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Author Topic: Yamaha XS750 1977 Help :(  (Read 1655 times)

Offline afr00t

  • Posts: 17
Yamaha XS750 1977 Help :(
« on: May 14, 2013, 21:50:17 »
I recently got a 1977 yamaha xs750 and was told by the seller that the reason for it not running is because the carbs are gummed up. So the first thing I did was that I cleaned the carbs perfectly and when I put the carbs back on the bike it would either start and backfire like crazy or just won't start at all. I'm pretty sure that the issue that I'm having is with engine/spark timing but I'm not sure of how to check either.   PS: the previous owner installed electronic starter/points on them and from what I've heard that they're not adjustable. Anybody got experience with xs750 triples timing that might give some tips? appreciate it

Offline hillsy

  • Posts: 4117
Re: Yamaha XS750 1977 Help :(
« Reply #1 on: May 14, 2013, 23:18:59 »
You'd be best off getting a workshop manual for starters.
 
If the PO has mucked around with the ignition.....and there's backfiring.....there's a good chance he has the coils firing in the wrong order.

Offline halminator

  • Posts: 26
Yamaha XS750 1977 Help :(
« Reply #2 on: May 15, 2013, 03:36:24 »
You'd be best off getting a workshop manual for starters.
 
If the PO has mucked around with the ignition.....and there's backfiring.....there's a good chance he has the coils firing in the wrong order.
x2
Yamaha XS750

Offline afr00t

  • Posts: 17
Re: Yamaha XS750 1977 Help :(
« Reply #3 on: May 16, 2013, 12:46:56 »
Thank you guys for the responses. I tried switching the spark plug wires around to make sure that the coils aren't switched around and firing in the wrong order but they seem ok because the way i have them now gives the chance a chance for the engine to start if i kick the bike over 20 times but when i switched them around it wouldnt fire at all.
Is there perhaps a way that I can figure the correct order of them and which coil belongs to which cylinder?

Offline hillsy

  • Posts: 4117
Re: Yamaha XS750 1977 Help :(
« Reply #4 on: May 16, 2013, 20:21:45 »
Next question - do you have a fully charged / good battery in the bike? It won't start without a battery even if you are kickstarting it.

Offline ApriliaBill

  • Posts: 846
  • Yeah...I'm old school.
Re: Yamaha XS750 1977 Help :(
« Reply #5 on: May 16, 2013, 23:21:58 »
Not that these guys can't help, but I spent a good amount of time on http://yamahatriplesuk.myfreeforum.org/sutra2406.php. I started with a triple that spent a couple decades in a museum, they talked me through everything and had the bike up and finished in three weeks...
"Do not neglect to show hospitality to strangers, for by this some have entertained angels without knowing it."

Offline DrFalken

  • Posts: 8
Re: Yamaha XS750 1977 Help :(
« Reply #6 on: Apr 30, 2014, 22:44:51 »
http://www.yamaha-triples.org/portal.asp

The "sister" site to the UK site is also great resource as another triple specific site.
1972 Suzuki GT750 LeMans - R.I.P.

2008 Suzuki C109R Boulevard - The commuter

1977 Yamaha XS750-2D - The skitzo mistress that puts you away with pains in places good common folk should never feel...


Offline matt.k

  • Posts: 13
Re: Yamaha XS750 1977 Help :(
« Reply #7 on: Sep 02, 2018, 01:04:56 »
I had similar problems with my 750. I got an online manual from here which helped a tonne. http://www.yamahatriples.com/files/5613/2786/4749/Yamaha_XS750_Service_Manual.pdf

If you pull the seat/tank you should see the three coils. The cylinders are numbered 1-3 from left to right when sitting on the bike. The coils will be mounted in a similar orientation ( the farthest left for cylinder 1 and so on ).  There are a few ways to make sure the wiring running to the coils is done right, each should have a red wire and then either orange, grey or yellow. From what I remember the wiring diagram in the manual is not much help in this department. I recall unplugging all three plugs leading into the coils, taking a spare spark plug and plugging it into the lead from the #1 coil and resting it against the engine, then trying the each plug leading into the coils until I could see spark when pressing the starter. Repeat for #2 cylinder and by process of elimination you will have the #3 cylinder sorted.

As for timing, pull the left side cover from the engine to see the timing unit and governor. On mine there was three screws holding in the plate that the triangular black box is on, which is essentially your pickup coils for each cylinder. Loosening the three screws will allow you to rotate this plate. The trick is the timing marks are on the governor plate behind the gold plate, and it has only one position on the crankshaft.  This makes it very tricky to do without a timing light. The manual in the link above only has points timing however it has good info on timing mark meaning and factory specs for advanced and retarded settings.  I had to do a lot of trial and error along with reading in forums to get it sorted sadly, so I hope if you still need this info this steers you in the right direction at the very least.

mK