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Chinese tachs
by: geh3333 - Jun 30, 2015 0:45:43 GMT -5
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Post by geh3333 on Jun 30, 2015 0:45:43 GMT -5
Are the tachs being discussed stock or after-market? Mainly stock , because the aftermarket TACHS are usually adjustable. These engines do fire every rotation right? I'm just trying to free my mind here. I'm stuck on this now , lol. I'm probably just thinking to much , but the rpms at idle just dont really seem as high as what the tach says. |
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Post by geh3333 on Jun 30, 2015 0:10:55 GMT -5
Thanks for the reply. You're right I have only done the work I mentioned in the first post, plus did a full oil change maybe 12 months ago. No other tinkering, I'm usually a bit scared I'm going to wreck something and won't be able to fix it. As soon as my feeler gauge gets here, I'll get into it. How many miles until u change your oil. ? It should be done at least every 1000 miles. I change mine on average about every 500 miles. |
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Chinese tachs
by: geh3333 - Jun 29, 2015 23:49:51 GMT -5
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Post by geh3333 on Jun 29, 2015 23:49:51 GMT -5
Here is another major issue. A 2 stroke tach is set for an every rotation fire. Many think these 4 strokes only fire every other revolution , however this is false. These 4 strokes fire every revolution just like a 2 stroke. So if our gauges are set to read every ignition fire instead of every true fire , then they are doubling the rpms to get the correct rpm. However by doing this they are doubling the true rpm.
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Chinese tachs
by: geh3333 - Jun 29, 2015 23:37:46 GMT -5
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Post by geh3333 on Jun 29, 2015 23:37:46 GMT -5
Remember, these are 4-strokes so 2 revolutions of the crank = 1 complete cycle - 1 spark (and 4 revs of the crank = 2 sparks). The tachs I have are both non-adjustable, made for 4-stroke engines. At best I can get to about 8k rpm's. Trust me - that little COX-airplane engine is NOT going 16K (and also is not only going 4 K). Actually these scoots fire on every revolution. They fire at tdc each time it hits Tdc, but there is only ignition on every other spark. So every full revolution down then up , the plug fires. So every other spark is wasted. Each cycle is 4 strokes or 2 rotations, but every rotation the plug sparks. So 2 sparks per cycle. Once on the fuel compression stroke , and one as the exhaust valve opens to let out the gasses. The second is the wasted spark. |
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Chinese tachs
by: geh3333 - Jun 29, 2015 23:31:52 GMT -5
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Post by geh3333 on Jun 29, 2015 23:31:52 GMT -5
Remember, these are 4-strokes so 2 revolutions of the crank = 1 complete cycle - 1 spark (and 4 revs of the crank = 2 sparks). The tachs I have are both non-adjustable, made for 4-stroke engines. At best I can get to about 8k rpm's. Trust me - that little COX-airplane engine is NOT going 16K (and also is not only going 4 K). Actually these scoots fire on every revolution. They fire at tdc each time it hits Tdc, but there is only ignition on every other spark. So every full revolution down then up , the plug fires. So every other spark is wasted. |
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Post by geh3333 on Jun 29, 2015 23:22:47 GMT -5
Remove everything on the fuel line from the tank except the fuel filter and the petcock. I'd remove the petcock also and just install a manual shutoff valve. Then block off all the vacuum lines. If you install a manual shutoff valve , you will be able to block off all vacuum lines.
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Post by geh3333 on Jun 29, 2015 23:18:29 GMT -5
The 130/70 will be 91 mm from the rim . so if you put the rim on the scoot and measure out 91mm , you will know if you have room for the 130/70. Also measure the 130mm between the shocks
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Chinese tachs
by: geh3333 - Jun 29, 2015 23:08:39 GMT -5
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Post by geh3333 on Jun 29, 2015 23:08:39 GMT -5
Anyone who has one of the digital TACHS can test this easy. From what I read about them , it that they usually have two or more settings . instead of going by the stock tach and matching the rpms , find out which setting is for every revolution and set it there. This will be the true rpms. From all the posts I've read , everyone just put it on the setting that matches the stock tach. His can be counter productive if the stock tach is wrong. I've read many posts from many sites , and many say that the gy6 only sparks 2 times every 4 revolutions , which is wrong . these China builders may think since there is only one true ignition every other rotation , that that's all it fires. So they install a tach that reads double.
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Post by geh3333 on Jun 29, 2015 22:36:51 GMT -5
I could tape a straw to the variator and hold out a piece of string, so the stew will hit the string every rotation. If its spinning slow enough to be able to count , then we will know the true rpms. George --- You KNOW I'm a big fan of us researching these machines to figure out what is really going on. However ... A tachometer is a very simple thing - just an IC that counts pulses. That is about as basic as an electronic device can get. True - some may be defective and not work properly (especially if made in the land of rice & pigeon's eyeballs). But aside from the defective units, they are probably reasonably accurate. How about this - since seeing something that is rotating at a rate of 15 times every second is close to impossible ... I have TWO tachs - one digital and one analog. The digital one isn't connected right now. but as soon as I get a chance I'll hook it up also and see how well the 2 compare. The odds BOTH would be wrong by the same amount are pretty slim. That work? I completely understand. And I'm sure you know I'm not trying to argue about it, and I'm know your not either. Most of the digital TACHS have a setting so it will either count every fire of the plug or every other and so on. I know you know this , but it seems like the regular TACHS could possibly be doubling the rpms. With my outcome of the not so accurate test. I could have been off slightly still. I came up with 600 rpms at 1300 rpms reading on the scoots tach. That's just about half . now considering my test may be slightly off , that means there is a possibility that the stock tach is doubling the rpms. Trust me , I know how this sounds , lol. It sounds like I'm nuts , lol. I just have to get some real numbers before I can admit defeat. I may be completely wrong , but I have to know for sure. The exhaust may be throwing out double of what I'm feeling and hearing , but as of now , I'm just about certain what I'm feeling an hearing. I'm also stumped when it comes to the rpms when the scoot is just about cutting out near 1200 rpms. You can honestly just about watch a spot on the variator as its turning, and there is no chance its spinning near 1200 rpms at this time, but the scoots tach is saying , yes it is . even at 1200 rpms the crank and variator should be spinning 20 times a second. If it is really spinning that fast , you would have no chance watching a spot on the variator do rotations . even at 10 rotations its nearly impossible . sorry buddy , I know what your saying and I'm not at all saying your wrong , I just need to find out for sure, lol Thanks George. |
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Chinese tachs
by: geh3333 - Jun 29, 2015 21:29:50 GMT -5
via mobile
Post by geh3333 on Jun 29, 2015 21:29:50 GMT -5
I could tape a straw to the variator and hold out a piece of string, so the stew will hit the string every rotation. If its spinning slow enough to be able to count , then we will know the true rpms.
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Chinese tachs
by: geh3333 - Jun 29, 2015 21:21:38 GMT -5
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Post by geh3333 on Jun 29, 2015 21:21:38 GMT -5
Yep , that's a perfect rpm range. I'm just curious why the engines seem to be be idling lower then what the TACHS say. |
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Post by geh3333 on Jun 29, 2015 20:32:32 GMT -5
If he has 3.5 inch wide rims , I'm pretty sure he will have room between the shocks. But is best to measure to be certain. I barely have any room between my tire and the engine block with the 70's. With his wheels being 3 inches smaller , so that's 1.5 inches difference from the engine block , but we have to take into consideration that his axle is closer to the engine block since its a short case. He must do some measurements, but I believe they will fit. He will prob have to modify the front fender lime I did. It was very easy.
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Post by geh3333 on Jun 29, 2015 20:25:57 GMT -5
Alright, 130/70 fits on a 3.5 rim. But, I think you need, say 10mm clearance width to make it work. Check how much room you have between your tire and swing arm, and tire and shock spring. I'm more concerned about the room between the Axle and the back of the engine block . |
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Chinese tachs
by: geh3333 - Jun 29, 2015 19:54:24 GMT -5
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Post by geh3333 on Jun 29, 2015 19:54:24 GMT -5
Thank you, sir. I will count tomorrow. I'm kinda worried that you may not be able to see every flash. Even if recorded and slowed down. Let's say you get the same readings as mine . the light will be flashing 10 times every second around 1300 rpms. A normal camera will prob not be able to record every flash. You may need a slow motion camera . |
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Post by geh3333 on Jun 29, 2015 19:48:49 GMT -5
you need to hang the valve cover vent hose up high and put some kind of filter on it, so nothing can get into the valve cover. I would also eliminate all the emissions crap and close off the extra vaccum lines. Alright I've got an extra fuel filter ill throw on there, right now i have the hose hanging down so that's probably not helping thanks for the responses everyone ill upjet tomorrow and report back I've been meaning to get rid of the emissions just been lazy, is it as simple as just capping off the second port from the intake manifold? Would it be a bad idea to switch both the idle and main jets at the same time? Or should I do one, see how it affects it, then do the other if no improvement just a pain pulling that carb out over and over in the hot florida sun I've got no covered area to work under It would be best to do one at a time. If you can post a pic of the emissions , we can talk you through it. Its as easy as removing certain parts ad capping off lines. |
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