1979-80 XS 750

Look what jumped on my trailer, I have to stop putting that empty trailer on my car. Anyway, this was a Facebook find, another sad story of a Grandfather passing and he had not driven her for at least eight years. I could not see from the pics on Facebook what size it was, so just took the 1 hr drive to see.

After talking with the young man we came to a deal and as I said above it jumped on the trailer. It is frozen up and for all I know it could be a blown motor, but there is oil in it still and gas tank is not too bad off.
20200305_180322[1] by Tim Brown, on Flickr
20200305_180309[1] by Tim Brown, on Flickr
20200305_180253[1] by Tim Brown, on Flickr
Oil cooler on this bike and a 4-1 header, looks to be in good shape.
20200305_170727[1] by Tim Brown, on Flickr
Also the normal critter stuff and that fuse boxes look to need a little TLC.
20200305_170543[1] by Tim Brown, on Flickr
And for all you VIN hunters
20200305_170235[1] by Tim Brown, on Flickr

 

That's a cool bike. It's a 1977 xs750D

Here's some info on the model line:
https://en.wikipedia.org/wiki/Yamaha_XS750#1977_XS750_“D”_and_“2D”

Tony

 

Thanks for looking that up, I am sure I will be a fun project to get started on. Need to soak the cylinders for a good week and hope to brake free the rings. I see from the pics that one header down pipe might have a split. #3 I think. Plenty of bad weather around here still so not too many bikes on the rd.

 

Sure wish I could change the thread name now to a 1977 XS750D.

Today was a good day, for the most part. Aired up front tire so I could more her, didn't help that much. Had to take off both front calibers to free up the front tire. Used compressed air to blow all the critter food that was in the battery frame area. Lots more came out than I could see. Put her on the table and started. Removed seat, carbs, air box (didn't find a place for filter will have to look at parts list), added mixture to all cylinders and took lunch. Came back and put in a new fuse box and started to trouble shoot power, lights. Got on her and put some pressure on the kick starter, it moved a little so I just let it slowly move and did that a few times. It came free and sounded good with no grinding or crunching coming from engine.

Looked up some wiring for the key switch as this bike has none. Red, Red/white (tied them together), Br, Bl and Bl/R (tied them together. Put power to the bike lights came on and no smoke or melting insulation smell, always a good sign.
DSCN0004 by Tim Brown, on Flickr
Trouble shot the swx for a while and I can get a good ground on one side of the solenoid connector, not sure what I should be reading on the other side. Jumped the solenoid and she turned over but no spark.
DSCN0008 by Tim Brown, on Flickr
Yes this old beast has points, not too sure how happy I am with that. Didn't pay much for the bike so if another day of trouble shooting for spark does not pan out, might just part the bike. Another interesting wiring job on a voltage reg.
DSCN0005 by Tim Brown, on Flickr
And at this time have no idea what this is.
DSCN0007 by Tim Brown, on Flickr

I have no power or spark coming from any of the three sets of points. This is one of those bikes that will turn over even if the emergency stop button is turned to stop, the button just kills the park. So three separate coils with three sets of points, this is going to be interesting.

 

Nice find.

 

Congrats! Pretty cool trailer to drag around and have neat stuff jump on to it. That motor is just 3 cylinders isn't it? I have never had one or ridden one but always wanted to. If you have a title for it it would seem a shame to part it out. Come to think about it I have a luggage rack hanging around in the barn that could be had for the price of shipping... there, now you have to rehab it.
Have fun and keep us up to date.
John

 

I will be looking into testing all the fun electrical bits tomorrow. Start off with the points, condensers and then coils. I think I need to track down the power issues going to the points and coils to make sure I have 12V. Give the points a little sand paper to take off the glaze of time. I just don't want to have to throw a lot of parts at her. I did know what I got into when I first saw it and having the engine stuck I knew it could be a basket case. Once I find spark I will take the time to do the carbs up nice and church clean.

 

Well the good and the bad...Good found this right away today, the PO had it taped together under the swx but not soldered. I soldered it, re-taped it and now the starter swx ckt works!
DSCN0009 by Tim Brown, on Flickr
Started to trouble shoot the spark, had spark on one cylinder but two were dead. A little 1k sand paper to the points, a quick check for voltage 8.96 V that seems low I think it should be 12V both at the points and the coils. It was not 12V. So before you say I have a bad batter (as is normally the case) I have a new car batter with 850CCA attached by way of jumper cables (and not the thin ones). From the pics above you can see that the OEM rectifier was replaced by another. I will have to check that out next but I still had to try to start her.

Got into the carbs a little, I just wanted to clean them enough to see if it would start, even on starter fluid I would be happy. I got a few pops and a little smoke, no running. But look what I found in #3 carb.
DSCN0011 by Tim Brown, on Flickr
I would guess this from ethanol sitting in it for long time? Something eat through one of the float post and eat one of the two floats off the brass holder. Took a long time to get that pin out of there without breaking there other post/tower. As for the float that will come at a later time but I had a good replacement around.
DSCN0012 by Tim Brown, on Flickr
Guessing the cast just devolved and ended up at the bottom of the bowl. I had the carbs in water and Dawn for a while with very warm water to clean them up. That could be the reason for white to be not dry and flaky.

Give it another day and see what she does. I could put a generic five (5) wire rectifier in and see if the voltage to the points and the coils jump to 12V. If not, I don't think the ignition system will work with such a weak spark.

 

A points ignition will make a spark. It will be a weak spark and not healthy and blue, but a spark none the less with that little bit of voltage. Points don't care. One of the good things about points.
That carb sets a new record I think. Even worse than that rack that I gave Hogfiddles and he posted about.
John

 

Next step will be looking at the wiring on the rectifier, remove header (lots of critter stuff in there from sitting outside). Still con confused as to why I am only getting 8V at coils and points but for now there is spark.

Those carbs are so nasty I don't even know if that one is savable. I guess I will have to look on line to see if I can replace for cheap or just start to take the bike apart and get shipping estimates. Two good days of working on her and she has potential but if she will not run will not spend time on the rest of the bike. Still have the Seca to work on yet.

 

Did a bunch of electrical work today, the plug caps were not showing any connection at all. Wide open some how, so got them to work or swapped out with something I had in the shop. The coils are good all read about the same. All the wires that were twisted together and taped have been converted to crimp or improved with electrical twist tops and grease. Checked the rectifiter and it works! So re-wired that with more current connectors and cleaned things up.

Did a comptression test and was not happy:
1=100
2=80
3=80

Tried to fire the bike with no carbs on her and just starter fluid, got a few pops and a flame out of #2 but that was it. Not looking good for a short turn around bike project.

I have to admit, I am not a big fan of points. I thought this bike was a newer model and not the 1977, but for the price I got it. So now comes the rub, not really feeling this bike. I mean it would be great to have a little 3 cylinder in my inventory and maybe even make it look good. But with the points and pain the but trying to get them even to spark correctly is and has been a few days work. The compression worries me but I have not check the valve clearance yet, work almost solely on the electrical and cleaning up the wiring.

I have thought about buying the CDI and pickup off ebay and converting the bike, but then will be about $150 investment, not too sure if that is prudent for this bike. Looking like selling for a parts bike or parting her out. Just hate to give up on her.

 

While not a big fan of points they do have advantages. A couple of years ago I re-acquired my Moto Guzzi California 2 that I bought new. I had put a Dyna 3 electronic ignition package on. In the years it sat in between the control box went bad. The points plate was still hanging in the garage, was found and immediately lit right up when put back. Sparks at least as well as the Dyna did.
Looks to me as though that carb issue will be the sticking/tipping point for rehab or part out. Sad that. They were unusual enough to be difficult to find a decent, cheap replacement. Good luck.
John

 

Check valve clearance today, only #1 intake is off by one size the rest are in spec. Rechecked all the coils and they are right on, but the spark plug caps are throwing me off. In the test it says primary and secondary should be 11K ohms +- and I have 10.8K ohms on all three. Here is the kicker, that is with the spark plug caps off. With them on the value goes way up. I might have to forgo the resister in the caps and just put a copper jumper instead of the resister. In the mean time going to let the rings soak some more to see if they are all frozen. The bike was seized up when I got it so the rings still might need to soak for a week. Take a look at the fine and see if my interpretation is correct, from primary or secondary through the cap should be 11K ohms?

 

My opinion is that your coils are fine. If you have some other known good caps I would put them on and try them, measure your resistance only after you have confirmed spark and not worry too much about the values. When you have confirmed spark put the questionable caps on and see what happens.
John

 

Yep it was the caps! Gutted them and just put thick copper wire in them to bring down the resistance to minimal. Now have great blue spark on all three! Wonderful. I will let her sit for a week to see if those rings let loose some and I have to work on one bold that broke off on the valve cover. Only one so I am happy and I can more or less get to it. 40 + yr old bike and not too nasty of bolts so far.

 

So while I am working on getting the rings to loosen up, I have looked at the exhaust. This has a old kerker system on it. It has been painted to death and the inside of the muffler is shot. I have been looking at some replacement baffling to get the should to be a little lower. If and when I get the end cap off I will have to pickup some exhaust baffling and see what I can do to replace what has rusted out.

 

Productive day, got the gas tank all rinsed out of the Evapo Rust. Got a little Mystery oil in there to keep it from rusting. Took the two petcocks apart, I think 1 will be good the other might work on PRI only. The inners were really dried out, not leaking but just would not flex with suction applied to the suction nozzle. Had a little more energy so went after the front brakes. I knew when I picked the bike up that they were an issues, the good old frozen to the disk and can't push issues. I was surprised how clean the pucks were no pitting at all. The inners were nasty brown crud in various stages of nasty. MC was in good shape and so far is not leaking from the plunger seal. That is normally what I run into when I take them apart and rebuild them, the plunger seal almost always is bad.

PB blaster on the rear brake and MC for that part, looks to be even darker brown through the plastic. As soon as I get the 700 air out of the way I can weld a nut onto the bolt that broke off when taking the valve cover off. I want to see if this bike will run! Pats for the 700 came in today!

 

Got that broken bolt off the head today, rolled the bike into the shop and welded a 10mm on it. Took a little bit as it was right under the frame but got it out. Was able to put valve cover back on this time with some anti seize on them. I just wanted to see if it wold fire with a little gas added to the intake, yes it did. Nice fire now, so one more compression check and then to see if it is worth saving.

 

Congrats on finding your spark! I am working on a 1983 XJ750 Midnight Maxim I picked up from an inmate here a couple of weekends ago. It too was missing it's spark but has now been found.
About your carbs. I was wondering if they are similar to the ones from the XJ's and could you remove #2 or #3 from a bank of 4 to make what you need. Or replace your fouled 1 with a single XJ unit? Any thoughts from Hogfiddles or KMoe?
John

 

Fuller56, if and when I get her to run I will at getting a replacement carb for that one. The tower is not only broken off but was totally dissolved in the bowl. I have not tried to put the float back together yet as I had another spar float to replace it and at least see if the bike will run. At this point I think the compression is still low 100, 80 & 80, if I can't get the rings to free up I am not sure I want to pull the top end apart to get the bike to work. With as much as I paid for the bike I will just part it out. Need to thin the herd but this weather is not helping.