Post by oldchopperguy on Jul 5, 2009 21:40:14 GMT -5
OK troops, I believe I learned something here that may save many of us some long, FRUSTRATING hours fooling with our stock-type carbs. This is a little long, but please read through, as it may apply to your problem too.
My ride (Xingyue Eagle 150) is as "standard Chinese-issue scooter" as they come. It's the same basic scooter as Tank, Roketa, Sunl and all the other typical scoots.
With the stock air-filter and long, rubber "tuba" snorkel-hose to the carb, performance was never teriffic. Ever since the scoot was new, it would run OK from stopped, to about 45 to 48 mph, where it would sort of "peter out" with a slight raspy sound. I always attributed that to a lean jet. I was WRONG!
I've read MANY posts about this same phenomenon, and many of us have drilled the air-box, re-jetted, adjusted valves, changed intakes, changed exhaust, changed rollers, etc. (all good advice) possibly getting some improvement, but usually very little if any.
I had fitted a very low restriction air filter up under the seat, to the stock rubber intake hose, with almost no change in performance, even with many jet/needle changes. FINALLY, to facilitate quickly changing jets and raising/lowering the needle, I just left off the entire air intake assembly, leaving the carb naked at the throat.
Bingo! With a couple of jet changes and needle adjustments, I had the scooter running like gangbusters in an hour. NOW, I installed the air filter, on that long stock rubber intake, and attached the intake to the carb. OOPS... The scooter ran very poorly again.
On a hunch, I removed the AIR FILTER only, LEAVING ON the big convoluted rubber "tuba" intake hose. NO DIFFERENCE!!! On the stand, the engine would rev to about 7,000 rpm and a raspy, "cackle" would begin inside that stupid snorkel. Along with the raspy noise, the engine would peter out just like when riding, and just "hang" at 7,000 rpm WOT. That rasp, has to be a disturbance in the big, convoluted "horn" of the intake, and causing a sputtering vacuum in the intake before air enters the carb.
I removed the rubber "snorkel" while running, and instantly, the engine ran hard and strong, right up past 8,500 rpm on the stand and I had to close the throttle to keep it from over-revving! Put the snorkel back on, and instantly the performance went south again!
What this tells me is this: We have often been trying to fine-tune these carbs with an intake that nearly prevents that, regardless of the filter used. Remember, this poor top-end performance was the same, WITH or WITHOUT the air-filter in place. IT WAS THE CONVOLUTED, U-TURN, RUBBER INTAKE HOSE CAUSING THE PROBLEM.
I'm now changing over to a small UNI style filter. In anticipation of this, I made an intake extension from radiator hose, to clear that miserable "cat-back" support that blocks an air filter from fastening directly to the carb throat.
Now, CHECK THIS OUT... A long rubber intake, even smooth radiator hose, ALSO killed some top end. I chopped it off a piece at a time, until I got it as short as possible, and engine performance INCREASED noticeably with every shortening. REMEMBER, THIS IS WITH NO AIR-FILTER AT ALL!!!
My engine, and I suspect most others like it, just does NOT like ANY kind of intake extension on the carb. It needs a free-flowing filter, attached directly to the carb throat.
This REALLY makes me consider reversing of the intake manifold, facing the carb FORWARD with the filter extending through the bodywork, as several of the troops have done.
It could be that the simple UNI "sock" filter is the simplest and best solution, as it fastens onto the carb throat, and can bend under the cat-back support.
At any rate, I believe many of us are fighting a losing battle with that demonic rubber snorkle. While some fellows ARE getting decent performance with them in place, I truly believe they are THE main problem in our carburetion, rather than the paper filter.
Of course, jetting and needle setting MUST be correct for your individual engine, BUT, I believe that combination is VERY DIFFICULT to ever achieve with the snorkle in place, but EASY to do without it. It is causing us to make mod after mod, with little improvement, and sometimes actually making performance worse!
If your scooter "peters out" at near WOT, and re-jetting, and other fixes just don't fix it, that long rubber snorkle may be the culprit, and I'm not willing to try to tune around it any longer. I am going with a better exhaust soon, and that will require more carb adjustment, but if I'm NOT fighting the intake, it will be easy...
Sorry to make this so long, but I've read SO many posts about similar problems, with no real fix through the standard procedures. I honestly believe I'd FIRST try a good filter with little or no extensions to the carb... THEN re-jet and tune without the snorkel. I am convinced that the snorkel intake to the seat area is the biggest obstacle to driveability we have to overcome on these style scooters!
Hope this helps some of the guys out there who don't want to make difficult hot-rod mods, but want their rides to pass an honest 50+ mph and run smoothly doing it!
Enjoy the ride!
Leo in Texas
My ride (Xingyue Eagle 150) is as "standard Chinese-issue scooter" as they come. It's the same basic scooter as Tank, Roketa, Sunl and all the other typical scoots.
With the stock air-filter and long, rubber "tuba" snorkel-hose to the carb, performance was never teriffic. Ever since the scoot was new, it would run OK from stopped, to about 45 to 48 mph, where it would sort of "peter out" with a slight raspy sound. I always attributed that to a lean jet. I was WRONG!
I've read MANY posts about this same phenomenon, and many of us have drilled the air-box, re-jetted, adjusted valves, changed intakes, changed exhaust, changed rollers, etc. (all good advice) possibly getting some improvement, but usually very little if any.
I had fitted a very low restriction air filter up under the seat, to the stock rubber intake hose, with almost no change in performance, even with many jet/needle changes. FINALLY, to facilitate quickly changing jets and raising/lowering the needle, I just left off the entire air intake assembly, leaving the carb naked at the throat.
Bingo! With a couple of jet changes and needle adjustments, I had the scooter running like gangbusters in an hour. NOW, I installed the air filter, on that long stock rubber intake, and attached the intake to the carb. OOPS... The scooter ran very poorly again.
On a hunch, I removed the AIR FILTER only, LEAVING ON the big convoluted rubber "tuba" intake hose. NO DIFFERENCE!!! On the stand, the engine would rev to about 7,000 rpm and a raspy, "cackle" would begin inside that stupid snorkel. Along with the raspy noise, the engine would peter out just like when riding, and just "hang" at 7,000 rpm WOT. That rasp, has to be a disturbance in the big, convoluted "horn" of the intake, and causing a sputtering vacuum in the intake before air enters the carb.
I removed the rubber "snorkel" while running, and instantly, the engine ran hard and strong, right up past 8,500 rpm on the stand and I had to close the throttle to keep it from over-revving! Put the snorkel back on, and instantly the performance went south again!
What this tells me is this: We have often been trying to fine-tune these carbs with an intake that nearly prevents that, regardless of the filter used. Remember, this poor top-end performance was the same, WITH or WITHOUT the air-filter in place. IT WAS THE CONVOLUTED, U-TURN, RUBBER INTAKE HOSE CAUSING THE PROBLEM.
I'm now changing over to a small UNI style filter. In anticipation of this, I made an intake extension from radiator hose, to clear that miserable "cat-back" support that blocks an air filter from fastening directly to the carb throat.
Now, CHECK THIS OUT... A long rubber intake, even smooth radiator hose, ALSO killed some top end. I chopped it off a piece at a time, until I got it as short as possible, and engine performance INCREASED noticeably with every shortening. REMEMBER, THIS IS WITH NO AIR-FILTER AT ALL!!!
My engine, and I suspect most others like it, just does NOT like ANY kind of intake extension on the carb. It needs a free-flowing filter, attached directly to the carb throat.
This REALLY makes me consider reversing of the intake manifold, facing the carb FORWARD with the filter extending through the bodywork, as several of the troops have done.
It could be that the simple UNI "sock" filter is the simplest and best solution, as it fastens onto the carb throat, and can bend under the cat-back support.
At any rate, I believe many of us are fighting a losing battle with that demonic rubber snorkle. While some fellows ARE getting decent performance with them in place, I truly believe they are THE main problem in our carburetion, rather than the paper filter.
Of course, jetting and needle setting MUST be correct for your individual engine, BUT, I believe that combination is VERY DIFFICULT to ever achieve with the snorkle in place, but EASY to do without it. It is causing us to make mod after mod, with little improvement, and sometimes actually making performance worse!
If your scooter "peters out" at near WOT, and re-jetting, and other fixes just don't fix it, that long rubber snorkle may be the culprit, and I'm not willing to try to tune around it any longer. I am going with a better exhaust soon, and that will require more carb adjustment, but if I'm NOT fighting the intake, it will be easy...
Sorry to make this so long, but I've read SO many posts about similar problems, with no real fix through the standard procedures. I honestly believe I'd FIRST try a good filter with little or no extensions to the carb... THEN re-jet and tune without the snorkel. I am convinced that the snorkel intake to the seat area is the biggest obstacle to driveability we have to overcome on these style scooters!
Hope this helps some of the guys out there who don't want to make difficult hot-rod mods, but want their rides to pass an honest 50+ mph and run smoothly doing it!
Enjoy the ride!
Leo in Texas
CAN YOU HELP ME OUT MAN,AS i LOST ME JOB DUE TO NOT BEING ABLE TO GET THERE?ANY INF