That's the beauty of building a bike for oneself, each of us can tweak it the way we want.

 

I have another little nugget of info that might be useful. Initially I set the bike up with the Fox adjustable shock set at the factory shock length. The bike sat really low at the tail end, which I guess is a fairly common issue on F1s that shows even more with the RR tail installed. Once I extended the length of the shock as far as recommended by Fox - maybe another 6 or 8mm (forgot to measure) - and got the spring preload adjusted to give about 15mm static sag, the rear end ended up about 20mm higher and the bike now has a bit more of the RR rake.

 

Oh yes that does look better. How's the ride?


I have the Progressive rear shock on mine. Will need to check adjustment. I do have a Fox Shock that I could put on there but was saving that for the other bike.


A little tease for the next Hurricane project.

 

Only did a little testing in the driveway so far. My second business really picked up last month and I have been juggling two jobs, so no time to ride. Taking the weekend off and hope to have a report on the ride tomorrow. It did seem kind of mushy before the adjustment. After doing the rear it seemed like the front really wanted to dive under braking, so I checked the sag at that end and it was almost as bad as the back end had been. I upped the fork pressure from 4lbs to 6lbs (with no rider) That combined with the rear adjustment seems to have gotten the rider sag pretty fair at around 35mm at each end, and it seems less prone to dive.

Looking at some photos of stock bikes I would guess that the RR has more rake, but this photo is pretty much a match for the rake of an F4i.
That subframe looks nice!

 

Turns out the ride is great. The bike seems way more composed and responsive now. Unfortunately I am still wrestling with carbs. Last time into them I replaced all the float valves, which cleared up a miss at idle that developed when warmed up. And it pulls great above 4K. However I still have a crappy miss from about 2k-3.5k, that seems to indicate I need to readjust the floats about a millimeter. The natural reaction as it bogs is to roll on the throttle to keep up, and the transition from blubba-blubba to Waaaah! at 4K is pretty unnerving in traffic.

I am getting pretty good at pulling that carb rack. And adding "fuel injection" to my want list for the next bike.

 

Doc,


This sounds like a jetting problem to me. With the less restrictive exhaust you have I would look at larger jets or moving the needles further up.


Have you done a plug chop...you may want to do it at the spot where it is missing...

 

The bike had a Yoshi on it when I bought it and main jets are already bigger than stock, but I can't recall the size at the moment. Maybe .114? Plugs indicate it's an over-rich problem, warm bike gets soggy and blubbers under load just at that narrow 2k-3.5k cruise range and with the throttle rolled on. Above that it runs very well, in fact the transition to running clean is quite abrupt and consistent around 4k. it idles very well, and runs great cold even thru 2-4k. I adjusted the floats when I recently replaced the float valves and my measurement may have been slightly off due to a homebrew float height gauge being used. The condition seems to fit the description in this jetting guide pretty well -

https://cbrforum.com/forum/cbr-600f-...et-kit-127567/

Gonna get into it when I get some time.

 

Carb problems can be all sorts of things, that's why I use a sniffer in the pipe to get accurate fuel/air readings.


Too much fuel from the float height doesn't make sense to me, not as you increase through the transition from pilot jet. Fuel level in the bowls shuts off when full... no matter when it occurs...so where would extra fuel come from? It has to pass through the jets to get to the throat of the carb...


Only way extra fuel could get through is if the float isn't shutting off (hitting the top of the chamber). Then you would have a leak. All kinds of other problems would be present too, due to raw fuel in the system.


Usually float height is adjusted due to fuel "starvation" cause by the float shutting off too soon. This comes into play at a much higher RPM than your situation.


The float is not a metering device. It just shuts on and off when fuel is needed.


I may be all wrong, but if it is running rich as you say it's a jetting problem. The fact that the bike had a Yoshi on it really doesn't matter much. Carbs need to be tuned to the set up you have. Pipe length, baffle type, diameter at the outlet, etc., all this come into play. Air filter also has an effect if it's a breather (K&M and such). Personally I would not assume it is right because things have changed.


You also say plugs show rich condition...did you do a plug chop with fresh plugs? You can't get a reading off plugs that have been in the engine...

 

I agree with your logic, and yet I also find that the rest of the guy's procedure seems pretty well though out.
I should do another plug chop, as the last one was before I replaced the float valve needles. Everywhere else - besides 2K-3.5K when warm and with throttle rolled on - the motor is running exceptionally well, and it seems like the description of the condition matches that in the article well enough that, though it's an unconventional suggestion, it's worth a try. You are right about a sniffer, it could be useful for this situation.

One interesting observation in all this is that the carb kit I bought was really only for 87-88 models, as the Mains included were 105 and the 90 uses 108 for the stock main jets. I also found that the float seat orifices on my bike are 2.4 mm and the ones in the kit are 1.6. That sizing does not seem to be mentioned in anything I have dig up so far so I don't know if the 2.4mm is stock for a '90 or not.

 

Not sure about the different sizes but I think the carbs were changed some in 90.


Did you see at the top of the page on the link you have, that it comes from Factory Pro? That is tuning for a Factory Pro jet kit (Racing). The method is based on the concept that you have to make sure each part of the circuit is tuned at each step. They come back to the float setting because it is critical to high end to full throttle operation and each part of the circuit "adds" fuel. They talk about running lean which is sometimes beneficial for racing but not what you want in a road/street bike. For a road/street bike the float setting is only an issue if you are starving for fuel at top end...shutting off too soon.


Doc, this sounds like an issue in the pilot circuit transition. The RPM is about right. Where are your pilot screws set? Have you tried to tune them with the engine running? Do you know how to adjust them to get the right fuel/air mix? I think we talked about this before...most How To's on the web are wrong about how to adjust this part of the circuit.


They are hard to adjust on these bikes because of where the screws are located. Most low RPM issues are pilot related. Either the wrong size jets, the wrong adjustment or dirt in the circuit. The pilot jets supply all the fuel up until about 2500 rpm. The transition between when the mid or main jet takes over can be a trouble spot if something is not right in the pilot circuit.


Plug chops are very hard to read with the clean fuels we have today...I used to use them only to verify that the engine is not running too lean after it is tuned and running good. It very hard to use them to isolate a flat spot. The fact that the plugs might look rich doesn't mean much in my opinion. Does it smell rich? Is it showing symptoms of being rich? Your description doesn't sound like this to me. It sounds like a jet issue or a pilot adjustment issue...an almost classic description.