Took the bike out early this season and it felt boggy, like it was running on 3-1/2 cylinders. Upped my Seafoam dosage and attempted a couple Italian tune-ups to no avail. Pulled fairings and found that a mouse had chewed halfway through #1 spark lead. Replaced the lead and thought that might solve my problem. It didn't. Next step was a full tune-up. Plugs showed a slight rich condition with 2-4 plugs all evenly colored. #1 was slightly darker which I attribute to weak spark from the mouse damage. All to no avail. Next up was a carb clean
.
Initial disassembly turned up a completely disintegrated breather filter element.(hence the slightly gritty substance I found in the float bowls). Finally worked the carbs off the bike and .did a quick visual inspection. Noticed that butterflies were open/closed at various positions. Whether this was factory or from a previous syncing, I don't know. I manipulated the slides and heard a solid whoosh and a good, snappy return. All four operated similarly. Removed float bowl covers and found those soft, yet gritty deposits evenly distributed. Removed top covers and found all of the diaphragms intact. Check all of the mixture screws. Mine are the ones down near the float bowls that have that annoying little tit on them that limits adjustment when assembled. All were only about 1-3/4" turns out. Removed them, plus the springs and o-rings and then the jets ( Yes, they were very clogged. Wondered how the bike even ran at all ). After careful disassembly, as thorough a cleaning I could give using carb cleaner and canned air, and an even more careful reassembly, I was ready install them back on the bike.

So I have carbs installed. Air box and all associated lines hooked up. I drain the battery trying to get it to start. Opened the drains on #1 then on #4 and found that they were dry. Check of all the fuel lines Everything looked good. I took the little vacuum line of #1 carb and gave it a gentle suck. Suddenly heard bubbling inside the tank. ( I guess it just need to be burped ) After waiting for the battery to get a good charge, I was back at it. Back at it a bit too early. Battery wasn't at full charge and bike still wouldn't start. Checked bowl drains and found they were now getting fuel. So I waited until the battery got a full charge and here's where my problem begins

Choke on full. Hit the starter. She tries to fire a few times but doesn't catch. Finally I hit the starter and she fires and catches. Immediately idle rises to 2,000 rpm and then shoots to 5,000 and stays there. Turn choke off and it stays at 5,000 Try adjusting idle screw but can't bring idle down. So, here I am asking for advice

A little background
1990 CBR 1000f, U.S., Non-Cali model.
17,000 plus on the clock
No apparent mods other that stock replacement K&N filter installed by me
Bike had been sitting a long time before I bought it on consignment from a local dealer.
Ran great until this year.
One question. If I bench sync the throttles, how open/closed should they be? Can't find data on that, other than a You Tube video of a generic method

 

"Noticed that butterflies were open/closed at various positions." Something's very wrong right there!

All butterflies should open and close together, then you use the idle adjusting cable to set the 'lift' from fully closed. If you fully back off the idle adjusting cable to start with, then try to get all the butterflies moving together and closing together. Finally, just have the idle adjustment a tad off fully closed. That's my 2cents worth.

Of course, also do a full carb vacuum sync on-bike, after you've knocked over the high idle issue.

Good luck,

Dennis

PS, when I know the carbs are dry, I give a good 10 sucks on that vacuum hose to get the bowls filled!

 

Well, well, well. Look who the cat drug in, Mr. Wooferdog. How ya been?

To answer your question about bench syncing, it doesn’t matter where you start. It just matters they are all consistent. I always use a sewing needle act as a gauge. Just place it in the carb throat and adjust until the butterfly valve just touches the needle.
Bench syncing isn’t the end as you still need to get a set of gauges on it. But it will get you headed in the right direction.

good to see you back.

 

I don't know about your carbs....

Just wanted to say hello to woof.

 

Howdy Boys! How they hangin'? I knew I'd get by with a little help from my friends.

How's everyone been coping?

Followed all y'all's advice and had success. Dmoh's comment about the various throttle settings makes me believe the dealer I bought from did a sync on those "barn fresh" carbs. I did a bench sync according to a you tube vid where the guy used a guitar string as a feeler gauge. .010 is the high E on my Tele, so I'm playing with only 5 strings now. Adjusted the idle screw so they had a little more opening. Hit the vacuum hose like a hookah, and she caught and fired. Running way over-rich, not snappy and quite smelly. Downloaded the service manual from SB's link and followed the diagram. According to the placement of the idle mixture screws per diagram, I should go 3 turns out. That seems way too much. Before I disassembled, I noted they were only about 1-3/4's out. Everything's just tacked in place so I'll have to pull them and go back to the preclean setting and work from there. Mixture screws are the slotted ones, outboard on 1 and 4, but inward on 2 and 3. My plan is to go back to 1-3/4 turns on all, use 1 and 4 to find the happy medium. Pull them and set 2 and 3 the to the same amount of turns, That should get me about right on the mixture until I can do a dynamic sync?


This bike has lived itself down in the farming valley where I work There's a certain type of dirt down there that spreads and sticks to everything. First time I pulled the fairings everything was coated with it and something had nested down in the valley behind the cylinders, but all in all, she's in good nick

Dmoh, Hams and hey Demon!

Thanks again for all the help. Any and all advice is welcome

 

3 full turns seems like a lot to me but I don't know the specifics of that generation. I will say that on mine part of the process (starting with #2) is to adjust the F/A mixture screw until the RPM's no longer rise. Then back it off by 50 RPM. Adjust the Idle Adjustment screw until RPM is at 1,200. The repeat this with the remaining carbs. This will get you pretty close to where you need to be. The only thing about this process is that it helps to have a bench tach as the one on the bike can be a little tough to read in increments of something as small as 50 RPM.

 

New problem. #4 mixture screw won't seat properly. Screw, washer and o-ring are intact. Screw threads look good . Screw threads in properly and it just spins

 

Just to verify, you’ve tried the screw in another carb?

 

Sorry for the delay.

Yes I have. #4 screw does it's proper job in #1 carb. #1 screw in in #4 carb just spins.

Go 'Hawks!

 

That is pretty odd. I would have guessed that the screw was buggered up. I can't imagine how somebody stripped out the carb like that. I understand it's somewhat soft aluminum but there's literally no torque required. The only other thing I can think of is maybe somebody screwed the screw too far into the carb and broke off the tip of the mixture screw into the carb body. That can definitely happen. One way to test that is on the #1 carb (with the mixture screw out) take something thin, like your guitar string or smaller, something that will fit down into the hole in the bottom where the mixture screw needle goes, and measure how far down it goes. Then repeat on #4. They should have the same depth. If not, there's your problem. The bad news is it's super hard to get the possible broken tip out. I've never been able to accomplish it. I've given up and purchased a new carb body. Of course it is also a good idea to look at all your mixture screws to insure they are all of equal length. You may have a broken one in there. If so, you definitely have to replace that.