Hey guys,

Another question for you good gents... I took the bike on the highway tonight, first time for that. I noticed a couple things that were slightly problematic. A little background on the bike... picked it up as a project: no fairings, removed the stock gauge cluster and replaced it with a Trailtech Vapor, Vance and Hines exhaust (loud as hell...), stock air filter, unknown if any carb tuning has happened, tucked wires under the tank, etc. Haven't done a ton of work, just enough to get my hands plenty dirty, and then get out on the road. I'm riding in Denver, CO, at a mile high elevation.

The first was that the bike bogs and surges, what I'm assuming is from the air intake. I've read that when guys strip fairings (as mine is), then they can sometimes run into problems with turbulent air causing issues at high speeds. In 5th and 6th, around 50, the bike starts to surge. If I cover the intake holes with my hand, it runs much better. So what's the best solution? I'm thinking about removing the snorkels that lead from the intakes to the airbox. My thinking is that this would present plenty of undisturbed air from under the tank. I'd also thought that this would be preferable to covering the intake holes with tape or something similar, as that might restrict the amount of air the bike could use. Any thoughts?

The second problem is that my RPM's seem a bit high for the speeds that I'm going. I was going down the highway at 85 tonight, and was in 6th gear, at about 7,500 RPM's. I'm still working on nailing down the tach, but I think it's pretty close. That seemed a little high for a CBR600 on flat highway. Can anyone chime in? I've spent plenty of time on the dirt, but am fairly new to the roads, and am not sure if that's unusually high. I haven't checked to see if the sprockets are stock or not.

Any input would be glorious! Thanks gentlemen!

 

You HAVE to play with blocking the air holes or rejetting the carb when you go naked. The Hurricane's air intake system was not designed for ram air. A naked bike with the ports opened becomes ram air. It is doable, but very picky to pull off. The easiest way is to partially block the air inlets, or put a cover over them with the airflow coming from the bottom.

 

Your getting too much air...but you also have aftermarket exhaust which improves the speed the exhaust escapes from the engine. You need to re-jet the carbs. Restricting the air alone will not solve the problem.


Have you done a plug chop? I wouldn't run the bike like this because you are likely running way too lean and could do damage to it.

 

Dennis, what's a plug chop? I apologize, I'm not terribly familiar with the term.

 

Is it better to partially block the vents, or to remove the snorkels from the airbox, thus removing the ram air effect? I've experimented with using gaffers tape to block the holes, and it definitely helped top end performance, and eliminated (for the most part) the bogging at speed, but seemed to make the bottom end a little sluggish.

 

Anyone?

 

Try it and see. It will be all about trial and error. You can also drill your airbox and block the main 2 inlets completely.

 

You need to re-jet your carbs...as suggested in previous posts. You need to do a plug chop or have the exhaust gas tested with an O2 sensor (sniffer) to determine fuel burn. The things you are doing with changing air flow are questionable at best and running wide open throttle with a lean condition (which is what you likely have) has the potential to destroy the engine.

Plug Chop how-to

 

Wow, I have never heard of cutting the spark plugs apart. Oil filter yes, but spark plugs no. You can see the ceramic tip without cutting the threads out. Your posted photos show a good range of plug operation.

There are a few caveats for reading plugs.
1. They only show the last 30 seconds of engine operation.
2. You have to kill the engine immediately, then yank them on the side of the road. Any idle down time or normal driving after the range you wanted to read them in is burned off by the other idle time.

It will shows significantly lean or significantly rich no matter what, but the actual operating range needs to be done immediately to see.

Then to tune the carbs read this:
https://cbrforum.com/forum/cbr-600f-...et-kit-127567/

 

Funny...that's why it's called a Plug Chop...because you chop them apart. If you read the entire thread they say you do not have to cut them apart but use a good light and magnifier to see to the very base of the ceramic. Your not looking at the tip BTW, you need to look at the base of the ceramic that is inside the plug...look at the pictures again. The tip can be white when the carb is set right...


That is what you want to look at. It's less than 30 seconds if you do the run and shut-down properly. You need to capture the burn at the throttle setting or carb circuit you are tuning. You can do plug chops at different rpm's to determine pilot, needle and main burn, as well as for issues like flat spots at a given point in the throttle position.


That's why you carry an extra set of plugs with you to put in the bike so you can get home and inspect the plugs properly.


Not sure what this means...a properly executed plug chop will show all ranges of burn...but an O2 sensor is better. I have one mounted with a gauge on one of my bikes on a bung in the pipe. It shows the fuel burn through the entire range...much better than a plug chop.