Carb swap

[TrikerBoab]

Hi all, just registered newbie so please be gentle with me.

The question i have, the reason for registering is this.
How many ducks does it take, OH sorry thats not it,


Can you do a straight swap of the carbs from an XJ onto an XS, and do the manifold boots (inlet rubbers) fit from an XJ onto an XS.

If this is covered somwhere on this site already i am sorry for raising it again, but i`ve looked and looked and could not find the answer.

The XS i have has a 3H3 prefix and was made for the USA in 1979, it has been (Oh my, you might not like this bit) triked here in the UK after being imported in 1999. And i just want to put new carbs on it, and a friend knows a friend who has a love of XJ`s and has a few carb banks lying around.
With the XS having been triked quite well it still has the standard airbox.
So can i, will they????????
Dont mind rejetting and setting them up, but dont want to get em to find out they wont fit.
Thanks in advance,
TrikerBoab.

[mitch]

Carbs

Im not gonna be much help but i know that the choke linkage is different its on the handle bars on the XJ, so that might be a bit of trouble. I would take your carbs off and compare them to the other set, another concern might be the vacume lines. Carbs and boots i think are fine just the linkage and vacume lines i would worry about, sorry i cant be more help......MITCH

[John]

The carbs will swap directly in but, like Mitch said, the choke is slightly different on the XJ. It uses a cable, with a thumb lever mounted on the left side handle bar switch housing. I am currenly running an XJ engine in my 80 Special, and everything else is the same. The jetting on the XJ is much smaller than the XS, and I'm not quite sure why, unless it's for emissions. The 78-79 XS had 137.5 main jets, 80-81 had 120 on #1&4, and 125's on 2&3. I've read that was done for cooling the middle cylinders, and the XJ has 112.5 mains. Another difference is the way the floats are set on the XJ. You have to 'wet set ' themusing a piece of clear tubing, and holdin the tube up to the side of the bowl, like a manometer, to check the float height. That is why the XJ carbs have the drain screw and port on the bottom of the bowl. The XS floats are set by holding them upside down, with the bowls off, and measuring the float height, and setting it manually. Hope this helps. If you should need a swtich housing, I have one I can sell you. The rubber boots are all the same, but the XJ airbox is different from an XS. Myself, I would go throught the 79 carbs. They are more tunable than the later models. The XJ pilot screws are sealed in the carb body with a plug, and may be very hard to remove. The old XS pilot screws are right there in the open and easier to access. The jet needles on the old carbs can be adjusted, and the XJ's cannot. Physically they are the same dimension so they will fit the XS.

[stuart]

hey there trikerboab.......its stuart from aberdeen here from trikes r us forum just thought i would give you a wee message to let you know i a m on here to..this is a good site plenty people to give advice...what about sending me some pics of your trike so i can have a look,i can send you some of mine if you want?????????????????

[TopCatGr58]

Hey there TrikerBoab,

John was sorta correct, but slightly incorrect in the jetting info. The 78-79 carbs mains are larger cause they also provide the fuel to the pilot circuit, whereas the 80-81s have a separate supply tube and pilot jet. The main jets on the 80-81's were only 110 and 120 outer and inner, although my 81 came stock with 110's straight across. The 78-79 has vent tubes for the tops of the carbs, the 80+ don't require them. The XJ has a different airbox just due to the styling and room difference vs. the prior models. The 81's as well as the XJ's used the wet bowl level technique for setting the height of the floats, but you can still get a decent setting by doing it the pre-81 way with a ruler/micrometer...whatever!

The pilot jet screws were capped in the 81 models and the XJ, but can be removed and access to the pilot screws obtained so you can fine tune them as desired!!! The XJ used a system called the YICS, Yamaha Induction Control system, but that was built into the head design, something about evening out the vacuum pulses or such. But the carbs are essentially the same as the 81's, so you should have no problem fitting them into your 79 frame and engine, just mounting and routing the choke lever.

The fuel supply lines will look strange cause the XJ and the Specials used the Octopus, but you don't necessarily need it. As long as you've got the vacuum lines hooked up to your petcocks correctly to control the flow, just remove all of that extra tubing and run the same lines that went to the bowls of your older carbs and put them onto the "T's" on the new carbs, and you should be good to go. If your 79 has open filters vs. the box, or 4-1 pipes instead of the stock, then you may need to go up a few jet sizes to prevent it from running lean! Search the tech tips for re-jetting, you'll find a nice guide! HTH.

PS, send us some pictures!!!!! Welcome

[Silk]

Lo Trikerboab, Im in uk also. I havent got a clue about your problem but I am very interested in ya trike conversion. Im seriously contemplating taking the plunge.
Nearly bought 1 off ebay :-)
Did u buy the rear end as a kit or do it yourself ? Url for piccies please

[TrikerBoab]

Hey you guys

Well what can I say, you guys are spot on. Thanks very much for all the replies. I think from the information you have all gave me i would be better keeping the carbs i have and overhauling them rather than changing them. So that is what i will do.
Stuart, how you doing, great to hear from you again, keep it in the wind dude.
As for pics of the XS trike, i took a few a while ago and a few others today and will post them as soon as i reduce them a bit so as they are not to large.
I ought to say i bought the trike as a trike, but having seen the way it is put together i can now say i could do it better myself, so when i post the pics i`ll go through the bits i think could be improved.
Again, thanks to all who replied, it`s great to find a site where the people on it really care.
Good vibes and thoughts to all, take care.
Triker Boab.