Hello All:

Trying to revive a 93 CBR 600 F2 that sat w/o stabilizer for 6 months and currently will only run on on full enrichment. Used the Search function in an effort to benefit from the misfortunes of others and it would appear I'm looking at becoming more familiar than I ever wanted to with the "carb cleaning" sticky. In the unlikely event there is something really simple I'm missing, thought I'd see if the collective wisdom of the Forum can help.

And as if things are not bad enough, the vacuum control on the petcock is no longer functioning and may have been left in "on", slowly replacing the gas in the float bowls with varnish in all the places it's not supposed to be.

Here's where things stand: At full enrichment, the engine starts and runs at about 2500rpm, and will accept throttle inputs although return to 2500rpm "idle" is somewhat slow. Even after allowing the engine to warm up for as much as 5 minutes, any effort to back off enrichment results in an immediate stall. Exhaust is clear and does not smell rich.

Only efforts so far have been to drain floats and replace with a shot of carb cleaner into the main fuel line from the petcock. Left to soak overnight, drained and reattached fuel line to petcock and refilled carbs with 6 month old fuel from the tank. Same symptoms.

Realized petcock may be in worse shape than I thought and when I pulled the vacuum line and sucked on it, was rewarded with a mouth full of 6 month old gas :-(. Pinched off vacuum line. Engine runs as before, but now enrichment can be backed off 1/4 inch before stall (progress?).

All pipes are hot. 2300 rpm "idle" is somewhat unsteady.

OK, so now that I've answered my own question, (see first paragraph) it's time for some of you who have "been there, done that" to weigh in.

Thanks for reading my thread.

 

How long before new posts appear on the site?

 

Usually instantly. I would start off by taking the carbs apart and cleaning them. Theres a helpful guide as a sticky.

 

I would think that this might mean that you're main/pilot jets are clogged. IIRC, the choke mechanism basically bypasses the main/pilot jets.

What's funny too is that your bike idles at 2500 rpm with the choke fully engaged.. my bike will end up revving up to 4-5k rpm if I leave the choke on too long.

 

Main jets have absolutely nothing to do with the idle circuit. They don't really affect anything under 6k. The choke mechanism doesn't bypass the jets, it's an enricher. It allows extra gasoline in to create a rich environment.

With the choke on, enough gas is entering for the bike to run, but not enough for a full blown rich environment like it wants. If it's properly rich, it will rise to 4-5k when warm like switched said his bike does.



Pilot jets are friggen tiny on bikes. They easily clog. You need to remove and clean those carbs. No way around it, no fuel additive you can make work... it needs a cleaning. Prepare to remove those carbs!

 

+1 clean the carbs.

 

That doesn't sound right shouldn't be any fuel in the vacuum line. It was the small hose on the back of the petcock right?

 

If it ran fine before, and then just sat for 6 months without stabilizer, definitely look into cleaning your jets. It's not that hard and will give you the confidence you need to further maintenance the rest of your bike. It is all doable and will save tons of money.

Just use the sticky. You can do it.

 

Hello again.


In an effort to not be one of those folks, I'm back with an update on my situation with son Matt's '93 CBR600F2. Just wish it was the "happy ending" mentioned above .

Let's start with the fuel petcock. Disassembly revealed a torn main diaphram that was leaking fuel directly into #1 cylinder through the vacuum line. $39 later and an easy repair. No more mouthful of gas when I suck on the vacuum line and the petcock functions properly.

As many suggested, Matt and I used the excellent post on carb cleaning and followed all the instructions to arrive at what should be a clean set of carbs (we also used a can of compressed air from Office Depot).

When we first pulled the carbs, we discovered the pull side throttle cable was down to it's final strands and the frayed end was likely causing the high "idle" (2500-3000), so the cable was also replaced. Good thing it didn't break during his trip to Cabo last year.

The old fuel was drained from the tank and replaced and the float bowls were topped off. Here's what happened on the first start effort: with full enrichment (choke) the bike fired immediately and revved to about 2000rpm. Warming the bike for 2-3 minutes and then backing off the choke results in an instant stall. Restart with full choke is immediate, and blipping the throttle results in good throttle response. It just won't run off choke.

Sounds like the carbs need to come off once again, and I'd appreciate any thoughts on areas that need special attention.

 

When last I reported in, the '93 F2 had just had a carb cleaning but still refused to run without the choke. Pulled the carbs again (gluttons for punishment may want to read my post at the end of the "carb cleaning" sticky :-), removed the float covers and soaked all the jets in cleaner overnight. Knew my likely trouble area was with the pilot jets, so special attention was given to them. Took all four out into the bright NV sunlight and could not see a thing through any of them (Yea, I know, the same ones I said I cleaned in the first sentance).

Could not blow carb cleaner or compressed air through, so took the tiniest wire I could find (copper from an extension cord) and pushed it through each jet. Finally able to blow air and cleaner through the jets, but was amazed how tiny the openings are.

Back together, hit the starter, and after a bit of adjustment of the idle control, the bike now idles off choke and throttle response is crisp.

Lessons learned:

1) Don't not let bikes sit for months with fuel switch on and a bad petcock diaphram. Gas slowly leaks into the float bowls, evaporates and leaves behind varnish in the pilot jets and other places it does not belong. (BTW, I'm not so enthusiastic about fuel stabilizer as I used to be. I'm thinking back when carbureted engines needed a highly volatile fuel, stabilizer was important because gas wanted to evaporate quickly, something about low vapor pressure, as I recall. I believe fuel injection made volatility less important and today's gas may not evaporate as fast...any thoughts on this? Anyway, I just shut off fuel to my '93 Nighthawk and it's fires right up 6 months later...go figure).

2) Research problems thoroughly on the CBR Forum before posting questions.

3) Pay special attention to the pilot jets. By comparison, the bores in all other jets are cavernous.

4) Check throttle cable routing...just because they were above the frame when you found them, does not mean that's where they belong.

5) Wear safety glasses when spraying carb cleaner into tiny holes .

6) Use a dremmel tool (tm) to cut a slot in the D-shaped pilot screws. If you are going to pass on a carb sync, the slot (that will extend into the surrounding collar) will at least let you put the pilot screws right back where they were (close enough for me :-).

7) Use a cordless drill with an adjustable clutch and a 3" extender to run the 746 Phillips screws on the air box assembly in and out...your forearms will thank you.

Thanks to everyone on the Forum who shared their 411!

Be safe.