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Post by magoconnor on Jul 29, 2018 22:02:17 GMT -5
Hello.
I have tried a few main jets with kinda the same result, right now I have a 94 main jet installed with the needle in the middle position ( out of five )
Well the problem is, when driving lets say around 50 kh and I wanna go full speed, I only reach about 60 kh! The rpms goes from crusing speed 6500 to only around 7000 rpms and pretty much stays there.
But when I slow down to around 20 kh and then spike it, I can reach a top speed around 67 kh. From 5000 rpms it jumps to 8100 and then drops down to 7200 rpms.
Any suggestion on how I can fix this?
Setup 72cc gy6 1000 rpm spring 5 grams rollers
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Jul 31, 2018 10:42:09 GMT -5
For top speed, your needle has no effect. That would only effect when taking off before it got up to higher rpm. With a cvt, that means it has very little effect. So don’t worry about it. The jetting seem a little rich to me, but that would depend a lot on what other mods you have. If you are using a pod filter and a more open exhaust, that might explain the big jet.
What you really need to do is a plug chop. Basicly run wot for as much time as you can, then while at max rpm, shut the bike off and stop as quickly as possible while keeping the throttle open. We want to “see” what the burn was like while riding at max RPM. Don’t let the bike drop to idle. Then remove the plug. What you want to look at is if there is ant color on the white part of the plug. We are hopping for a nice light tan color. If your too rich, the plug will be darker. If thebplug looks white and “chalky” its too lean. If it’s dark and sooty, your too rich
as far as why you do better when accelerating from a lower rpm, my only guess is slippage. If the engine is already at a high rpm, it is already at high RPM, it is pretty much already locked up tight. When yo start from lower rpm, the clutch is going to slip more and allow the engine to jump up to 7200 rpms before it come to its max load spot. Because the clutch is slipping a little it can pull ove that “hump” and let the bike slowly move up a few KPH. Basicly, at 6000rpm it dosent have enough HP to pull more then 60 kph. But at 6200, it dose have enough hp to pull past 60
as far as how to fix it, I don’t really know. I know nothing about “tuneing the CVT.” I’m sure there is some way to make it lock up at a higher RPM so you get the slippage you need to get over the hump. The other way would be increasing you HP at 6000 rpm. This is very hard to do. When we increase hp, we normally do it at higher RPMs. Getting more at a specific RPM, is much harder. Of course your first best place to look is your jetting, and we covered that above. It could be done with “tuneing the exhaust. But that is not practical for most because you need to fit the muffler at a sertain place.
im not going to go into the whole intake/ excuse tuneing theory, but here is a taste. When your exhaust valve “opens” it creates a pressure wave that travel down the exhaust pipe. When it get to the end of the exhaust pipe, a pressure wave starts back up the pipe. We can time that wave to help “ram tune” the engine. When we know how many degrees ther are between the opening and closing of the valve, and we know what RPM we want the ram effect to take place. Then it’s just math. At the given RPM, we know how much time it takes. Then we can say that if the pressure wave is traveling at the speed of sound, how much distance do we need to travel down the pipe and back up.
the other way to take advance of this is to know that length, and make a slowly increasing diameter “pipe”. In other words a megaphone exhaust.. of course that creates a lot more noise. So the best balance is to the have a decreasing cone to dampen some of the noise. That’s a long way to say that an excuse with a reverse cone megaphone should make more HP then one that just has a “can” muffler. But that assumes that the megaphone is at the right length in the exaust system.
when I was a kid on my Honda 50 super sport , I actually pulled the muffler, cut the pipe shorter, and for some pipe tha just fit over my exaust pipe. That way I could slide it in or out to change the length ( and cut it to make it shorter. I was very pleased with my self to find the length I had calculated was very close the the length I found by expetmiting.
sorry, I guess I went a little off subject. That’s what you get from 50 years of “bench racing”. (Btw, I have the fastest Honda 50 around, really a “Honda 70” because I bored and stroked it!
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Post by magoconnor on Jul 31, 2018 18:26:12 GMT -5
Thanks for your very informing answear, and please go on I find it very interesting. I have touch upon the subject regarding intake runner length :http://49ccscoot.proboards.com/thread/23058/intake-runner-length-experience-needed I setttle on a 15 cm intake runner with a bell mouth. I dont know if this could be the issue. I've messed around with the main jets again today, seems to run a little better now, with a 90. But I still can't get passed 7200 rpms, I just seem to be lacking power. ( from stand still it still shoots up to 8000 ? My cvt: malossi multivar 5gr. rollers - fairly new belt - naraku alu starter wheel. I have recently installed a performance torque driver with straight grooves, could this be the problem? I did not have rpm or a speedometer before I installed the torque driver, so I really cant say if its gotten worse. I have tried a sronger spring with bad results. I just need to find a way, to get more rpms. As for exhaust I use the leovince titan : www.racingplanetusa.com/leovince-qmb139-racing-exhausthm-titan-139qmb-scooters-p-165737-1.html#.W2DsTr1MSUk
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Jul 31, 2018 23:40:45 GMT -5
Well ofcourse I’m just guessing on stuff because I don’t know what all you have done.
Have you run a compression test on the bike?
I’m guessing you have an aftermarket carb, what size?
Have you changed the cam?
One the best ways to improve your preformance at higher rpm is a fatter cam and big carb
Have you “upgraded” the ECU? I don’t have a lot of experience with these little guys, but I have done a huge number of racing engings ( mostly about 20x bigger). In my limited experience, the two “racking” ECUs DECREASED preformance. I ma big fan of going back to stock to prove an upgrade really is an upgrade. Working on a friend’s bike, I installed a “racking” ECU. When I didn’t think it was doing us any good, I went back to stock and tried it. The bike was almost a second and a half quicker getting to 25mph by going back to stock, and gained 1 mph in top end. He sent that one back, and the store talked him into one that was almost twice as much. The second racking ecu, took longer to get to 25mph and was slower then stock. I had the same kind of luck with the coil. Back in the day, I had a love for thumpers. These were 500 cc single cylinder ( British) bikes. Everyone knew they were a bitch to start, and hard to get to idle. My favorite trick was replacing the British coil with a car coil. Yes, my BSA 500 single had a Chevy coil in it. Once I had the better coil, I was able to run much larger spark gaps. A big fat spark across a .035 gap mad a huge difference on those bikes. So when my friend gave me a “racing” coil to install, first thing I did was see if it’s better spark could jump a large gap.bbto my surprise, the new hot coil could not jump as large a gap as the OEM coil. The important byproduct of this was that I could we could run a lot more gap with the stock coil,
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Post by magoconnor on Aug 1, 2018 8:10:16 GMT -5
Hello again.
Well I haven't aquired a compression tester as of yet, but the bike seem to pull nice at lower rpms.
As for carb I have bought a nice 18,5 mm naraku carburetor, I have tried a 21mm carb but I was unable to dial it in.
I have got a performance cam installed, made by a german company. Its nothing crazy that would lower the compression too much, it should be meant for a 50cc. But it should still keep the ports open a little longer.
I have tried a few cdi boxes or ecu, all unlimited. The one I got in now is from a good company "naraku", I also have a adjustable cdi, but it seems to advance the timing too much, and in turn cause spark knock.
But the bike ran better with that cdi, maybe I should try it again and see far I can retard the timing to avoid detonation.
I was a little unsure about the stock coil, so I replace it with one made in japan. It should be able to deliver 33,000v.
I got my ngk plug cap at 0,6mm.
What did you think about the intake runner length? Is that something you have dealt with?
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 1, 2018 9:16:52 GMT -5
I spent many hours screwing with intack length on my drag bikes. I can’t remember the math, but the result was almost always that longer was better. The exception was my Sons 600, but that engine we tuned to run 16,000 rpm! Back when I was racing I had a huge advance of having unlimited use of the Dyno. I also had two bikes with the same engine. At any rate even my 13,000 rpm drag motors had long stacks on them. My old Norton drag bike had a 9000 rpm motor. That bike had the carbs mounted almost 6” father away from the head and still had 9 inches of stack. I set and held the national record with that bike for B modified motorcycle. I did a lot of test runs with that bike and the very long intake runs gave me about 11% more HP in the 6500 to 7500 RPM range over the stock carb intake length. So I guess I’m saying, long is good
Do you have access to a dial indicator? I would love to see how much lift and degrees of of open you are getting with your after market cam. The 6000 rpm prouble you seem to have just screams “ cam” to me. With all the work you are putting in to this, I think it would be worth your time to swap the stock cam back in ( with no other changes) to see if that after market cam is really doing you any good. Some times I think about stuff like this and I get a nagging thought, and in this case it keeps sayin cam. Also when you pull the valve cover, turn the engine back wards about a 1/4 turn then bring it up to tdc ( on the fly wheel) and check if the two little holes in the gear are exactly lined up. I’d hate to find out that all this time your cam has been running slightly retardated. Be sure to use lots or assembly lube on those lobes when installing the cam and when yo have it torqued down, turn the engine ove a couple of times and recheck that the little holes are both half covered when the flywheel indicates TDC
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Post by AtariGuy on Aug 1, 2018 10:11:18 GMT -5
With a 47mm bore, the cam, and the straight groove torque sheave, it sounds like you're tuned just a little low on your roller weights. Most cruising rpms should be closer to 7k. My suggestion is to pick up a set of 4g rollers and swap them in. The lighter rollers will let the engine rev slightly higher during the shift allowing the engine to stay in power band. If 4g rollers end up revving too high, use 3 4g and 3 5g rollers (alternating, 4g, 5g, 4g, 5g... around the variator) to give an average 4.5g roller weight. Make sure that they're balanced in the vari or bad things happen. Give that a shot and report back
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Post by magoconnor on Aug 1, 2018 13:22:33 GMT -5
Ratdog : The cam has also been on my mind, for some time now. But I'm affraid I have "lost" the stock cam, I'll see if I can get my hands on a new one and some gaskets. Have you any experience with using rtv to replace the base gasket? that might raise compression a bit. Im little unsure if it will hold thou.. and also how much to apply. I dont want that stuff in my oil cannal. As for the dial indicator Im afraid not, but maybe its time to get some new tools Atari: I definitely need some more rpms, but I always thought 4 grams would be dangerously light, but if it works Im all for it. I will add them to my shopping cart.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 1, 2018 15:03:00 GMT -5
Something that most don’t understand. Raising compression limits RPM. I would not be trying to raise compression. You know you can get a A9 cam so cheap mail order, why not just order one and try it out? I think you can get one cheaper then a dial indicator (G)
I have not messed wit the CVT, but it really sounds like that is what you need. Basicly more slip to get you over 6000 rpm. I don’t know why, but I have had a guy tell me when I get the BBK installed, I should go to sliders instead of rollers
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Post by magoconnor on Aug 2, 2018 18:55:21 GMT -5
Import taxes get pretty crazy where I live..
I tried going wot down a slope, I could hardly hit 8000 rpm. it seems like the faster I go the more the rpms drop.
Just when I hit 37 mph the rpms drops from 7200 to 7000/6900. I want the rpms to increase the faster I go, not the other way around.
I wonder if the 4 gr. rollers will be enough or if I should go 3,5 gr. To really see a difference. I would like to raise the rpms with about 1000 or 1500, to really be in the sweet spot.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 2, 2018 19:59:43 GMT -5
wOW! How much can I Port duties be? I see the A9 cams from several sources for around 15 USD and server all other sources still under $20. Just wondering, where do you live?
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Post by humanshield on Aug 4, 2018 10:45:21 GMT -5
Something that most don’t understand. Raising compression limits RPM.
Where did you get this info?
AFAIK, RPM is more a factor of inertia and rotating mass, materials used etc.
My sportbikes have higher compression ratios than my other vehicles and turn 14,000rpm. My minivan has the lowest compression, and is only capable of 6,000 rpm.
Normally aspirated race cars normally have very high compression ratios and turn very high RPMs
Can you post some links backing your claim? Maybe there is some new information out and available?
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Post by magoconnor on Aug 9, 2018 22:16:42 GMT -5
I have managed to pull some more rpms.
Of cause the increase in rpms will wear down the engine faster, but what is the save zone? Would it be okay to hit 9000 occasionally?
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Aug 10, 2018 5:28:42 GMT -5
Every builder of high preformance engines knows that higher compression is a way to build torque but reduces your ability to rev. Of course this is offset in our little 600 cc 4 cylinders by having a wilder cam. When you build an engine for max hoursepower, you are building an engine to turn as many rpms as possible. The cam in my 600 opens way earlier, closes way later, and has more overlap then what you can get in these little 50s. If you put the same cam timing as these 50s have in a 13’000 rpm 600 motor, that motor woul only run about 11,000 rpm. Remember we are talking about compression, not compression ratio. I have 13.5 to one pistons in my 600, but because I have a big cam, the compression stroke is much shorter then the actual movement of the piston.
Now my 600 is set up to run on E85. I use a lot more of it, but it allows more compression and more advance. If I ran even 260 gas in my bike, the engine would destroy its self
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Post by magoconnor on Aug 14, 2018 14:18:08 GMT -5
With the lighter rollers rpms are way up.
From stand still going wot, the rpms shoots up to 9000 and back down to 8200. but a funny thing occurs exactly when i hit 41 mph (every time) the rpms drops from the 8200 to around 7300.
The speed keeps increasing slowly, but what could be the cause?
It feels like I hit maybe a little to a high a gear, or atleast to quickly which would indicate the need for a stronger torque spring.
Could this be the solution?
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