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Post by buster on Jul 17, 2021 10:41:45 GMT
my vb31 carbs on the 'thing' are still not quite right (stood for probably 20 years or more) and its a low speed running glitch which usually says to me the pilot circuit. this diagram is not SD but it shows nicely how the pilot system works  so on our carbs we have the air intake  the pilot jet (under the rubber bung), I'm told that its fed by a little crossover hole from the main jet hence the bungs  and the upper part of the pilot circuit  and finally the inlet  |
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Post by buster on Jul 17, 2021 10:49:50 GMT
personally I'v always favoured an airline for cleaning carbs but I confess I'm struggling to get these perfect. the problem is I cant get the nozzle directly onto these two brass fittings to give them a good blast out, the circled one seems (oddly) to go to the pilot jet itself so I'm assuming the other one goes to the inlet? the arrow is just the air intake. hmmm, might have to bite the bullet and get one of these fandangled supersonic cleaners after all... |
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Post by comstar on Jul 19, 2021 5:02:19 GMT
Fantastic info this.
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Post by terryc on Jul 19, 2021 9:59:25 GMT
personally I'v always favoured an airline for cleaning carbs but I confess I'm struggling to get these perfect. the problem is I cant get the nozzle directly onto these two brass fittings to give them a good blast out, the circled one seems (oddly) to go to the pilot jet itself so I'm assuming the other one goes to the inlet? the arrow is just the air intake. hmmm, might have to bite the bullet and get one of these fandangled supersonic cleaners after all... I use a double action air hammer pump (for blowing up air beds and the like ) they come with a cone shaped adaptor that fits nice and snug in those tiny holes and gives them a good blast through |
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Post by CTB on Jul 19, 2021 21:04:16 GMT
Hi Buster, if you want to post them I’ll put them through my ultrasonic cleaner, see if it works.
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Post by buster on Jul 20, 2021 6:33:42 GMT
Hi Buster, if you want to post them I’ll put them through my ultrasonic cleaner, see if it works. thats a really kind offer carl and might take you up on it if thats ok. I'll dig out a set of 450 carbs and try those over this weekend just to see what difference if any they make |
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Post by buster on Jul 30, 2022 14:08:10 GMT
so a little more on the pilot jets, I had to be sure so...  carbs off and float bowls off, then main and secondary removed (just gives better access) and time for drastic measures. drilled at 3.5mm (I know but I couldnt find my 3.3mm bits) and tapped at m4. got to be really careful when drilling  then with an m4 bolt, nut and some washers the pilot jet can be extracted  hold the bolt still and tighten the nut down and bingo  |
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Post by BritPete on Jul 30, 2022 15:20:33 GMT
Paul put them in the post (not for a week) and I will put them through my Ultrasonic for you
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Post by buster on Jul 31, 2022 8:02:58 GMT
Paul put them in the post (not for a week) and I will put them through my Ultrasonic for you thats a really kind offer pete but its more that I had to satisfy my own curiosity and see for myself what state they were in, it also allows you to see that part of the pilot circuit is working as it should. I wouldnt recommend it (unless its really a last resort and your carbs are otherwise scrap) as theres only so many times they will go in and out being a press fit |
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Post by buster on Jul 31, 2022 13:32:55 GMT
if this turns out to be the culprit I shall be more than a bit miffed. I'll also order a couple of 250 o rings and do away with the cut off valves. an interesting aside, I went to my set of 450 carbs (was going to rob a diaphragm out of them) only to find the diaphragm assembly had had the ball cut off the end, some scanning around online would suggest that no one makes a replacement for that type of carb. it also rather neatly explains the popping on the over run when I had those carbs on the 400 thing back to the culprit  loads of straggly bits of rubber when I took it out, could have been blocking airways? |
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Post by buster on Jul 31, 2022 15:50:43 GMT
a minor modification  and its faired up so a run up the road. its better but not perfect, so took the (pattern) air filter element out and tried again, this made it run like a bag of sh*te below 5000rpm but it pulled really cleanly from 5000rpm to 9000rpm (probably could have redlined it but it is over 40 years old) time to search for a better air filter element maybe... |
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Post by buster on Jul 31, 2022 18:38:34 GMT
experiment apparatus one set of working vb carbs, half a cotton bud, one gob (for preference someone elses)   method place gob around area marked in red and blow plug one of holes with the cotton bud and repeat conclusion the slide lifts quite easily when you blow down the holes but if you block one it becomes much harder to get the slide to lift. so if I drilled a third hole could I tune the carbs to run with a less restrictive air filter? I'm thinking start small and work in drill bit sizes that suit taps... |
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Post by BritPete on Aug 1, 2022 8:58:48 GMT
Do I remember correctly on the later carbs the Pilot jet is removable?
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Post by buster on Aug 1, 2022 9:30:18 GMT
Do I remember correctly on the later carbs the Pilot jet is removable? looking around online it appears so, removable on mine now  |
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Post by johnjones on Nov 12, 2022 13:23:06 GMT
Have you tried the redex and petrol soak mix method ?
Also squirty oil can method ?
Many many many years ago twin Choke Webber, oil can method worked for me. I still use that method, messy yes but it works...
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