Not-so-smooth sailing...

If it's broken or just needs tweaked

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DammitDan
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Not-so-smooth sailing...

Postby DammitDan » Thu Jul 06, 2006 10:29 pm

Well, I'm 95% sure that the smoke I'm getting is from leaky valve seals. I've come to this conclusion because from everything I've read, worn rings will smoke more when the engine is revved, and in my situation it puffs for a second but goes away almost immediately. Also, if I let the bike idle when it's hot for about 15 seconds the smoke gets noticably thicker. All of this points to valve stem seals (which I stupidly forgot to change when I rebuilt the head).

My second problem has been with low power output and "rough" running after my carb rebuild. I can get the bike to idle smoothly around 1200, and can even get it to stick around 1k but the engine coughs and gags somewhat around that RPM. I can also rev it up and it responds like a champ, jumps up to the RPM and immediately drops back to idle speed.

Problem is, whenever I open the throttle and start moving, it acts like it wants to die and I have to open the throttle considerably to pull out. After this point it seems to "chug" along, making the bike sound quite mean (but I know it's not supposed to sound THAT mean!). On top of this, when I get on the throttle it is sluggish. Not in response... response is pretty decent... but in acceleration. I can go WOT in gear and the bike doesn't act like it's going to buck me off like it used to when I went WOT. To finish it all off my top speed in 4th and/or 5th gear is around 65. Doesn't matter if I max the throttle, it just won't go any faster. It starts to lightly surge if I open it up and keep it open.

When I pull the plugs they're a little dark around the outside edge and white-ish on the tips. I have stock airbox/filter and jetting, but a new MAC 4-1 exhaust. What's wierd is, before I rebuilt my carbs they were running super rich. The bike was running great but it was overheating and coughing and sputtering after about a 40 minute ride (along with the carbs leaking randomly) with jet black plugs.

How is it that I'm running (seemingly) lean now, but didn't change anything?

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Volker_P
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Re: Not-so-smooth sailing...

Postby Volker_P » Fri Jul 07, 2006 1:41 am

I agree with your suspicion on the valve stem seals. Piston rings would mean white smoke at high revs.

Low topspeed and bad acceleration at white plugs, that's typical symptoms of running (much) too lean. Maybe even the engine gets hotter now (different smell/ ticking sound after engine stop when hot?). However the CB650 stock setting is closer to lean than to rich and my spark plugs also tend to look a bit white.
I think the reason for being too lean now is the new exhaust. If you still have the previous one, you may just try to change it back for a check. Aftermarket parts may change the flow system considerably and usually also cost top end power as Honda usually did a very good job in composing the components. So you maybe gain by rejetting, but you might not get up to the previous performance. Before any rejetting experiments, you can check for air leaks in your airbox and make sure that the air filter really is in place correctly and check for forgotten vacuum hoses on the carbs first.
Anything else changed but the exhaust?
I bet your fuel consumption went down considerably. :P

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Vatch
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Postby Vatch » Fri Jul 07, 2006 7:24 am

I too think you are running too lean. This happened breifly to my bike when I rebuilt the carbs. I'd check the fit and seal of all the rubber connections from the air box to the engine intakes.
'99 1500 Drifter

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Ibsen
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Postby Ibsen » Fri Jul 07, 2006 7:36 am

I agree with the others, both about the valve stem seals, and the carbs running lean. In addition to checking for any air leaks in the intake system, have you synched the carbs properly after the rebuilt of the top end and the carbs?

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DammitDan
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Postby DammitDan » Fri Jul 07, 2006 5:18 pm

Yes I've re-synched the carbs since the rebuild. I also forgot to mention that I get a lot of pops when I brake with the engine, and many times get a quick pop backfire when I pull the clutch while I'm accelerating to change gears. I know, it's running lean. I'm working on moving up a size on my slow jet and a size or 2 on my main. Gotta have $$ for that kinda stuff though! ;)

But my big question is, why would it suddenly start running lean after the rebuild when it was running so rich before the rebuild? Before the rebuild it would run great up until about 45 minutes of straight riding, then I think it would heat up to the point where it was starting to sieze.

And will a lean condition really limit your top speed by that much? I'm assuming that if the cylinders aren't getting enough fuel they will just only hold a certain RPM...

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Vatch
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Postby Vatch » Fri Jul 07, 2006 8:00 pm

Running lean will limit top end performance on these bikes. My bike would not break 80 mph on full throttle in 5th when I bought it. After the carb rebuild I've had it to 105 mph when I started thinking about orininal bearings and such and backed off.
'99 1500 Drifter

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Ibsen
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Postby Ibsen » Sat Jul 08, 2006 1:07 am

Yes it can run that bad if it is running extremely lean. The spark plugs are your eye into the engine, and if they are white, the carbs are running lean. I don't know how the compression in this engine was before, but if it has been increased after the rebuild, it can explain why it is running leaner on the same carb jetting. And with the 4-1 exhaust, you might have leaned it even more.
Another thing to check if you haven't already, is the camshaft timing, just to be shure it is correct. Also check that the ignion is set correctly.

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Volker_P
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Re: Not-so-smooth sailing...

Postby Volker_P » Mon Jul 10, 2006 3:46 am

DammitDan wrote:But my big question is, why would it suddenly start running lean after the rebuild when it was running so rich before the rebuild? Before the rebuild it would run great up until about 45 minutes of straight riding, then I think it would heat up to the point where it was starting to sieze.
And will a lean condition really limit your top speed by that much? I'm assuming that if the cylinders aren't getting enough fuel they will just only hold a certain RPM...


I tried to follow your postings. As you did not only change the muffler, but also the pipes, the whole lean setting may come from that. I suppose the pipes inner diameter is considerably higher than the previous ones and also the muffler is much less restrictive. Resonance effects may additionally increase geometrical effects. So it might be difficult to adjust an engine with an aftermarket exhaust without loosing power against stock, especially for older Hondas like the CB.

And to your second question. If you are willing to do your top performance without having breakfast, I might have a job for you. :mrgreen: :mrgreen: :mrgreen:


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