Hello,

I'm new to this forum as well as being the new owner of a 93 cbr1000f.
The bike is in good shape but it seems to stumble or bog down when I roll
on the throttle in 6th gear and the rpm's are below 3K. It also seems to surge
when cruising at a set speed. The bike appears to have a V&H SSR2 muffler
but I don't know how to tell if the pipe is stock or aftermarket.
I don't know if it's had a jet kit or not. I'm pretty new to all this performance
stuff anyway since my first bike was an 81 kz440.

Thanks for any help you can provide.

 

I'm not a CBR expert but here are some ideas:

If the bike produces full power and has a good midrange, which I assume since you are not reporting such problems, I would go thrue the following to fix the low rpm bogging. They are not written in a best to do order, I would goe thrue the easiets ones first and on.

- Check the plugs and replace them if they seems outdated. If they are unevenly coloured, that will indicate a problem in a specific carb or cylinder.

- If the valve lash has not been checked for long, it might be worth doing, the intake valves are prone to be to tight (i.e. be open if lash is negative). This would normally lead to starting and cold running problems, while the engine later runs fine when warmed up.

- Check that the choke activation goes on/off correct and that the choke wire clamp on carb is securely fixed.

- Clean the carbs including the throttle surfaces and throttle bores. It might be something other than clogged carbs, but after doing that they can be taken off the suspect list for years to come if you also install an in-line filter in the fuel line.

- Check that carbs vacum diafragms are not cracked and that they are correctly seated/sealed. Some grease in the carbs diafragm grooves will make the installation easier so they will stay in groove until locked by the carb/diafragm top cover.

- While carb are removed, check the intake hoses (carb-to-cylinder head) for cracks. The dont seem to be prone to cracking, but i'ts worth checking. To start with, you can check that the hose clams are tightened when the engine is fully warmed and the hooses are somewhat softer.

- Before assembling carbs, set the float levels to spec. I have them set to 9 mm and the bike doesn't hesitate at any rpm.

- Adjust the pilot screws, the initial setting should be 2 1/2 turn out, I would try to open them a half more turn to check if that cures the bogging. Maybe this should be the first check, to aviod more extensive carb work to start with.

- Check carb sync with vacum gauge if carbs are not removed, or just set the carbs to the same throttle blade opening at idle position when the carbs are removed. You could check that they have the same opening by comparing the light stream thrue carbs or use a feeler gauge.

- If the carbs has not been tuned to the aftermarket exhaust system, rise the throttle needles a few millimetres by putting a washer under the needle top button, or lower the needle locking clamp if the needles are adjustable.

Hope that could be of any help and that some other will pinpoint the fault-reason more specific to save you work.

 

Not to be a smart *** but why are you under 3k and in 6th.. You need to downshift if you are going that slow you, your in the wrong gear. I will look when I go to work tomorrow to see where I am shifting but I know I am @ or over 4k.

 

I would check the carb sync first if it were my bike.
Surging is a sign of uneven power.
When the carbs are out of sync you also get loss of power at low RPM.
I would start there because you don't have to take things apart.

Oh, almost forgot... welcome aboard.

 

I would say the same as Stinky...

If you want to ride at low rpm's, then you should get a Suzuki SV1000 or similar

i would say that you shouldn't get below 3000 rpm unless you are in the lower gears [8D]

 

I agree with that, this engine is not designed to be used below 3 k at all during normal driving. But, the engine is very flexible and will not hesitate if by some reason let down to 3 k and the throttle is opened to increase speed.

 

Part of the problem is due to the pipe that is on the bike. The V&H SS2R is known for causing a low RPM stumble.

 

Ok I did some testing on the way to work today.. 3k in 6th gear is 45 miles per hr. and the engine is at total idle (me giving little to no gas)

When shifting extremely conservatively (something that I just do not do into 6th) I am still shifting at 4k

If you are going to run the bike in 6th at 45 mph you are going to get in trouble because you will have no engine braking. So if you have to make a quick stop no only are you going to be stopping the motion of the bike you will be fighting the motor (that is going to be pushing you to till it dies and then locks up the back)

Do not be scared to open the thing up. Unless you are not use to the power. When I am normally ridding I shift at 4.5k or 5. When I get on it up around red line 9- 10

 

Did a few tests today regarding low rpm performance on 6th gear. At 3 k and when the throttle is partly or fully turned, the bike pulls surprisingly well, no horse kick but the fork will raise and there is no hesitation whatsoever. At 2.5 k rpm there is also no real problems but the engine feels real week at acceleration and also begins to run choppy if one stays at 2.5 k rpm at constant throttle on 6th gear. Any acceleration above 4 k on 6th gear feels quite strong, althouh one should gear down several steps if max acceleration is wanted at this modest speed.

 

Sounds good to me. I am not familiar with the pipe. Is it a 4-1? If so, and if the bike is truly having trouble outside of the norm, maybe the head pipe is leaking, if someone did a poor job installing it. When this happens cold air is sucked into the pipe where it meets the head and expands in the pipe when the next high temp. and high pressues wave is sent when the EX valve opens, causing blockage. It is like having a potato shuved in that Ex pipe. Some loss of power at high end but not as much as low end.

In that case I would try to listen for Ex leak at head pipe.