Need help tunning vm34 carbs, after Big Bore!

Flash1977

Flash1977

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So I got the bike running pretty good . Without baffles that is. I have dual 1.5 inch open exhaust, but I had put a set of slightly modified eBay baffles in. I have a 35 pilot 180 main and I have the clip four down on the jet needle. I have played with it 5 down and I believe 3 down. I think It was 3 down with everything else the same as before I did the installed the big bore kit. I'm 1 turn out and I have checked the throttle cable . I have volocity stacks on it with a screen in front and another screen with a piece of foam in front of it for the filter. I have the aftermarket aluminium to hose intake? So you know it ran great last year pretty much the same way minus 1 position on the jet needle (I think). So here's the problem the bike idles fine and when I get past 1/4 throttle it's good to but right when your turning the throttle in every gear or at least first second and third it seems to stumble and buck . It's worse if you are getting going on a incline. It reminds me of when I learned to drive a standard for the first time. It's not terrible and I get through it but I'd like to get it right. I'm leaning towards ordering a set of 37.5 pilot jets . With that said I'm gonna order a set of longer baffles to quite it down and retune it but until then I need to ride it. I would like to get a good setting here because it may take a while to get the a sound I like. I haven't had any luck getting it to sound good. Also it's worth mentioning that yesterday when I started this process I was trying different amounts of fiberglass around the baffles to get it running right . It wasn't until I pulled them out that the bike came alive. It sounds a lot better with no baffles then it did before. Going from 650cc to 750cc made a big difference in the sound the bike makes. Anyways I'm sure this has been asked before but I never have much luck searching the forum, so if you can point me in the right direction of just give me your opinion that would be great . Thanks. I put a couple pic up to.
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Nice looking bike Flash. Assuming timing is good and valves set,camchain adjusted. What plugs,gap and heat range ? Also have you done a plug chop
to view the plug for colouration and carbon ? I 'm at 2,500' elevation and have a 750 KIT,34 vm CARBS1'1/2" S WRAPPED ASCOT 1/2 MILE TYPE EX.uNI
4" LONG FOAM FILTERS,NEWTRONIC IGN with dyna 7kv coils, My jetting is as follows
Main 170 ,Pilot #25, needle 6F9 2nd groove (from top) Needle jet P6, slide cutaway 2.5,Float height24mm, Plugs BPR6EIX gap.040 due to the iugn setup
fora healthy fat spark. Bike pulls cleanly through the gears will pull healthy thru the rev range. Plugs are a light tan when I did a chop. Won't quite pull thge last 500rpm in top but I did drop 3 T off the R.sprkt. Still giot an indicated 110mph so I'm happy. If I were to suggest anything after your observation from pulling the baffles and getting an improvement. I would pull the foam covers oiver the velocity stacks to let her breath in more air and see if that free item wakes it up more. Although No filters isn't a good idea for top end longevity., I hope this helps in some way and you make good progress.
 
gunk said:
Nice looking bike Flash. Assuming timing is good and valves set,camchain adjusted. What plugs,gap and heat range ? Also have you done a plug chop
to view the plug for colouration and carbon ? I 'm at 2,500' elevation and have a 750 KIT,34 vm CARBS1'1/2" S WRAPPED ASCOT 1/2 MILE TYPE EX.uNI
4" LONG FOAM FILTERS,NEWTRONIC IGN with dyna 7kv coils, My jetting is as follows
Main 170 ,Pilot #25, needle 6F9 2nd groove (from top) Needle jet P6, slide cutaway 2.5,Float height24mm, Plugs BPR6EIX gap.040 due to the iugn setup
fora healthy fat spark. Bike pulls cleanly through the gears will pull healthy thru the rev range. Plugs are a light tan when I did a chop. Won't quite pull thge last 500rpm in top but I did drop 3 T off the R.sprkt. Still giot an indicated 110mph so I'm happy. If I were to suggest anything after your observation from pulling the baffles and getting an improvement. I would pull the foam covers oiver the velocity stacks to let her breath in more air and see if that free item wakes it up more. Although No filters isn't a good idea for top end longevity., I hope this helps in some way and you make good progress.
Click to expand...
Thanks for the detailed response. As far as I can tell the timing, valves and cam chain are all good but time will tell.i have had the foam covers off but I don't think it makes much difference either way they are just for looks as far as I can tell. The screens stop more debris then the foam does I'm sure.I have not done a plug and never have. Im sure that's the best way but it always seems like, a little more fussing than I wanted to go through and so far I have gotten close enough for the street. With that said I still have more work I'm sure at WOT . The rpms don't quite rev high enough before I have to shift. I also changed the rear sprocket for better highway speed but haven't gotten out of third yet, I'm still riding around town trien to get her dialed in as well as taking it easy for a break in period. I have the Hughes Hand Build ign. And charging system and haven't changed the plugs yet so I don't know what they are. They say HHB where there should be a ID#. I will find a set of like the ones you have tomorrow if available and order a few jets in each direction. I may look into a dyna coil as well . The one I have comes with the HHB kit. I would love to get a set of nice chrome ascott pipes but they don't fit with the forward controls that I'm not willing to part with, so I'll have to keep playing with the sound with different baffles I find to modify. I see a set of 8"and a piece that's 24 inches long that I can make a 12 inch baffle with. I think I'm gonna try that. The bike is ridiculously loud and not a good either. I don't know if I mentioned before that it seems to get a little bit worse, not a lot but a little worse when warm. And it has stall a couple times but rarely when coasting in first gear.
 
gunk said:
Nice looking bike Flash. Assuming timing is good and valves set,camchain adjusted. What plugs,gap and heat range ? Also have you done a plug chop
to view the plug for colouration and carbon ? I 'm at 2,500' elevation and have a 750 KIT,34 vm CARBS1'1/2" S WRAPPED ASCOT 1/2 MILE TYPE EX.uNI
4" LONG FOAM FILTERS,NEWTRONIC IGN with dyna 7kv coils, My jetting is as follows
Main 170 ,Pilot #25, needle 6F9 2nd groove (from top) Needle jet P6, slide cutaway 2.5,Float height24mm, Plugs BPR6EIX gap.040 due to the iugn setup
fora healthy fat spark. Bike pulls cleanly through the gears will pull healthy thru the rev range. Plugs are a light tan when I did a chop. Won't quite pull thge last 500rpm in top but I did drop 3 T off the R.sprkt. Still giot an indicated 110mph so I'm happy. If I were to suggest anything after your observation from pulling the baffles and getting an improvement. I would pull the foam covers oiver the velocity stacks to let her breath in more air and see if that free item wakes it up more. Although No filters isn't a good idea for top end longevity., I hope this helps in some way and you make good progress.
Click to expand...
Hey I noticed that I have a 2.0 round slide cut away on the left carb and a 2.5 on the right carb. This is how they came from tc bros. The left side is a vm34B 168 which also puts the air mixture screw on the inside or right side of the car . I did some googling and found that many times this set up is for front and rear cylinders like say a virago. It has worked so far on this parallel twin but being that I'm having so much trouble dialing in the mid section of the throttle Im wondering if I need to change jet needles, but then I discovered the slide difference.
 
Flash1977 said:
Hey I noticed that I have a 2.0 round slide cut away on the left carb and a 2.5 on the right carb. This is how they came from tc bros. The left side is a vm34B 168 which also puts the air mixture screw on the inside or right side of the car . I did some googling and found that many times this set up is for front and rear cylinders like say a virago. It has worked so far on this parallel twin but being that I'm having so much trouble dialing in the mid section of the throttle Im wondering if I need to change jet needles, but then I discovered the slide difference.
Click to expand...
I got my carbs from 650Central rEAL GOOD SERVICE AND knowledge all the way. fortunately both carbs came with2.5 cutaways. yOU'LL NEED ANOTHER 2.5 or 2.0 DEPENDING ON WHICH You choose.
The 2.5 will give slightly more air flow . A good thing if you are too rich. Try contacting t.c.bros and informing them of the mistake. to clarify take a pic and clearly indicate which side of the slide the guide pin slot is on that you need. I have the same issue with the pilot screws L.H. carb has the screw on the inside and the r.h one is on the outside so easy on that one.. So I bought a long thin slotted blade driver and it's either under the seat or slid down between the h/lite and top bar clamp to be handy . It reaches the l.h screw over the intake bell on the r.h. carb. Need a small flashlight in low light . Hope the carb slide issue works out with T.C.Bros. for you.
 
Flash1977 said:
So I ordered the 2.5 and it does run better but I'm still having trouble the mid section. I keep wondering if there's a different jet needle I can try. Maybe a double taper or something. Are you aware of any options.
Click to expand...
What colour are your spark plugs coming out? I ordered 4 different needles all researched in the SUDCO Mikuni Carb Tuning manual that is IMO
the bible for anyone wanting to nail down carb tuning. Each needle has it's dia. measured in the manual every 10mm along the needle FOR EVERY TYPE
of Mik. carb. Having tried them all and making a tuning chart to record every change including needle groove selection. I wound up back at the 6F9 needles
Michael Morse from 650Central installed and recommended when I bought them. A big tip of the hat to him and I had a big helping of humble pie myself.
But it was a real good learning process. What trouble is it having? If your plugs are sooty black drop the needle by going UP a couple of grooves. that will lean it out a bit on 1/8 to 1/4 throttle roughly. Also a small cheat it to drop 1 size on the main jet if you have a 190 or 180 in there. It will slightly reduve the amount of fuel to the jet needle and hence the needle jet over the throttle transition. FYI I am No expert but I've gained some others far wiser and learned thru my mistakes and successes. I hope my advice helps you get closer to a good running bike.
 
gunk said:
What colour are your spark plugs coming out? I ordered 4 different needles all researched in the SUDCO Mikuni Carb Tuning manual that is IMO
the bible for anyone wanting to nail down carb tuning. Each needle has it's dia. measured in the manual every 10mm along the needle FOR EVERY TYPE
of Mik. carb. Having tried them all and making a tuning chart to record every change including needle groove selection. I wound up back at the 6F9 needles
Michael Morse from 650Central installed and recommended when I bought them. A big tip of the hat to him and I had a big helping of humble pie myself.
But it was a real good learning process. What trouble is it having? If your plugs are sooty black drop the needle by going UP a couple of grooves. that will lean it out a bit on 1/8 to 1/4 throttle roughly. Also a small cheat it to drop 1 size on the main jet if you have a 190 or 180 in there. It will slightly reduve the amount of fuel to the jet needle and hence the needle jet over the throttle transition. FYI I am No expert but I've gained some others far wiser and learned thru my mistakes and successes. I hope my advice helps you get closer to a good running bike.
Click to expand...
I believe I have 185mj and a 32.5 or 35 pilot. The problem I seem to be having is while I have got the 1/4 and wot pretty good the middle seems to stumble. So I have gone up and down on both jets a couple with every combination of them and all 5 needle spots and all I manage to do is mess up the the 1/4 and wot while the middle seems to stay for the most part the same, or just a little worse. During the the process I discovered the different round slides and have now changed them to 2.5 ,but still the the mid section has stayed while a little better, the same. This has got me questioning what could I be missing that effects just the mid section that I could try . I'm pretty sure I have read everything I could find on here and elsewhere but I do recall not being able to find a link to to one of the suggested readings . Do you have a link for the Bible your speaking of. It may be worth going threw again.
 
Flash1977 said:
I believe I have 185mj and a 32.5 or 35 pilot. The problem I seem to be having is while I have got the 1/4 and wot pretty good the middle seems to stumble. So I have gone up and down on both jets a couple with every combination of them and all 5 needle spots and all I manage to do is mess up the the 1/4 and wot while the middle seems to stay for the most part the same, or just a little worse. During the the process I discovered the different round slides and have now changed them to 2.5 ,but still the the mid section has stayed while a little better, the same. This has got me questioning what could I be missing that effects just the mid section that I could try . I'm pretty sure I have read everything I could find on here and elsewhere but I do recall not being able to find a link to to one of the suggested readings . Do you have a link for the Bible your speaking of. It may be worth going threw again.
Click to expand...
Hang on. I'll go grab my carb book and get it off the cover
 
From my own experience I wound up too rich with 35 and 32.5 pilots and 190 then 180 mains.The leaner I went the less the bike acted up in
the same way. I'm wondering. Do You have any other pipes you could swap on for a test ride ? My hunch is that the long pipes may be causing excess back
pressure and the extra displacement and breathing can't exit out at the flow rate needed. Not criticising your choice of pipes.
 
Flash1977 said:
I believe I have 185mj and a 32.5 or 35 pilot. The problem I seem to be having is while I have got the 1/4 and wot pretty good the middle seems to stumble. So I have gone up and down on both jets a couple with every combination of them and all 5 needle spots and all I manage to do is mess up the the 1/4 and wot while the middle seems to stay for the most part the same, or just a little worse. During the the process I discovered the different round slides and have now changed them to 2.5 ,but still the the mid section has stayed while a little better, the same. This has got me questioning what could I be missing that effects just the mid section that I could try . I'm pretty sure I have read everything I could find on here and elsewhere but I do recall not being able to find a link to to one of the suggested readings . Do you have a link for the Bible your speaking of. It may be worth going threw again.
Click to expand...
Still have not confirmed what jets are in the carbs?
How the hell can anyone help?
 
AUTOMAN said:
Still have not confirmed what jets are in the carbs?
How the hell can anyone help?
Click to expand...
10-4
I posted the jetting that worked in my similar engine . It's the best I have to offer on my limited knowledge.
Still no reports on spark plug colouration. Sadly as well there seem to be a lot of bike shops/retailers selling inferior carb kits.
 
Ok, so I have finally got some more info on plug color and the emulation tube size. The rest of the jetting is listed in the original description (I believe). I would have gotten back sooner but I have a lot of other stuff going on and I just haven't had the time to take the carbs apart or plug check . Anyways I have discovered that I have a 159 Q-2 on the right and a 159 P-6 on the left which makes sense because my right plug is rich and my left pug is lean and they seem to stay that way no matter what position I shut the bike of at in relation to my throttle. Also I put a new set of plugs in ( NGK bpr6es) and gaped them to . 04 I believe. And I just did that to match what Gunk had posted . I also ordered a set of NGK bpr6eix for the same reason. Right now I plan to order another Q-2 to richen it up . The fact that I get slite backfire (through the carbs) mostly when cold and it's seems to studder mid throttle coupled with the fact that it seemed to get a little better when I replaced the same left carbs 2.0 round slide with a 2.5 round slide to match the right carb makes me think that I need to start by make ing the carbs the same for one but also making the left carb richer so solve both fuel problems I'm having. Anyways Your thoughts? Also I am currently retorqing the head or all the bolts on top of the rocker box as well as the three on the head.
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