Author Topic: First run on the modded XBR  (Read 761 times)

iansoady

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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.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

Itsme

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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

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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

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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 HONDA ST70

iansoady

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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.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

iansoady

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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.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

xbally

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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 HONDA ST70

themoudie

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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

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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 🍷🧀

AleXBR

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Re: First run on the modded XBR
« Reply #9 on: May 21, 2024, 05:35:21 PM »
My XBR does the same.
I've had the carb off and checked everything and included the recommended jet upgrades (which removed the notorious stalling symptoms).
The only thing which has been suggested is to raise the needle a tad, using suitable washers as spacers.
To be honest, working on the carb is such a ball ache I've decided to ride around the glitch; no big deal, just annoying.

iansoady

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Re: First run on the modded XBR
« Reply #10 on: May 22, 2024, 09:12:35 AM »
Hi Alex, glad to hear you're better.

The problem eventually tuirned out to be dry solder joints on the CDI unit. I think I did a description on the Adv riders' site and maybe even here. I actually found a cheap pitbike version from ebay worked (but not until I'd wasted over £100 on one from Belgium).

Sadly the XBR and its Greeves-Triumph stablemate were stolen earlier this year so didn't have much chance to enjoy it.
Ian.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250

AleXBR

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Re: First run on the modded XBR
« Reply #11 on: May 25, 2024, 08:56:54 AM »
Jeepers!
Astonished to hear of your stolen bikes. From your garage?
They have my curses upon them.
Still got the Norton?
Take care, my friend.

iansoady

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Re: First run on the modded XBR
« Reply #12 on: May 25, 2024, 09:10:48 AM »
Yes, from the garage. Gained entry via the back garden. Fortunately they didn't do any other damage and left the Norton.

I've stepped up security now. Almost literally bolting the stable door......
Ian.
1964 Norton Electra
1969 BSA-Suzuki
1992 Yamaha SRV250