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Carburettor Jet Cleaning - Page 4 - Fuel System/Carbs - The Lotus Forums Jump to content
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simonf

Carburettor Jet Cleaning

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What keeps the fuel mix from dribbling through the progression holes before the butterflies move past them?  Does the air rushing past it keep it in place?

Probably, that & the small size of the hole restricting it due to surface tension, remember that the air/fuel mix is being sucked out on the downstream side of the butterfly by the vacuum created by the piston.


Cheers,

John W

http://jonwatkins.co.uk

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Upgrade today to remove Google ads and support TLF.

At last got my carbs running the way they should be, after hours of black magic trying to set the ballance and miture and never getting it to idle properly i noticed loads of empty space in the fulle delivery line, went to the boot and found the pump was only sporadically pumping. Bit the bullet and ordered another new pump from SJ, thanks Steve for superfast delivery, fitted the new pump, ballanced the carbs again and hey presto probably ticking over better now than hse has done for a long time. Another job of the tick list.

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All the twiddling in the world won't help if there's no fuel !! That's the sort of problem you never think of, as it's soooo obvious.... I remember when I disconnected the fuel pump by dislodging the connector to the inertia switch.  This was just after I had fitted a new cambelt following the original breaking, first week of ownership.....I'd booted the inertia switch whilst grovelling in the back... Engine started, ran nicely for a few seconds, then stopped and wouldn't restart. Took me hours to realise the cause.......(!) Ran perfectly for years after that.


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Yep, but aint it great when you find the fault and she goes like a dream again.

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John, did you take the opportunity to upgrade the pump or go for a direct replacement?

I ask because I gave up trying to set the points on my original SU, and invested in a Facet - must add that i don't get starvation problems anymore, but did have to fit a fuel regulator.

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I went for another SU but contactless, bit more expensive but then add the cost of a regulator to the price of a Fawcet it wuld be much the same, in saying that I have just fitted a Fawcet to my S3 with no problems.

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The fuel volume screw allows more or less fuel engine side of the butterflies the butterflies control the air so with limited air you adjust the slow running volume (mixture) screw to get the correct mixture at slow running. when you get over say 3000rpm the mains take over they have there own jets matched from air control top jet. fuel main jet bottom one. so it delivers a fuel air mix carb side of butterflies aided by the vacuum pull from the air flow through the carbs which is determined by the amount butterflies are open andy b

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I was cleaning the detritus out of the carb bowls yesterday, if the main supply of air was supposed to be via the butterflies at idle, then how is that the acetone was held back by the butterflies?

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No vac being pulled

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Surface tension and the meniscus effect. Air will readily flow through places that liquid won't. Also, with the carburetters stripped, the butterflies are probably fully shut...whereas on the engine they aren't, or it won't run.


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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Are we back here again?

Can a mod please insert an auto loop back to the first post every time you get to the end, save retuning all that stuff out and arguing over the same things again! :)


Chunky Lover

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Surface tension and the meniscus effect. Air will readily flow through places that liquid won't. Also, with the carburetters stripped, the butterflies are probably fully shut...whereas on the engine they aren't, or it won't run.

It's the carb with the idle speed screw, so it has the butterflies at the same position as idle,. With acetone there's not enough surface tension to stop it running through a reasonable gap, the sort any reasonable volume of air would get through.

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sorry people my fault read page 3 did not notice it went to 5 the end

andy b

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Once I've seen an engine running at idle with all four chokes blocked, then I might become a believer. Won't ever happen.


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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I rebuilt my carbs but I fear that I neglected to give the jets a good clean. They had been running ok but looked in a terrible state.

After refitting them, I now get a "cough" back through the carbs.

At first I thought it might be a timing issue and since the books say to check the timing before going too far with balancing, I looked to check the timing first. This was at 6 BTDC but then I noticed that the rotor arm was for a 25D distributor and my S1 (sold the S2 & 89 turbo for this late 76 S1) is fitted with a 43D4 so I fitted the correct rotor arm and as a result the timing is now 8 BTDC. This is correct according to the manual, but I see many ithers are running nearer 12 BTDC. Should I increase?

I've set the butterflies so they are both open the same amount. With a Carbtune II meter fitted, I've now seen that the carb nearest the flywheel as running sweet with good vacuum, but the carb nearest the front of the engine has NO vacuum whatsoever. I've opened the idle by-pass screws so the amount the butterflies are open shouldn't matter, but no difference. Should I adjust the butterflies so that the carb on the right (nearest the engine front) is open more?

I've replaced the distributor cap, fitted magnacore HT leads, new plugs and a new coil. The engine starts fairly easily. All plugs are sooty (therefore rich) so why would it be coughing, I thought that was a sign of a lean mixture? Changing the mixture just effects idle, the cough is there whatever the set up.

I've tried spraying carb cleaner around the O rings but don't get any change in idle, but I didn't replace them when I did the carb rebuild so will take the carbs off again and fit new misab rings just to be sure.

Only other thing I can think of is stripping down the righthand carb again and this time pay more attention to cleaning or replacing jets.

All views and comments much appreciated.

Thanks guys

Bill

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Having read more threads on here, I think I've answered this myself - I've cut corners on the carb rebuild.... Shall remove and do again, but will be more thorough next time!

Bill

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