Changed my pipes,need some advise on Jetting.

[XS650D]

This is for my 77D.Note i am running Uni filters,with 30 pilots,Needle dropped 1 (Leaner) 135 Mains.Gearing
17/30.Stock motor. I just installed new Mikes Commando Muffs on my Mikes manifold upswept pipes.
(I had BSA style pea shooter Muffs with custom baffles and Packing) I am getting some running problems since adding these New Commando,s.Starts fine,idles fine and pulls off the line good but flattens out around 4000 to 5000 rpm then its like a switch is flipped and the motor surges from 5000 to 6000 rpm on and off up to redline.Not really sure were to start on jetting changes.Starting to think it may be the lower gearing throwing the power curve or band but not sure,may be jetting.Any ideas were to start.Could that be timing not set correct.Cruising around takin it easy motor will run good up to 4000 rpm then everything goes south from there if i throttle hard.Another guess is my needles set to rich and mains set to lean but finding that hard to believe with what i have in there.I had a buddy ride it and he says it feels like the mufflers are not letting it breath at 4-5 grand as they go quieter.

 

[XS650D]

Thinkin about going up on rear sprocket from 30 to 32 to keep the rpms up,try to keep
the motor runnin in the power band.Not sure if i will notice much though as the i purchased the bike with 30 rear and never tried the stock setting.I have a bud with a 77D ,he runs Bubs exhaust Hot coils and PMA rotor,stock gearing.His runs really strong and seemless all the way to redline and pulls hard
in any gear.Our compression numbers are the same.

 

[5twins]

Your mains may be a little too big. I'd try some 132.5's and see if they improve things. Yes, your gearing is rather high. Remember, you're only dealing with about a 50 H.P. bike here. It probably won't even pull to redline in 5th with the 30. A 32 would be better, and a 33 even better than that. I run a 33 on an 18" rear wheel and feel it is ideal for this motor's power output.

 

[grizld1]

"Could be timing is not set correct." D, I'll offer this one more time: Before you play with the carbies, make sure everything else is right, especially ignition timing. And as 5twins tells you, your gearing is too high. I use 17/32, but wouldn't use that gearing on a stock motor.

 

[gggGary]

These guys are carb guru's but it sounds like you are saying that the dropped needle jet is making it lean as the slide rises, then if you can nurse it up to the main you are good again. Well hell, raise the needle, heck I'd go down two slots and see what happens. How easy is that to try? Once you change the mains you are back to scratch on the needle settings.

 

[gggGary]

IMHO the gearing is not relevant to this discussion. You like what you like.

 

[grizld1]

"Guru?!" Gary, you've never seen me with a #*@# turban on my head! I gotta lose that label.

Only commented on gearing because the OP brought it up. But right, if he likes it, that's fine. Too much lugging will eat up mains and low end, but if he keeps the rpm's up with proper gear selection, he'll be alright. If he tries to tractor the bike around like a Hardly Ableson, though, unpleasantness could result.

Re. needle position, if he raised the clip to start with I figured he'd get around to dropping it again, but I'm going to stand by what I wrote on procedure--everything else before touching the carbies.

 

[gggGary]

Never wrong to do the full drill first birthday boy!

In spite of your tender age I think I have seen you charm a good running carb out of a pile of cow flop...........
The resto mod started showing a bit of iffyness at idle so started by setting the valves and cam chain and checking compression. Still haven't gotten to synch and idle screws but have put a few hundred miles on it and all seems good for now. Been kinda busy getting an RSV road barge ready for a Lake Superior Circle camping Trip. The pile of discarded parts has filled a large tote box so far and more is coming off. Burp. I'll never get that pig below 800 pounds.

 

[grizld1]

Now see there? I only suggested that OP do what you'd do before fooling with carbies! We'll miss you at the Rendezvous, but have a great ride!

 

[XS650D]

OK the all

 

[gggGary]

I did do a tube in the bowl drains float level check also...........
That bike runs best of any of my XS650s; commandos on stock headers and UNI foam on stock filter frames but it has 78-79 carbs so the jetting is different than yours.

I'm kind a thinking it might have just been some poor gas from a can.

 

[5twins]

Experimenting with needle settings is easy but I find it hard to believe that a '76-'77 carb set would be too lean through the midrange. The Z-8 needle jet they came with was the largest ever put in a 650. Setting the needle back to it's center slot (stock) will probably make the upper midrange too rich, causing break-up under heavy throttle applications. Heck, I couldn't even run 135's with the needle leaned a step without that happening in the set I tried. 132.5 was the largest I could go. But, you can try it, if for nothing else than to verify your current setting is correct.

Swapping mains is even easier than changing the needle setting. You can do it with the carbs still in place using a stubby screwdriver. When I'm tuning a set of these, I sometimes even do it on the side of the road. Dropping down one size on the mains shouldn't require any other changes (needle, pilot). Like I said, I think you're too big to begin with using a 135.

 

[TwoManyXS1Bs]

...I am getting some running problems since adding these New Commando,s.Starts fine,idles fine and pulls off the line good but flattens out around 4000 to 5000 rpm ...

Try a forum search on 'reversion'...

 

[XS650D]

OK was wondering if the mikesxs manifold pipes I have (with tipped up ends) might be the problem.
They are a lot longer than stock,maybe 8 inches,when I slide the Commandos on I had to slide the entire
Tipped up 5 inch section into the mufflers together them to line up and bolt on to rear foot peg
Properly.So their is a least 5" off manifold pipe up in the muffler .Would the extra length off the manifolds
Cause problems ,should I cut off maybe 3" of manifold pipe so it doesn't insert so far into the muffs
I

 

[XS650D]

"Guru?!" Gary, you've never seen me with a #*@# turban on my head! I gotta lose that label.

Only commented on gearing because the OP brought it up. But right, if he likes it, that's fine. Too much lugging will eat up mains and low end, but if he keeps the rpm's up with proper gear selection, he'll be alright. If he tries to tractor the bike around like a Hardly Ableson, though, unpleasantness could result.

Re. needle position, if he raised the clip to start with I figured he'd get around to dropping it again, but I'm going to stand by what I wrote on procedure--everything else before touching the carbies.

Grizld,u may be on to something here,i tried riding around in a lower gear than usual and the motor seems to respond much better,will still look at the timing (can only do it manual way with a 12 volt light) dont have or know how to use a timing light.Hopefully that will be ok!
I did try changing the jetting but no diff (went down to 132.5 main and also tried raising the needle 1 clip to stock but got breakup on upper end.I am going to try a different rear gear 32 or 33.Thx

 

[retiredgentleman]

Static timing with a light bulb or VOM is only a rough setting. You need to buy a timing light to get an accurate adjustment. In this hobby certain tools are a "must have" .............i.e. timing light, torque wrenches, manual impact tool, VOM, feeler gauges, etc.

I can't understand why anyone would run a 30 rear sprocket. Its take all the fun out of riding the bike, and would tend to lug the engine. Buy a 33 sprocket and you will enjoy your bike much more. The 33 works well in town and on the road for long trips,

 

[XS650D]

ok thx,Got all the tools u mention except the Timing light.Clymer manual only shows doing it
with a Volt meter,Buzzer or light.I guess a U-tube video is in order!

 

[5twins]

Have you installed the included block-off bolts in the Commando baffles? You might try it with and without them to see if it makes any difference. I have mine installed and prefer the sound that way. I never really tested them at high speeds and RPMs without the block-off bolts.

 

[XS650D]

I got some short bolts (allan hex head and lockwasher) thought they were supplied
for attaching the pipes to the frame mount,no directions with pipes.They are approx 3/4" long
and maybe 3/8" thread thickness.If those are the bolts u mention,were exactly do they go?

 

[5twins]

If you look in the end of the muffler, you'll see a threaded hole in the center of the baffle plate. They screw right in there .....

Easy enough to try and honestly, I think they sound better with the bolts installed.