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Post by johnjones on Nov 29, 2022 9:32:55 GMT
Eeks, that is a dangerous thing to do, disconnecting a plug whilst engine running, but yes, proves a point I suppose...
GET SOME NEONS !!! You will be glad you did.
Carb number please.
I assume there is fuel in the float bowl...
And which side carb is being problematic ?
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Post by rustyrescue on Nov 29, 2022 13:55:50 GMT
I have flashing plug leads, but pulling totally proves that cylinder is nor running even though it has spark. Its wasted spark so both spark t0ogether too so the coil is always able to discharge the spark! It is the left cylinder causing issues. and I think only lower down the rev/throttle range though not ridden it. I will double check fuel in float bowl but there was when I last opened both up! Being a 400n it has the round air valves on the side....what symptoms do they give if they are not good? because I just took the left one out again for another inspection and although the diaphragm looks ok, no light seen through I think it leaks, it is like fabric sandwiched in rubber and the rubber looks creased on both sides in one place and I am fairly sure it leaks through the fabric inner.
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Post by buster on Nov 29, 2022 16:41:33 GMT
I suspected those diaphragms on my 400, tried it with 450 carbs on (diaphragms bodged by a previous owner) and it popped a bit on a closed throttle but nothing out of the ordinary, so I got a set of 250 orings to do away with the diaphragms, never got round to fitting them yet though, my problem was pilot jets
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Post by rustyrescue on Nov 29, 2022 17:04:22 GMT
I can blow through the idle jet and air comes out in the throttle body, so its not blocked....I can't tell if the fuerl to the jet is blocked though. Put new well sealed plugs over them too. Perhaps somebody can say what symptoms are with a leaking air stop valve diaphragm.
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Post by rustyrescue on Dec 3, 2022 20:18:43 GMT
the air valve is done on the left carb (not right as yet cos cant get to it on bike) It now seems to run on 2 cylinders at idle speed when warm BUT idle is generally poor. It sounds lean...little pops and spits and the occasional stall. The air screws, how do they work? do they lean out if unscrewed or go richer? I am not sure if by letting more air in (unscrewed) it draws more fuel through the idle jet.
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Post by buster on Dec 4, 2022 15:18:02 GMT
the pilot screws make the mixture richer as they are screwed in (tightened) this can be seen at the plug as it go blacker. opening the screws will therefore make it leaner ( theres a saying in racing that lean is mean) that will show up at the plugs as white/grey. if its running lean its also likely to be running too hot and that much closer to detonation, its much safer to run on the edge of rich, a nice brownish tinge on the plugs says its about right.
I'd start from the factory setting, one and a half turns out from fully closed and see what happens. very minute adjustments have quite a large effect if everything is working as it should
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Post by rustyrescue on Dec 6, 2022 19:04:25 GMT
thanks Buster, I'm quite good at doing carbs.....just been setting up a four cylinder four stroke with bigger idle jets, main jets and moved needles plus an extra drilled hole in the piston. That is as a result of pod filters, different exhaust etc. I just could not fathom these carbs on the SD, I think they may need a further clean, It is only lean on very slow speed...its not even ridden for test yet. It ticks over at about 1200rpm, but occasionally spits/pops on one...actually I think right hand one now. The revs pick up and drop a bit too. I will add I cant get the exhausts sealing well yet on the new collector box seals and the left down pipe to head seems to be puffing a bit....none noisy, just can see fumes.
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Post by rustyrescue on Mar 9, 2023 15:48:58 GMT
An update, The 400N sat in the garage in disgrace for a while after the ongoing running issue whilst I played with other projects. I have now taken off the carbs again, replaced the diaphragm valves/springs/o rings on the carby sides and cleaned them again. Back together on a remote tank it started easy!! both cylinders and ran fairly well before final tweaking other than left carb is overflowing. Hopefully I can drop the float bowl and clean out the needle valve or even put the original needle back in as I replaced them from the overhaul kit.
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Post by buster on Mar 10, 2023 5:40:26 GMT
sometimes the float valve needs a bit of help seating, when I turn the petrol on after any carb work I have a couple of plastic handled screwdrivers in my hands and tap the float bowls with the handles as they fill, once they find their way they are usually ok
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Post by rustyrescue on Mar 10, 2023 11:31:48 GMT
Buster...good call but already tried that with my plastic hammer!! I do it on other bikes too. I have dropped the bowl and blown air though, will try and check float level in situ too in case I messed it up whilst in bits last time.
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Post by rustyrescue on Mar 13, 2023 19:05:33 GMT
the leaky needle valve seems ok having dropped the float bowl and fiddled, and the float height was correct. It starts easy, runs well in workshop but not test ridden yet. It has adjusted to a nice steady idle and carbs balanced. The only issue is if I rev it steady at say 3000rpm in neutral is has the occasional pop through the exhausts. It may be lean but all is good in the carbs, however despite all new sealing rings on the collector box I have not stopped exhaust leaks....they can be seen after start up fuming. I wonder if these are causing the odd pop through the exhausts? perhaps a good ride and getting warmer may help the seals.....one down pipe seal is leaking on the head too so needs new copper seal ring.
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Post by rustyrescue on Mar 16, 2023 22:13:50 GMT
Losing the will with this one!! I thought it was sorted but no.......left cylinder still an issue. It starts on two lovely, it warms up on both pots. But once choke is off it runs on one cylinder at idle speed or up to near 3000rpm where the left cylinder kicks in. when it is running on right one only if I pull the choke out a bit the left one starts up!! It rides well, other than below 3000rpm of course! It has good compression. It has spark on both even when the left is not running at lower revs..... Can only be carb related I think but not sure where on the carb. Idle circuit?? I cna remove them with my eyes shut now
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Post by buster on Mar 17, 2023 8:32:29 GMT
could be worth trying a carb rebuild kit, keyster do a reasonable one, the needles can wear and cause low speed running issues
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Post by rustyrescue on Mar 17, 2023 9:35:43 GMT
maybe, the needle did not look worn when doing the other bits on carbs. A couple of things....
the idle air adjust screw......is that air as it says so further out is leaner? or does it actually meter fuel at low revs? I notice it does not have much affect on the left one compared to the right one.
At low revs below 3000rpm I would assume it is the slow running circuit that is most important and a likely culprit still? usually needles control about 1/4 to 3/4 throttle, idle circuit up to about 1/4 and main jet the final 1/4.
The bike had sat a long time before me, I still feel something may be blocked despite looking at it all!
Anyone got a left carb for a 400N?? just the main body would be fine.
Could be worth a try using another carb.
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Post by buster on Mar 17, 2023 11:59:00 GMT
I'd agree it does sound like pilot circuit, if the mixture screw isnt having much effect I'd have another look at that, tiny adjustments should have quite major effects if everything is working properly. I'v probably said it before but the o ring on that screw is good at breaking down and getting stuck in there, maybe a fishing session with a good torch? I think the mixture screws are available as a kit, maybe worth considering too
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