Why am I still lean?

[barelycompetent]

Ok so I have been putting some miles on my bike after getting my carbs cleaned up and the bike running really well. I started at 45 pilots, and 137.5 mains, 3 turns on the screws and the bike ran and pulled really hard. At highway speeds when I grabbed a handful of throttle to get around someone the RPM's went up before grabbing and taking off. So checking my plugs they were white, and running lean. Had about a 100 miles on them by then so I moved up to 140 mains. Same thing, but a little bit better. 100miles or so that way, went to 3.25 turns on the screws and still running a little bit lean. So the other day I put 142.5's in on the mains and went for a spin. Grabbed a handful of throttle at 70 miles an hour and still had the same problem, RPM's go up, then it kicks in and takes off. Pull the plugs and they are white. I should also mention that I do have one shim on the needle, the carbs are bs34's and I have followed the carb guide. I am now 3.5 turns out on the screws and same thing, still running lean by the looks of the plugs. The weird thing is each main jet, 137.5, 140 and 142.5 all ran really well with them, and pulled hard, each one pulling a little bit better then the last, but still I am lean. I dont want to go anymore out on the screws and I hesitate to go another size up on the mains, for one I dont have that size lol, and two I dont know that it needs to go that high. My float heights are dead on at 23mm. My bike cruises along at 70mph with no problems, the RPM's are only about 4-5k, its when I grab that handful of throttle I get that little burst of high RPM's before it kicks in, and Im still lean. At idle I can pull the plugs and I have the nice light tan color on them, but under load and at mid and high range its white and lean. Could I be lean in my midrange? My needles are the non adjustable ones which is why I have one shim under them. Any thoughts? Sorry for the long post and I appreciate the help, Im out of ideas on this one.

 

[CDNTX650]

Sounds like clutch slippage if it revving then taking off. Im at 140 with mine, and i show lean at high rpm cruise. Im waiting for our weather to warm up though. Ambient is too cold for jetting. Think ill buy 142.5 and 145. Didnt think id have to go tha high, but symptims and plugs dont lie.

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[barelycompetent]

Could be the clutch, Im hoping its not but it could be. Thing is it got better the higher I went on the jets. All three sizes pull hard and run well, so Im scratching my head as to why Im still lean. Weather has been 60-70's here, and the miles have been put on over the last couple of weeks so I dunno lol. Its only that last gear at highway speeds that it does this. Course it still doesnt explain why Im still lean. Is it common for these bikes to run at highway speeds at 4-5k RPM's? That seems low to me, my Honda's always cruised at highway speeds in the 6-7k range.

 

[CDNTX650]

Yeah thats normal cruising rpm. Id hope these dont cruise at 7k...redline is at 7500...

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[itsatoy]

I'm no expert. My uneducated guess would be spark plugs too hot? or something causing restriction between the tank and the main. I probably only know enough to make myself look stupid but there you go.

 

[5twins]

You may not be as lean as you think you are. When you read plugs, what you should be looking at is the "mixture" or "smoke" ring. This is a ring of color at the very base of the porcelain .....

Here's the plugs from my bike. The porcelain does remain white on top. The electrode strap turns grey eventually. Outer edge by the top of the threads is black, that's normal .....

As you increase your main jet size, it bleeds over and also richens the upper midrange. Eventually, it will make that area too rich and cause stumbling under heavy throttle applications. When that happens, you've reached about your limit on main jet size unless you lean the midrange. You can't adjust your midrange so that stumbling would be it for you. Generally, you step back down a size then, to the last one that ran clean. To test for this, you need to use absolute full throttle from about 3.5K on up to near redline. You will be looking for stumbling in the 4 to 5K range. These CV carbs are somewhat forgiving and won't show all the little jetting glitches unless you push them hard.

Also, at 23mm, your float heights are at the lean end of the setting spec. You might want to try 22mm, as long as that doesn't cause carb over-flowing. The 34s are very sensitive about their float settings. They can have a big effect on how rich or lean they run.

 

[gggGary]

I went looking and found this. It's so helpful to know how the bike is set up...........

View attachment 41242

 

[5twins]

Pretty free flowing from the looks of things. Maybe the mains aren't big enough yet. A couple sizes up works for most, but not all. I'd keep going up. Sometimes one more step up makes all the difference in the world.

 

[barelycompetent]

Sorry Gary I thought I had explained the setup. That is indeed my bike. 5twins, my plugs look just about like yours do. I cant really see the smoke ring inside the plug to tell. It pulls clean thru the midrange, and pulls hard at redline, I dont get any break up at redline, just the initial high rpm's before it kicks in which as pointed out might be my clutch. I will continue to put some miles on with my current jetting and see how it goes, course thats going to have to wait till I get my rear wheel back on. I was out riding it yesterday and had just pulled into my driveway. Shut it off, pulled my plugs to check them, then went to roll my bike backwards out of the driveway and my rear wheel locked up. A sprocket bolt had backed out, and my chain adjuster had dropped down, shearing off that bolt, and it locked up the rear wheel completely. Had it happened 5 minutes prior, I wouldnt be here talking to you all right now. Not to get to far off topic but heres the damage.

 

[gggGary]

Yes the high rpm is the clutch, what oil are you running? Make sure you have a touch of freeplay at the ramp adjustment. See 2many's excellent clutch series. Ippy has an 8 plate conversion that should help.

 

[barelycompetent]

Im running rottella t 15w40, if I remember correctly. I just changed it about 300 miles ago, and I am within the specs for level. I will check the tech section for those posts, thanks.

 

[Sparky]

you eat too much fish?

hey! that same rear sprocket thing happened to me the other day, except i was going about 50. fortunately just made alot of noise and didnt lock up the wheel.

 

[barelycompetent]

Well sparky its not something I want to experience! Im lucky it was in my driveway so hopefully didnt damage the threads on the wheel. As for the fish, I cant stand fish lol, wait that all depends, never mind..........

 

[gggGary]

I think I would change oil to a motorcycle specific oil. Valvoline makes an ATV 10-40 thats good and rated for wet clutches. It used to be branded motorcycle but can't be used in the new cat equipped street bikes because it has ZDDP (zinc) a good thing for our old tech engines..

 

[5twins]

Yes, it sounds like new clutch springs are in order. I recommend one of the brand names from 650Central, not the no-name ones from Mike's. I have yet to encounter an old Jap wet clutched bike that doesn't need new clutch springs.

Yes, the smoke ring can be difficult to see. Shine a flashlight down into the plug to look for it. No ring at all would indicate you are still too lean. Coloring extending half way up or more on the porcelain would indicate you're rich. Reading plugs today with the new cleaner burning fuels is more difficult. They just don't color up the way they used to. Brown or tan has always been suggested as ideal. You may not get that any more and instead, be dealing with shades of grey.

 

[barelycompetent]

I will give that a shot on the next oil change, which shouldnt be to far in the future. I just need to get my wheel back on and continue putting the miles on. I feel a little better after seeing 5twins plugs, I know that mine look about the same. Come to think of it the clutch didnt start doing that till I changed the oil, and neutral became just a touch harder to find. Hmmm, maybe I will change it sooner then later and see if that helps. Again pending installation of the wheel lol.

 

[TwoManyXS1Bs]

It's hard to see in that pic, but the clutch cable routing looks a little odd. Could be that too much cable tension is in there to get your lever freeplay adjustment, which would prevent full clutch engagement. May want to revisit your clutch cable setup...

 

[retiredgentleman]

Sorry Gary I thought I had explained the setup. That is indeed my bike. 5twins, my plugs look just about like yours do. I cant really see the smoke ring inside the plug to tell. It pulls clean thru the midrange, and pulls hard at redline, I dont get any break up at redline, just the initial high rpm's before it kicks in which as pointed out might be my clutch. I will continue to put some miles on with my current jetting and see how it goes, course thats going to have to wait till I get my rear wheel back on. I was out riding it yesterday and had just pulled into my driveway. Shut it off, pulled my plugs to check them, then went to roll my bike backwards out of the driveway and my rear wheel locked up. A sprocket bolt had backed out, and my chain adjuster had dropped down, shearing off that bolt, and it locked up the rear wheel completely. Had it happened 5 minutes prior, I wouldnt be here talking to you all right now. Not to get to far off topic but heres the damage.

Considering the seriousness of the hazard, I just have to ask...................have you been using a quality torque wrench to tighten the sprocket bolts, and other bolts on the bike as well?

 

[barelycompetent]

RG I never touched the bolts on the sprocket. When I took the rear wheel off I only had a new tire mounted on it. I do have a quality torque wrench, but the sprocket bolts with their peened locking plates never crossed my mind to check. They will now, you can bet on that. By the way, would you happen to know the torque specs for the sprocket bolts? 81 special.

 

[retiredgentleman]

RG I never touched the bolts on the sprocket. When I took the rear wheel off I only had a new tire mounted on it. I do have a quality torque wrench, but the sprocket bolts with their peened locking plates never crossed my mind to check. They will now, you can bet on that. By the way, would you happen to know the torque specs for the sprocket bolts? 81 special.

I use 27 ft-lbs for the rear sprocket. While you have the torque wrench in your hands, check the brake disc bolts are at 14 ft-lbs.

Those so called "locking plates" are only a back-up to proper torquing. In your case, they didn't even perform as a back-up, so their value is questionable.

I've gone to split lock washers for my brake disc bolts, and the next time I change my sprocket I will go with split lock washers there as well.