Engine Trouble Revs

Discussion in '2-Stroke Engines' started by icecold037, Mar 18, 2012.

  1. icecold037

    icecold037 New Member

    Seems like when im riding my bike it never reaches max revs. It revs A LOT faster when im stopped, pull in the clutch, and open the throttle 100% then when im actually riding it and open the throttle 100%. What may be the problem? I've tried setting the carbs needle in every position but the max revs stays the same in all. Adjusting the needle only seemed to affect the engines low end.
     

  2. HeadSmess

    HeadSmess Well-Known Member

    yes. yes, there is a major problem here.

    its called "load". gravity is part of the issue, friction another.

    pop the clutch in a car and give it full throttle and see what happens... :jester:

    not really sure how you fix it, either :(
     
  3. Neon

    Neon Member

    You can always reduce the "load". Put the bike on a diet, put yourself on a diet. run smaller rims and tires. Then there is also a matter of rev limiters. Don't really know if these have one or not. I'm guessing they don't. Friction also plays a big part in this as well not just gravity.
     
  4. jaguar

    jaguar Well-Known Member

    The fact that the 2 strokes Grubee engines are not optimized with their porting causes them to not reach maximum revs under load. Click on my signature link to find out about porting.
     
  5. Big Red

    Big Red Active Member

    Engine Load.

    Hey Ice, Seriously check out Jaguar's stuff. He knows what he's talking about.
    Big Red.
     
  6. shell shock

    shell shock Member

    Not only is this limited by physics (grav, friction and the like) but if our engines ran at the no load max RPM we would surely detonate!
     
  7. TOTAL CARNAGE

    TOTAL CARNAGE Member

    Don't worry about it!!!!!!!
    If you are reving it to 100% throttle with the clutch in and riding it wide open all the time it's not going to last long anyway!!! :jester:
     
  8. icecold037

    icecold037 New Member

    thanks jaguar! i've never done any porting with my engines but i was thinking of fixing the transfer ports like shown in your signature. wish me luck lol.
     
  9. icecold037

    icecold037 New Member

    Also, do you think if i change my sprocket from the standard 44T to a 56T that i would gain both low and top end since my engine isn't reaching max rpms under load anyways with the standard sprocket?
     
  10. HeadSmess

    HeadSmess Well-Known Member

    most people tend to go to 36, not 56, but if you think it needs to rev faster, go for it...

    not helping, am i?

    :jester:
     
  11. motorpsycho

    motorpsycho Active Member

    if you go to a bigger sprocket you will lose top speed but gain bottom end torque. the bike will be quicker (from 0 to top speed) meaning that it will get from 0 to top speed alot faster. but your top speed will drop from (for example) from 30 mph with a 41 tooth down to about 25 mph with a 56 tooth
    if you go to a smaller sprocket, you will lose bottom end torque but gain top speed. the bike will be slower on take off and you would probably have to peddle to keep the engine fron dying. think of taking off from a stop, in a stick shift car, in 3rd gear. it will be very slow to accelerate, you'd have to feather the heck out of the clutch and work the throttle, but eventually it will get up to speed.
    you can also alter your gear ratio by tire and wheel sizes. going to a smaller diameter rear wheel and tire will give you more bottom end / acceleration, but less top end speed. going to a bigger diameter rear wheel and tire will take away from the acceleration, but give you slightly more top speed. but, if you go from a 26.5 inch tall tire to a 27 inch tall tire, you won't see much difference. the change in wheel and tire size has to be drastic to see a big difference (like going from a 26" wheel to a 20" wheel).
    the only way to get the best of both worlds is with a shift kit....but a shift kit can set you back double of what a new engine kit will cost you.
     
  12. Big Red

    Big Red Active Member

    Hey Ice, Moto is right about everything, even about the shift kit. BUT, If you put a shift kit on it in MOST states it would no longer be a Motorized Bicycle. Shifting gears on a motorized bike is not allowed in any state I can think of. But I can't tell you not to do something, It's your bike, not mine. Also, a shift kit might help, but the engine should wind out fine without it. A lot of times it's just a carb issue, but it could be other problems too. Try to find out what your issue is before sweeping the problem under the rug with a shift kit or different size sprocket. For example, Have you checked for air leaks in your intake? Have you replaced the chinese plug and plug wire with a better quality? Are you using a good grade 2 stroke oil? (and mixing it right?) Take care of ( and make sure of) just those 3 things THEN see how it runs. If it still runs like carp get back to us and we'll try to figure it out.
    Big Red.
     
    Last edited: Mar 19, 2012
  13. motorpsycho

    motorpsycho Active Member

    it sounds to me like his complaint is that the engine revs fine while sitting still, but seems doggy while trying to ride it.
    well, take into consideration that while riding, the engine is under the load of trying to move him and the bike, and of corse, any engine under a load will rev slower than when it's not under a load.
    while sitting still and "free revving" the engine, it's not pulling any weight and has virtually no load on it. so it will rev a lot faster.
     
  14. Big Red

    Big Red Active Member

    Yer right Moto, Any engine will rev quicker without a load. But it should still have a steady pull all the way to the top of WOT even with a load. He say's it's doggin out in mid range then FINALLY, after a minute, hitting higher revs. A lot of things could cause that, and since we don't have the engine in front of us, all we can do is use our best judgement, (guess a little too,) and between all of us hope we can get the thing running right for him. I just got a customer engine in thats doing exactly the same thing but haven't had time to look at it yet, so this thread might help me too. The thing pulls fine off the line, bogs in mid range, then slowly gets to top rev. I wont have time to look at it for a day or two so perhaps someone smarter than me will come up with the solution by then. It'll make my job easier, cause I really am a lazy old phart like that.:jester:
    Big Red.
     
  15. motorpsycho

    motorpsycho Active Member

    I'm not disagreeing with you, but here's exactly what he originally wrote:
    "Seems like when im riding my bike it never reaches max revs. It revs A LOT faster when im stopped, pull in the clutch, and open the throttle 100% then when im actually riding it and open the throttle 100%."

    After reading this again, it still sounds like he's wondering why it revs so quick while sitting still, and why it doesn't rev as quickly while trying to ride it.
    I don't see where he said that it revs good, bogs down, then revs up again while riding.
    However, you could be on to something and it could be (in my opinion) an ignition issue (spark plug, wire, boot, worn out woodruff key causing the magneto to move back & forth which could change the timing as you ride, cdi, a wire grounding out on the frame, bad wire connections, etc) or a carb jetting issue, fuel - oil ratio, a plugged fuel filter, kinked fuel line, etc. that could cause these symptoms
    but I honestly think that he's confused about why it revs so quickly while sitting still as compaired to how slowly it revs while riding.
    I could be wrong, but that's my thought.
     
    Last edited: Mar 20, 2012
  16. Big Red

    Big Red Active Member

    You could be right there Moto, But seems to me if it pulled steady all the way to top rev, (of course a little slower to top rev under load,) he would'nt be complaining about it. I don't think he's THAT naive to think an engine will rev just as quick with a load on it then without a load. And the thing should still hit pretty high rev's and "sing" so to speak. It sounds to me like he may be losing some power under load and not reaching top rev. Then again, he may just be a noob (no offence meant Ice,) with a cheapo 49cc and and thinks the thing should run like a ninja. Like I said, the engine ain't in front of either of us, so the only opinion we have to go on is his. Maybe it is running OK and he thinks it should run better. If either of us were to ride it we would know in a heartbeat if it's runnin right.
    I hope his engine is running great and he just don't know it, BUT again, I was kinda hoping his problem could also solve my customer engine problem too. Like I said, gets off the line OK, then hits midrange, bogs, and takes FOREVER, (and then some,) to hit top rev. Helps if it gets a little downhill run. Once it hits top rev it will hold it, (till the next stop sign.) Then another 12 blocks to get past midrange to hit the high revs again. Any idea's on this would be welcomed. I'm hoping it's something simple like a intake leak or a bad plug. I guess I'll find out one way or another when I have time to get to it.
    Big Red.
     
  17. Neon

    Neon Member

    Let's go back to his original post. First off we don't know what engine type he has. Is it 48cc, 66, 68.5, I don't know do you? Is the engine even broke-in yet? How heavy is he? What's his tire pressure? It seems there needs to be a lot more information given before anyone can can call anything.
     
  18. Big Red

    Big Red Active Member

    Yer right. And I thought about telling him to give it a little break in first, then forgot. I did mention that he MIGHT have a 49cc cheapo, (and those always need a little work.) I don't think he's over 300lbs or he probably would have mentioned it. And if he's runnin with low tires he needs to ride a slow bike anyway.
    I'm kinda wondering what the plug looks like. That alone will tell a lot about what the engine is doing. But again, yer right, He didn't really give a lot of info about his bike. Most of the time I assume, sometimes wrongly, that most people have either the 49 or 66cc HT engine and working on those are about the same for both. I have both kinds, the 49cc cheapo scooter engine on my tadpole trike and a 66cc HT on my cruiser. 99.99% of my builds over the years have been HT's so perhaps I assume things when I shouldn't. But usually, unless the guy say's different, he's talking about a HT.
    I just Thought of another name for the Happy Time (HT) analogy. How about H ongkong T imebomb. Hey, I thought it was funny.
    Big Red
     
  19. Neon

    Neon Member

    Hongkong Timebomb I like it.
     
  20. HeadSmess

    HeadSmess Well-Known Member

    :jester:ha:jester:ha:jester:ha!:jester:


    or in this case the hongkong tortoise?
    :whistling: look at it go! :whistling:
     
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