yamahaty250xox Posted June 2, 2008 Report Share Posted June 2, 2008 hi im having difficulty finding the correct mixture screw setting on my rev3 125 dellorto carb. does any one know what the best setting is please? thanks in advance max Quote Link to comment Share on other sites More sharing options...
jse Posted June 2, 2008 Report Share Posted June 2, 2008 hiim having difficulty finding the correct mixture screw setting on my rev3 125 dellorto carb. does any one know what the best setting is please? thanks in advance max The "best" setting on a mixture screw will vary from carb to carb and engine to engine, and also be dependent on ambient weather conditions (temperature, humidity, barometric pressure). Probably the "best" way to set it for your engine is to warm up the engine and, from idle, quickly blip the throttle (turn on/off rapidly) and adjust the screw to give the best throttle response. You can also try turning the screw 1/4 to 1/2 turn richer after getting the best response and sometimes that will give the best performance, but I've usually found that the Dellorto works well at the "blip/best response" setting without going a little richer. Jon Quote Link to comment Share on other sites More sharing options...
jaylael Posted June 2, 2008 Report Share Posted June 2, 2008 The fuel screw setting also varies depending on what pilot jet is in it. A typical 2000 and up trials bike with a DelOrto carb comes with around a 30 pilot in there. I have had better idle, starting and off idle performance with a bigger pilot from stock, say number 38 - 40. With the too small pilot jet these bikes oftem come with, you need to put a tiny dab of loctite type thread locker on the screw threads and set the mixture screw so there are about three threads showing. This amounts to allot of turns out. Basically doing this gets the most fuel through the circuit, that the pilot jet will allow. When a typical trials bike is set this way it usually runs barely rich enough to perfom decently. If you have say a #38 pilot jet, then try starting at 3/4 turn. Go in or out from there if the machine presents symptoms described above, such as hesitation upon giving it the gas at low revs, or it can demontrate being too rich at idle by excessive popping at the exhaust upon decelleration. This may be a vague answer, but it was a vague question. Quote Link to comment Share on other sites More sharing options...
jse Posted June 3, 2008 Report Share Posted June 3, 2008 hiim having difficulty finding the correct mixture screw setting on my rev3 125 dellorto carb. does any one know what the best setting is please? thanks in advance max Max, Probably the best thing to do is re-set the mixture screw and if that doesn't solve your problem, take the carb apart and make a list of all the jet sizes and other settings and let us know. If you don't know where you are, you won't know which direction to take. The smaller the engine, the more critical the jetting is. There are a lot of things that can affect the off-idle response, those mentioned, as well as slide cutaway, needle profile, needle jet size, float setting, type of fuel etc. You might be having trouble with the mixture screw, but the cause may be something else altogether and unless you can eliminate the other factors, you may be treating the wrong symptom. Chances are you are o.k. in the jetting department (in the range of #36/38 pilot and D-34/35 needle) and if you bought the bike new it should be good, but if it's a used bike, previous owners can be pretty creative in what they put in the carb from what I've found. Jon Quote Link to comment Share on other sites More sharing options...
yamahaty250xox Posted June 3, 2008 Author Report Share Posted June 3, 2008 hi thanks for all the replies i had the carb off and gave it another damn good clean. then i did as it stated on the delorto website to ajust the mixture screw. i ended up screwing it in 1/4 of a turn for the best response. its strange how such a little ajustmnet will drasticly change the running of the bike. it now runs sweet! i also had a look at the jetting, from all i could see the largest jet was a #60! probaly my eye sight as from what you have said this is way out. however im not to botherd now as the bike runs perfect! thanks max Quote Link to comment Share on other sites More sharing options...
fkrisztian Posted June 3, 2008 Report Share Posted June 3, 2008 or it can demontrate being too rich at idle by excessive popping at the exhaust upon decelleration. Is popping to some limit okay upon deceleration? Mine pops sometimes, is this okay? Quote Link to comment Share on other sites More sharing options...
jse Posted June 3, 2008 Report Share Posted June 3, 2008 hi thanks for all the repliesi had the carb off and gave it another damn good clean. then i did as it stated on the delorto website to ajust the mixture screw. i ended up screwing it in 1/4 of a turn for the best response. its strange how such a little ajustmnet will drasticly change the running of the bike. it now runs sweet! i also had a look at the jetting, from all i could see the largest jet was a #60! probaly my eye sight as from what you have said this is way out. however im not to botherd now as the bike runs perfect! thanks max I wouldn't worry. The bike runs well and the #60 jet you saw was probably the "starter jet", which is on the end of the brass tube with an o-ring on it and only used when the "choke" lever is up. Jon Quote Link to comment Share on other sites More sharing options...
copemech Posted June 4, 2008 Report Share Posted June 4, 2008 Is popping to some limit okay upon deceleration? Mine pops sometimes, is this okay? Yes,, Jon can probably go into some two page thing about this, but as the dellorto screw controls fuel rather than air, it is also more sensitive! 1/16 turn can make a difference! And they seem to vary a lot, therefore your occasional fluctuations! 1 Quote Link to comment Share on other sites More sharing options...
jse Posted June 4, 2008 Report Share Posted June 4, 2008 Yes, Jon can probably go into some two page thing about this, but as the dellorto screw controls fuel rather than air, it is also more sensitive! 1/16 turn can make a difference! And they seem to vary a lot, therefore your occasional fluctuations! Geeeeez. I think I actually agree with Copey (image of Jon, upon fully realizing the import of the last statement, one hand to forehead, other hand clutching chest, gasping for air and staggering around in circle and falling face first on office floor). As an addition to this jetting stuff I might also add, always check your plug when making jetting changes or now and then just to see how things are going on inside your engine. The plug is probably your best, direct link to what's happening in the combustion chamber. Once you understand the "language" the plug speaks (color, deposits etc.) it can give you a great deal of information and help keep your engine healthy. For instance, I used to tell how much fuel a nitro burning Top Fueler needed, in part, by counting how many threads on the new plugs turned blue from combustion heat after a tune-up run. Jon Quote Link to comment Share on other sites More sharing options...
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