Help bring an old flat track racebike back to life!

[gggGary]

I'm loving it!
Sorry, re; the reality of running that rocket on the street. Sounds like it'd be a hoot!
You may have to mix and match motor mounts a bit. Front mount will probably need to be custom made. The mount hole on the 70-71 is a bit further back than later motors because the engine casting changed there. 10mm diff. IIRC.

 

[Apexdc]

That was what I was thinking. I didn't remember what it was but there was something nagging me that the later motors were different.

Thanks for the help. I was thinking of doing a later motor so I could get electric start. I know it is not a great starter, but better than trying to kick this sucker! If I can't ge the motor mounts to work, I might look at building a lower compression motor. I don't really want to try to calm the original motor down. The good part is that it SOUNDS TOTALLY BADASS!!!!! It revs INSTANTLY!

 

[gggGary]

Thanks for the videos! IMHO that idle (mabie pilots?) sounds lean. Might slap some air filters on it? and see how it idles with them.
Thinking out loud, lean idle mix may be more of an issue than light flywheels. That said like you feel, some race cams are radical enough to prevent decent running at idle. But I'd make a shot at richening the idle.
Um just cuz; VM carbs have an air screw for idle mix, tightening the screw richens the mix. 3/4 turn out from lightly seated is the initial setting, adjust it in to richen the idle. HTH
Have you documented all the jets, needles, slides, in those carbs?

 

[YamadudeXS650C]

I can't verbalize my appreciation of your sweet bike better than Gary:
"I'm loving it !!"

As a matter of fact, Your bike has adorned my winter workshop since it appeared in the calendar.
Visitors have asked me, "So where is that great motorcycle, in the living room?"

 

[Jim]

Agree with Gary... sounds lean at idle.
Love the way it revs though.

 

[Apexdc]

Hi, Jim, Dude and Gary!

As usual, it is such a great pleasure and honor to have so much support of the old gal!

I had the idle screws set at 3/4 out. I normally have K&N filters on, but have been keeping the carbs synced using drill bits for indexing, so had the carbs off. I'll try first with 1/4 in on each carb and go from there. I am a decent amateur mechanic, but know nothing about these bikes. I'm learning, though!

I will have to check back on my notes on jets. The bike was run in an area that is about 4500 feet in elevation. I am about 400 in Palm Springs, so I had to make significant changes, but dont recall where I ended up.

Sure, I love working on bikes and cars, but this journey has been so much more than just shop work.

I was so lucky that my friend, Larry Baughman, sold me the bike, essentially entrusting me with her resurrection.

I will do a followup shortly on her history. I am still working on that. When I bought the bike, neither Larry nor I knew anything about the past. I now know who originally built the bike, who did the paint and have talked to three different guys who raced her, including the 1976 Pike Peak run. Lots of old pictures, too. When I have it organized, I will post a wetransfer link for the pdf download.

In closing,

Dude, that makes me feel so good to see the picture in your shop. This has all been a labor of love and it has been so great to have so many traveling companions as we all chug along on this journey.

And, I have no garage queens. A few years ago, I did a massive restoration on a heavily modified 92 Ducati 900SS. I have had the bike twenty years now. After the restoration, it was perfect, perfect, perfect. FAR better than new. I showed it once at the Quail Motorcycle Gathering and after that a close friend asked me what I was going to do with the bike and I said, ride it, of course.

My whole trip on getting Prom Queen street legal is because I want to ride the bike, not let it sit in the garage. If I did that, it is just a dead thing. No bueno!

Thanks so much, guys!

 

[Apexdc]

I just went back through my notes on how the bike is jetted now. Oh, I just refitted the K&N filters and closed the pilot jet down to 1/2. It was at 3/4 out.

At 4500 feet, the bike had a 35 pilot and a 150 main. My elevation is about 400 feet, so I fitted a 190 main and a 22.5 pilot. I also have a spare 20 & 25 pilot.

Slide is a 2.0, floats at 23mm, Needle is a 6DPI (I think). I also think it is in mid position, but am not positive on that. Would need to check to be sure.
Plug is BR7ES NGK, set at about .7mm or .026".
Valve: Int-.004+ Ext-.006

I will give it another try tomorrow. It has always started on first or second kick. I have race gas in it, but am also wondering if it has lost some of its POP.

Oh, bike has no chokes. So, I am kicking through once with throttles closed, ignition off, then ignition on and kicking again with throttle cracked a bit.

Again, thanks for all the help.

 

[gggGary]

190 main
22.5 pilot. I also have a spare 20 & 25 pilot.
Slide 2.0
floats at 23mm,
Needle 6DPI

My fairly similar, hot cam 750 is set like this.
Carb: VM34
MJ: 180
PJ: 25
NJ: 159-P6
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: ?
Float valve 3.3
So you might try going up to 25 on the pilot?

 

[Apexdc]

I gave it another try this morning. It was coolish here around 58 degrees and cloudy. After kicking several times, I couldn't even get a cough, so sprayed some starter fluid into each air cleaner. It then fired up fine and idled much better. It also sounds better, more solid and not so "hollow". I have experienced that in the past on bikes running lean, but normally I knew what they sounded like when running right.

So many thanks to those who suggested richening up the idle circuit.

I rode it for a mile or so and than came back to the house. When I got to midrange, it was breaking up and not wanting to rev more. I pulled a plug when I got back and it was dark tan. Not too bad. At least not white or black.

I have it up on the stand now, as the throttle cables are catching up somewhere. When I turn the bars to the right, it revs up quite a bit. I'll get it sorted out.

Oddly, the kickstand I had made by Trackmaster broke! It is pretty thin material. I will send it back for a redo.

 

[Apexdc]

I pulled one of the jets and it has 180 mains in it now. I took what was left of the choke out on one and it is the style choke that uses a cable and it had been plugged. I can clear the plug, but think it would be better to just fit the chokes with a lever on each. They appear to be readily available. I'm thinking it was just too cool for it to start easily, since it fired right up when I hit it with some starter fluid. The last time I started it in the video, the weather was a little warmer.

I think I have the throttle cables sorted out. I thought that letting them sort of run free would be better, but I ziptied them tight to the top frame tube and all seems ok now.

I'm not giving up yet on running this engine on the street!!

 

[YamadudeXS650C]

I pulled one of the jets and it has 180 mains in it now. I took what was left of the choke out on one and it is the style choke that uses a cable and it had been plugged. I can clear the plug, but think it would be better to just fit the chokes with a lever on each. They appear to be readily available. I'm thinking it was just too cool for it to start easily, since it fired right up when I hit it with some starter fluid. The last time I started it in the video, the weather was a little warmer.

I think I have the throttle cables sorted out. I thought that letting them sort of run free would be better, but I ziptied them tight to the top frame tube and all seems ok now.

I'm not giving up yet on running this engine on the street!!

Would love to see more videos !
I shared your previous ones with friends; they are loving it !

 

[YamadudeXS650C]

I pulled one of the jets and it has 180 mains in it now. I took what was left of the choke out on one and it is the style choke that uses a cable and it had been plugged. I can clear the plug, but think it would be better to just fit the chokes with a lever on each. They appear to be readily available. I'm thinking it was just too cool for it to start easily, since it fired right up when I hit it with some starter fluid. The last time I started it in the video, the weather was a little warmer.

I think I have the throttle cables sorted out. I thought that letting them sort of run free would be better, but I ziptied them tight to the top frame tube and all seems ok now.

I'm not giving up yet on running this engine on the street!!

I'm not giving up yet on running this engine on the street!!

Go For it, dude !!

 

[Apexdc]

When I get it going again, I'll do more video! Thanks for the support!

 

[Apexdc]

OK, here is a new twist! In working on the history of the bike, it has now come into question whether the bike is a 650 or 750. There are two people who ownded it that now don't agree on that. Also, there is a possibility that someone who owned it after them might have made it a 750.

Soooooo, my question is, is there a way to check the displacement without taking the head off? I understand the principle of cc'ing a motor. The stroke would be known, so by knowing the amount of liquid used, the bore could be calculated. EXCEPT, I would need to know something about the volume of the combustion chamber, piston top shape, etc.

Any ideas?

Thanks, as usual.

 

[MrBultaco]

Find someone who has a stock 650 and ride it. Even a hopped up 650 won't be the same as a hopped up 750.
___just my

 

[Apexdc]

Not a bad idea, but my bike probably weighs at least 100 pounds less. Having said that I think the character of the motor would still show.

I did find this:
http://www.xs650.com/threads/750-kit-your-opinion.3151/#post-33372
Which is on answering that question.

At the end of the day, taking the head off is probably the most straightforward way. Doesn't look that bad.

 

[Jim]

At the end of the day, taking the head off is probably the most straightforward way. Doesn't look that bad.

Some of the old race bikes had their head studs slotted so the head could be removed without removing the engine. Might be worth taking one of the acorn nuts off and have a look.
Have a read here.

 

[Apexdc]

I will check it out. I know they used to change cams with regularity and it looks like there might be enough room to remove the head without pulling the engine, but they might have just removed the studs like you are showing.

Really good info, thanks!

 

[Jim]

On some of the old Honda's I worked on, they used a reusable master link on the cam chain. So you might get lucky there too.

 

[Apexdc]

I was wondering about that, as I knew the original was pressed and had to be ground off. I am in contact with one of the last owners. I will ask him. He told me he did cam changes.

Thanks,