Jetting a 2 stroke? Confused now...

[SpannerMonkey]

So, everything has been fitted to the Tomos...
I've got dellorto jets from 50-72, it should run a standard 52 jet in without any performance mods... so far I've tried a myriad of jets in that range and no matter WHAT jet I use, she doesnt seem to run right. I've only had it run right for 5 seconds and that happened after I turned the choke off on a 65 jet... revved out fully for 5 secs, then bogged out

Mods to the bike are...:
Bigger carb from later Tomos engines
Larger intake manifold
Expansion chamber
Airsal 65cc bore kit
High compression head
reed valve conversion


I just cant seem to get her to run right, plug seems to say I'm constantly running richcoming in at a dark choc brown no matter what jet I use. there are no air leaks and all is turning sweet... just cant seem to get it right! Any suggestions???
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[P.addy]

Lots of carb fiddling awaits you

Changing the needle position to get it perfect/changing jets. I'd start 10 above normal and work your way through that.

[SpannerMonkey]

[serlant]

you can't put any washers under the needle?
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04 CBR1000RR, 1995 Husqvarna TE410, 1998 VTR1000(Sold), 1990 XJ600(sold), 1996 KH125(dead and sold)

[SpannerMonkey]

It's one of these carbs... https://www.dellorto.com/merchandise/products.asp?CategoryID=2&PartsectionID=55
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[pepperami]

Are you using the standard air-box?
Possibly? maybe? = bigger bore + bigger carb = more suck = standard air-box & standard airfilter not able to deliver??.

Are you using an aftermarket bolt on air filter like a K&N? = possibly? maybe? = new airfilter allowing to much air = poor detination = wet plug/partially burnt fuel ?

Larger inlet manifold playing havoc with the "Venturi effect" ????


just an idea/my
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I am the sum total of my own existence, what went before makes me who I am now!

[SpannerMonkey]

There is LOTS of suction from the carb, it runs a LITTLE bit better if I remove airbox and filter... but not enough to even move me from a standstill
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[pepperami]

????? hmmm? is the exspansion pipe you have on there so open that you`re not getting any back pressure?.

In the bad old days of me trying to wring extra power out of small strokers (YB 100`s, A 100`s, ) I seem to remember that putting on a spannie sometimes used to move the power further up the rev range, depending where the spannie came from ie was it the right one for that bike?

I know it might sound like a silly question ? but is the slide going all the way up when you twist the throttle?.

Are the reeds to stiff and not letting the carb operate properly?
can you mount the carb without putting the reeds in?, just to see if that gives an improvement?


Just a thought
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I am the sum total of my own existence, what went before makes me who I am now!

[SpannerMonkey]

She's running brand new carbon fibre reeds designed for this bike. the expansion chamber was on the bike before I fitted all the other parts and she ran sweet as a nut
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[pepperami]

I`m just going through the sort of things I would look at if it was my bike.

How many ports on the old barrel?
7 on the new one .

I`m guessing that when you got the the new 65cc kit, it included matching piston and rings?

Is it points ignition? and now you have a new bore/stroke, do you need to adjust your timing ?

Crickey! i`m running out of ideas
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I am the sum total of my own existence, what went before makes me who I am now!

[SpannerMonkey]

Points ignition yes, and only the bore has changed, not the stroke. so all my timing should still be the same I would have thought :S
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[pepperami]

Now you have a high compression head, do you need to change your plug for one with a different reach?

now I`m stumped
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I am the sum total of my own existence, what went before makes me who I am now!

[SpannerMonkey]

Nope... just says to use a heat range 7 plug... running a 6 but shouldnt make that much diff
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[hmmmnz]

put the smaller carb back on and try again,
change 1 thing at a time,

see if you can get it running ok on that carb
then switch to the next one,
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[Johnser]

will it run at WOT? you need to jet it for this first and worry about mid/low ranges after. If you cant get it up into a rev range where WOT is pulling, you could try bumping it down a hill using the hill to coax it up the revs. When the engine is fairly high up in the rev range and the throttle is open fully, much of the complexity of the carb/engine system is rendered irrelevant (more or less) i.e. throttle slide fully out of the way and needle tube fully open.

If you cant get it to run right up here something more fundamental must be wrong.

.... apologies if I'm teaching egg sucking but couldnt tell how you had been trying before!

[dougon2wheels]

try a smaller main jet,think of the engine as a pump,your now drawing more air through the carb,thus drawing more fuel through the main jet,you need to decrease the size of the jet to get the right mixture,i had the same problem with a big bore cagiva,as well as using cagiva dellorto's on my 350 ypvs mito,at a guess id try a 45/48 main to start
cheers

[SpannerMonkey]

[Johnser]

[/quote]
It runs at WOT yes... but no power.[/quote]

enough power to move with you on it? even slowly, in 1st, on the level?

if so, run along at WOT, and slowly close the choke. if it picks up, try a larger main, if it bogs down more, try a smaller one - removing the airfilter might help tell you the same (but the other way round)

this is of course assuming everything else has been set up right.

tuning the other throttle openings comes after.

I know nothing about this carb/bike but assume they are sensibly matched? too big a carb will not have the air velocity required to operate properly.