Slight "flat spot" at 4K

[bubba]

Hello everybody, I have an '82 850 with 13K on the clock. Just had the valves adjusted carbs cleaned and balanced, new Suzuki petcock. Starts great. Goes down the road great too. I think I have a small "flat spot" at about 4000 rpm. It will accelerate quickly from there with no hesitation. I say "I think" because I am not familiar with this bike and I am wondering if it is all in my head. Could I possibly have a coil going bad? No popping at decel and great voltage output with the help of dunnage and one of his Honda RR's. Any ideas? Or am I just nuts?:-D Thanks.

[bubba]

Maybe I stumped everyone with this one, I am now running a can of Seafoam through it. That may be helping. The bike runs sweet in the lower gears, just this problem at about 4000 RPM in 5th. Almost seems like it is running out of gas. I no longer think it is in my head, but does not happen all the time. A real head scratcher. I guess next I will look at the coils/wires. I hear the wires are not replaceable, So I guess it would be a set of Dyna coils or an Accell kit.

[smagnusen]

I'm probably not the right person to answer this but since no one has I'll put in my two cents. I hope the sea foam works for you.

Your coils are probably okay, make sure you're getting a good blue spark. You could check your timing and make sure it's set correctly.

Also, even though you've rercently had your carbs cleaned and balanced, you may have some room for tuning. Here's a great article on the subject that's been posted here before. It takes a couple reads if it's your first look at carb tuning but well worth it. Good luck.

http://au.geocities.com/ozcross250/needles.html#carbtuning1

[KEITH KRAUSE]

A feeling of hesitation or fuel starvation, most noticable at steady cruising speeds as you mention, can be related to clogged or kinked float bowl venting lines or passages. Be sure any lines are routed correctly and you can easily blow into them, which should also verify the vent passages to the float chambers are clear. Even a semi-blockage will effect venting and cause some fuel starvation.

[BassCliff]

Hi Mr. bubba,

If I'm in top gear and I roll on the throttle at 4000rpm, it will accelerate, but at a fairly "leisurely" pace until it reaches 6000rpm, then it really takes off. 4000 is at the bottom of the power curve so there's really not much "umph" there.

If you really want to accelerate quickly, you'll keep the revs above 6000 as you go up the gears. When I'm in 5th at 4000rpm I'm doing about 60mph. If I really need to goose it from there I'll drop a gear and twist the throttle. At 60mph in 4th gear you motor is turning about 5000 and can accelerate a little quicker from there. Heck, our bikes can do 65mph in 2nd (at redline)!

I'm not sure if you really have a "flat spot" or if you're just lugging your motor when trying to accelerate in top gear from such a low rpm. But perhaps one of the "more seasoned" owners who knows more about carbs and ignition can enlighten both of us.

Have we seen pics of your bike yet, Mr. bubba?

Thank you for your indulgence,

BassCliff

[Dave8338]

I had a very similar issue with the 650 and found the solution to be, raising the jet needles about 1/2 a notch using washers (I had them on hand-but they can be purchased at Radio Shack or similar) and the problem was gone. I wouldn't say it is a problem, except that I don't like turning 6000RPM before shifts (unless I WAN'T TO) :twisted: and mine will now lug solid, without hesit.. ta....ttation, from below 2000RPM's, up to where ever I want "9000RPM's" when being flogged by a local Harley guru that lives up the road from me. Just don't like the smell of Harley exhaust, I guess. :-D

[hikermikem]

how many washers is half-a-notch?? Or better yet, what does that translate to in mm (in)?
]
thanks

[Dave8338]

how many washers is half-a-notch?? Or better yet, what does that translate to in mm (in)?
]
thanks

I installed two of the ones that I had per slide (thickness varies) and is equal to roughly .5mm.

[hikermikem]

Thanks Dave.

.5mm or approx. .020" I assume is the thickness of EACH washer then?

only asking because I'm trying to get a thumbsuck on how much to raise the ones on my "85 550L to "enhance" the performance - I have a bunch of #4 SS washers on hand, & I believe I'll just use one under each needle to see what happens.

Thanks,

[bubba]

Thanks. I just bought a Clymers off e-bay so maybe I will have a better idea of what you are talking about with the washers. Do I need to take the carbs apart for that? I had the carbs cleaned and synced by a mechanic. One carb doesn't bother me but four are kind of intimidating. I would hate to mess up my sync job. No Basscliff I have not posted any pics yet but I will soon. I have to say I have learned so much about these bikes in the short time I have owned one, and it is all from this site. I can't believe the amount of activity here. I would have thrown in the towel a long time ago if not for all the knowledge here.

[RotaryRodder]

All you have to do is take the top cap off and pull out the jet needle. You will need some circlip pliers (at least on mine) to take off the cap holding the jet needle in. Then its just pull it apart and put a washer in the bottom before you put it all back together.

[KEITH KRAUSE]

Maybe I stumped everyone with this one, I am now running a can of Seafoam through it. That may be helping. The bike runs sweet in the lower gears, just this problem at about 4000 RPM in 5th. Almost seems like it is running out of gas. I no longer think it is in my head, but does not happen all the time. A real head scratcher.

I'd still look into my first suggestion because it's easy to do.
As for raising the jet needles, I'm not against others suggestions but if the carbs jet needles are in factory position/condition, the factory jetting can't be at fault for your symptom. You'll just be compensating jetting, which really just causes other problems. If your bike is running lean at all or not flowing fuel correctly, it's not because of stock jet needle position.
Also, it's not about rpm, it's about specific throttle position when testing the various jetting circuits.

[bubba]

O.K. I took the bike out today and the problem is getting worse. I poked around the air filter and found that it was not fully latched on one end. I put it in correctly but no help. I will look into the venting issue next. Putting the choke to the 3/4 position helps a lot so now I am starting to suspect the o rings on the intake boots. I ordered a set and replacement screws today.Less than $10. The boots themselves look to be in good shape. I may attempt the surgery myself, or I may take it in. Would my carbs have to be re-synched after this? This whole thing has been a PITA but it's a lot cheaper than a new bike.\\/

[KEITH KRAUSE]

It's always a good idea to vacuum synch the carbs if you don't know when they were last synched.
Replacing the manifold o-rings now, wouldn't effect a previous synch as long as there were no intake leaks during that synch. Any valve clearance adjustments or ignition timing changes or just normal riding could change the synch.

[KEITH KRAUSE]

Also, if you had any significant intake leaks, you would notice the fully warmed up "idle" rpm's would be quite a bit higher than at first start up/still not at normal operating temperature rpm's. That's the classic intake leak symptom.