Starts with Choke.. dies with any touch of the throttle..

[davexs250s]

Hi Guys

Hopefully the last hurdle till my project is registered and on the road.

I replaced my needle & Seat assy to stop a leak, prior to this the bike was running fine. Now it starts with choke... as soon as i TOUCH the throttle with the smallest twist it cuts out.

If i put the choke on full, it revs really high... then when i give some throttle it just dies down (but revs stay high enough for bike to not die)

any ideas? is it too lean now? float levels looked right. Or is there an air leak possibly??

Heelllppp

[davexs250s]

from reading around it suggests the jet is clogged... i gave them all a thorough clean and it was running before.. all i've done is change the needle and seat assy... hmm.

it is new fuel tho... (?)

[thro]

check for air leaks.

the symptoms are definitely too much air, not enough fuel...


you sure you haven't put one of the carby vacuum hoses in the wrong place, or left it unattached by mistake?

[davexs250s]

Woke up this morning with a possible solution!

When I reinstalled the carbs I didn't attach the tube from the air filter holder join and the engine... Bike is far too noisy to test this morning but fingers crossed

[davexs250s]

Didn't make any difference...

everything is plugged in and looks sealed up.

Could something with the new valve assembly be causing this???

If i put it on Choke and let it race to about 6,000rpm the throttle revs the bike and it drops down slowly

Soon as it's lower than this the throttle bogs it. won't idle without the choke on even after a bit warm.

[firewrench]

Either a humongus vacum leak or no fuel passing through pilot jets in carbs. Since you state that everything looks ok on the outside, try this. Pop off the carbs, take off the bowls, (one at time), remove the jets and clean with carb cleaner, blow them out with compressed air, (use a rubber tipped air gun, forces the air through the passages), screw the jets back in, make sure your needles are mounted properly, set the float level with a ruler to the height required for your model, reassemble, reinstall, turn the gas on and have a nice day.

[davexs250s]

pulled apart carbs, re-checked float levels, checked all jets (all clear)

no improvement at all.

[davexs250s]

Just had another thought.. Before I replaced the float valve assmeblies one was leaking so that float bowl was always full to the top, does this mean it was really rich?

The bike has no muffler (straight pipes) and pod filters, should I set the floats so more fuel can be let into the bowls than standard settings?

Would being really lean cause this prob?

[g0zer]

is the bike meant to have an air box or pods?

the fuel is sucked up the jets and into the carby's venturi by the induction vacuum.. if you fit a free flowing intake system with virtually zero vacuum to a carby that has been setup for a restrictive intake system then there will be more air flowing through at the same time as there is less fuel being sucked up

but i think you have more problems than that, i agree with thro's air leak diagnosis and reckon you may have missed a hose so that air is bypassing the closed slide somehow which explains why the engine rpm rises even though you dont open the throttle, when you give it more fuel by opening the choke.

edit: at the end of the day, if the throttle is closed there is no way the engine should get enough air to rev to 6000rpm no matter how much fuel you feed it with the choke.

[Satan1]

Starts with Choke.. dies with any touch of the throttle..??

I know how one thing can lead to another but you are probably throttling her too hard, women can't take much of a beating.

[thro]

check the carb(s) are mated up properly to the motor and that its not leaking air around there?

if all the vacuum hoses look good, but the carby isn't seated properly and its leaking air there, then that would cause it to run pretty damn lean, too.

ditto for cracks in that rubber gasket/grommet (not sure of the terminology for it, the rubber bit between the carb and the head).

if you're sure there are no air leaks, and that fuel supply is not blocked - disassemble carb and double-check...

[davexs250s]

unfortunately mechanic time i think :S

can't find a leak (checked carb holders, all hoses etc)... gave the carbie another real thorough cleaning... still no luck.

could it be a more serious problem with the engine????

fked if i know !

[davexs250s]

Would a fouled spark plug cause my problems??

[davexs250s]

changed the plugs - with about half choke will start and idle around 1500 revs... but still any twist of the throttle just kills it.

i hear a bit of a wheezing sound when i kick it over, dont know if thats the engine or something else.

[jules_1972]

wHAT Colour are the plugs?

[SpeedTrip]

Is it a CV carby?
I had the same problem on my KLX after a needle/seat change.
The vaccuum diaphragms have a tendency to stretch/swell when removed and dont reseat correctly(even though they look like they are). You end up with an air leak, runs Ok at idle, but any twist of the throttle and it sucks air and the slide doesn't pull correctly, bogs down and dies.

[g0zer]

Would a fouled spark plug cause my problems??

uhhh

you said before the engine revs to 6000rpm with a closed throttle if you open the choke...

firstly, where is it getting the air to burn enough fuel to rev to 6000rpm from?

and secondly, how does a fouled spark plug make an engine rev to 6000rpm with the choke open and the throttle closed?

[davexs250s]

Hi Gozer,

It's being temperamental - and I have no idea why a fouled plug would cause my problem but i'm running out of ideas so trying anything and everything.

latest is it will idle at an acceptable RPM with choke on, will not run without choke and dies with throttle.

i'll check the colour again, plugs i just removed are dry dark black but that was after I went through the leaking needle & seat and assumed the flooded bowls would cause it to be really rich and make the plugs black



Speedtrip -

Thanks for the idea... From what I understand the vacuum diaphragms are the black soft rubber parts in the top of the carbie, right? I never removed these to change the needle and seat, i've opened the lid to check them out a month ago or so, but have never removed them as they look like they won't budge.... is there anyway to test if they are the problem or not?

[g0zer]

It's being temperamental - and I have no idea why a fouled plug would cause my problem

chicken before the egg

fouled plugs do not cause poor fueling but are caused by poor fueling

[thro]

does it blow black smoke?


it definitely SOUNDS like too lean from the problems you describe, but if its blowing black smoke and causing the plugs to go black, its running rich.


edit:
what g0zer said. fouled plugs are a symptom, not a cause...