Jetting question

[MAXIMAN]

I've been researching jets for various 1100 models. According to the OEM parts schematics...

I noticed for:

79 XS - Main------137.5
80 XS - Main-------125
82 XJ - Main--------112.5

As far as I can see they all have the same carbs and same engine so why the radically diff jets???

I know my XJ sure seems lean. I also know my 80 Special has way more "kick" than Zilla. I assume the main difference is jetting.

Any explains....anyone??

WOuld it hurt to jet Zilla same as Kong?

[John]

The big difference between the 79 and 80's is that the carbs are different internally, with different passages for the pilot circuit. The pilots in the older carbs get there fuel supply from the main jets in the older carbs, and they have there own supply in the newer carbs. The main nozzles are configured differently also, due to the changes in the pilot circuits. I don't see why you couldn't increase the size of the mains for the XJ. I used to have an XJ engine in my 80SG for many years. I used the carbs for the 80, and then I changed to some 78 carbs. I had no fuel problems at all with that setup. I don't think it would hurt anything to increase the jetting up to that of an 80 model, but don't go any bigger without changes to the intake or exhaust systems.

[MAXIMAN]

Ok...so even though the carbs may look alike on the outside...the guts are different.

Well I assumed the 80 XS was same as 82 XJ. I had planned on using a K&N for the Maxim and drilling out the air box......But I can't find a K&N for the 1982 XJ1100. I do know the filter box and element of Zilla is totally different from KONG.

[John]

It seems that the air filter for an XJ is indeed a rare beast. I know Uni does not offer one, but have you looked on ebay? I parted out two XJ's but neither had a filter, and one of the airboxes was missing the access cover for the filter. I recently discarded the the airboxes. I had no use for them, if they were incomplete. You may be able to 'adapt, modify, or jury rig' the airbox to hide some individual filters, if you should decide to go that route. An XS airbox will not fit into an XJ frame either.

[chevy45412001]

jetting

john is right on this one.DON'T rejet the XJ without first doing some kind of modifications to either the intake or exhaust side of the coin.i to this day am kicking myself for dumping the stock air box.Just seems like the factory was spot on with the setup they had. Still have not got back the arm pulling from socket power i was used to.I am currently running a 137.5 jet,raised needle,4 pod filters (no names) and 4-1 kerker header. I was all the way to a 155 main, wow. still want to go a tad smaller this coming season,plugs a lil black.

[MAXIMAN]

No doubt the air intake for the XJ is hard to find parts for. Paper filters are pretty common still. I've gotten them through Bike Bandit.

As far as the jetting is concerned...137.5 would be a huge step over the stock jets now on my XJ...which are an anemic 112.5. I am certain that is why the exhaust on my Maxim are so hideous looking. They have blue and turned the typical "burnt" brown from a lean F/A.

I doubt I would go anywhere near 137.5 but probably step up to 125 like my '80.

And speaking of arm pulling power...Kong has it....Zilla really doesn't. Zilla runs good but nothing like Kong and I really can't see much reason why other than jetting and advance.

thoughts?

[John]

Jetting, compression and timing are all different than on the XS. That changed a few times over the different XS models too. Don't go as big as 137.5 Try around 120-125 range.

[MAXIMAN]

.oopz

[MAXIMAN]

John

You seem to be well informed of the differences between the XJ and other XS models.

I've heard the XJ had a retarded timing curve. True?

Also have you ever used a performance CDI or TCI? There's a company out of Auckland that builds a igniter for the XJ and XS that they claim has hotter and longer spark with a modified timing (advanced) curve. Ever hear of it?

[MAXIMAN]

more jet questions

A little research at the Yamaha OEM Parts site reveals:

78, 79 and 82 employed Air Pilot Jets.

80 and 81 did not. I'm sure there was a port that sucked air but no removeable jet. Why?

Also...in general....as time progressed the jets got smaller...WHY? Was it emissions? And also...did 78, 79 , and 82 have same carbs while 80 and 81 had different carbs?

1978
main - showed three diff sizes (130, 137.5 & 140)
Pilot - (45)
Air pilot - (210)

1979
main - (137.5)
pilot - (42.5)
air pilot - (180)

1980
main - (125) #2&3 (120) #1&4
pilot - (42.5)

1981
main - (110)
pilot - (52.5)

1982
main - (112.5)
pilot - (47.5)
air pilot - (170)

[skids]

Re: more jet questions

The 81H carbs that I have contain 185 air jets. I am fairly sure the 80sg also had the same. I do not know if they are stock... The threads are different from the newer carbs (80 and 81) compared to older carbs (78).

Originally posted by MAXIMAN
A little research at the Yamaha OEM Parts site reveals:

78, 79 and 82 employed Air Pilot Jets.

80 and 81 did not. I'm sure there was a port that sucked air but no removeable jet. Why?

[MAXIMAN]

Now that you mention it that's right. The OEM parts list doesn't show a replacement for the air pilots...but I remember vividly when I rebuilt the carbs on my 80 SG (Kong) it definitely had air pilot jets. But they don't show it in the parts that I saw on microfiche.

[chevy45412001]

Maximan

if you are looking for jets let me know. I have a varied assort. in that 120-127 range. There yours for a self addressed stamped mailer or envelope or whatever. (would'nt suggest enevlope they get stuck in post office machines. If interested e-mail or pm me. chevy45412001@yahoo.com. Remember to put xj in title or i delete. also mine had the 112.5 stock but i got to a 137.5 by drag racing the snot out of her.it runs the fastest so far with 137.5 but i'm going down a few myself.

[RS Thornton]

maximan,
I looked at your jet list for the 78 and have a question. Does that mean that some carbs that have the same internals have differenent mains? I have a set of parts carbs and I noticed that they have 130 mains, I was assuming that the carbs are interchangeable with the set that has 137.5
The pieces seem to switch OK, but if I would the carb bodies be interchangeable too?

My clymers shows a different p/n for the sf carbs, but I always thought that was because of the those shiny caps on 1 and 4 carb.

one final thought, is there any identifying marks to tell you what carb you have?

[MAXIMAN]

Thornton,

I derived that list strictly from looking at all the carbs for all year models of XS and XJ. The parts list is at the Yammy official website. It shows the different jets for the different years. best I can tell some of these parts are interchangeable...some are not...as some years had different bodies. This is evidenced by the fact that years '80 and 81 appeared to have no removable air pilot.

I can only assume the air pilots on these models were pressed in or fixed.

I'm not sure if there are any specific marks that would show this. I am certain somebody on this magnificent forum will no doubt be able to answer that.