Could somebody help ? Sorry for the long post.
Stock CBR1000fh no mods
My bike hasn't been started for a while, since last year when she had new plugs. When she started it was on three cylinders. OK I thought, no problem I'll clean the carburetor jets. So removed air box , pulled off carbs and tilted them upside down back over the cylinder head. Removed the bowls and the jets inside and cleaned out the crud inside. Re assembled , filled the bowls with fuel via the exit pipe from the fuel pump and reconnected ready to start. When I did the engine turned over for about 1second and she fired up just like a new bike. Lovely.

Went for a ride for about 10miles where all was fine until just before arriving home I noticed she was firing on three cylinders when throttling down for junctions. She pulled away ok though. Stopped at home still running at tick over but roughly ( on 3 ?) also had some petrol leaking from a carb bowl no.3 .


So the night took off the carbs as above used a small amount of silicon gasket to seal the bowl. Restarted but still very rough idle. Seemed like exhaust down pipe 3 wasn't getting hot so maybe not firing ?

Today took off carbs again and found a lot overspilled silicon inside bowl no.3. So I thought that must be touching the float and causing it to stick. So removed silicon 'flashing' and tried again.

BUT engine starts ok on choke which can be removed easily but still very lumpy and sounds noisy and clumpy. Revs OK but not very responsive and still cant convince my self its not missing as I think I can hear it try to pop and fire on 4.

Cant understand why the very first time I cleaned the carbs, all worked well , unless the leaky bowl was miss leading and something else has gone wrong during the ride.

Any body got any Ideas. Cheers

 

Air leak on the carb rubbers ? seal 'em good

 

Check plug leads and plug for the cylinder not firing. Maybe some silicon got into the jets......so maybe another clean may be necessary
BTW silicon is NOT recommended for float bowls - ...........

 

thanks for the advice. I'm going to get good at taking them off.
It could be an air leak on the manifold hose rubbers, but the carbs are hard to pull off and put back on with only a compression clip to tighten the rubbers to the carb body. Should i be using any sort of sealant ?

Did check the jets for any broken of sealant and they were ok . And I will source some new float bowl gaskets.

Will check for a good spark today and go for a quick run to see what the performance is like under load as I think she will be fitting on all 4 then. Its the noisy lumpy tick over that has just started and doesn't sound right.

Hope to post more info later today

Thanks
mikey

 

OK an update. Checked spark plugs and made sure that there is a spark. Started up and squirted some light oil onto each down tube . With 1 , 3and 4 the oil vaporized instantly . With no. 3 the oil sat on the downpipe for 0.5s ish before it boiled off. So cylinder 2 does not seem to be running right.

To be sure I removed the HT lead from no.2 and started up. Yes absolute no question . I now know the sound the bike makes running on 3 cylinders and its worse than this. So am I mad ?

So I've posted a youtube video for you to listen for yourself.Note the slow die down after a rev up . It has sounded far better than this. Here is the link

http://www.youtube.com/watch?v=MxXsXyqXj3E

This was after a quick two mile run up the road where everything else seems ok as in pulled up to to 50MPH ok and cruised at this no problem.

I have found in the Haynes manual a statement about putting some engine oil on the carb inlet ( manifold ) rubbers. But I think thats just to aid pushing them back on . And just to recap , its only carb 3 with a small amount of silicon gasket onto of the original to seal it.

Any advice would be great
thanks
mikey

 

Next time you lift the gas tank, check for the little rubber cap on the tubes for balancing the carbs. If the one on #3 carb is missing it will run extremely lean. Don't ask how I know this.

 

I was sat there this afternoon thinking what can I do next. So I did this.

1.Started from cold
2.Sprayed each downpipe with light oil as soon as I could , within 30s of starting
3. no.1 and 2 the oil took a little time to evaporate
4 3 and 4 vapourized it straight away.


Hmmmmmm so is No. 1 and 2 getting a weak mixture ?

5. Carbs off to inspect those jets again
6 No.1 carb pilot jet had a bit of crud inside after a prevoius clean, of a resonable size.
7 No. 2 had a hair up the outside of the main jet

Still need to do 3 and 4 .
So I'm hoping thats it as if I understand correctly, the pilot jet has an effect on idling etc.


Thanks Slowpoke , but I've got all 4 rubber caps. But are they sealing ? something to check tonight.

Thanks every one for listening
Mikey

 

100%.
So easy to plug those little jets if you get any bit of crud in there.

 

Any time you pull the carbs apart you need to re-sync them. It sounds to me like they are out. If #3 butterfly is not as open as the other three the head pipe will feel cooler when you start the bike up. If the bike pulls hard at full throttle then I would have to say the carbs need to be synced.

 

Thanks guys. Nice to know about the pilot jet and I've been thinking about carb balancing as I'm not sure when it was last done.
As I type I've just finished putting them back on with a little grease just to help seal them to the manifold. Now I've just eaten and I'm struggling to get back out of the chair