Jetting- L5 and 2+2 cam

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morini_tom
Posts: 919
Joined: 05 May 2006 13:47
Location: Northampton

Jetting- L5 and 2+2 cam

Post by morini_tom »

I'm just about to fit an L5 cam to my 501 engined dart which has been running a 2+2 for over 15 years.

Jetting with the 2+2 was about right after quite a while of mucking about, and I would like to avoid that pain again.

I'm interested in the difference in jetting needed purely between the two cams without making any other changes to intake/exhaust etc.

So, the question- has anyone else gone from a 2+2 to an L5 (or the other way round) and how different did the jettng need to be.

My dart has quite different intake and exhaust to probably anything else, and I run a fuel pump so the absolute settings I use will differ from pretty much everyone, but it would be good to know 'drop the needles a couple of notches and it'll be fine' or 'The L5 and 2+2 will run happily on the same jetting' or 'they have such different requirements you may as well throw everything away and start again' type pearls of wisdom.

Thanks,
Tom
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72degrees
Posts: 1549
Joined: 31 Aug 2007 21:24
Location: West Midlands

Re: Jetting- L5 and 2+2 cam

Post by 72degrees »

I went from 2+2 to L5 on the 375 (with PHBH28s) - but that was > 30 years ago, so pass ;)

All I can say is that the 'mystery cam' in the 350 I rebuilt required much smaller main jets than the L5 equipped 375. When I first tried it with the same jetting, it was absolutely awful 'WFO'.
'It must be a .....'
Posts: 365
Joined: 12 Sep 2010 12:25

Re: Jetting- L5 and 2+2 cam

Post by 'It must be a .....' »

Hi Tom, an interesting quest

What carbs/settings are you currently using and the difference the fuel pump makes
Plus what are your intake mods

I would try getting the main jets right first, then the needle height and tune from there

Also the adjustment of the pilot jets will indicate whether you need to change them (too many/few turns out)

Good luck, Ian
morini_tom
Posts: 919
Joined: 05 May 2006 13:47
Location: Northampton

Re: Jetting- L5 and 2+2 cam

Post by morini_tom »

Off the top of my head I can’t remember the jetting but I’ve got PHBH30 carbs. The fuel pump is a mikuni vacuum one like the 90s ducatis had and because of the fuel pump I’ve gone smaller with the needle jet. For all I know it might be ok without the pump but the dart tank sits quite low compared to the carbs, especially with the 500 installed (ie the fuel pipe runs uphill from the tap) so it seemed a sensible step and the bike runs so well that I’d be reluctant to change it. Which is part of the reason for my question regarding 2+2 vs L5 jetting- I don’t really want to spend ages chasing decent fuelling again. Especially in the dart where the bodywork does make a difference and getting to the carbs is a right pain.

I know when I was struggling in the early days Alex at NLM spent an afternoon with the gas analyser and eventually settled on some atomisers which he drilled to suit. I’ve never noted down what the new drillings were though so I will do that when the carbs are apart.

Intake mods wise I’ve got ported heads. There isn’t much room for decent runners or airbox in the 501 dart, certainly not ones that would give both cylinders similar conditions so I actually have k&N filters directly on the carbs at the moment. Not ideal for high overlap cams I know but it ran pretty well with the 2+2 like that and was a reasonable compromise compared to having an airbox which makes balancing the carbs and routing throttle cables next to impossible on the dart (access). If the L5 runs badly like this then I may go back to trying to integrate some kind of airbox.

Sounds like suck it and see initially then, will run it as I was on the 2+2 and take it from there
harrymuffin
Posts: 292
Joined: 07 Apr 2014 16:06
Location: west midlands

Re: Jetting- L5 and 2+2 cam

Post by harrymuffin »

From purely experimental reasons I see your logic in what you are doing. From purely riding expererience on the road I am fuddled. Narrow power band, nothing below 6-7000revs maximmum power up above 10,000 with an already over loaded big ends, constant changing gear as you come off the cam, you must be the organist in the local church. I have a similar set up on a five speed bottom end but with 28mm carbs but to keep the torque and max power in a usable place, I retained the standard 500 cam, radioused inlet valve seats and knife edged, solid steel inlet pipes not the rubber things, but hindsight the best cam for fast A & B riding I should have fitted the sport cam. Remember these engines follow the principles of major Heron who developed the head to give greater compression and more torque - small valves, high compression without detonationwith low octane fuels for WW1 aero engines. The power band is in the 5500 to 8000 and comes in with a surge at the lower speed and is perfectly dosile in the lower rev range. Cruising is dependent on the rear chain wheel, which I swap depending whether contry -Welsh Marches or commuting. Country riding once in top is above 70ish when the power starts to come in and keeps going only regulated by me as it is a bit difficult to go round some of the bends above 90ish, but no need to change gear because you are already in the torque/power range, only having to drop a cog if overtaking a mobile chicane or gypsy caravan.
Regarding you jetting as you will be in the higher reves most of the time I would be inclined to increase the main jet as I had to for starters and then try it at max revs and pulling hard, if she goes faster when you back off, too rich, if she keeps going then too weak. Don't bother with a plug chop, there isn't any lead to give an indication. You need a long straight gradient as in the sixties and early seventies we were able to do on the A45 past B'ham airport and the Meridon bypass, many an after weekday afternoon we would be setting up the carburation with the local cops assisting.
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