Topic: Mo the 80 CB650 Custom: "As the Spanner Turns..."

[manjisann]

Sweet, thanks for the info guys!  I'll have to save some money so I can get me some new shocks.

I went for another ride, it was kind of short, only 15 miles. With the advance all the way clockwise, once she warms up she'll idle nicely at about 1200rpms, doesn't even take much choke to get her going. She responds to the throttle pretty well, although is a little sluggish above 5-6k. I did find that once she warmed up though, every now and then she'd bog horribly and wouldn't go past 4500rpms no matter what I did with the throttle. Any thoughts?

At this point my plan is to fiddle with the advancer a bit, and also lean out the carbs on the upper end like Soos was saying. When she starts bogging she is burbbling which I believe means way too rich. I did try moving my legs around to see if it had anything to do with the airflow, but the results were kind of mixed so I'm not positive there. I may also set the airscrews back to the factory setting and start from there. I'm going to do small adjustments so that if something changes, for the better or worse, I'll have a good idea what it is.

My speedometer is also being weird. It will read consistently for a while then suddenly start bouncing a lot or not really go up when I speed up. I'm wondering if there is something wrong with the magnet in it. For now it will get me by, but I don't have a lot of faith in its reliability. I'm going to troll eBay and see if I can score a decent replacement.

All in all though, it was a promising ride. Oh, and my right front marker light keeps burning out! The blinker will keep working, but the marker burns out. Whne I rev the bike the light dims. Any thoughts? I'm going to try and find some sort of LED replacements for them anyhow, but it's obnoxious.

Brandon

[Hush]

Brandon, you keep talking about your "advancer", are you talking about moving the electric pick-ups where most bikes have their points?
I think maybe you need to go behind that area and check out your automatic advancer weights and springs, they may well be jammed/rusted or the springs too slack.
Made a huge difference to my 650's acceleration when I found mine rusted up in there.
The good news if you have to go in there is that if you mark your pick-ups with a marker so you can put them back in the exact spot after you finish playing with the auto advancer, you don't have to play with re-timing the motor.

[manjisann]

Pickups, thats what I'm talking about  I think my advancer is working fine, it was easy to move and springs back when I twist it by hand, but since I'll be replacing the pickups screws I'll pull the advancer and check it and lube it. I'm wondering if I advanced the pickups too far forward. Basically, I just need to fiddle with some settings and see what happens.

Brandon

[manjisann]

I went and had a new tire put on the bike. They only had two in my size, one for $99 and one for $127, so I opted for the $99 one even though it has HARLEY DAVIDSON on the side. I am hoping the motorcycle Gods will overlook this minor blastphemy considering the amount of money I've sacrificed... er invested in redoing this bike.

I got home and cleaned the speedometer drive of old grease and put new grease on it and the axel. I'm going to replace the wheel bearings at some point, but for now they'll just have to last. The tire spins pretty well so I'm really not too concerned about it. I did as was suggested and lubed up the speedo cable as well. Upon riding I found it to be every bit as jumpy as always AND even with the proper 100/90/19 tire on it the speedo still reads approx 5mph under what I'm actually going. Looks like I'll be replacing the speedo at some point. But for now I'll just have to make do with what I have. If I knew for a fact I could fix it I'd take it apart, but with how much fun the tach was, I'd rather wait till I had a spare.

I did as Hush and a few others suggested and dissassembled the pickup and advancer, cleaned it up, lubed it with some white lithium grease and reinstalled it. Everything looked ok, although from the looks of it she was dry and hadn't been lubed in a while. Good call Hush! I set the Pickups further back from where I had put them prior. I'm still not completely positive what that does, but it seems to help with the idleing once she's warm.

Once she was all back together I took her for a spin. Just as in the past she would run great while cold, although I did notice that even when cold she wasn't too keen on the upper rpm range, slow speed up. I just had a though, I wonder if that could be do to the pickups being moved clockwise, maybe I should try moving it counterclockwise just a bit and see what happens. Anyhow, between what Soos suggested, the fact they are off a 750, and my own limited knowledge of how carbs work, I think I'm running uber rich. I'm going to take her and get the safety done first thing after school tomorrow, that way I can get the tags and not have to worry about that anymore. After that I'll pull the carbs and start tinkering. I'm going to check the airscrew settings as well as move the needle clip up one position (I believe that will lean it out). While I have the carbs off and I'm fiddling I want to clean the bar that they pivot on, and see if I can't get the throttle to smooth out some as far as actuation, right now it seems a little not so smooth. I'm also going to check what jets I have in case I have to order different ones, but I'm not planning on that for now.

Well, cross your fingers that I can sort the carbs out.

Brandon

[Hush]

Er Brandon, if you lift the needles one notch that will open up the mouth of main jet so it will run even richer!
Try putting your finger in the top of a bottle, as you pull your finger out you will notice hole gets bigger, this would be same as raising the needles in your carbs.
Dropping the needles a notch will have the opposite effect of leaning it out as the hole made as the needle lifts is smaller therefore less gas getting sucked up.
Perhaps you should set your pick-ups by the book for a change mate?
At least to start off with anyway.

[Zaipai]

Sounds like you were busy.. How about some pic's of the HD tire?

.: Scott :.

[manjisann]

Perhaps you should set your pick-ups by the book for a change mate?

They were set by the book and when the engine was warm she wouldn't idle properly and the throttle response was even worse. I may go ahead and set them back while I try and adjust the carbs, just so I'm only having one variable at a time.

I said move the clip up one position, which would drop the needle itself one position, so same as what you are saying Hush, just different way of saying it 

Sounds like you were busy.. How about some pic's of the HD tire?

I dunno, I mean how many blastphemies will the Honda gods overlook?? 

Well off to school, got a presentation on my english class, wish me luck.

Brandon

[razor02097]

Take a turn hard enough and you'll wear those bad words right off the tire

[manjisann]

Take a turn hard enough and you'll wear those bad words right off the tire 

I think that's a case of the cure being worse than the disease 

As requested here's a pic of the HD tire.

After school I zipped home and took the bike and got the safety done, she passed, no surprise there. I then went and got the tags and plate and she's all official now.

When I got home I got to work and dropped the pins one notch. I didn't do anything else just that. I then took her for a ride. What I'm beginning to notice is as long as I don't twist the throttle too much she is pretty responsive but once she warms up if I go over half throttle for very long she begins to bog down. I decided to try and go up a hill and she bogged so bad she died. I turned the fuel valve off and tried running it that way for a while to see if things would improve as the fuel level went down, but not much changed, I didn't try for too long. I got back home and put her up for the day. The weather is supposed to be nasty the next few days. I'm going to try and read up more on carbs and tuning. I'm going to try and drop the needle to the last position and see if that helps any at all. I'm beginning to think that I may have to get smaller main jets (or whichever is controled by the needle.) Since the carbs originally came off a 750 I was kind of expecting to have to jet smaller anyhow. It seems to me that just dropping the needle wouldn't be enough, thats more just for fine tuning I would think.

I seriously hope I can get this to work here soon. I'd really like to start riding more here soon.

Brandon

[Zaipai]

Ok first, I am being lazy so with out going back and rereading the thread, what do the plugs look like? If those carbs came off a 750 some jetting might be at issue, it seems the slow jets are working fine, so the main jets seem to be the issue. Having said that I could be way off base, so don't take my word for it just thinking out loud more then anything.
The tire seems fine, no raised white letters saying HD so you are good!

.: Scott :.

[manjisann]

I haven't done an official plug chop, but they are sooty. I think I need to get it to start bogging then pull the plugs at that point and see what they look like. When the weather dries up a bit I'll have to do that. I think the stock mains were supposed to be 120's, at least according to what I've been reading. The ones in it right now were marked 107.5, at least the one I bothered to look at was. I think the 650 mains were 90's, I'm wondering if the sizing is universal. If 90 is the 650's stock size then I definately need to go down probably to at least 100. I'm guessing with the K&N pods on the bike has increased the airflow so a 90 would probably be to small. I need to see how much they are, hopefully not too much seeing as I need 4 of them.

Brandon

[Kurlon]

You've got to be very careful comparing main jets across carbs, Kiehin's are marked by the bore of the opening while Mikuni's are marked based on 'flow'.  Different size carbs will also react differently on a given bike, assuming nothing else changes the larger carb may need a larger main due to less 'signal' from the motor while a smaller carb will see a stronger signal and want a smaller main to keep from running rich.

If you listen to the motor, it'll usually tell you which way it wants you to go when it's misbehaving.  A 'wet' or 'soft' cough is usually rich while a sharper sometimes cracking stumble is a sign that you're lean at that particular point.  Another way to test is to partially block the airbox opening(S) or cover part of the pod filter surface with tape which richens up the mixture.  If it responds well, richen things up, worse, it wants to be leaned out.

Get the bike so it'll idle steady and the revs drop back to idle quickly when you blip the throttle using the pilot screws.  If you go too rich on the pilots the idle will actually dip below where it should be before settling.  Too lean and it'll be slow to drop revs, sometimes hanging with a high idle.

Next, play with the mains so that you get good WOT pulls.  Plug chops do work here although you'll want to be sure to start with CLEAN plugs for good reads.  If your mains move a ton from where you are now, you may end up playing with the pilots again.  Normally you're supposed to get the mains set first and THEN dial in the pilots but it's a royal PITA to work that way on a street bike if it refuses to idle.

Once you have the mains dialed in, what's left is playing with the needles for partial throttle response. This is a trial and error game, the motor will tell you by sound when you're way off (stumbles) but you'll need to go by feel when you get close.

[Zaipai]

I have heard what Kurlon said from others, so I would think he is correct. However given that these carbs are off a 750 any chance you can just get carbs from a 650 about your year and throw them on? I am thinking there (and I could be wrong here) is no real advantage to going with 750 carbs unless you have no other (and cant get any) 650 carbs.

.: Scott :.

[Frankenkit]

there is an advantage in that you can actually change the jetting in the 750 carbs BUT seeing as you can get new press-fit slow jets from siriusconinc for the 650 carbs, that main improvement is now kind of nullified.  the only improvement 750 carbs over 650 now is that 650 rebuild kits are $45 each.

[Hush]

Brandon, don't forget to change down a gear or two when climbing hills eh!

[manjisann]

Brandon, don't forget to change down a gear or two when climbing hills eh! 

Damn, you mean 5th gear isn't for hill climbing???   

I went with the 750 carbs because they are cheaper to rebuild and they don't have that lame choke cable with the plastic (pronounced "Unobtanium") parts that are easily broken. Besides, the bottle cap carbs are pretty cool looking, AND I have already altered the fuel tank to fit the 750 carbs.

Also at this point I want to get these puppies to work right, mostly for the educational value as anything right now. I don't know if I'll be able to get these to work like the stock ones, but I'm sure I can get them to function well enough that I'lll be happy. I started out riding a 73 CB500 so it's not like I'm expecting modern sport bike performance. I'm sure with enough time I can get the jetting right, and I'm learning a ton in the process.

I've also read what Kurlong is saying elsewhere, including the FAQ. I've tried to be very concious when riding the bike as to when it starts stumbling and acting weird. I'm pretty convinced that it's running really rich in the main jet since I don't run into problems until I'm running 1/2 throttle or more for a period of time. If I just rev it a bit or keep the throttle below 1/2 the bike remains pretty responsive. This coupled with the lack of backfiring really makes me sure of the overly rich mixture.

It occured to me that I have a set of 500/550 carbs in the garage and I'm wondering what jets are in it. If the jets will fit it could be a good way to test my thinking. Now that school is out I'll have more time to fiddle with the carbs. I'm pretty sure it's fairly close and just needs some fiddling.

I need to compare bore sizes between the 650 and 750 to see if the sizes are the same or not. And according to what Kurlon is saying since the two bikes use Keihins so the jets should translate across carbs, assuming the bore sizes are the same.

Brandon

[manjisann]

So that's a no on jet compatability between the 500 and 750 carbs. The 500's are push in while the 750's are threaded. I dropped one of the carb bowls and measured the jets so I knew which ones I needed to order and ordered 2 sets from Jetsrus.com. I ordered 100's and 90's. I ordered the 90's since the stock 650 carbs had 90's in it, and 100's cause well it's smaller than the ones in there so it was a good mid ground. I tried to find the slide size for the 650's but couldn't. Hopefully the jets will get here mid next week and I'll see what happens. I may have to get different sizes, or even have to replace some of the other components, but this is a good start and will hopefully allow me to dial these in.

Brandon

[Kurlon]

If you think it's rich, pull your air filter out and see how it does in that range?

[manjisann]

If you think it's rich, pull your air filter out and see how it does in that range?

I am currently running K&N 2-1 pods on it, so I could remove the pods, but I don't think they are offering all that much restriction AND Utah has pretty dusty air, so while I wouldn't mind an overbore, I'm not really interested in doing it that way.

The stock jets in a 80 650 are 90's or 85's I think. The air intake throat is about 5mm bigger in diameter. Unfortunately I can not find any specs on the slide size (soos, any chance you want to measure that for me??) My simple reasoning is that there was much more air going through the 650 carbs than is currently going through the 750 carbs, and with a larger main jet, at 1/2 to WOT I'm getting significantly more fuel to air mixture than I want. According to my thinking I may even need to step down to a smaller main than 90, but it seems like a good point to start at.

I'm sure many out there are wondering why on earth I don't just switch back to the stock system. I've already outlined several reasons but at this point I'm just learning a ton and sorta (sadistically) enjoy the challenge. These carbs are much simpler (not to be read as better, just fewer parts and such) and cheaper to rebuild. Plus if I choose to get it running perfectly at Utah elevation and then want to ride to Texas or California or some such place, switching mains is a VERY simple process since the bowls are just clipped on and with a flat stubby screwdriver it is super simple to remove the old mains and insert the new. Another reason is I'm going to start on my cafe racer soon and I'll be using my spare 650 engine which will hopefully have a set of pistons Soos modifies. The displacement will be roughly 750 cc's and I plan to mate some of these 750 carbs to it, so this will help me understand a little better where to start out from when attempting to tune that puppy.

At this point it's mostly about the learning.

Brandon

[scunny]

just to throw the cat amongst the pigeons, my 650 had 98 mains, now running pods and 120(drilled) mains and suffer a stumble on constant throttle at about 6200rpm

[Kurlon]

Ok, tape over half of each pod, and see if the problem gets worse. : )

[manjisann]

just to throw the cat amongst the pigeons, my 650 had 98 mains, now running pods and 120(drilled) mains and suffer a stumble on constant throttle at about 6200rpm

So you think the 120's are too rich then?

Ok, tape over half of each pod, and see if the problem gets worse. : )

Weather is supposed to be nice next week, I'll have to try this, it would be a good way of confirming my suspicious

Brandon

[scunny]

I've been drilling the jets in .05 steps and ended up at 120 being the best. now just have to order some jets, going to try 110 to 115.

[manjisann]

Interesting, what carbs are you running, are they stock 650's or something else?

Brandon

[manjisann]

I decided to go for a ride today and try out Kurlon's idea. I rode the bike until it started bogging down. I rode home, put some Duct tape over a little over half of the pods and rode around like that. The bike actually seemed to perform better with the tape over the pods, but it would still bog or surge a wee bit, but all in all it seems it was better. After a while it did begin to bog down, but with the tape it took much longer. Once it began to bog with the tape I stopped to pull the tape off so I could see what would happen. Once I stopped the bike died, the idle dropped too low and just died. I pulled the tape off and then tried to start the bike again. Long story short, no matter what I tried the bike wouldn't start. Choke, no choke, throttle, no throttle, it made no difference, no go. I ended up pushing the bike home about a mile or so, fortunatley it wasn't too bad and it was cool outside (Hush's wisdom in action  ). When I got home I pulled the plugs from 1 and 4. They weren't sooty as I was expecting but pretty clean, and the little part that bends over the center was really white (which normally suggests lean I believe, but that doesn't make any sense) Long story short, I'm a bit confused about what this test determined as it shouldn't have ran lean with the tape over the intakes, if anything it should have ran richer. I'm going to try and get her in a few days and see what's going on. I'll have to clean the plugs off and try to do a more thorough test.


Brandon