Bike carbs - fitted and first test run

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-JC-
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Bike carbs - fitted and first test run

Postby -JC- » Sun Aug 19, 2018 3:05 pm

https://youtu.be/dNpLPUThAKY

Running pretty badly. I can think of a few things that might be causing it, but I'm not smart enough to know what it's likely to be, can any of you clever people hazard a guess? Things I'm thinking could be issues like :

-Vacuum leak (different manifold - alloy/alu with a bit of flex)
-carb mixture setting
-lack of vacuum advance on dizzy (capped off for now, will switch over to megajolt soon)
-timing?

I spotted and fixed the fuel leak you might notice in the corner of the video btw
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Paul G
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Re: Bike carbs - fitted and first test run

Postby Paul G » Sun Aug 19, 2018 3:24 pm

Are all four throttles opening at exactly the same time and are carbs balanced, ie sucking equal amounts of air?

Difficult to tell from that video but no 1 looked a bit lazy. Probably need to get them set with a carb balancer or mercury tubes.

-JC-
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Re: Bike carbs - fitted and first test run

Postby -JC- » Sun Aug 19, 2018 5:17 pm

I think so, yes. The butterflies seem synced up, the slides I think were too, but they only seemed to open at quite high revs and I didn't want to overdo it, especially as the cooling system is dry atm
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nigecapri
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Re: Bike carbs - fitted and first test run

Postby nigecapri » Mon Aug 20, 2018 3:15 pm

Trial fitted the manifold to my spare head, and it's not flat


How long have you been fitting these???

If that set-up hasn't been running on the car before then I would suspect head-manifold air leak. Two gaskets with plenty hylomar between each face & well tightened should work unless it is bent rather than just out of flat.

If the black tops have been off & it's not run properly since then take them off again and check that the tiddly O-rings are still in place, easy for one to be dislodged as the top is being refitted.
Basic timing should be o.k. to get it to run.

Main fuel jets ought to be something near 17. Fine tuning relies on lifting or dropping the needles with a little circlip having usually three available grooves. Also possibly small fibre washers under or over the circlip which can adjust a bit more, this will need a lambda meter to get it right, preferably on a rolling road or get one fitted in the exhaust system.

-JC-
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Re: Bike carbs - fitted and first test run

Postby -JC- » Wed Aug 22, 2018 11:52 am

nigecapri wrote:How long have you been fitting these???


I was hoping nobody would ask that :oops:. I've had them in the shed for ages, but only started getting them sorted back in the spring. Got really lazy over the summer heatwave and didn't fancy getting burnt to a crisp on the driveway.

Pretty sure the o-rings are ok, I had trouble with that upon reassembly so made sure. It's only slight off flat, when one end was pushed flat against the head, the other end was maybe a few mm away. It looks nice and flat now, although I know looks can't tell enough. I haven't touched the jets at all. My plan was to get it running as best as I could without that, then take it somewhere to get it properly done. Would you say this is worse than it should be given all that? Oh, should also mention that I don't know how long it was since the carbs were last used - the seller didn't know.
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nigecapri
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Re: Bike carbs - fitted and first test run

Postby nigecapri » Mon Aug 27, 2018 8:43 pm

Could always try the squirty test with WD40 or brake cleaner sprayed along the manifold edges to see if it lifts the revs.

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Re: Bike carbs - fitted and first test run

Postby -JC- » Wed Aug 29, 2018 8:19 am

Thanks, I will try that too
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"Hard work often pays off after time, but laziness always pays off now."