i admit i need help

[BhamminXS]

i have an 81 xs850 motor final drive etc. on a 79 xs750 frame using the wiring harness from the 79 as well and carbs. my issue is after 8 months of putting bike together i have spark but thats it .was i supposed to do something to make everything work since im usung the 79 harness on a 81 engine

[IanDMacDonald]

Howdy from a fellow 750/850 owner

Wrong site. This is the 750/850 big brother's site. However, it's pretty much a straight swap. Are you using the Hitachi's from the 850, or the Mikuni's from the 750?

[IanDMacDonald]

You'll need to bump those jets up on the pilot and main circuit.

[kboehringer]

79 harness on a 81 engine

BhamminXS,
Shoot a note to member "Radioguylogs". Mike has a couple of those and is likely a very good source for XS750/850 information.

I have ABSOLUTELY NO IDEA if Yamaha did similar upgrades/changes to its 750/850 in '81 as it did to the "Big Brother" XS11.....BUT the mechanical advance and CDI were changed so if your combining any of those parts on an XS11 across those years you're in for trouble. I know it would be best to discuss this with a person with REAL knowledge, not a guesser like me on this topic.

Mike would very likely be a great source of solid and correct information.

Sincerely,

[IanDMacDonald]

I have two 750's, and three 850's.

It's a straight swap. His only issue would be if he had a '77 2D, which did not have electronic ignition, but he's using the '79F engine. He's got spark, he's got fueling issues. The '79 used the better MK II's. As I said, you'll need to increase your jet sizes.

[Radioguylogs]

Spark Timing?

I don't see any inherent reason why your combination of parts wouldn't work.

One common problem is the timing key on the end of the crankshaft is a small pin that can slip too deeply into the crankshaft, allowing the timing to be wrong.

Apparently, you are using the Mikuni carbs on an engine that had Hitachi carbs when it was built. Like Ian said, it's not a problem...just need to adjust the jet sizes for the larger displacement. You can find the information by searching on the Triples website:

http://www.yamaha-triples.org/category-view.asp

If the valves are in good order, and the engine is getting gas, and there is a spark, then it seems the spark timing is in left field.

[BhamminXS]

I understand these are the xs1100 forums but thought I posted u
Under the other bikes discussion forum

[3Phase]

I understand these are the xs1100 forums but thought I posted u
Under the other bikes discussion forum

You did and you're good, don't sweat it.

[IanDMacDonald]

Mike is referring to the "reluctor". It fell out on me before too, and caused a no-start condition.

[Radioguylogs]

Picture of the pin

I was thinking about the pin #9 in this diagram:

http://www.partzilla.com/parts/searc...NOR/parts.html

Until I looked up the '81 models, I had no idea the three pick-up coils changed to discrete parts in place of the 3-in-1 module used in '78-'80.

[IanDMacDonald]

Yeah Mike. I remember the issue of those pins "disappearing" into the case for many forum members.

[BhamminXS]

mike are you saying one of the pins themselves could of fallen out maybe when i switched out the frames seeing as i did it alone using the lay on side and remove frame method,( was the only way i had actually). Ian ive been through both repair and owners manuals and nowhere did i see mention of a reluctor, im so confused now.

[BhamminXS]

just trying to sort out things, so i need to go big on the jets , both jets or only the mains, and the coils since i used a 79 harness and coils ( they came off the same bike and they are three separate coils not a three into one setup so where do i go with that?

[BhamminXS]

nevermind ian on which jets ui see the post on both pilot and main jets

[BhamminXS]

the mains im good on as i ordered the right size from the yamaha dealership but ive been told that might not be a safe bet anyways as the dealerships dont use mikuni jets so it could still be wrong if thats the case does anybody know where i might quickly find and get mikuni jets?