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Post by kiwivin on Jun 27, 2011 8:35:49 GMT
If i have wound the idle mixture screw out more than 3 turns and it still bogs down on opening the throttle and revs still drop back down reasonably quickly which jet do i need to change?
and do i need a larger or smaller size?
I assume this is running too weak?
Once past 1/4 throttle it picks up fine just bogs on the initial opening unless you open it really slow.
Cheers
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Post by stiltthewilt on Jun 27, 2011 9:20:24 GMT
I'd say your air screw is ot too far for a start. then it sounds like it's getting too much fuel so I'd try downsizing 1st
Jetting's a bit of a black art - a lot of trial and error
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Post by kiwivin on Jun 27, 2011 9:26:04 GMT
I started at 1 turn out and worked up from there, maybe im going the wrong way?
I have just fitted a fast flow fuel tap so you may be right.
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Post by Perkin on Jun 27, 2011 10:41:34 GMT
 Is the mixture screw an air screw or a fuel screw? I can never remember...
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Post by Jimmy D on Jun 27, 2011 11:36:26 GMT
Sounds like you need to drop your idle jet...
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Post by jbcollier on Jun 27, 2011 12:27:03 GMT
It would help if we knew which particular carb you are using.
If the low speed (idle) adjust screw is located next to where the carb attaches to the manifold, then it is an idle mixture screw. In (clockwise) leans the low speed mixture, and, out (anti-clockwise) richens the low speed mixture.
If the low speed (idle) adjust screw is located next to where the air filter attaches, then it is an idle air screw. In (clockwise) richens the low speed mixture, and, out (anti-clockwise) leans the low speed mixture.
Idle mixture screw + three turns out + not rich enough = larger idle jet.
Idle air screw + three turns out + too rich = smaller idle jet.
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Post by kiwivin on Jun 27, 2011 13:55:57 GMT
Ok sorry ill be more specific.
Dellorto 24mm, malossi kit, standard rotary valve.
Screw in question is on the rHS of the carb towards the rear (manifold ).
Usually i set it at 1 - 1.5 turns out and it works well. I have now fitted a fast flow fuel tap and larger fuel valve. and now it bogs down on opening throttle from closed to 1/4 open.
I am currently on 3.5 turns out from fully in and still it hasnt made a difference to pick up. If it bogs down is it too rich or too weak?
I am under the impression that the air screw purely increases / decrease tickover speed and is the screw located to the right of this one (closts to air filter)
Cheers
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Post by jonnysnatchsniffer on Jun 27, 2011 17:27:24 GMT
just not to confuse anyone the manifold end of the carb is the front
screw it out one turn and start it, set tickover quite low let it warm up, then screw mixture screw in or out to get the highest tickover then set the tickover to what you want using the tickover screw and not the mixture screw, if you have to screw out too much then go up one on the pilot or vice versa
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Post by charliec on Jun 27, 2011 18:31:42 GMT
screwing out leans the mixture and in ritchens it, that how i renemeber it, so if you have to screw it out you need a ritcher jet
im going to try that idea of yours next time johhny though i like the sound of that!
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Post by spiderwebb on Jun 27, 2011 19:57:55 GMT
It would help if we knew which particular carb you are using. If the low speed (idle) adjust screw is located next to where the carb attaches to the manifold, then it is an idle mixture screw. In (clockwise) leans the low speed mixture, and, out (anti-clockwise) richens the low speed mixture. If the low speed (idle) adjust screw is located next to where the air filter attaches, then it is an idle air screw. In (clockwise) richens the low speed mixture, and, out (anti-clockwise) leans the low speed mixture. Idle mixture screw + three turns out + not rich enough = larger idle jet. Idle air screw + three turns out + too rich = smaller idle jet. yep... sounds like the screw is the gas one (controls gas flow @ low speeds) = out richens by allowing more gas pass it & in leans by decreasing gas flow pass it bogging (4 stroking) is a sign of overly rich mixture screw... so set it to around 1.25 turns out and test still bogging = try 1 turn out not bogging but has hanging revs = try 1.5 turns out you can also test the mixture setting by removing the air filter (or just the mesh) for a short ride to see if she likes the leaner conditions & then of course put it back on after you know which way to go on the jetting or mixture screw... plug chops |
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Post by jonnysnatchsniffer on Jun 27, 2011 21:39:44 GMT
if you put a fast flow tap in and a bigger float valve it could well be over rich at the bottom end due to flooding, did you have problems with the valve that comes with it ? the float height can also affect this quite alot
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Post by jbcollier on Jun 27, 2011 22:12:45 GMT
Are the fast flow fuel tap and larger float needle and seat the only changes you made?
If so:
1st guess - disturbed crap in tank has plugged your low speed jet. Remove carb, disassemble and blow out low speed jet.
2nd guess - larger needle and seat not sealing properly or it's larger flow has changed the float level/fuel frothing from normal. Put back in the old needle and seat and see if everything is fine again.
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Post by kiwivin on Jun 28, 2011 9:03:08 GMT
Ok mixed responses on which way to turn to richen so maybe im going the wrong way, will have a play weekend
1. start at one turn and work back and see if that helps
2. check the jets are clear and refit the original fuel valve and see if that rectifies
3. order a larger jet and see if that helps.
cheers, will keep you posted.
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Post by Perkin on Jun 28, 2011 9:26:14 GMT
 I suspect the mixture screw is an air bleed screw; that's the more normal way of doing things...
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Post by jonnysnatchsniffer on Jun 28, 2011 10:10:32 GMT
there is only 2 ways to turn it dependent on where the screw is,
i think you getting confused with the front and rear of the carb
the manifold end is the front of the carb and if the screw is here it is a fuel mixture screw and turning it out will make the mixture richer
the air filter end of the carb is the rear of the carb and if the screw is here it is an air mixture screw and screwing out will weaken the mixture
this is the same for every carb i have ever had
if its rich it will 4 stroke and if its lean it will go bwoooor and die
put ya choke on and see how it goes, if its better then go up from say a 50 to a 55 pilot
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Post by charliec on Jun 28, 2011 17:44:07 GMT
ha i would say the airfilter end is the front  whenever i put my carb back toghether i reset it to 3/2 turns and i got just about spot on once! - what a geus it was haha and i usaully screw my tickover out till i think its not effecting the slide any further and skrew it in 4 times, that way when i put the choke on its above what i want it and its very easy to adjust, upon ajusting the carb if you momentaraly put your hand over the carb i find that it helps with setting up the carb by what i would say 'reseting' the carb back to were it would be in the first place, are we sure he doesnt need to go rither if the addition of air is making no change?, if he turns it it and it runs better, then he is adding more fuel so he needs a bigger piolot jet, kiwi, try srewing it in and tell us what happens it wont take long, your air mix should be beetween 3/2 and 6/2 i beilieve but usaully it doesnt need to go 3 out and i wouldnt whant it running at above 9/4 out but if it works best there thats were it goes |
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Post by jonnysnatchsniffer on Jun 28, 2011 18:34:06 GMT
there is no right and wrong amount of turns it needs to be, its just that if less than 1 or more than 3 a different pilot will be needed, then adjust screw to achieve the best running, you need to do it a tiny bit at a time and let it settle before the next adjustment
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Post by kiwivin on Jun 29, 2011 11:08:43 GMT
yep thats what its doing unless you open the throttle really slowly. Its definately the screw thats closest to the manifold. The other screw just increases the idle speed by lifting the slide does it not. Il wind it back to 1/2 out and see, the biggest pain is the fact that i have to loosen the carb and turn it 45 degrees to get to the screw before adjsuting as theres not enough clearance otherwise. certainly sounds like i need a larger pilot jet though. |
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Post by jonnysnatchsniffer on Jun 29, 2011 18:40:12 GMT
i drilled a small hole in the side and use a screwdriver thru it to turn the screw as you do really need it running when you adjust it so as you can hear the engine note
what happens when you bang the throttle wide open from idle ? if you have more of the same try raising the needle 1 notch
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Post by charliec on Jul 1, 2011 14:10:05 GMT
i just use a little screwdriver bit that is flat headed, with a magnetic holder then turn it by hnd and it does it fine try the hand over carb thing johnny and see what you think just dont keep it over fo to long!! - had to do it on my dads when it kept wating to die after 10 seconds or so |
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