Thumper Club Forum

Technical => Bike Problems/Questions => Topic started by: richardeblack on July 06, 2021, 01:31:49 PM

Title: Replacement for XBR500 carburettor
Post by: richardeblack on July 06, 2021, 01:31:49 PM
Hello All,
Anyone fitted a non-CV carb to an XBR?  I am having so much trouble getting one of  my XBRs to run right.  Seems ok on the carb from my main XBR but even with all the internals from my road one, none of my other carb bodies seem to work properly.  Nothing obvious, cleaned them all out thoroughly etc.
Main reason for asking for help is that I'd like to fit a simple carburettor on it. 
Has anyone fitted a concentric?  They are so simple if a little crude.
I am Thinking of a 40mm carb.
If anyone has any ideas I would be very grateful.
Thank you.
Richard.
Title: Re: Replacement for XBR500 carburettor
Post by: TB on July 07, 2021, 01:33:55 PM
Hi Richard,
Not considering how much you would like to spend, this is what you should get:

http://mainjet.de/nws/product_info.php?info=p61_vergaser-mikuni-tm-40-kpl--mit-adaptern.html

Bolt on modification, no more idle stalling and runs great.
Had it on my old XBR and now on my GB.

Br TB
Title: Re: Replacement for XBR500 carburettor
Post by: welland99 on July 07, 2021, 07:13:38 PM
I think I've seen that model of carb advertised on eBay before.
Title: Re: Replacement for XBR500 carburettor
Post by: SteveC#222 on July 07, 2021, 09:21:40 PM
I know that if you are tuning an XBR for more speed/power they generally use a Mikuni TM40 flat slide carb. Quite expensive though.
Title: Re: Replacement for XBR500 carburettor
Post by: themoudie on July 07, 2021, 10:59:50 PM
Aye Richard, the TL is very nice, but at ~£350, not cheap. An alternative could be the VM38 as used on GoldStars, G50 and SR500.

My friend who has made many Mikuni single carb conversions to Norton Commandos recommends this supplier, Motocarbs. So, here is the link to their website:

Motocarb_Mikuni_VM38 (http://www.motocarb.com/vm38-9.html)

I hope this helps.

Good health, Bill
Title: Re: Replacement for XBR500 carburettor
Post by: TB on July 08, 2021, 07:04:21 AM
It's in Euro's so ~£300.  :)
/TB
Title: Re: Replacement for XBR500 carburettor
Post by: richardeblack on July 08, 2021, 01:54:45 PM
Hi Richard,
Not considering how much you would like to spend, this is what you should get:

http://mainjet.de/nws/product_info.php?info=p61_vergaser-mikuni-tm-40-kpl--mit-adaptern.html

Bolt on modification, no more idle stalling and runs great.
Had it on my old XBR and now on my GB.

Br TB

Thank you very much for that.  Indeed it is a little expensive for me considering I didn't pay much more than that for my main XBR.  I might consider it on one of the XBRs I am planning to put together but I am not interested in outright performance on my road one.  Do you know if it has an adverse effect on MPG please? Also, do you know what jetting your carb is set up with please?  A friend has an old VM40 which I might try although it is probably fairly worn and I suspect the jetting will be very different for the flat slide one.
Thanks Bill, I emailed  MotoCarb about the VM38 as it might be a better option for me considering I rarely use more than 5000 rpm.
Thanks also to SteveC and Welland99.
Cheers,
Richard
Title: Re: Replacement for XBR500 carburettor
Post by: blew on July 09, 2021, 05:01:44 AM
My XBR carb was running slightly rich (probably worn needle/needle jet) so I fitted a carb of identical size (39mm) off a bigger model.I can't remember now if it came off a 600 or 650,but it runs fine and idles perfectly.
Title: Re: Replacement for XBR500 carburettor
Post by: mthee on July 09, 2021, 10:58:39 AM
Here's a link to a catalogue download with loads of detail on the Mikuni carbs. I used it before moto63 very generously sent me the flat slide he had replaced. The TM40 comes with a 230 main jet as standard 👍

http://www.sudco.com/sudco_catalog_vol_38.html