My rebuild journey. (old title: Future owner - Help me identify this 650.)

[Sudonate91]

Yes!! Boy, you are new to this, lol. The mix screw is an adjustable tuning part. You set the screws so many turns out from closed. The more open they are, the more fuel/air mix they allow into the carb (and engine). If you do have them closed up snug, that's why it won't idle and why it's popping so much. Try backing them out about 3 turns, you'll be quite surprised at the difference it makes, lol.

So I turned both mix screws 3 full turns. Now it will idle at about 1200rpms with full choke on. Giving it gas seemed to kill it and letting go of the choke killed it also. I will need to revisit it tomorrow when I can open it up a bit more without waking up the baby.

 

[5twins]

The only other main adjustable setting is the idle speed, done with the screw on the left carb .....

You use that along with the mix screws to achieve your best and smoothest idle of about 1100 to 1200 RPMs when the bike is warmed up. There's also a sync screw between the carbs you use to get them both running at the same speed. For the time being, you should be OK as long as that's close. If you set the idle at 1200 when the bike is cold, it will idle too fast once it is warmed up. None of the cold running speeds are controlled by a computer like on modern vehicles. You are the "computer" on this old bike, lol.

So, it sounds like your idle speed may be set a little too low now. Usually, running on choke produces higher than 1200 RPM running. When you turn the choke off now, the speed is dropping too much and the bike is stalling. So, this is something you're going to need to tinker and play around with. Evetually, you'll get the hang of it and find a good setting. The idle speed will be below 1200 when cold, maybe at like 900 or 1000, but it will start climbing as the bike warms. The trick is finding the setting that will not let it go too low when cold (so it stalls) or too high (above 1200) once it warms up.

You were right about not over-tightening all the other jets. You want them tight just not too tight. I install them using a stubby screwdriver. This lets me get them tight enough without making them too tight.

 

[Sudonate91]

The only other main adjustable setting is the idle speed, done with the screw on the left carb .....

You use that along with the mix screws to achieve your best and smoothest idle of about 1100 to 1200 RPMs when the bike is warmed up. There's also a sync screw between the carbs you use to get them both running at the same speed. For the time being, you should be OK as long as that's close. If you set the idle at 1200 when the bike is cold, it will idle too fast once it is warmed up. None of the cold running speeds are controlled by a computer like on modern vehicles. You are the "computer" on this old bike, lol.

So, it sounds like your idle speed may be set a little too low now. Usually, running on choke produces higher than 1200 RPM running. When you turn the choke off now, the speed is dropping too much and the bike is stalling. So, this is something you're going to need to tinker and play around with. Evetually, you'll get the hang of it and find a good setting. The idle speed will be below 1200 when cold, maybe at like 900 or 1000, but it will start climbing as the bike warms. The trick is finding the setting that will not let it go too low when cold (so it stalls) or too high (above 1200) once it warms up.

You were right about not over-tightening all the other jets. You want them tight just not too tight. I install them using a stubby screwdriver. This lets me get them tight enough without making them too tight.

Should I been messing with the idle adjust or the mix screws at the moment? Since its not idling correctly the natural idea would be to mess with the 'idle' speed adjuster's screw.

Also how long should I expect a 'warm' state. And what is the best way to warm it up? Just hang out holding the throttle at a desirably rpm? 2-3k?

 

[Raymond]

Set tick-over with the idle adjust first.

Screwing the idle adjust screw in, ie clockwise, will raise the tick-over speed. Screw in far enough for the bike to idle without you holding the throttle open. As the bike warms up, the tick-over will rise - you can back the screw out a little to reduce to a reasonable speed, like 1200 rpm. Then you will be able to tinker with the mix screws - do as 5T suggests, wind them both out 3 turns then carefully adjust in small increments to get the highest idle speed. If that is too fast, adjust the idle screw again to bring it down. Then re-adjust the mix screws to get best tick-over. Once they are set, you shouldn't need to adjust these again unless you change something, like the air filters or exhaust.

From now on, it's really fine tuning. When you come back from a run and the engine is hot, set the tick-over back if it's too high. If the bike keeps stalling at junctions for the first couple of miles on a run, bring the tick-over up a little bit.

 

[Sudonate91]

Set tick-over with the idle adjust first.

Screwing the idle adjust screw in, ie clockwise, will raise the tick-over speed. Screw in far enough for the bike to idle without you holding the throttle open. As the bike warms up, the tick-over will rise - you can back the screw out a little to reduce to a reasonable speed, like 1200 rpm. Then you will be able to tinker with the mix screws - do as 5T suggests, wind them both out 3 turns then carefully adjust in small increments to get the highest idle speed. If that is too fast, adjust the idle screw again to bring it down. Then re-adjust the mix screws to get best tick-over. Once they are set, you shouldn't need to adjust these again unless you change something, like the air filters or exhaust.

From now on, it's really fine tuning. When you come back from a run and the engine is hot, set the tick-over back if it's too high. If the bike keeps stalling at junctions for the first couple of miles on a run, bring the tick-over up a little bit.

I imagine I figure this out, but screwing 'in' the screw will make it idle higher or lower?

 

[Raymond]

I imagine I figure this out, but screwing 'in' the screw will make it idle higher or lower?

As I said, screwing the idle adjust screw in, ie clockwise, will raise the tick-over speed.

 

[5twins]

The idle adjustment screw pushes against the arm that the throttle cable connects to. Screwing it in pushes the arm down and that rotates the butterfly shaft clockwise. This flips the butterfly plates open more, both of them because they're connected through the linkage. The sync screw in the middle of the linkage adjusts the opening on the right butterfly plate only. This allows you to match it to the opening on the left butterfly plate and "sync" the carbs.

 

[Raymond]

As I said, screwing the idle adjust screw in, ie clockwise, will raise the tick-over speed.

There's no mystery - you can see what happens, as you turn the screw in, it shifts the throttle arm in the same direction that the throttle cable pulls it. So the screw is doing the same job as you opening the throttle slightly.

 

[Sudonate91]

https://photos.app.goo.gl/nuHrYTsgZthGKYKs6 got her idling!

 

[Jim]

got her idling!

...and the crowd goes wild.

 

[5twins]

Now that wasn't too hard, was it, lol. Sounds pretty good too. No excessive popping or anything. But as I mentioned, you are probably going to need to re-jet a little for that 2-1 pipe, at least on the mains anyway (up a couple sizes probably). If it won't take the throttle and transition from idle into the lower midrange then you probably need a larger pilot jet too.

 

[Sudonate91]

Now that wasn't too hard, was it, lol. Sounds pretty good too. No excessive popping or anything. But as I mentioned, you are probably going to need to re-jet a little for that 2-1 pipe, at least on the mains anyway (up a couple sizes probably). If it won't take the throttle and transition from idle into the lower midrange then you probably need a larger pilot jet too.

I just took her around the culdesac. Didn't get out of first because only the back brake works. Seems alot more aggressive than I was imagining. Clutch seems to be released pretty well. I am having a hard time finding neutral but that's probably practice. The starter doesn't seem to grind as much either

 

[Jan_P]

Mr 5twins is a genius
Now just to be on the safe .. ..side ....What Oil did you pour in ..I get the feeling it is running a bit hard / heavy / rough on the cylinder heads
Does not know how these pipes affects
If the oil is OK No supermarket low budget .. fix it all .. Snake Oil ... Dishwasher out of specs smear
Then perhaps a valve check / adjustment could be something on the To Do list

 

[Sudonate91]

Mr 5twins is a genius
Now just to be on the safe .. ..side ....What Oil did you pour in ..I get the feeling it is running a bit hard / heavy / rough on the cylinder heads
Does not know how these pipes affects
If the oil is OK No supermarket low budget .. fix it all .. Snake Oil ... Dishwasher out of specs smear
Then perhaps a valve check / adjustment could be something on the To Do list

I put the following in it. I really wanted to put royal purple in it but you cant get that at autozone in 20w50.
Castrol GTX Engine Oil Conventional 20w50

 

[Sudonate91]

Now that wasn't too hard, was it, lol. Sounds pretty good too. No excessive popping or anything. But as I mentioned, you are probably going to need to re-jet a little for that 2-1 pipe, at least on the mains anyway (up a couple sizes probably). If it won't take the throttle and transition from idle into the lower midrange then you probably need a larger pilot jet too.

What are the signs of needing to modify the jet? How does one know which jet to go with?

 

[Jim]

I put the following in it. I really wanted to put royal purple in it but you cant get that at autozone in 20w50.
Castrol GTX Engine Oil Conventional 20w50

Unless that can says "Motorcycle" or "for wet clutches", you'll want to drain it out of there today. It has slickness modifiers that don't play nice with wet clutches.

 

[Sudonate91]

My next thing is the front brake now. I imagine

Unless that can says "Motorcycle" or "for wet clutches", you'll want to drain it out of there today. It has slickness modifiers that don't play nice with wet clutches.

Good to know! Now that it runs and I am gonna go full blown restore. I will order proper oil. Probably good to use this cheaper stuff to flush it out anyway(hopefully). I also gotta still fix that bottom filter since it is blown out on one side. Do you have a recommendation on oil I could purchase online?

 

[Sudonate91]

Any recommendations on how to get the front caliper going? I see some kits on mikexs. The master cylinder is scuffed up from the bike being dumped so I might just replace it all. The I probably will try to rebuild the caliper is possible.

 

[jetmechmarty]

Unless that can says "Motorcycle" or "for wet clutches", you'll want to drain it out of there today. It has slickness modifiers that don't play nice with wet clutches.

20w50 is usually exempt. But, I haven’t looked at the Castrol label.

 

[Jim]

Do you have a recommendation on oil I could purchase online?

You should have an Advance Auto Parts near you. Every one I've gone to has a "small engine" section in the back. There's motorcycle oil there.
look for the word motorcycle or this symbol...