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Post by Jimmy D on Oct 12, 2021 10:14:23 GMT
Hi chaps,
Two questions, potentially related...
1.
What could be the reason for revs hanging when pulling up to traffic lights etc even with a 55-60 main in a PHBL26? Surely 55-60 couldn't be too small for a rotary Polini 130?
If I blip the throttle it immediately settles down, it's only if I roll off the throttle when coming to a stop.
2.
When first kicked from cold with the choke on, the engine immediately SCREAMS up to 9000 rpm. Close the choke and it settles to around 3-4000 rpm and then after about a minute down to 1000rpm, then it's good.
I've never had an engine that behaved like this from cold (usually the opposite, have to hold the throttle open etc while warming up), any ideas?
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Post by jbcollier on Oct 12, 2021 13:07:23 GMT
You have an air leak. An engine can't go to 9000 rpm unless it's getting air. Once you solve that, jet it properly. Go up until it is too rich and four stroking wide open, and then back down.
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Post by Jimmy D on Oct 12, 2021 13:44:14 GMT
You have an air leak. An engine can't go to 9000 rpm unless it's getting air. Once you solve that, jet it properly. Go up until it is too rich and four stroking wide open, and then back down. Thing is, I've leakdown tested it multiple times and once pressurised it stays like that for hours if not days. It was set up a few months ago on JB Tuning's dyno and runs brilliantly from 1/8 throttle to WOT, but there's something weird going on at idle. I did wonder if it's a fuel supply issue but the float seems to fill fine. |
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Post by jbcollier on Oct 12, 2021 16:54:05 GMT
Glad you did a proper leak down! So many people don't. A leak down test is usually with the carb and exhaust off, sometimes with the intake manifold off as well. Check all that over carefully. Seems to be linked with the choke, so look closely there. Cracked carb body?
Ditto with the jetting, glad you got it set up properly. So many posting here simply want to throw in a jet and go.
Back to your running issue, it is pretty normal for a engine to idle a little high after a run and settle with a blip or two. How much higher is idling when pulling up to a stop?
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Post by mark on Oct 12, 2021 17:44:36 GMT
I say , steady on old chap 😀
Throw in a jet and go ? I always double check the size first !
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Post by mark on Oct 12, 2021 17:52:52 GMT
I’m afraid my practical skills are negligible but it’s not for lack of trying.
I have to rely on Henri & Rich along with you guys to keep me going and bail me out quite often .
It’s the love of Smallframe’s and 2 wheels that counts👍
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Post by Jimmy D on Oct 13, 2021 13:36:53 GMT
Glad you did a proper leak down! So many people don't. A leak down test is usually with the carb and exhaust off, sometimes with the intake manifold off as well. Check all that over carefully. Seems to be linked with the choke, so look closely there. Cracked carb body? Ditto with the jetting, glad you got it set up properly. So many posting here simply want to throw in a jet and go. Back to your running issue, it is pretty normal for a engine to idle a little high after a run and settle with a blip or two. How much higher is idling when pulling up to a stop? It's taken 10 years to learn those lessons...  Leakdown test all done with carb and exhaust off, though part of me wonders whether the carb could be sucking air from somewhere? It's brand new and came with a 60 choke jet which I can't imagine is too big but could be! As you say, it may well be normal. I also have CHT set up and temperatures stay constant - around 100c around town up to 170c on long 65mph runs. How much hider idling... not loads. Maybe sits around 3-4k? And as I say, easily settled with a blip. None of this feels like it's going to cause problems with the bike, though I do worry the sudden extreme revving might offend neighbours... I'll try and get a video next time I start from cold, see if that helps. |
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Post by jbcollier on Oct 14, 2021 12:52:01 GMT
The 9000k at start up is DEFINITEELY not normal.
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Post by Jimmy D on Oct 14, 2021 13:07:41 GMT
The 9000k at start up is DEFINITEELY not normal. Yeah, I'll try to get a video next time to give you a better idea. I wondered whether it was something like the float sticking closed initially so the fuel/air mix being off. |
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Post by jbcollier on Oct 15, 2021 12:46:34 GMT
No, I wouldn't think so. The engine needs air to turn that speed.
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on Oct 16, 2021 8:38:54 GMT
Have you got another carb you can try?
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