Rich conditions if mixture screw is not fully unscrewed

[ronnie]

Hi guys !
I think, im not newbie in this "category" , but i would like to kindly hear your ideas, since im totally lost and disappointed now... The topic is bit more complex and i try to describe everything. If you dont have time or energy for reading, please skip.

Scoot/Engine : Keeway, 1E40QMB, classic chinese 2stroke copy of Minarelli, cca 4000KM

Issues :
First issue i realized after buying the scoot for my wife was, that the scoot idles on cold starts very low. Im familiar with Idle speed adjustments, but there isnt the "choke" effect of revving up for 2-3minutes after cold start and then settling back to desired to idle. If i match the idle for cold start to be high enough, then after warming up the idle is even higher (revving, moving rear wheels etc...). Besides mentioned issues, the scooter start in every condition, everytime.
Workarounds :
- Changed e-choke 3x (aftermarket, another aftermarket, factory). When i mounted-replaced the choke last time for new factory choke, the cold start appeared to be OK, so it revved up after start and behaved as should... Maybe for couple of starts. Then the upper mention situation repeated and still remained.
- Changed ignition to fully new (factory)
- Changed carb-intake hose to new
- Changed airbox and filter to new (was-is factory)


Second issue is bogging (rich) after full throttle for some time. Lets say, you are running full speed on straight approaching roundabout. Inrelease the throttle and slow down a bit, then apply again throttle to accelerate. This is the point where maybe the scoot start to bogging for a second, no power, the runs as it should. It is uncomfortable and dangerous. This "overfilling" appears also if you let scoot run on idle for 20-30seconds and would accelerate (on intersections, or you have to open the garage doors). The first seconds are just bogging
Workarounds:
- The only way i can avoid bogging is fully unscrewing the mixture screw (the screw of course remain in the carb, but is unscrewed to the max). The trouble with this workaround is, that during acceleration is a huge lack in mid rpm. So the scoot accelerates without hesatition on full throttle, catches quickly some rpm and speed, then huge fading in power and acceleration appears between 40KM/h-50KM/h, and after 50KM/h it goes again great till cca 70KM/h (42MP/h).
- Rejetting Main Jet from 55 to 64 (55, 58, 60, 62, 64). It doesnt matter which main jet i use, if i touch mixture screw, bogging appears. My
Idea was, that maybe during WOT is engine overfilled and that causes bogging on throttle release. It sadly doesnt work, since also with jet 55 happens the same and the power drop in upper described range and also on highend is huge here.
- Played with needle position, but the only result was loosing power on leaner position
- Changed factory carb to Arreche 17.5mm. Bogging was still there with smallest pilot and main jet that company manufactures ! Experienced also troubles with starts. Scooter start only once after assembling everything together. After some running you are able to start the scoot after covering the air filter BUT only for a second ! If you cover it longer, it overfills the engine and it also wont start. If you didnt cover the airbox, it also wont start. Happens with every single size of main and pilot jet. I dont understant what causes this trouble here, since the scoot is running rich as described ! Why i need to cover the airbox for specific time to start ? My idea was, that engine cannot suck in the mixture for some reason. But why only after first start ? However the throttle response, running, vmax, torque was absolutely improved and im really sad that i cannot run this carb.

Im totally lost now guys...
If you have any idea, please share it with me.

Thank you very much !

[repherence2]

seems like a Pilot Jet issue from the way you describe your mixture screw setting. having to back out the mixture screw a that much would indicate to me that a change in pilot jet is needed.

how much is your idle screw turned in? your carb might be set like one "octave" higher. it's not really an "octave" but that is how my brain makes sense of it. it is like your idle screw setting is on the high side and you start "chasing" after it with the mixture screw. but in the end, there is never any consistent results with the adjustments. for me, the way i stop the insanity, is to get it running and let it warm up for 5-10 minutes. once i feel that it is warmed up, i start backing out the idle screw until it is not contacting or lifting the slide. along the way, i adjust the mixture screw accordingly to keep it running. once i can get the engine settled and idling with idle screw back out for zero effect, then i start the mixture screw tuning and hunt for the highest idle rpm.

warming it up ensures that you are not fighting the enricher while you are tuning the mixture screw. seems like you already looked into the enricher, so i rule that out. you have factory air box and filter. that being such, then your stock pilot jet should be the proper jet for it to idle properly. if your 1E40QMB engine was stock and you did not remove airbox and change the exhaust, the jetting should be good from the factory. that is what leads me to believe that your carb mixture/idle setting is an "octave" too high. for me, a "bog" normally translates to lean and "sputtering" for me translates to rich. the way i see it, if your mixture setting is full-blast open, something is not right.

are you still running the stock vacuum operated fuel petcock?

[ronnie]

repherence2 - Thank you very much for your time and response !

The bike was factory restricted with vario ring and longer exhaust pipe-only the pipe, not the silencer itself (from the engine to the silencer). This two "performance" pieces was changed by me alongside with parts as filters, belt, etc... Because of derestriction, ive had to change the Main Jet also (the kit for derestriction comes already with bigger jet 60). Regarding factory informations the IDLE JET should be 22.5, MAIN JET 57.5 for 45KM/h restricted model of scoot. However, i realized that somebody had changed the MAIN JET already, since there was exactly the "60" dimension. The "troubles" with Idle was present also before derestricting. I started the cold scoot and idle was like "500rpm...". After some time it goes higher, and after longer rung the idle was like "3000rpm". This was the first thing i noticed, but my opinion was, that maybe the choke is faulty and after change it will behave as it should = higher revs on cold start and settle back. But it still persists... For me, it looks like it runs rich also on cold start. Too much fuel, that it could not rev. It is also near impossible to drive if choke is "ON". No power, only rich bogging for a minute (if you dont wait standstill, till it warms up). Also if the scoot is warm, you can start only with throttle. As i wrote, i bought lot of MAIN JETs to find the issue Lot of smaller and bigger dimensions. The latest try was "55", which should be actually smaller as the factory restricted JET should be. Cold start "issue" was the same, and the 1sec bogging by "WOT - release - throttle" was also still present. The only thing what changed was performance, huge lack of power in midrange. BUT, if i unscrewed the mixture JET, bogging disappeared... It sound for me like some IDLE JET issue, which is too big and with enricher is the engine totally overfeeded, you can "smell" and see the unburned fuel, but i cannot imagine that somebody has changed the idle jet to bigger jas it was-should be, since regarding documentation the mounted dimension 22.5 is correct. Even all aftermarket carb, Dellortos or Naraku copys had at least this size, if even bigger is more common...

I had today a bit time, and i had given the 17.5 Amal/Arreche carb another try. Was expensive and it should be really different quality carb as the stock 12 chinese carb. Cold starts still remained "slow" (i really dont understand this now), but it it also dies after 10seconds because of overfeeding if cold... The IDLE JET is the smallest (15) available. But at least it starts (not like last time, described upper). Finally i can "play" with mixture screw, since it has immediate impact on idle and i could set it up to run under cold conditions.The bogging after WOT - release - throttle was again present But at least i realized, now it is caused by MAIN JET as you mentioned, which is sadly the smallest available (45) available for this carb, and it looks like is still too much. So i set needle to leanest position, gave bit more air from filter. It looks like it runs, but the performance is the same as with factory carb, also huge lack of power on full throttle after reaching cca 45KM/h, cold start remained unchanged, and the fuel consuption is now clearly "visible" on the gauge. Till now, with old carb the consumption was cca 6L/100KM - so like a modern 200Horsepower diesel or nearly 3x too much as my 300 X-Max. Now its clearly even more... I had to play tomorrow with setup, but the isnt really much i can do. I really dont know and dont understand what could be the issue, why behaves the engine under every condition like overfeeded, with all carbs and jets. Im really disappointed.

Im running the factory vacuum operated fuel system. The today changed carb is the only piece which is not from factory (if we dont count the "derestricted" exhaust pipe.