Topic: At certain RPM's the bike feels like someone is holding it back...

[BarryKelly]

Hey Everyone.

Ok,  78 CB550 that I just put a cam chain/tensioner in, so I had the top end all apart.  I put it all back together, it started up after 3 kicks (yipee!) and let it idle for about 20 minutes before changing the oil.  Then, I ran about 30km (~20mi) and changed the oil again.  Since, I've put about another 70km on it and it seems that everything is tip top shape.

However, I tried it out on the highway, and I noticed something at a certain RPM speed.  Just before 5000RPM (so, just before roughly 100km/hr (60mi/hr), if I tried to accelerate quickly.  It started to really pick up but suddenly it felt as if someone was pulling me from behind.  It's hard to explain, but I guess a sudden loss of power.  It quickly got over this and resumed it's previous peppiness.  I've noticed this happen a few times, always at the same RPM and throttle (just over a quarter maybe, hard to say exactly), but it is not always noticeable.

My question is:  Could this be a jetting issue?  I.E. is one of my jets partially clogged?  The timing and advance is bang on, and everything else seems to be running well.

Thanks and thanks again,

Barry

P.S. I just posted about how I put on a new larger front sprocket.  I did this after I noticed this problem, so the problem is not related to the sprocket.

[heffay]

what kindof air filters do you have on the bike... the reason i ask is if they are more open to the air than normal, the bike could start to run different at higher speeds, due to  different airflow.  i remember on an '89 kawi ex500 i owned i put carb mount k&n's on it and i had trouble with jetting for a while due to the same problem.  so let us know if it happens in all gears at this rpm range or if it is just at highwayspeeds.  if it is at highway speeds this might get you looking in the right places. 

[kghost]

Do the Carbs have vacuum Slides? I'm not really up on the 550.
If it does... sounds like one of the slides is sticking.
If not might be a little piece of trash intermittantly getting sucked over an orifice.

[jvalbuena]

Hey, I'm not a 550 guy so I'm not sure about the carb setup. I have a 77 750 that has an accelerator pump on carb #2. I had very similar symptoms on my bike when the diaphragm on the pump went bad and again when it was out of adjustment. Just a thought.

[Zip]

what kindof air filters do you have on the bike... the reason i ask is if they are more open to the air than normal, the bike could start to run different at higher speeds, due to  different airflow.  i remember on an '89 kawi ex500 i owned i put carb mount k&n's on it and i had trouble with jetting for a while due to the same problem.  so let us know if it happens in all gears at this rpm range or if it is just at highwayspeeds.  if it is at highway speeds this might get you looking in the right places. 

My chop has pods and at highway speeds the bike would bog somethin awful.  I built a cover to go over the top of the pods so that they draw air only from the dead air space right behind the block.  Runs perfectly now.

Zip

[BarryKelly]

Hmmm... That's interesting.  It seems to bog at all speeds... although it's not too bad, I just finished a four hour drive out on the highway and everything ran tickity boo.  I'll check for air flow, and I'll check for the filter being clean.  I wonder, could it be a dirty jet?

[heffay]

yes

[BarryKelly]

Well, I found out the problem in an interesting way.  I have an older battery on the bike, and driving around in the city won't charge it that well.  I was driving around, and (interestingly enough) the bike quit just in front of the shop that I usually get all my parts at.  The whole thing just quit.  I wheeled it around to the back and checked the fuses - figured that that was the problem.  They're all fine, so I thought it might just be a dead battery from too much idleing and not enough high RPM revving fun.  I asked the mechanic for a boost, he came over and pulled the side cover off (he's also got an old 750) and laughed - the battery terminal had come off.  I hadn't tightened it up enough after all of the work I've done on my bike and I guess it rattled loose. 

Anyway, he quickly tightened it up, we had a good laugh, I picked up some parts that I had ordered earlier, and I took off in a plume of happy tire and smoke.  The bikes runs like 200% better.  It has lots of pickup, it revs smoother at lower RPM, it never bogs - it's likea new bike again.

So, I guess the problem was just a poor connection at the battery.  The bike wouldn't be getting enough "juice" for when I really gunned it.

Alls well that ends well, and once again I learn something new!

Cheers

Barry

[gratznic]

Thanks for the follow-up Barry.

I'm running a 550 also. And I have a similar problem right now. It started a few months ago (with weird sluggishness while on the highway), and I found that the problem had to do with my points. One of the point connections was slightly loose - and so it wasn't always making contact. Mech replaced it, and the bike worked fine.

...for a month. And then similar symptoms returned. But now it's even more along the lines of what you've described. I watch my RPMs - at any gear - and it will stick at 4,400 or so (it varies). Then, as the bike warms up (perhaps the battery, um, "warming"?) it will get stuck at higher and higher rpms, until it's running almost normally (occasionally slugging, but just ever so slightly -- enough to keep me worried while I'm on the freeway). Then I park for a while, and I have to start all over when I go again.

Anway, I doubt it's the points again. So I'm going to check the battery!
I cleaned out my jets a few months ago, and that didn't fix the problem (the first time, since it was the points, so maybe I should try that again). I also changed the air filter, and oil.

-Ryan

[BarryKelly]

Unless you're in an extreme temp condition, I don't think the battery needs to "warm up".  Although when they're cold they definately have less power, any motorcycle driving weather shouldn't make a difference.  If it's related to warming up, maybe it's a fuel/gas ratio problem?  I'm no expert, but my bike sure runs differently in the cold compared to the warmth, until it warms up.

Regards

Barry