Topic: Help with runability (jetting issue?) 750 k6

[Cannibal]

Well, I got the bike about 2 mo ago and it's been torn apart for the last month. Finally got it back on the road after a tune-up and light cafenation. It had a hesitation when tipping in from 1/4 throttle cruise and really didn't pull well over 4000. I figured because it had pods and 4 into 2 it would be lean, but with bypass screw 1 turn out, it would fire up cold without the choke and the plugs were black. I eventually ended up 2 turns out on bypass screws and 0 to 1/4 throttle got better, the rest didn't seem to change.

While it was down, I opened up the carbs and found them to be clean, so I set float height (it was only barley off) and put them back on. The jets were 40 and 105. I didn't check the rod height. Adjusted valves, filed and set points at .014, plugs at .030, static timed, chain tensioned etc...

Anyway, I synced my carbs, they were way off, using a home made manometer filled with ATF. Took it out for a test ride and I've made things worse. I'd bet carbs were adjusted before to cover up a jetting issue or something, and now that I've got things right on, all problems are very apparent.

So, it will take off from a stop fine, up to about 4000 rpm while giving it 1/4 throttle. After 4000, it starts missing/backfiring and popping in any gear at any speed. If I take off from a stop faster (over 1/4 throttle), above 2000 rpm it goes: pop, pop accelerate, pop, pop, pop, accelerate, etc...

Also, while idling, I can rev it up to about 1/4 to 3/8 throttle, but if I try to rap it with a quick 1/2 or more throttle, it just goes buaaagh and doesn't really rev at all.

From all I've read on the board, I probably need to re-jet. Any guidance on where to go from here and other adjustments that might need to be made?

Thanks,
Steve

[martino1972]

did you try lowering the clip on the needles???
1/4 to 3/4 is mostly controlled by the needles..
it sounds like shes way lean in that area,if you lower the clip on or 2 grooves,it will raise the needles..
give that a try..

[Cannibal]

did you try lowering the clip on the needles???
1/4 to 3/4 is mostly controlled by the needles..
it sounds like shes way lean in that area,if you lower the clip on or 2 grooves,it will raise the needles..
give that a try..

Thanks for the reply, I've taken the carbs back off and disassembled, and found that of the 5 grooves, the clip was on the 4th from the top. I'm in the process of swapping all of them to the bottom groove. I'll get it put back together, synced and let you know how that works.

Steve

[MJL]

What kind of air filter is on the bike? Kinda sounds like the 650 issue of new pipes and the restrictive airbox cover.

[HondaMan]

did you try lowering the clip on the needles???
1/4 to 3/4 is mostly controlled by the needles..
it sounds like shes way lean in that area,if you lower the clip on or 2 grooves,it will raise the needles..
give that a try..

Thanks for the reply, I've taken the carbs back off and disassembled, and found that of the 5 grooves, the clip was on the 4th from the top. I'm in the process of swapping all of them to the bottom groove. I'll get it put back together, synced and let you know how that works.

Steve

Steve;
Try 2nd from the bottom. That's the most common setting.
The black, sooty plugs themselves will cause the symptoms you're describing, even if the carbs were perfect. Gap the plugs at .028", unless you have Dyna 3-ohm coils installed, then try .035" to .040".

If the bike's been sitting long, the air bleed to te emulsifier is probably clogged or partially blocked on one or more carbs. This is the little brass jet in the air horn: it goes in about 1/8", then down about 1/4", then forward to meet the top of the emulsifier (i.e., "mainjet holder"). It gets blocked about halfway to the emulsifier jet, from moisture entry and dirt or corrosion. It's easiest to clean with a small mechanic's wire, worked in thru the bends, then dragged back & forth 5-10 times, then remove the wire and spray carb cleaner or trichlor thru the hole. You must remove the emulsifier tube to be able to see the wire arriving at this location in the carb, it's hard to see in the small space. This will make the engine run rich above 4000 RPM, no matter what jetting or idle settings you use.

After going to 2nd-from-bottom clip slot, try setting the idle screws back to about 1 turn before making further judgements, too.

One more thing: make sure your spark advancer is actually advancing. It should show full advance by 2500 RPM on a K6.

[Cannibal]

Thanks for all the info. Bike came with cheap pod air filters. They are clean and in good working order.

Mark, the needle (rod whatever the correct term is) was already set at second from bottom. I moved them to the bottom because of the lean issue at 1/4 and up throttle. I stuck some new plugs in and gaped to .028". I did not check the air bleed passage, maybe I'll have to look into that. I had cleaned up the old plugs and reused because I figured I'd just toast a new set if I put them in before tuning.

I synced carbs and took it out for a test. WOW. What a difference. Pulls pretty strong all the way up. I still think there is a bit more to be gained. I was suspect of the advance but have no way of checking it. I didn't realize that a normal inductive timing light wouldn't work (at least the one I tired). I'll have to figure something out. Right now, it's static timed only. Thing runs really well but going from hard acceleration to full throttle quickly gives a small hesitation. There is also a small hesitation when transitioning from decel or light cruise to light/moderate accel. It's not bad, and I can live with it, but I can still see some room for improvement (might be timing issue).

I'll pull plugs maybe tomorrow to see what the conditions are. I just got back from putting 30 miles on the bike, and found out (the hard way) my reserve doesn't work. The fuel on setting sucks the tank dry. Luckily my wife could run some gas out to me. 

Steve

[martino1972]

now if the clip on the needle is all the way on the lowest,i would suggest to go to a one size bigger main jet on the carbs,that way you can bring the clip back to middle position,and have room to tinker around with the clip
running better on the lowest clip means your main jets are too small...

[eurban]

If your carbs aren't clean and or working properly, fiddling with main jets, needle clip positions and idle jets/mix settings is a absolute waste of time.  Doesn't sound like you did a very thurough carb inspection. . . .I would follow Hondaman's advice.  Might keep you from chasing your tail and lightening your wallet unecessarily. . . . .

[Cannibal]

Thanks for the replys. The guy I bought the bike from said he went through the carbs because it had been sitting for almost 20 years when he got it. When I opened them, I found that the jets and everything I could see all looked clean, but didn't investigate much more than that.

He probably moved it to the 2nd from bottom setting because of the Mac 4 into 2 and pods he put on. Then he took out some baffles from the mufflers and probably never changed anything after that. So me putting it on the bottom groove, probably adjusted for the baffles being out. I'll probably order some new main jets and put needle back on 2nd from bottom, and clean air bleed while I'm in there.

So what size you think I'm looking for? From what I've read, probably 115 or 120s?

Steve

[martino1972]

depence on what your main jets are right now,its different for each setup,and things like alltittude etc.
i would go one size bigger then what you have right now,that would bring you closer to perfect already,but you might end up going 2 sizes bigger..

[Cannibal]

Its a 105 and I'm at sea-level. So I should go 110 and move clip back where it was at 2nd from bottom? And if lean, go up to a 115 and leave clip 2nd from bottom.

[martino1972]

that sounds about right,yes
jetting a engine is more of an art then math...finding where the engine is happy,and where the engine is safe(too lean can cause engine damage)might take some trail and error..

[Cannibal]

Ok, thanks. I'll get some ordered up and "play around" with it.

Steve

[martino1972]

good luck,and let us know your findings