Author Topic: First run on the modded XBR  (Read 182 times)

iansoady

  • Hero Member
  • *****
  • Posts: 1601
First run on the modded XBR
« on: May 30, 2023, 10:57:51 AM »
I've just popped out for 30 miles on the revamped XBR500. Thoughts? Comfortable riding position especially with the raised bars, nice handling, light enough, decent power. BUT - it has a terrbile stumble / misfire at around 1/4 throttle opening / 3000 rpm. Idles fine and higher up the range runs well and sounds good with the Goldie silencer.

So I'm suspecting a blocked jet. CV carbs are something of a closed book to me and the carb is notoriously tricky to remove / replace. I wonder whether I can drop the float chamber off to see what's going on in there?
Ian.
1952 Norton ES2
1986 Honda XBR500
1958(ish) Grumph.....

Itsme

  • Hero Member
  • *****
  • Posts: 671
Re: First run on the modded XBR
« Reply #1 on: May 30, 2023, 04:24:36 PM »
Hi Ian

Glad to hear that the XBR is mostly pleasing you. Any first thoughts on whether it has been a worthwhile project? I truly hope that it ends up being the bike you wanted when you set out to make it.

Carburettor stumbles, oh help! Usually there is a blocked jet or something isn't there as you say, but with a cv carb is the diaphragm also a suspect? I found a  tiny hole in the Mighty Midget carb diaphragm so replaced it and it definitely runs better. Also how about float height? I notice that any bike I have had with a cv carb on seems to be more sensitive to float height than a slide carb. No idea why but that is what I've noticed.

Enjoy the fruits of your hard work and hope it is easily sorted.

Ian

themoudie

  • Hero Member
  • *****
  • Posts: 4591
Re: First run on the modded XBR
« Reply #2 on: May 30, 2023, 04:58:00 PM »
Aye Ian,

The Ducati had a similar stumble, when coming off the pilot jet onto the slide and propensity to stall on a closing throttle, once hot and coming up to a junction!  :-[

Took the AMAL MKII #3 slide out and popped a #3½ slide in. No more stumbling, but trashed the rest of the jetting! So, dropped the pilot jet down from #25 to a #20 and all appears to be well.

I know CV carbs are different, but fuel level/float height and primary jet adjustment would be my first thought for a check/twiddle!

If you need new diagphrams, 'O'rings etc, then "NRP carburettor replacement parts" would be worth a try. Link: NRP_Carbs_spares

They supplied good quality kits for both of the SRX 1½ slide/CV carbs when I was rebuilding them.

Hope that you can sort the "Old Bird" out and enjoy the rays, although my preference would be for a canter the the ES2!  ;D ;D ;D ;D ;D

Good health, Bill

xbally

  • Hero Member
  • *****
  • Posts: 935
Re: First run on the modded XBR
« Reply #3 on: May 30, 2023, 06:25:10 PM »
Hi Ian. Thanks for the magazines by the way.I'm afraid l can't offer any useful advice on XBR running problems. Fortunately most of mine ran ok but I would endorse what Bill says. Glad you have now been able to ride your modded XBR . Did you make any changes to the carb set up?
HONDA CB250RSA ROYAL ENFIELD CONTINENTAL GT535

iansoady

  • Hero Member
  • *****
  • Posts: 1601
Re: First run on the modded XBR
« Reply #4 on: May 31, 2023, 08:50:41 AM »
Thanks all, apparently I can get the top off without removing the carb so may have a look before we go on holiday. No rush.

I have to say Bill that the Norton is a far more reliable starter and runner!
Ian.
1952 Norton ES2
1986 Honda XBR500
1958(ish) Grumph.....

iansoady

  • Hero Member
  • *****
  • Posts: 1601
Re: First run on the modded XBR
« Reply #5 on: May 31, 2023, 11:35:59 AM »
Now removed the carb and stripped it. I think I've found the problem - the main jet (152 size) is partially blocked with dark brown deposits. While it's apart I may as well change the 2 jets as advised in the Honda service bulletin. The bike had been stood for a long time before I bought it....

The 2 large rubber O rings on the manifold and spacer (mine has the 2 part sandwich arrangement with a heat insulator) are also well past their best. But the diaphragms (main and air cut off valve) look good.
Ian.
1952 Norton ES2
1986 Honda XBR500
1958(ish) Grumph.....

xbally

  • Hero Member
  • *****
  • Posts: 935
Re: First run on the modded XBR
« Reply #6 on: May 31, 2023, 12:24:12 PM »
Sounds promising you will be able to sort it then
HONDA CB250RSA ROYAL ENFIELD CONTINENTAL GT535

themoudie

  • Hero Member
  • *****
  • Posts: 4591
Re: First run on the modded XBR
« Reply #7 on: May 31, 2023, 01:25:21 PM »
Be able to REELAX on the holibobs in France, now then!

Have a good one, Bill

Moto63

  • Hero Member
  • *****
  • Posts: 3719
Re: First run on the modded XBR
« Reply #8 on: May 31, 2023, 07:03:01 PM »
Yes definitely sounds promising Ian. As Bill say go and enjoy the hols 🍷🧀