Low RPM bogging
 

I've got a 92 CBR600 F2. It's having some bogging issues at low RPMs. I've been doing maintanence to it for the past few weeks. It's got a full D&D exhaust, K&N air filter and a factory pro ignition advance. It may have a jet kit, I haven't taken the needles out of the slides to check for sure. It may also have some internal work. Maybe a big bore or welded and re-ground cams.

What I've done in the past few weeks (in order).

1
- New chain and sprockets (520-14/45)
2
- exhaust repack
3
- valve adjustment
- spark plugs
- carb clean (same time as valve adjustment)
4
- manual cam chain tensioner
5
- clutch (friction plates and springs)
6
- another carb cleaning
- air filter cleaned and oiled

I broke down the other day, because the bike stalled while stopping at a light. Incidentally, the positive also became loose so I couldn't restart it. The bike dying seemed to start after the valve adjustment. However, it was more having to do with the idle more than anything. Fixed that, ran great. It wasn't until after the clutch being replaced that it broke down because of the battery connection loosening.

The dying seems to be a problem that has progressively gotten worse. But what became more apparent now, was an irregular idle and it ran weird. So I'm thinking vacuum leak at this point. Check the carbs, air filter pull them off, re-seat them and tighten everything down. Did nothing to help the idle.

So I cleaned the carbs again and re-seat the vacuum diaphragms just in case. I cleaned the carbs the first time with brake clean, (my research on that was a 50/50 split if that was ok). So I cleaned them the second time with carb clean and a guitar string just in case I missed something and/or the brake clean left a film or varnish. Get them put back on, along with the cleaned and oiled air filter (cleaned, sat to dry for 24hrs. Oiled and sat for 30 minutes.). The bike starts right up and has a good strong, smooth idle. Sweet, throw my helmet on and jacket... Get going and it starts bogging down at low RPMs, get to the mid-range the bike wakes up.

Do some searching for similar issues. Maybe I over oiled my air filter. So I pull that out, turn the bike on and slowly roll the throttle back. I can hear the bike bogging down at low RPMs and then waking up in the mid-range.

So I'm at a loss. I pulled the computer out from the harness to reset it, on the off chance it just isn't coping well with all this work being done. Not sure it it matters with this type of computer, but it can help with other cars.

I also did an oil change with full synthetic and k&n oil filter the same time as the clutch service.

You seem to have done most all of the right things. Sounds possibly, like a jetting issue,
but you're sort of wandering into my "voodoo science" area. Did you sync the carbs and then
do the idle adjust after the valve adjustment and carb clean?
If not, that can make a big difference.

Only other thing that comes to mind is the r/r is failing (look for heat sign on it and the connector).
However, usually the "bog" isn't limited to the low end.
It's more related to the r/r getting hot and failing to supply sufficent voltage to the
ignition circuit.

Ern

I haven't done a carb sync, which may very well be part of the problem. I don't have the cylinder adapters to attach the manometer to. Any idea where to get some. My FZR could use TIG welding tips, so I grabbed a set of those, they were too big.

I haven't synced the carbs. I was going to, but between these issues I've mentioned, and the fact I don't have the vacuum port adapters I'm SOL on the carb sync for now. I don't know where to get them, or if there is a hardware store alternative. I tried MIG welding tips (which work on my FZR600), but no luck.

Sorry about the double post, my phone didn't show that it had posted the first one, so rewrote it.

I got my adapters from the Honda dealer, if they are the same as the F3 they are the 5mm.
Cost is about $2.50/per adapter. Why hunt for make-shift when the correct piece is so cheap.
You should only need 1 (if any). I thought the f2 (with the vacume line to the petcock)
had all 4 nipples. My F3, using a manual shut-off only needed the #1 carb, the other
3 were there, with a teeny-weeny little boot over them.

To do the idle adjust, you will need a RPM guage accurate to +/- 50 RPM and the 'd'
adapter tip for the pilots. Unless you have little-bitty hands a right-angle wrench will
be needed to reach the pilot-jets when you do the adjustments (with the engine running).
Here's the one I use...Motion Pro - Carb Tool 90 Degree w/Bits

Although they have less espensive models, as well. Here's a link to all of their carb
tools...Motion Pro - Quality Motorcycle Cables, Tools and Controls

Hope this helps, Ern

Hey, Thanks for the help MadHattr059.

As I figured, either it was the excess oil, or I just happened to miss something while cleaning the carbs last time. So going back through fixed the problem.

Basically I did a quick clean of the pilot jets, and made sure both main and pilot were tightened properly. Got the carbs put back on, the way that I cleaned them left fuel in the bowls, so I started the bike up sans filter and tank. It bogged down like before, but something seemed different, it sounded less choked. So going out on a limb, I threw the cleaned and lightly oiled air filter and gas tank on. Started it up, and with each blip of the throttle, the bogging slowly went away until it eventually vanished.

So now it's onto adjust the idle screws, and then a carb sync.

Speaking of the idle screws, on my FZR they could be tuned purely off of the header temp of each cylinder. There was basically an optimal operating range, and you tried to sync the temps as close together as possible (+/-5 degrees). I'm don't remember if that was just an FZR community thing, or was a method in the manual they cited. Has anyone else done that with the CBR? If so, what's the general operating range?

I think you can synch to temp on most anything but I don't think it's overly accurate. Another way to adjust your mixture is to plug chop but that can be a royal pain on these bikes. I've heard of people on the Yamaha forum I'm a member at having good luck using colortune plugs but I've yet to try them.

Strictly a personal thing here but I was having a similar issue. After tons of reading I finally decided to scrap the K&N all together. I rejected for my emgo paper style high airflow filter and it runs like a top now.

I also read another member here, Kurishomo or however he spells it, fixing this problem on an F3 by replacing that air seloniod on the bottom of the intake box. Sorry I forget the exact name of it off the top of my head lol but hopefully you know what I'm talking about. I think this tends to cause more a bucking sensation rather than bogging but it's something to look at I suppose.

rejected = rejetted
Have to love the auto correct on my phone lol.