Salt
Junior Dawg
Posts: 6
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Post by Salt on Aug 30, 2008 17:48:04 GMT -5
I have a 2 stroke 49cc Venice TNG . I have owned it since new and when it would run it would run quite well, although it would be extremely difficult to start when it would sit for more than a couple of weeks. But I would always manage to get it started and again, it would run quite well. Now I cannot get to run at all. I thought at first it was a carb issue and purchased a replacement carb. The new carb has been installed, along with new spark plug, fresh fuel and new battery. When the engine is turned over using the kickstarter or elect. starter the headlight will begin to illuminate And if you test for spark at the spark plug, it has a blue, but very thin spark. The engine will not fire even if you inject fuel directly into the inlet of the carb. I know that I have a couple of times, turned the engine over, with the ignition on ang failed to properly ground the plug. Frankly I am quite embarrassed that it has me stumped. I am pretty impressed by many of the posts I have seen, and hope someone could suggest what should be checked next.
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Post by 90GTVert on Aug 30, 2008 19:40:43 GMT -5
I would take the spark plug out and spray a whiff of carb cleaner or ether in there, then put the plug in, and start. I like that method, the more common method is to spray carb cleaner or ether into the carb to start. It tends to work much better than regular gas. Sometimes it's just the vacuum pump not wanting to get fuel moving to the carb, and this will usually get you going in that case.
If you think your spark looks weak, check the connections on the coil and make sure the plug wire is in good shape. The plug wire just kinda screws onto the coil and boot or sometimes is just pushed on, so that may come loose. Make sure everything looks good inside the boot. I have also found that iridium plugs can help a hard starting scoot fire up a little easier.
Make sure your air filter isn't really dirty/clogged. Check it over for any hoses out of place or cracked. Try doing a compression test fi the rest of the stuff gets you nowhere.
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Post by motomech on Aug 31, 2008 3:11:54 GMT -5
How many miles?
What brand of oil do you use?
Did you check for the correct jets and adjust the new carb?
(B.T.W.-carbs don't wear out, they get cleaned on the inside, you didn't need to spend the money for that).
Take the muffler off and see if it will start.
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Salt
Junior Dawg
Posts: 6
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Post by Salt on Aug 31, 2008 10:03:37 GMT -5
I have tried spraying starting fluid directly into the combustion chamber, through the spark plug hole, checked the coil connections, wire and plug is new, still no luck. The compression is 90-95 psi, The spark I get at the plug is blue, but very thin.
The scooter has less than a 1000 miles on it, I was using an inexpensive ashless 2-cycle oil, I planned on using Amsoil if and when I get it back on the road. Even with the old carb, (which I cleaned inside and out) I cant't get it to at least fire. The new carb I istalled as is, it came with the enricher and my last several attempts starting have been with the muffler removed. I had mentioned in my original post that I have (not intentionally) turned the engine over, with the ignition on without properly grounding the plug, could I have damaged something in the CDI?
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Post by 90GTVert on Aug 31, 2008 10:32:46 GMT -5
The compression is 90-95 psi The 1E40QMB service manual lists 198psi standard and 139psi service limit compression. Before tearing anything down, you can try and torque your cylinder head nuts and re-test to see if it improves. Make sure the threads in your cylinder head aren't damaged while you're there (you prob would have noticed by now... just making sure).  Other than that, a damaged reed valve can cause compression loss, though I don't know that it would be that severe from a reed. If neither of those are the culprit it's probably time to pull off the cylinder/head and see what's going on in there. |
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Post by motomech on Aug 31, 2008 13:00:46 GMT -5
<<<...could I have damaged something in the CDI?>>>
Ck. for spark again.
My experience with compression testing has shown me that readings can vary widely. Techniques(throttle open, right?), gages and length of hose can cause different readings, especially on small engines.
To be sure, place your thumb over the plug hole and crank over with the throttle open. It should pop your thumb off with authority.
If you suspect the compression is low, the next thing to do is to remove the muffler again and look into the exhaust port. If the rings are stuck(seized), you will see the scoring lines on the piston skirt.
You may have to rotate the engine, of course.
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Salt
Junior Dawg
Posts: 6
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Post by Salt on Sept 2, 2008 21:44:27 GMT -5
When I first did the compression test, I wasn't quite sure what the compression should be, I've tested many automobile engines and large marine diesels over the years. I was convince that the compression on my 49cc scooter engine would be very close to my best running string trimmer, which is about 100 psi. After pulling the muffler off, the rings look quite good, shiny, definately not stuck, and it appears you can still see cross hatching on the cylinder walls. This bike has way less than 1000 miles on it. I still have spark at the plug, I put one of those adjustable spark testers in the place of the plug and it looked as if the voltage at the plug was 2000- 3000 volts. I was thinking that even with low compression, it would try to at least fire. I like to troubleshoot ignition more, but besides checking for the presence of spark, I am not quite sure how to static test the stator, coil and cdi, any ideas?
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Post by motomech on Sept 3, 2008 4:57:52 GMT -5
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Salt
Junior Dawg
Posts: 6
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Post by Salt on Sept 3, 2008 19:45:34 GMT -5
The adapter on my compression tester was preventing me from getting an accurate reading. I changed the adapter, re-tested and it came out to more like 130 psi! But the spark is very weak, I used an ignition spark tester to check. It was 2000-3000 volts at best, thats barely enough to even put a spark across the gap! What would be the correct order for trouble shooting stator, coil, cdi ect. for weak spark to the plug?
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Post by Karl on Sept 3, 2008 20:35:01 GMT -5
Salt, you're just below service limit if 130 psi is accurate. To verify, you're holding the throttle wide open and using the kick starter not the e-start, right?
First test a new spark plug, then coil, then stator, work your way down. I don't think these 2 strokes have CDI's but let someone else chime in to verify. I haven't seen a CDI on any of my 2-stroke scoots.
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Post by kevinx on Sept 3, 2008 21:14:23 GMT -5
I had the same problem and if you hve 90 to 100 compression something is wrong with the cyilnder cause it should have 148 psi. my scooter only had 11 miles when the it burned up most likely cause these scooters are set up to lean. found a 68 main jet in it. also i don't trust the oil injection system that is why i premix now 2 stroke motors are great but you need to understand how they work. learned the hard way and found all this out after the fact. Just go to provoscoot and buy stage 1 and 2 and see how a scooter should really run.
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Post by 90GTVert on Sept 3, 2008 21:33:44 GMT -5
I don't think these 2 strokes have CDI's but let someone else chime in to verify. I haven't seen a CDI on any of my 2-stroke scoots.  |
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Post by Karl on Sept 3, 2008 22:12:15 GMT -5
Very good, thanks Brent!
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Salt
Junior Dawg
Posts: 6
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Post by Salt on Sept 3, 2008 23:19:20 GMT -5
When I did the comp. test, throttle was wide open. And it was being kicked over. I don't have a service manual for this scooter, but I'm sure the correct procedure for conducting the test, like most other engines, would be to warm the engine up first. With the engine warmed up, if this engine could run, the compression pressure would be quite a bit higher.
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Post by motomech on Sept 4, 2008 15:14:40 GMT -5
The adapter on my compression tester was preventing me from getting an accurate reading. I changed the adapter, re-tested and it came out to more like 130 psi! But the spark is very weak, I used an ignition spark tester to check. It was 2000-3000 volts at best, thats barely enough to even put a spark across the gap! What would be the correct order for trouble shooting stator, coil, cdi ect. for weak spark to the plug? Forget the ign. tester and lay a new plug on the head and tell us what you have. Usually, the stator is not a concern with the spark except that the pulsar(trigger)coil is often wired into the same pig-tail harness. The CDI is a go/no go device and if you have any spark, it can be discounted. The plug cap should be removable, so unscrew it and ck. the inner wire for corrosion. Then remove the little adapter on the end of your new plug and stick it directly into the wire and test for spark. If the spark is still "weak"(a subjective call),ck. the other end of the wire if it is not molded into the secondary coil. If the spark is still weak, Ck. resistance values of pulsar coil. Pulsar ck.s good, then take the secondary coil to Yamaha shop for testing or buy a new one. Or try and start it with starting fluid like I suggested a few posts back. |
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Post by lbo on Sept 4, 2008 18:39:10 GMT -5
<---- interested in this thread. Not because I have a similar problem but because there is a lot of knowledge here and one day I might. There is a lot of good advice here and nothing I can think of. So it ran well when it ran, but hard to start after it sat for a few weeks? I think that is a big clue and what ever it is could be traced back to this as a symptom. Or try and start it with starting fluid like I suggested a few posts back. Post 3 he states he tried starting fluid, is it the method (airbox when cranking vs. via spark plug hole) that is important? |
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Post by 90GTVert on Sept 5, 2008 9:44:39 GMT -5
Post 3 he states he tried starting fluid, is it the method (airbox when cranking vs. via spark plug hole) that is important? I would think either way should work. The main reason I pull the plug on mine is that I can get the plug out and back in way faster than I can get my big hands in there to remove the airbox. The main goal is to be sure you are getting fuel into the cylinder, either should accomplish that. Maybe motomech has some knowledge on this I don't? |
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Post by motomech on Sept 5, 2008 10:55:13 GMT -5
I remove the filter element and shoot a couple of short shots directly into the air boot.
Often we read here disclaimers about damaging cyl. wall with starting fluid. This is not really a concern with four strokes(unless the cyl. just gets drenched), but is on two strokes, it is.
If there is spark*, and if it doesn't start and want to run with a little either, I stop and re-evaluate the whole situation. This would be unusual and one has to start thinking about unusual problems, like crank seals or reed valve.
If it does take off on either, I know it's a fuel problem.
*This "weak spark" situation is a little perplexing. With Japanese solid-state ign. systems, this is incredibly rare(It was common with the old contact breaker ign. systems).
I often think that maybe the person looking isn't doing it correctly or doesn't know what he is looking at.
But one thing I've learned here, is not to carry the comparisons of Japanese to Chinese too far, despite the family connections.
What "never" happens with a Nippon unit, can happen with a Chinese.
If these scooters rely on a source coil to power the secondary coil(runs without a batt.), then I suppose there could be a problem there.
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Post by rallyrrr on Sept 5, 2008 15:12:41 GMT -5
Could a poor ground/battery connection at some point be a possible cause of the weak spark condition? Sometimes when it comes to poor low voltage connections a spike or "high current" will temporarily clear a poor connection, making it conduct sufficiently. After power is removed and air and moisture do their thing the poor connection returns.
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Salt
Junior Dawg
Posts: 6
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Post by Salt on Sept 8, 2008 22:26:59 GMT -5
Hey guys, just wanted to say thanks! The perplexing weak spark turned out to be a bad CDI. I took the QJ for a victory lap through the neighbourhood this evening. I guess the ol adjustable spark tester can go back in the tool box. So much for the CDI being a "GO/NO GO device. I've been told there is no way to do a static test of a CDI, is that true? I have noticed some pretty strong opinions on synthetic lubricants, Now that I got her running, I think I am going to start using a good quality 2-cycle oil, I know I can just look through the Forum and see what you guys use, But I'm old, it's late and if I sit at the computer too long, I'll just fall asleep. My wife will come by while I'm asleep, shut the computer off, I'll wake up in the morning pissed, and I won't remember what the hell I was doing on the computer to begin with! So just tell me, what oil do you guys recomend for the small 2-strokes? Thanks again...........Salt
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Post by 90GTVert on Sept 9, 2008 6:34:45 GMT -5
Glad you got it going. I dunno about testing the CDI. I used Mobil 1 MX2T, but they quit making it. I'm switching to Amsoil Saber Professional 100:1 premix when I get going again. It's supposed to be good at 50-80:1 for hard use/racing or 100:1 for normal use. Motul and Bel-Ray are pretty popular synthetics.
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Post by lbo on Sept 9, 2008 7:54:48 GMT -5
glad to hear it's running. I use BelRay Si7.
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Post by w8tlftr on Sept 22, 2008 14:16:52 GMT -5
This is maybe a shot in the dark,but sounds like a problem with your on off switch,from what I have read it should fire right up, mine has an ignition switch and an on off knob, I wish I had the magic words to help you ,but from what you have discribed it has to be eletrical in my opinion.
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Post by w8tlftr on Sept 22, 2008 14:20:42 GMT -5
ahhh my bad I didn't read the bottom, I see you fixed it thats great!!!
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Post by motomech on Sept 22, 2008 20:47:24 GMT -5
Hey guys, just wanted to say thanks! The perplexing weak spark turned out to be a bad CDI. I took the QJ for a victory lap through the neighbourhood this evening. I guess the ol adjustable spark tester can go back in the tool box. So much for the CDI being a "GO/NO GO device. I've been told there is no way to do a static test of a CDI, is that true? I have noticed some pretty strong opinions on synthetic lubricants, Now that I got her running, I think I am going to start using a good quality 2-cycle oil, I know I can just look through the Forum and see what you guys use, But I'm old, it's late and if I sit at the computer too long, I'll just fall asleep. My wife will come by while I'm asleep, shut the computer off, I'll wake up in the morning pissed, and I won't remember what the hell I was doing on the computer to begin with! So just tell me, what oil do you guys recomend for the small 2-strokes? Thanks again...........Salt <<<So much for the CDI being a "GO/NO GO device.>>> Well, later I said; "But one thing I've learned here, is not to carry the comparisons of Japanese to Chinese too far, despite the family connections. What "never happens with a Nippon unit, can happen with a Chinese." The Japanese units really are go/no go devices. <<<I've been told there is no way to do a static test of a CDI, is that true? >> Yes, that's correct. " |
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Post by Karl on Sept 22, 2008 23:31:59 GMT -5
........But I'm old, it's late and if I sit at the computer too long, I'll just fall asleep. My wife will come by while I'm asleep, shut the computer off, I'll wake up in the morning pissed, and I won't remember what the hell I was doing on the computer to begin with! So just tell me, what oil do you guys recomend for the small 2-strokes? Thanks again...........Salt LOL!!! Congrats, Salt, on finding the issue! |
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