hs4 carb needle problems

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ratrodmog
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hs4 carb needle problems

Post by ratrodmog »

So bare with me.
I'm running an HS4 on my 1098 that came with an AAC swing needle installed which supposedly is the stock needle for a 998 Mini. It starts and idles fine but there is a definate 'flat spot' on acceleration and hesitation on cold mornings which I think I'm right in saying means it's running too lean (even with the mixture wound down a fair way to richen it up). I've since bought an AAA needle which was recommended to me and it does pick up nicely, however it's running far far too rich (black sooty plugs, smokes like a train when you give it a bit of throttle and using fuel like it's going out of fashion). I've tried weakening the mixture off but no noticable difference so I'm back to running the 'weak' AAC .
Has anyone got and needle suggestions for a good mid ground? Set-up is pretty standard, HS4, alloy inlet, nothing special.
Cheers
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philthehill
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Re: hs4 carb needle problems

Post by philthehill »


amgrave
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Re: hs4 carb needle problems

Post by amgrave »

If you have got engine oil in the dashpot change it for a thinner one, see if it helps.

bmcecosse
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Re: hs4 carb needle problems

Post by bmcecosse »

Thinner oil will make it worse - use engine oil. The AAA is for a modified engine - not suitable for a bog standard unit. Is the float bowl vertical ? Check if the float bowl is overflowing - when you switch on, does the pump give a couple of clicks then stop - or does it keep on clicking?
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ratrodmog
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Re: hs4 carb needle problems

Post by ratrodmog »

Ok so a few point there to get me going. Slightly unsure needle wise, the AAB doesn't have any info attached however something like the AAU is rated for stage one use in a 998 mini, whatever that meens? I've got some 2in1 oil in the dashpot which I've used in several other carbs with good reults, not sure if the spring rating makes a difference on a fairly standard engine?
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ratrodmog
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Re: hs4 carb needle problems

Post by ratrodmog »

Should have said, the float bowl is vertical yes with no sign of fuel overflow around the breather.
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panky
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Re: hs4 carb needle problems

Post by panky »

Stage one is usually down to fitting decent inlet and outlet manifolds to help engine breathing, the richer needle supplies a bit more fuel for the more efficient engine set up to burn. I've gone a little bit further and have an AAU needle which works well for my engine.

Have a look at this to compare a few needles. Select your carb from the links at the top and select your current needle then a few more for comparison. The higher up the graph the richer the needle at a given point (station) along it's length

http://www.mintylamb.co.uk/suneedle/
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ratrodmog
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Re: hs4 carb needle problems

Post by ratrodmog »

Just to close this thread, I've used that Mintylamb site and it came back with the AAU being a good all rounder. I've fitted one and it does indeed run a lot better, not quite 100% but no flat spot on acceleration and the plugs are a good light brown, not jet black as before.
Thanks for everyone's input. Cheers
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panky
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Re: hs4 carb needle problems

Post by panky »

I got round the same kind of flat spot on my camper by filing a little flat on the thickest part of the needle to give a little more fuel where needed as the needle starts to come out of the jet. Or you could simple try pushing the needle carrier further into the piston rather than having it flush with the piston face - and try engine oil in the dash pot.
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