Carburetor holders

[rshane53]

Hi all. I have recently acquired a set of 78-79 carburetors and installed on my 71 XS1B. I want to replace my old original holders with a new K&L set. Can I use the stock 71-73 style or do I need to change to the later 74-77 angled style. The carburetors seem to fit into the stock original holders and the bike runs, but when the engine got warm, the idle started to oscillate up and down, so I am thinking its an air leak once warm.

 

[gggGary]

Those straight early holders tip the carbs forward. mebby a float adjustment?

 

[rshane53]

Is that a vote for the later angled holders as replacements??

 

[gggGary]

They also move the inlets down a bit so alignment with factory airfilters would be affected.

 

[rshane53]

So for the float adjustment, adjust for more fuel in the bowl?

 

[gggGary]

good question but I'd prolly go less first.
mebby find a steep hill put it nose up, see if it changes idle?

 

[rshane53]

Sounds reasonable. It's pretty cold here in southeast PA right now, so I may get to it this weekend. Thanks for the input.

 

[gggGary]

PS out of synch will cause a hanging idle

 

[DogBunny]

Hi all. I have recently acquired a set of 78-79 carburetors and installed on my 71 XS1B. I want to replace my old original holders with a new K&L set. Can I use the stock 71-73 style or do I need to change to the later 74-77 angled style. The carburetors seem to fit into the stock original holders and the bike runs, but when the engine got warm, the idle started to oscillate up and down, so I am thinking its an air leak once warm.

The only K&L boots (the rubber part) that I know of are angled, and will only fit a 74 and later holder (the metal part). You need to stick with all straight parts, or you will have interference issues with your side covers.
So, you need to keep your original straight holders (the metal part), and you need to buy straight boots (the rubber part). The straight 70-73 boots are hard to find new. I think there might be some expensive ones from Germany on eBay, and I am pretty sure that you can find them from Heiden Tuning, slightly less expensive.
Your 78-79 carbs will fit and work fine on your 71 as long as you use straight boots and holders.

 

[rshane53]

I was just reading on the post "71 Built for dad" where gggGary commented on the float level and the angled boots, so that will be my starting point. I also just installed a reproduction exhaust. That was an ordeal. Reproductions do not always fit like OEM. For now I plan on making a ramp to get the front end elevated once the engine is warm to see how that effects the idle.

 

[DogBunny]

If you are using your original boots and holders, then your 78-79 carbs are not tilted, they fit exactly like your original carbs. They aren't going to tilt until you use angled boots and holders. And when you go to angled boots and holders, you will have issues with your side covers and/or your air box or pods.

 

[rshane53]

As long as I can prove the original boots are not leaking, I will stay with them. It just takes a lot of effort and lube to get the carbs in and out. It ran well with the original carbs. I wanted the later models linked together to make synching easier and more reliable.

 

[DogBunny]

Idle oscillating up and down does sound like an intake leak, likely either at the boots or the throttle shaft seals. Check by spraying the boots and shaft ends with starting fluid while idling.

 

[grizld1]

JBM Industries offers high quality ethanol resistant straight carb boots for early models: www.jbmindustries.com.

 

[rshane53]

Soooo, it's raining in southeastern PA today, so it seemed like a good day to check out the carburetors. In the process of removing them, I discovered lots of fuel hanging on the outside of the carbs. There was some fuel in the intakes, so I dried them out. I pulled the dipstick and smelled the crankcase but did not detect any fuel odor. The intake valves are tight. After removing, I found the source of some of the leakage. The crossover fuel line was rotted and cracked, missed that on the first install. I took the fuel bowls off to check the float height, and lo and behold one float is oozing fuel. Seems there is a crack in one side of the float and it got fuel inside. That would be the source of the rest of the excess fuel, that float doesn't float, and there is no overflow on these carburetors. In checking the float height one float was 25mm +- and the other was 23mm +-. I soldered the crack in the leaking float, and reset both carbs floats to 26mm +-. Installed a new crossover fuel line, and reassembled the carbs. I checked the main jets and they are 137.5, pretty big. These carbs were an ebay purchase so the previous owner must have changed them. I will run the bike again when I get the carbs installed and see how it performs. I may need to reduce those mains as I am running stock air filters. Possibly a rebuild kit in my future... Keep the rubber side down, and ride em, don't hide em.

 

[grizld1]

The float chambers in your carbs do have vents ("overflow"); they have to be vented in order to keep the float chambers at atmospheric pressure as fuel is depleted, fuel overflow isn't the primary function. Each 78-79 carb vents through the upper pair of holes in the back of the intake bell. Hope the solder repair holds for you.

 

[rshane53]

It's thirsty Thursday Today I reinstalled the carburetors and took the bike for a ride. Apparently the issues I found yesterday were the problem. Today the bike seems to run fine. No leaks and no funky idle. I took it for a short check ride just to see how it ran, and now it seems to run normal. As long as the float I repaired holds up, it should be good. If I have any more float issues I will be getting rebuild kits complete with jets and floats. I sprayed starting fluid around the carb boots and the butterfly shafts to check for leaks, and there was no difference in the idling. Now that it's running well again and I have the replica exhaust fitted, it's time to replace the 12 year old Avons. I will be going to Dunlop K-70's similar to original. I bought this bike from my son in 2010 and he had put the tires on some time before that. Thanks to everyone for all your input. This is a great site for any XS enthusiast.

 

[5twins]

Rebuild kits really aren't recommended. The quality of the aftermarket parts in them is hit and miss, and often the jet sizes are wrong. About the only useful item you get is the float bowl gasket, lol, and many times you don't need to replace that anyway. The originals are very robust and last darn near forever. If you do need to replace some parts, genuine Mikuni float needle and seat assemblies are recommended, genuine Mikuni jets too.

If your repair fails, floats from Yamaha are ridiculously expensive but 650Central sells genuine Mikuni replacements for a good price.