Weak Midrange RPMs. Loss of "Pull".....goes flat...

[EvenmoreXS]

Things are getting better. Im now trying to get even pull through all rpm ranges. Pulls ok early, not too bad, flattens out midrange regardless of gear, once rpms hit a point pulling resumes. Pulls ok if I bypass that rpm range......go a little faster in 1st gear and change at a higher rpm. Not my typical riding style, not trying to win any races,,,,except the ones with the 5.0 ... Just looking for even pull throughout. I think its carb related. I have 2 new main jets ordered. I think its lean in the midrange. My best guess. Ive seen a few slipping clutch comments....could be i guess, but I dont think so. Here is a quote i found here on the site....



- 2. Midrange (full throttle /2500 to 3500 rpm)
Step 1 (Best Main Jet) must be selected before starting step 2!
 Select best needle clip position
o To get the best power at full throttle / 2500-3500 rpm, adjust the needle height, after you have already selected the best main jet.
 If the engine pulls better or is smoother at full throttle/2500-3500 rpm in a full throttle roll-on starting at <1500 rpm when cool but soft and/or rough when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
 If the engine pulls better when fully warmed up but still not great between 2500-3500, try raising the needle to richen 2500-3500 rpm.
 If the engine pulls equally well between 2500-3500 rpm when cooler as compared to fully warmed up, the needle height is probably properly set.
 Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets (Step 1) that produce the best power at high rpm. You will deal with the low-end / cruise next.



Because it pulls well at high rpms, i think the needle is ok.????

Pulls fine at low rpms, pilot should be ok?????

Weak midrange.........size up the Main jet???

Going to open pipes with baffles soon, running a 2 into 1 now.



Opinions on how to get my midrange back. Am i on the right track?

 

[pamcopete]

Evenmorexs,

Well, if you still have the stock TCI ignition system, then your symptoms could be due to a defective TCI box of a weak trigger magnet in the alternator rotor. The simple test for this possibility is to unplug your reg / rect as a test to see if the symptoms go away.

 

[EvenmoreXS]

Proud owner of a PAMCO ignition. No black box or pickup.

Thanks Pete.

 

[pamcopete]

EvenmoreXS,

OK. That's cool. Did you check for a binding advance rod? Here is a video that shows how the rod should work with no binding.

 

[EvenmoreXS]

I didnt, but I will check that next. Its all brand new, 2 months old. Rod was well greased when inserted. I like what your thinking though, start simple.

I failed to mention this first, but the bike has always been weak in the mid range. Ive owned it almost a year.

Thanks Pete.

 

[5twins]

Since the bike has always been this way, both before and after the ignition change, that would pretty much rule out ignition and ignition related components. I'm thinking your problems are intake/exhaust related with some improper carb tuning thrown in the mix. Somebody chose a really terrible mix of upgrade parts to install on your bike. From an old thread on your carbs, I see you have the tiny round tapered K&N clone pods. Those are probably about the worst air filter on the planet for your carbs. You also have a 2-1 exhaust which sits pretty much at the bottom of the list as far as what exhaust type works well on these bikes. Combine those things with lean-from -the-factory BS34s which you probably haven't re-jetted at all and I'm surprised the bike runs as well as it does.

The bad pods may be helping at this point. They could be restricting air flow and making the carbs run richer, just like re-jetting would. Installing proper pods (UNIs) will probably make the carbs run much leaner. I would suggest upping the pilots one (to #45s) and getting the next 3 larger main jet sizes (135, 137.5, & 140). Your needles control the midrange. Unfortunately, the stock BS34 needles are fixed and can't be adjusted. However, usually just increasing the mains and pilots is enough to fix the midrange as well. Those larger jets bleed over into the midrange and make it richer, the pilots from the bottom and the mains from the top. The adjustable Canadian needle and needle jet combo is available but I wouldn't go there unless this normal tuning routine fails.

I also mentioned your exhaust. Most 2-1s aren't designed with performance as their primary objective but rather just to fit on the bike. Things like header length, header diameter, collector size, etc. aren't chosen for best function but rather for best fit. You mentioned changing soon to open pipes. That may or may not help. Down at the bottom of that exhaust list, right next to the 2-1, is the straight pipe. The midrange performance on them is bad too. They don't call them "drag" pipes for nothing. They produce most of their power up near or at redline and make less power than stock elsewhere.

And finally, a few words on testing your jetting. These CV carbs are very forgiving and can mask over minor jetting errors. To properly test them, you need to push them hard. Large handfuls of throttle and even wide open throttle tests are needed to really show the glitches. Riding the bike easy and gently may not show the problems.

 

[hard_y_rd]

Apologies for the stupid question, this is my first engine build. In the vid the rod is binding i take it. What's it supposed to do?

 

[5twins]

No, it's not binding in the vid, it's acting as it should. If it was binding, it wouldn't return smartly to the fully closed position as it's doing, it would hang open.

 

[pamcopete]

Apologies for the stupid question, this is my first engine build. In the vid the rod is binding i take it. What's it supposed to do?

Sorry about that! I re read my post and corrected it. Thanks 5twins.

 

[hard_y_rd]

I'm kinda thick when it comes to understanding this stuff. I interpret what i read. Mine is doing the same as the vid.

 

[ippytattoo]

One thing you can do to correct a lean needle on the BS34's is to get some washers from a good hardware store that fit the needle and are 1/2 mm thick to use as adjusting shims in order to raise the needle a half step at a time. I am running EX500 carbs on my chop and I had to raise the needle 1mm or 2 shims in addition to the other jetting changes and it has worked beautifully.

 

[EvenmoreXS]

Thanks 5twins,

I've long since updated my air filters since that post. Those silver ones were shite. Im running xsperformace pods now.

I just got my 135 and 137.5 main jets friday. Gonna try em today i hope. Didnt order a pilot, after lots of reading I didnt think I need it. Starts on the first kick and idles well even with poor tuning. Not horrible, just poor. I'll see how it runs with the new jets. Probably going straight to the 137.5 due to the new pipes. Bet the mid range is better.

New pipes now come out just behind the pegs and turn out. Original headers with extension with turnouts welded on. Im probably going to cut the extensions with the turnouts off....about 20 inchs total maybe. I would like to put baffles in the open headers and wrap em. Any suggestions on baffles.

These changes arent permanent. Working with what I have for now. As a daily rider, or will be again i should say, I want best performance in and around traffic. The mid range. No drag racing. Cant afford parts, cant afford tickets. Math.....

But for now, carb tuning. I'll probably change the pipes in a couple weeks. They are severely ugly right now. Seriously. Gonna blast em and paint em first.

Thanks for the help everyone. I'll let you know how the new mains work out.

 

[EvenmoreXS]

Ok, so my main jets are currently 140's, so my new jets wont really help. Seems I may want to go up 1 on the pilot ??? Not sure what the pilot is yet. I will check it out sometime soon. Gonna ride a bit and check the plugs.

Gotta replace my clutch push rod seal too. Seeping a bit.

Gotta take the chain off again to do that.

 

[5twins]

If you haven't ever checked it, you may want to pull a slide and check that the needle has been installed correctly. There should be a thin washer on the needle above the e-clip and a thicker plastic one below it. If those two parts have been switched around, the needle will sit too low and your midrange would be lean .....

Increasing the pilots is pretty much S.O.P. on these 650s when you start doing mods. Some of the earlier carb sets may require two sizes up but one size up is the usual routine on the BS34s. You increase the pilots AND you increase the mains. There are three circuits in your carbs and they overlap the one next to them slightly. Changing one affects the circuit next to it. Larger pilots will also richen the lower midrange a little. Larger mains do the same to the upper midrange.

So, if you're still running stock pilots, you haven't completed all the steps usually required to properly re-jet a set of these carbs. Both larger pilots and mains are needed to "fix" the lean factory midrange on this carb set. Also, one of the first rules of jetting is that when you think you're right, try the size above and below to be sure. Obviously, you're not going to want to go leaner on the pilots. I'm mentioning this more in regards to your main jet. I would try that 137.5 you just got now. It's easy to over-jet these CV carbs due to their forgiving nature, especially on the mains. If the bike runs worse, then you've proven to yourself that 140s (or maybe even larger) are what you need.

 

[EvenmoreXS]

I havent made any carb changes since I bought the bike, a cleaning is all. Everything else is done by the PO. Gonna check the needle and I may put in the 137.5 also.

 

[EvenmoreXS]

Pics of my spark plugs after about 20 or so miles.

Sorry im being slow. Been a busy last couple of weeks for me.

I just put on the open pipes. I like the sound . I will run them and check the spark plugs again and see how they look. Once I decide on my pipes, baffles and pods, I can tune my carbs to suite.

 

[scabber]

Your plugs say your running ritch. Xs John worked on the Bs 34 carbs alot. The example five twins of the overlap pay heed to and his other fine advice. XSjohn never went bigger than a 135 or 137.5 main jet with straght pipes. He used a 49 piolet. He sent a wire with his kit to drill out the 42.5. He liked the odd sizes. Since the amount of fuel the piolet circuit delivers is regulated by the mixture screw. I don't think it matters that mutch 49 or 50. With the 49 piolet he used 1 3/4 to 2 turns out for a starting point. You can not buy his needles since john passed away. His needles were to ritchen the midrange also. The dimensions were posted on this site probably a search you can find them. The plastic spacers under the needles came in two thickness .132 thousand and .122 thousand. He would use a shim if it was the latter. I would work with the stock needle and work with the piolets and main jets first. Ippytatoo advice about the shims also good if the piolet and main jets do not fix the mid range. Getting the most out of your bike with the least amount fuel is best.

 

[EvenmoreXS]

Your plugs say your running ritch. Xs John worked on the Bs 34 carbs alot. The example five twins of the overlap pay heed to and his other fine advice. XSjohn never went bigger than a 135 or 137.5 main jet with straght pipes. He used a 49 piolet. He sent a wire with his kit to drill out the 42.5. He liked the odd sizes. Since the amount of fuel the piolet circuit delivers is regulated by the mixture screw. I don't think it matters that mutch 49 or 50. With the 49 piolet he used 1 3/4 to 2 turns out for a starting point. You can not buy his needles since john passed away. His needles were to ritchen the midrange also. The dimensions were posted on this site probably a search you can find them. The plastic spacers under the needles came in two thickness .132 thousand and .122 thousand. He would use a shim if it was the latter. I would work with the stock needle and work with the piolets and main jets first. Ippytatoo advice about the shims also good if the piolet and main jets do not fix the mid range. Getting the most out of your bike with the least amount fuel is best.

I will check the pilots and put in my 137.5 mains and see how that goes. Will also try to check the clip and spacer on the needle.

The rich plugs were BEFORE the open pipes. Not sure of any effects of the switch yet.

Once I work out my "Psssss" sound when I open the throttle, I think I will be able to get a good tuning done. Throttle shaft seals ordered. Mikes

 

[EvenmoreXS]

Since the bike has always been this way, both before and after the ignition change, that would pretty much rule out ignition and ignition related components. I'm thinking your problems are intake/exhaust related with some improper carb tuning thrown in the mix. Somebody chose a really terrible mix of upgrade parts to install on your bike. From an old thread on your carbs, I see you have the tiny round tapered K&N clone pods. Those are probably about the worst air filter on the planet for your carbs. You also have a 2-1 exhaust which sits pretty much at the bottom of the list as far as what exhaust type works well on these bikes. Combine those things with lean-from -the-factory BS34s which you probably haven't re-jetted at all and I'm surprised the bike runs as well as it does.

The bad pods may be helping at this point. They could be restricting air flow and making the carbs run richer, just like re-jetting would. Installing proper pods (UNIs) will probably make the carbs run much leaner. I would suggest upping the pilots one (to #45s) and getting the next 3 larger main jet sizes (135, 137.5, & 140). Your needles control the midrange. Unfortunately, the stock BS34 needles are fixed and can't be adjusted. However, usually just increasing the mains and pilots is enough to fix the midrange as well. Those larger jets bleed over into the midrange and make it richer, the pilots from the bottom and the mains from the top. The adjustable Canadian needle and needle jet combo is available but I wouldn't go there unless this normal tuning routine fails.

I also mentioned your exhaust. Most 2-1s aren't designed with performance as their primary objective but rather just to fit on the bike. Things like header length, header diameter, collector size, etc. aren't chosen for best function but rather for best fit. You mentioned changing soon to open pipes. That may or may not help. Down at the bottom of that exhaust list, right next to the 2-1, is the straight pipe. The midrange performance on them is bad too. They don't call them "drag" pipes for nothing. They produce most of their power up near or at redline and make less power than stock elsewhere.

And finally, a few words on testing your jetting. These CV carbs are very forgiving and can mask over minor jetting errors. To properly test them, you need to push them hard. Large handfuls of throttle and even wide open throttle tests are needed to really show the glitches. Riding the bike easy and gently may not show the problems.

Can you recommend which UNI's would be best for my setup?

 

[scabber]

What pipes do you have on the bike now ?