friggin carb

[Glen]

Hey all,

playing with the dreambike again trying to get the carb sorted - i think im making some progress but just want to check a few things out.

when i start the bike it just wont rev smoothly at all. starts on the first pull everytime and idles smooth - top end is also fine but its the progression thats really bad. sometimes itll just sort of bog about half throttle and takes a good 5 seconds or so to hit the power band and take off. thats only about a minute after starting it..

after this it will rev up but seems to rev up in a "step". it picks up speed quick - stops maybe half rpm for a half second or more than continues up. if you continue to rev it past half the max rpm it seems to have no problems.

have tried fiddling with the needle and seems to still do it to a degree. atm its third clip from the top and thats where it seems to do it as little as possible. am thinking it maybe something to do with the atomizer so may just swap it out for my soldered up one tommorow and see what happens..

Setup is in the signature - have blown the carb out with carb cleaner - just swapped the reed block for a bzm one with fibreglass reeds (which are surprisingly excellent and that made no difference to the problem so its not a reed sealing issue like i was perhaps thinking.. (the bzm block kicks ass over stock btw - it flows so well i had to bump up the idle screw a good two turns )

someone humour me and say i need to warm the bike up more or something like that :P ive let it run at idle for about 5 minutes and it doesnt seem to go away. but in saying that ive seen most other guys bikes at the track rev hard from start up as does my gp3.

testing its a bit hard in the middle of suburbia. and i dont want to smash my T43s on the road either.

really need help

[barnsey]

maby go down a jet size or 2

[mac90]

yes thats what i was thinking

go down one or two jets & see if that changes anything

[Glen]

would the main jet really affect the progression? i always thought that the atomizer and needle where the only things that could affect it

but ill swap the atomizer first thing and if that doesnt help ill change down the jets.

cheers

[mac90]

the jet could do it if its too big it sorta drowns out the spark or creates a boggy spot until the engine catches up the the mix

i see in your sig you run the 18 mm (has it been jetted up to suit) u may need to go to a 19 mm to even out the air fuel mix for larger jet sizes

but like you say if it has the 4 stroke style atomizer in it that could be the problem


best way try give it a test run but vary the above & below throttle in the suspect spot
on shutdown pull & inspect the plug

if its getting black then u know u can lean it out a jet size

[bennyboy213]

hey glen, wow you have the exact same problem as me! and i cant figure this one out.. only difference is that your running a way more expensive bike with a different carby :P im running a walbro. i have to half throttle it until it builds up a bit of rpm.. then i can full throttle it for it to fly.. otherwise if i full rev it from the beginning it sort of dies out.. it chokes and wants to stop and as soon as i let off the accelerator it starts idling again.. ive adjusted and leaned and richened my screws in every way possible and it hasnt fixed it. so i dont know if maybe its not your richness or air mixture..
try the other things cause it definately hasnt been fuel or air mixture with me..

GOOD LUCK MAN! cause i know how annoying this is

[Glen]

on the cag quad i have a 15mm walbro - i think its just the way a walbro is designed - to run at full power all the time - although i did drill a hole in my reed cage where the pulse hole goes IIRC. i did it a fair while ago. but seems to go okay.

[bennyboy213]

yeah i think your right man.. do you reckon i should change over to a dellorto sha 14/14 replica? you reckon it would be better than a hp carby with v stack? (also rep)

i also like the idea of the cable choke.. so i dont have to use friggin pliers all the time to twist the choke closed and open on the walbro :P
instead now i just take the air filter off and push it shut :P hahah

[Glen]

i had pretty good luck with the sha but in saying that the walbro i have now is working much better cause you can prime the thing up so it starts first time and the venturi is way larger.

look about the forum someone put up a huge walbro post ages back about drilling a hole for the pulse hole etc.

[bennyboy213]

ah i see, but ive cut out the internal bar on my reed cage to fit polini reeds. would that have anything to do with it.. ?