I'm beginning to evaluate the recently bought CBR 1000 F -92. Valves checked and adjusted OK, carburators synced OK today. When I try to rev the engine it begins snappy and fine up in rpm, but start to go very rough and unclean with misfires above 6000 rpm. Suddenly it can loosen up and go above 10000 rpm, but not without interruptions. Plugs are new, the coil and ignition cables looks like they never have been changed but seems OK. It happens already in the garage, i.e the engine is not loaded by driving.

Pulse generator restistance is within spec. Resistance between 1-4 and 2-3 plug connectors is about 20 kohms and seems to be OK. It should be an ignition related problem since engine´is unloaded and it feels like a rev-limiter going in at about 6 k rpm in the garage, but I really dont know. Ignition advance varies with rpm and seems OK.

Thankful for any advice, what would be the first thing to check and so on...

 

This is my problem currently (See post 7,000rpm anomaly https://cbrforum.com/m_41913/tm.htm)
The bike is good until 6.5 -> 7k
The difference here is that the bike only does it under load (weather I easy it up or gun it, but not with the clutch in)

I gave the air box a good clean; check lead and fuel/vacuum hoses from the tank and tighten the "Air Ducts"
Now, the bike goes better; the problem is more pronounced and misfires at 7k to 8k then comes good

I did a bit of research last night on the web for this problem in general on any bike and I couldn’t find anything specific, what I did find were Coils; Exhaust (if the pipe fiberglass was stuffed)?; leaking coolant into the cylinder; Carburetion or leaking "Air Ducts"
(This info is only what I found and shouldn’t be taken as gospel)

My next step, for me is to check the coils and take the Carbies out and clean them.

 

Checking the resistance of the pulse generator doesn't work. You have to check the ignition timing with a timing light to see if the pulse generator is working correctly. For high-rpm, the main jet hardly ever clogs up. But the jet needle pulling out of the main jet can be slow if the jet needle/pistons are sticking in their bores. The tops of the carbs have to come off to clean them.

 

Do the Carbie have to come out of the bike to do this?

 

Probably could, but I've always done them out so I could also clean the float chamber jets. But you can test the carbs first.

First, make sure you don't have much gas in the tank. Turn the petcock off, and remove the vacuum hose and gas line from the petcock. Disconnect the fuel tank sensor at the red connector on the left side. Remove the two bolts holding on the front of the tank. Raise the tank and hold it up using the strut rod. Using a needle-nose pliers, take out the cotter pin holding the strut rod to the slide. Put the tank down and take out the bolt in the tank hinge. Carefully lift the tank off the bike. This works better with two people.

Now loosen the four hose clamps holding the snorkels of the airbox to the back of the carbs. Then take out the two bolts holding the side of the airbox to the bike frame. Move the airbox to the rear. With the engine off, stick a finger into the carb opening. Lift the bottom of the piston. There should be slight resistance, but the piston should move smoothly upward. Let the piston drop down. The piston should smoothly drop down. Any stickyness whatsoever, and they have to be cleaned.

Now I remember why the vacuum chambers can't be cleaned on the bike. There are 16 phillips-head screws holding down the four vacuum covers. If you are lucky, you will only strip 15 of the heads. Then you have to use a hacksaw, vice-grips, and a Dremmel tool to take the screws off. I replaced all my screws with M4x0.7, 10mm-long allen-head screws. When you get the covers off, there is a spring under the cover and a thin rubber diaphram attached to the plastic piston. You have to clean the piston and piston walls, without getting carb spray on the rubber diaphram. You also have to clean all the air bleeds with carb spray (wear eye protection). Use some Vaseoline in the groove to hold the edge of the diaphram in the groove. You don't want an air leak at the cover. Installation is the reverse.

 

I'm looking at the manual as I'm reading you post, I think I got the jist of it,
I also notice some sealant around the snorkels where they connect to the air box, would a leak here cause a problem?

Sorry R1000, don't mean to hijack you post.

 

True dat. Nice description of the job.

An extra tip: If you have the carbs out of the bike or at least the airbox off, you can reach a finger inside the bore and hold the slide in the full up position and flip the diaphragm down to mate at the carb. In this position, the molded ring is in the natural position to stay in the groove without trying to flip out. Once the cover is on, even just hand held in place, it holds the diaphragm position correctly and you can release the slide and install the screws. Otherwise, the grease as advised is the only way to do it.

 

A leak here would allow unfiltered air to the carbs. A leak between the carbs and the intake manifold would be a vacuum leak. And that would lean out the mixture.

 

hi r1000 if you need some specs to check coils etc you might find this site use ful just copy paste u will go straight there www.partspartners.com/html/cbr1000.html keep us up dated as i would like to know what the answers is cheers bud
and remember popping and farting at 7000 rpm disturbs your concentration so stay off the beer lol

 

I found a small but probably major fault tonight causing the bad run over 6000 rpm. Primary and secondary resistance OK on coils. The engine reved about 1 k higher with full choke when warm, indicating a fuel delivery problem. I opened the carbs and found that the little spring loaded pin in centre of float valve was totally stuck on 2:nd and 3:rd cylinder. I released them by WD40 and some light preassure. Once pins were released, I noted that float levels differed a lot (almost 5 mm !!) between carbs. I'll adjust the float levels and remount the carb package later this week. I'm quite convinced that it will run much better with working float valve components and settings.