Advice on where to go for help with carburation?

Tom Gaynor

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Carburation tips

I always mark the throttle of any bike at closed, half-throttle, and full throttle. That way it's easy to tell if a problem is slide, needle, or main jet. In my experience slide is more often a problem. The air levers can be used to check if it is too weak at any point - in fact I've just done it. (The rear slide is a bit weak, spits a little.)
What I haven't done, but plan to do, is to check the balance with a gauge I bought for a Guzzi Le Mans. For that I'll have to tap holes into the manifolds, like wot modern bikes have. However, when I balanced the Guzzi carbs, I found that synchronising the slides was only part of the job. It was balanced at tickover, went wildly out of balance when the throttles were opening. This meant much twiddling of mixture screws, but the motor was noticeably smoother once it was done.
If you are tempted to go the same route, do not buy a gauge with "dials". They aren't sensitive enough. Carbtune is the way to go.

 

Tnecniv Edipar

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Was just about to advise similar to andygbsmith !! Although our cherished machines are low tech in a high tech world , they can benefit from that high tech ! Plug reading and other seat of the pants methods of AFR (air/fuel ratio) adjustment are ok to an extent , but with worn carbs you don't have a prayer of getting it any where near correct over the full operating range. New carbs or a carb overhaul is a prority before you proceed with fine AFR adjustment. An AFR meter as recommended is great , but the best way to set up carbs is on a Dyno !! Find a local bike Dyno shop , arm yourself with jets , slides & needles (they won't have any !) and knock yourself out ! It will feel like a different bike ! Economy will be optimised , no rich running so the engine will last longer due to the engine oil not being diluted with fuel and it will be so smooth you won't believe it !
 

captain vincent

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Non-VOC Member
Clean out the large banjo bolt that holds the float to the carb body which is notorious for holding water that ingresses via washing/or riding in the rain.This gives the excact symptom you descibe as the water goes up and down depending on the air velocity cuting off the fuel.If you ride your bike alot in Scotland on original carbs you have to do this every couple of months.

Regards

El capitano.
 

Rapide998

Active Forum User
Non-VOC Member
Depends on the throttle opening that the symptoms appear, if you were running on the "pilot" it could be partaly blocked,
A number of years agooo I found this on mine and came to the conclusion it was because I used fuel from different branded petrol stations and with the "Devastator" sitting in the garage until the Weekend arrived, the fuels reacted with each other which may be the reason there were very small hard granuals sitting inside the float bowls some of which had been sucked into the pilot jet.
Perhaps that was not the reason after all and I was thinking a load of boll.x, but I cleared the detritus from the jets and now use only fuel from one brand of pertol station (where possible) and have had no more problems.:)
 

Tom Gaynor

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VOC Member
Water in the carb base nut.

El Capitano makes a good point. If the bike will run at low speed and cuts out as soon as the throttle is opened, you can be almost certain. My Rudge does it a lot probably because of the way the bellmouth is placed (it has a bigger than standard carb).
It ought to clear after a while, but in my experience, that's "a long while". Easier to stop and fix it.
A refinement is to tip the contents of the base nut into the palm of your hand. If it is water, the globule of water will be clearly visible in the pool of petrol. It produces the warm glow of satisfaction you want when a guess turns out to be correct.
 

Pharquarx

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Non-VOC Member
Buy yourself and air fuel meter, it is the best money you can spend.
you will be amazed at how rich the bike is running on standard setting.
http://www.innovatemotorsports.com/products/lm1.php
check them out and decide for yourself.
I have done 3 Vins now and they were all to rich and ran much better after some rejetting(considering the limitations of the Amals)
Andy

Hello all,
Finally got the Comet roadworthy for rides here in California. Now that I have been put out to pasture, I have time for projects like this. Have a question - I am going to buy one of the LM-1 meters as recommended as it is really the only way that I can satisfy myself that I have done this correctly. Plus as you can see below, I have lots of vintage machinery, so it will also be useful elsewhere. When using this meter, does one set everything at idle or is it a progressive thing at various speeds. I am running an Amal 229/L12R on my 1950 Vincent Comet.
Thanks guys,
 

Hugo Myatt

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VOC Member
Don't know all about this chopsticks stuff but surely you can hear throttle/cable synchronisation. If you close the throttle slowly with a dead engine the slides will come to rest with a single click if the cables are synchronised. If not you will get a double click and one is closing before the other. I can still do this even with 40% loss of hearing.
 
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