igniter boxes

[SFSPECBIKER79]

is the 80 and 81 xs 1100 black boxes interchangeable, the only difference is 80 has 2h7, 81 has 4ro stamped on them, the part nums. are the same on yamahas parts lookup.

[DiverRay]

NO they will NOT interchange! The 2H7 has the vacuum advance, and mechanical both on the crank. The 4R0 has the vacuum as part of the box, IIRC. The "part number" you are looking at is only the middle of the number. 2H7 and 4R0 are BOTH prefix numbers for the parts. Normally Yamaha kept the prefix from the fist year model the part was used on, but they would change the prefix if they made a minor change for a later year. Some of the changed parts, such as oil filters, will still work on earlier year bikes. Other parts, such as the TCI box, will not.

[SFSPECBIKER79]

NO they will NOT interchange! The 2H7 has the vacuum advance, and mechanical both on the crank. The 4R0 has the vacuum as part of the box, IIRC. The "part number" you are looking at is only the middle of the number. 2H7 and 4R0 are BOTH prefix numbers for the parts. Normally Yamaha kept the prefix from the fist year model the part was used on, but they would change the prefix if they made a minor change for a later year. Some of the changed parts, such as oil filters, will still work on earlier year bikes. Other parts, such as the TCI box, will not.

thanks diverray, wasnt sure, so now, i know. wantin to help member get his ride going.

[DiverRay]

No problem, but the 4R0 IS hard to find. IF you change out the left side of the crank, and put in the earlier advance and vacuum bits, you CAN use the earlier 2H7 box. IF there is a "spare parts" engine nearby, that can work.

[crazy steve]

Actually, you could use the 4R0 box on an early motor. The difference is the 4R0 has the 'mechanical' advance built-in (done electronically) but still uses the same vacuum advance. To use the 4R0, you'll have to 'lock' the existing mechanical advance so it can't move, set your timing to the correct initial mark and you should be good to go.

But the only reason for doing so would be if you had a 'spare' 4R0 box and couldn't afford to get the right one. Like Ray said, they're hard to find....

[bikerphil]

Ok, similar question. Gonna be working on a 79 Std, replacing the engine with one from an 81 Special. I have a 4RO TCI, can I plug it in the 79's wiring harness and use it that way or do I have to change the ign. plate over and stay with the 2H7 TCI?

[crazy steve]

I don't see why not. Now mind you, I haven't personally compared these for differences (but I've seen numerous references to the fact that they will interchange but work badly with the 'wrong' motor), but if the wiring plugs match up (or can be made to match by moving a few wires) it should work. IIRC, the '81 uses 3 ohm coils, so you'll have to swap to those and may have to do something with the ballast resistor wiring. But none of these things are insurmountable, so this should be doable...

[bikerphil]

Yep, the 79 has 3 ohm coils already. Thanks Steve, I'll give it a try. Sorry for the hi-jack.