mk5 carbs

[digcot65]

Morning, I have stripped and cleaned both carbs, but I found it is not possible to lock the choke plunger down.With it being so cold I cannot start the bike I held the choke slide down and turned the knob, but no luck.I suppose with this weather below freezing it is asking a bit much to start without choke I also found one of the carbon brushes in the magneto is missing which I have to order.Does anyone know the best place to obtain these brushes? Len

[eddie]

Len,
       If the choke plungers don't lock down, the spring clip is most likely worn or missing. In the carb top, there is the hole for the choke slide, across that hole there is a narrow slot. This slot should have a 'hairpin' spring in it that locates in the cut in the choke plunger. Having said that, the bike should start without the need of the choke slide (providing you 'tickle' the floats).
  You say you stripped and cleaned the carbs - did you remove the choke blocks? With the choke blocks removed from the carb bodies, on the engine side of the block and just below the main choke, there is a shallow drilling (about 4mm dia) - that drilling has a small hole going up to the main choke, another larger drilling to one side, and a very small drilling in the centre - this is the slow running petrol feed and can easily get blocked (resulting in no tickover and difficult starting).
  Regarding the magneto brush - these can be obtained from any of the magneto repair specialists.

  Regards,
                Eddie.

[digcot65]

Thanks again for the excellent help.I will remove the carbs tomorrow and check that these holes are clear.I called into a local classic car spares place this morning and they gave me a new carbon brush, great !!!

[digcot65]

Thanks for the help, I take it that the choke block is the brass fitting inside the carb body as on the photo.I had a look at one the other day and noticed how tight it was in the carb body, is this normal? Also, do you remove it from the bottom or the top of the carb body?  Len




[Attachments converted to linked images. 03Dec21 -Doug, Admin]

[eddie]

Len,
       Yes, the choke blocks often are a very tight in the carb bodies - this is usually due to corrosion forming between the brass block and alloy body. I usually resort to a liberal spray of WD40 around the base of the carb, then with the base fitting replaced, but wound back about 1 turn and a suitable sized socket placed on top of the choke block, give the whole assembly a gentle squeeze in the vice until the block gives up and moves. Progressively unwind the bottom fitting 1 turn at a time and squeeze again. At this point, it should be possible to tap the block out of the carb body. It is quite possible a lump of the corrosion has caused a blockage in the small drillings. You will find there is also a small drilling in the bottom of the bore of the carb (just above the slow running screw) that needs checking for any blockage.
  When rebuilding the carbs, apply an extremely light smear of grease to assist with the replacement of the choke blocks (and subsequent dismantling) - to much grease will tend to block the small drillings and adversely affect the carburation.

  Regards,
               Eddie.

[digcot65]

You have helped again.I removed both choke blocks which were quite tight and it does look as though the holes may be blocked.I am soaking the blocks in cellulose thinners and then I will blow them out with the air line.Thanks again Len

[digcot65]

I`ve just contacted the restoration company I bought my classic car off ,and they will ultrasonically clean the parts for me ,which is ideal. Len

[Hampshirebiker]

Stick to thinners (long soak) & airline for the jet (choke?) block. IMO.

[Daren W Australia]

Hi I use one of these www.ebay.com.au/itm/Aucma-600ML-Ultrasonic-Jewellery-Watch-Glasses-CD-Cleaner-Sonic-Wave-Clean-AU/152878816608?epid=2157600720&hash=item2398499d60:g:pLMAAOSwHtJafqkt I clean all my carbs in it just use metholated spirits you would not believe the crap that comes out Daren

[Hampshirebiker]

I bought one for about £100 & wasn't impressed. It seemed to rely more on temperature & addative than agitation of the liquid. A mini dishwasher in my book. OK for cleaning surfaces, but not effective on carb. jet blocks etc.
Meths I'd never considerd and will give it a try. What about temperature? I'm a bit wary of that with a combustable fluid.

[digcot65]

The company I bought my classic car from are a high-quality outfit.The ultrasonic sonic cleaner they have cost over £1000.Since they restore cars worth up to£ 1.5 million they have the best Len

[Rex]

I'd still want to poke the orifices through afterwards...

[digcot65]

I love poking  Len

[Doug]

There are ultrasonic cleaners, and there are ultrasonic cleaners. We were given a very small commercial one, probably originally intended for the jeweler's trade. It always worked feebly. Perhaps turned on too many times without any fluid in the tub (supposed to be bad for the ultrasonic element.) The larger one where I once worked was noticeably much louder in the spiky noise department, and worked very well.

So it is probably to do with the condition and power of the ultrasonic element used under the tub. Vigour is everything!

Not that it stops anyone, but flammable liquids are no-no.

-Doug

[digcot65]

I have just collected the carbs after being ultrasonically cleaned, they look very very clean, now I have poked all the holes to make them absolutely clean.I am waiting for a new main jet, the original one was in the needle jet at an angle for some reason.Possibly I will not receive them till Monday so will have to find another job to do. Len