the air jets, they are 180s. Sooo...I found the 185 jets I had in my carb parts pile. Well, the air jets in the 78-79 carbs are not the same jets as in the 80-81s. So now I need new air jets.

I also need to find a long nose C-clip tool. Guess I only thought I checked needle position. CRS sucks!!

So, now I know why they have not run correctly anyway.

[bikerphil]

I've drilled out air jets in the past to lean them out with a numbered drill bit set. I would try a leaner setting with the floats before fooling with the air jets. Also, those are pilot circuit air jets you know.

You do have the screw covers over the pilot jets correct?

[LuckyEddie]

floats

Just reading your post..... do the carbs you are useing require the rubber plug in the jet tower? Are they in place? Don't ask how I know about that...

[DGXSER]

Yep, I know those go to pilot jet for air, just thinkign if air is restricted, really reaching for a cause at this point. It seems to idle decent and it runs fine in the lower RPMs. I also just looked at the micro fiche on CSMNL site and the 79 versions have 180 air jets, the 78, 210.

I do have the screws over the pilot jets and the washers. I am going to try the 25.7 setting on the floats.

Just to be sure I put my 81 carbs back in and it runs great, so it is something in these carbs. Now I really want to check the needle positions, need to find some REALLY long nose c-clip pliers.

[DGXSER]

time to buy those long nose snap ring pliers. Got the clip out, needle in middle position, but getting it back in has been impossible so far.

[bikerphil]

Check the number on the needles, someone might have switched them, that for sure will cause them to run like s__t, BTDT. Check the emultion tubes too. The older type carbs are usually very forgiving as long as you have the correct parts in them.

[natemoen]

I have plastic floats in my 78 carbs. My bike runs great till about 7 grand and then leans way out and starts running out of fuel. I need to at some point go back in there and drop the floats to 22mm. I did set them to 23mm originally.

[DGXSER]

Nate, did you also switch to the XV920 float valves? The ones with the VITON tips?

I have the Z66 X-2 emulsion tubes, and the 5GZ6 needle in at least one carb. (Waiting for the long nose snap ring pliers to mess with the others.) But if it was right on some and wrong in others I would suspect the correct cylinders plugs would not be coated in black carbon. I did verify the needle was assembled in the correct order also.

I know the XV920 valves are a little taller than the XS11 ones, but the float height has to do with fuel level in the bowl, not the valve height, so that should not change where it needs to be set. These are aftermarket jets, but I have never had a problem with the kits from GeorgeFix before. They are marked 137.5 on the mains. I used 42.5 pilot jets.

At this point, I will need to wait till I can get that clip back in the slide to do any more testing.