Low power under 5k rpm

[johnfellows]

Hey yall, just trying to figure out if there's something wrong with my bike or if it's the nature of the beast. I previously rode an sv650 so am used to that type of power delivery. Anyways when I gun the bike in first gear, it feels quite underpowered below 5k/6k rpm, and after that it starts flying. Could this be a carb issue, a fault with the exup valve, or is it just how these bikes run? The bike only has 9k miles on it and seems like it was well taken care of.

More clues...So I took it out again and noticed immediately after I was giving it full throttle I could smell gas coming from the engine area. It got even worse when the radiator fan kicked on. The bike also seems to bog down more when it is hot. Is it most likely a carb issue?

[djalbin]

Most likely a carb issue. If the bike idles OK, then the pilot jets are probably working ... but the float levels may not be set correctly, a float may be sticking or the carbs may not be synchronized. The excessive smell of fuel points in the direction of the floats. Best thing is to have the carbs serviced. The bike should pull pretty strong from 2K to 3K RPM, idle smooth and not smell like overflowing gas. Should check the EXUP valve while you're at it. It usually affects high RPM if it's not opening but can affect low RPM if it's stuck open (typically it stays closed if not operating correctly). The bike has only 9K miles which means it was not used on a regular bases. These bikes are great when tuned up and running right ... but they must be used on a regular bases to keep them running smooth ... otherwise the carbs will plug-up and run rough.

[johnfellows]

Thanks for the tips. Yeah the bike seems to idle just fine. The last owner said he had the carbs rebuilt about 5 years ago, but I don't believe they have been cleaned since, so I assume it is overdue. The low mileage is also due to the fact that we live in Minnesota and cannot drive half the year, but I'm sure winter storage is not great for carbs either. Could carb issues also be part of the reason the bike seems to bog more when it is hot, or is that likely another issue?

[djalbin]

Could carb issues also be part of the reason the bike seems to bog more when it is hot

If the carbs are supplying too much fuel (possible float issue) the engine will run better when it's cool/cold. Typical cold start uses the choke to provide extra fuel. When the engine warms up you close the choke - eliminating the extra fuel. In your case, you're getting extra fuel all the time and it's like having the choke open after the engine warms up. Other things that may be contributing to it - the carbs may not be synchronized and/or the extra fuel in the cylinders is fouling the spark plugs.
In addition to servicing the carbs - check the spark plugs and replace them if they show signs of carbon fouling (black sooty deposits).
Sitting dormant during the winter can plug the carb jets (main jets, pilot jets, etc ...) Take the time this next winter to properly winterize your bike and you will have a better time of getting it back on the road in the spring.

[johnfellows]

Ahhh ok that makes a lot of sense. It seems likely that is the case, because sometimes on cold starts putting the choke on does not seem to help the bike get going (because it's already getting too much fuel) and I have to burp the throttle a bit. I think the engine is fine though, since the bike starts up immediately when it is warm. Thanks again though, I will check the spark plugs as well when I go through the carbs. I had a fuel injected sv650 before this, so it's all new to me.