I cut pieces out of sheet ABS that I buy on line. Basically make new pieces to replace the lost or broken part.

 

I agree on this.

One great stuff for repairing ABS is Plastex. PLASTEX, PLASTIC REPAIR KITS, FIX CRACKS, REPAIR PLASTIC

I fixed some cracks of my fairings with it. It holds really good, in fact it fuses completely with original plastic. My biggest repair was to build a entirely new mounting lug on the lower cowl.

But I did one mistake. I painted the plastics about two days after the repairs. This was not long enough as the plastex shrunk a little bit afterwards, showing minor imperfections on the paintjob. I should have allowed more time for curing and maybe in raised temperature.

 

On thegsresouces.com site a very well respected restorer prefers this Plastic Repair Epoxy.
Here's a link to his current project: V50 Guzzi re-paint. He's repairing a GS1000S fairing with the epoxy

 

Let me know what you find with the stumbling at steady speed. This is the last problem that remains with my 87 Hurricane. It accelerates great and runs pretty smooth when cold (for 3-4 minutes). Then, it will hesitate when I am just cruising, especially if I am off the gas and go back on the gas slowly (if I hit it hard, it usually just goes). It feels like some kind of vacuum leak, but the carb mounts are new and not sure I can identify any source of vacuum leak. I am running a set of used carbs from an 89 that I bought and only fixed fuel leaks on, so definitely could be that the carbs need some work. I have the original rack of carbs that I have cleaned and replaced jets and slides on. I thought these had an issue but that might have been due to the electrical problem I ended up fixing (battery would start to fail when warmed up). Now the bike runs at 14 volts steady, even at idle thanks to the new MOSFET RR recommendation from the fine folks on this forum. Please post what fixes this for you since it might help me. I will do the same.

 

FYI: The MOSFET regulator is great. Constant 14v at pretty much any engine speed. No more flickering LED headlight. I highly recommend this conversion.

 

Currently working on my Suzuki GSXR track bike, have a track day this Saturday and the carbs in the Suzuki are also damn old with strange issues.
As for the CBR, yeah at any speed including idling it's uneven, seems like it has a regular pattern of up and down. (clue #1)
If it's a regular pattern that don't change with rpm, it ain't the carbs.
Mine has a manual timing chain tensioner. Been reading about how to adjust it, and will try that soon.
Other opinions I've heard are fuel pump, like it's surging on and off as gas level in the bowls drop, raising fuel pressure up and down.
It could also be whatever sensor is used to switch the fuel pump on and off.
Just some theories I'm considering. Need to know more about how the fuel system works.

 

Not sure if it is useful, but I have noticed that my bike seems to start ticking quite a bit when it starts to have its problems. So perhaps it is time chain slapping due to tensoner issues as you describe. On my bike, I think the fuel pump is ok since I heard it go off the wall one day when I forgot to turn the fuel on; so it certainly will pump like crazy when necessary. I have a second carb rack that I rebuilt; I am going to try that one out again now that my voltage issue is solved and if it shows the EXACT same behavior; then I would tend to think you are right that it is not a carb issue. I will keep you up to date also in case things apply.

 

When I looked for OEM tensioners, none were available-discontinued. Then I learned people replaced them with the manual type because the OEM would stick and were too loose, causing bent valves while using engine braking during deceleration.
A fuel pump test I thought of would be to bypass the pump with some hose, see if the up-down idle becomes steady.
Another cause may be the float needles leaking or just a couple of them. replacing all would not be too costly, but they should be included with good rebuild kits.

 

So I already have a set of carbs where the needle valves have been replaced. It will be interesting to see how that pans out now that the voltage issues are fixed. Will find out soon.

 

Started the painting process. Will spray the red first, then mask off the stripes and paint all else black.
F_ckups changed the plan: had to spray more layers of red because it was a bit transparent, won't be hard enough to tape until next morning.
I painted the fairings that will be all black but darn, missed some undersides on the front cowl, so will have to go over that again tomorrow also.
Using my antique DeVilbiss air compressor.