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Post by jon on Dec 8, 2019 17:29:59 GMT 1
Went for a run on my LC hybrid today, and pootling around was fine. Even short bursts of lunatic behaviour.
However on sustained WOT for say 1/2 a mile or so, I got a little fuel starvation. Now I’ve never had this before, and need to start working out the problem.
One of Norbo’s taps, fresh fuel and carbs fully cleaned out a year or so ago.
Any ideas?
What should an LC tap flow in litres per minute?
My first thought is gummed needles as the last time I blew the cobwebs out was the summer.
Jon
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Post by beardy on Dec 8, 2019 19:15:34 GMT 1
Maybe a bug hibernating in your fuel cap vent?
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Post by rigga on Dec 8, 2019 19:21:12 GMT 1
As said tank vents through the key hole of the standard cap, try again with the cap slightly undone (low fuel level) see if that changes the symptoms
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Post by marrcel on Dec 8, 2019 19:36:12 GMT 1
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Post by jon on Dec 9, 2019 19:40:50 GMT 1
I’ve been thinking about it a bit, and I’m not convinced of the cap blockage (though won’t rule it out).
If it were the cap blocked surely it would get more and more vacuum.
It seems to run out of fuel at sustained WOT and then when it’s dropped off regain quite quickly.
I could understand float heights wrong but they haven’t changed since the summer.
Jon
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Post by midlifecrisisrd on Dec 9, 2019 20:52:14 GMT 1
Easy to test the vent, did it myself to test a billet cap was venting ok last week
Couple of things you can do to test
First take off the fuel line and fit a foot or so of spare line
First open the tap and let fuel flow for a couple of minutes to check the flow doesn't die off as time goes on
Then time how long it takes to flow 1L
Then connect the fuel line to the carbs and open both bowl drains with a jug underneath them
Turn the fuel on and time how long it takes to get 1L
The time from both carb drains together should be longer than the time from the tap
This will prove the tap flows more than the floats filling demands
The questions I would ask now are:
Is one or both of the float needles sticky so not reacting fast enough?
How old is the fuel? We have all heard about fuel going off
If fuelling is on the limit for one of the above or any other reason it may just be the transition from open or part throttle to full throttle causing the fuelling to lean out
Steve
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Post by 4l04ever on Dec 9, 2019 23:00:07 GMT 1
Sh1t under the fuel needle valve... ;-)
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Post by bare on Dec 10, 2019 0:17:16 GMT 1
Fine rust in the Tank impeding flows thru the taps' gauze filter thing ?
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Post by jon on Dec 18, 2019 22:12:49 GMT 1
Well, it’s not from the tank.
I tested the flow from the tank with the cap on and off and it made no difference.
Both gave a healthy 680ml in 30 seconds, so over 2 pints a minute.
The carbs had a minuscule amount of what I assume is rust specs so fine they must have passed the filter.
I’ve ordered new carb kits from Norbo, but suspect it may be float height.
Jon
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Post by skalmeje on Dec 19, 2019 8:41:57 GMT 1
Hi Jon. I have had same problem, raised float height (PKW28) and all good, like you suspected. Søren
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Post by jon on Dec 19, 2019 8:54:34 GMT 1
Hi Jon. I have had same problem, raised float height (PKW28) and all good, like you suspected. Søren I did think about float heights but can’t work out how it was fine before and I haven’t changed the height? It is possible I’ve never pushed it so much and the need adjusting? I seem to remember I overcooked it when setting up a few years ago and the floats overflowed so I backed them off. I’ve got new valves and seats coming from Norbo, so I will try this weekend all being well. Jon
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doggs
L plate rider.
Posts: 40
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Post by doggs on Dec 28, 2019 13:40:09 GMT 1
hi i had a similar problem high speed run - ok for a while then a misfire - like fuel starvation - backed off for a while and then all was good again if this matches your symptoms - i checked tap.float heights etc but in the end it was a sticking float needle valve on one carb - new needle valve sorted it
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Post by marrcel on Dec 28, 2019 15:52:33 GMT 1
After installing new rubber tip floath valves a few months later the floath heights sunk 0,6mm. That was after using E5. My thoughts are that the tips got swollen a bit. There is more MBTE in E5 and especially E10. Aethers are known for swelling rubber. Just my 2cts
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Post by steven on Dec 28, 2019 16:30:23 GMT 1
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