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Post by magoconnor on May 20, 2019 22:34:19 GMT -5
Hello. I have just finished rebuilding my engine. Im having some problems getting it to start and hold idle. I can keep it alive for a few seconds with the throttle, but it is not running smooth at all. The very first startup ( each day that I tried getting it to run) it sounds normal, you know like a engine should, but after a few tries it starts to sound weird. I hope you can hear it in the video. Link : www.youtube.com/watch?v=A_JhTQ2y4XkIts definitely getting fuel, the spark plug is black as death and a bit wet. Also the carburetor was full of fuel when I took it off to clean it. I got the neddle in the middle postion and I have tried going down from a 98 main jet to a 94 jet after seing the spark plug. The air/fuel screw is out 2 turns. It did not do anything. I have also tried removing the air filter. The float valve is closing and opening like it should, and the floats are set correctly. When cleaning the carb there were some black residue on the butterfly valve, I believe it was a tiny bit of oil. I have tried swapping the cdi - measuring the cdi connection from the magneto - checked the coil- checked the spark plug ( tried several). checked all the grounds. All seems to be good. I've got good compression and its only possible to start the damn thing with a car battery, hooked up directly to the startmotor. As you can see me dodging the sparks in the video. First I thought it was the timing or the valves, but it appears to be fine. I have tried a straw down the spark plug hole just to be sure that tdc is the same on the flywheel. The valves are also set correctly. Please Help! The engine was put together with the following parts: kymco 139qmb block. Naraku HD crankshaft + new oil seals. New oil pump New chain My tried and true sport camshaft Naraku 90cc kit head + cylinder New spark plug 20mm carburetor 98 main jet Leo vince exhaust Naraku coil All new gaskets.
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Post by lilpinny on May 20, 2019 23:24:07 GMT -5
I think you have an air leak. When you put it back together something didn’t seal and is letting air in and it’s throwing off the mix. When it idles with lots of gas and then dies that’s kind of a symptom too much air getting into the mix. That’s what I’d think after trying all that you did. I’d look for that first. Then I’d move on to other possibilities.
not sure why you have to use a car battery. That might be another problem.
Good luck!
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Post by magoconnor on May 21, 2019 0:13:37 GMT -5
Okay, so too much air huh? Could it just be the manifold, or is it more extensive? It will only idle when I feed it with the throttle, anything els and it dies. I have tried screwing the idle screw all the way down, and it still would not hold idle Did you see the black smoke coming out of the exhaust, in the video? Its definitely running rich. What size main jet should I try, while trying to get it to idle? Thank you so much for helping out
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Post by KSR Moto on May 21, 2019 2:11:40 GMT -5
Try with a different camshaft
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Post by magoconnor on May 21, 2019 3:08:43 GMT -5
The camshaft has always worked tho.. on multiple builds and it appears to be in good shape.
One thing I forgot to mention.
On the very first start up, it did sound very healthy and and held a very smooth idle, for about 20 sec then I turn it off. Next day, when I was just ready to go for the first ride, I started it up again and again it held a smooth idle for about 1 min. And then it stalled out.
Every since then, it cant hold idle and sounds pretty rough like in the video.. It sounds good tho on the first attempt of the day, but it still wont idle. After the first attempt it just gets worse.
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Post by KSR Moto on May 21, 2019 6:23:47 GMT -5
In that case I would say that someting must have happened internally,I am sure that it is the top end problem, what is your current compression reading, have you taken it apart to re check everything,make sure your intke manifold is in good shape and that your intake spacer is not broken
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Post by magoconnor on May 21, 2019 9:22:53 GMT -5
I dont have a way to measure the compression, but I do need a car battery to turn it over fast enough to start it. So the compressiom seems to be good. I can freely turn it over by hand and all seems to be good.
I have not taking it apart yet, cause it turns over nicely. I hope I dont have to.
It did not make a bad sound or anything like that when it stalled the second time. The funny thing is that it does sound normal, granted is only for a few seconds before it stalls. After that first glorius attempt, it sounds like crap in the video. This gives me hope that its not somthing internally.
I will check the manifold and spacer today.
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Post by 90GTVert on May 21, 2019 10:58:28 GMT -5
I'd double check both valve and ignition timing. Make sure nothing is off now, hasn't sheared off the woodruff key for the fylwheel or anything like that.
Also investigate the black stuff in the carb further. Does the intake have the same crap in it? Try to figure out what it is. Is there anything going on upstream that could cause it, like a crankcase vent in the inlet path? No intake valve sticking?
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Post by dexameth on May 21, 2019 11:06:44 GMT -5
IMO - that black smoke is RICH. Way too rich. It honestly sounds like fuel is spilling down the vacuum line from the petcock into the intake... that would be my next inspection if you say everything else is in order (timing, valve lash, etc)
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Post by magoconnor on May 21, 2019 11:52:04 GMT -5
Hi guys thanks for joining in I have checked the valves again - seems to be fine. how do I check the ignition timing? The black stuff in the carb is mixture of fuel and oil I believe. The intake is clean tho The same stuff is on the sparkplug. It does sound rich and it smells like it to, I've tried going down to a 94 main jet on my 20mm carb. I will inspect the vacuum line, but it would pretty weird if fuel made it that way. Has that happend to you? I do have a 24mm on hand, would this be better? If so what main jet should I start with.
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Post by GrumpyUnk on May 21, 2019 11:59:03 GMT -5
I vote for too rich a mix to run. Whether you ruptured your vacuum petcock diaphragm with a backfire after the first start, or the float is sticking, you have too much fuel. Black plugs do not lie, from what I know. If you have a manual petcock, I'd try another carburetor, or make absolutely certain that your float valve works, and the float level has not been messed with. Hard starting requiring an auto battery indicates possibly 1)weak battery, 2)corroded connections, 3)frayhed conductors 4)loose conductors, 5)bad ground of the battery to frame or engine to grame, 6)crappy starter relay with worn points, 7)cam timing off 8)too much friction with new rings/piston too tight, 8)messed up circlip on the wrist pin that's scoring the cylinder wall ... Is that enough?
tom
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Post by jackrides on May 21, 2019 12:16:52 GMT -5
Sucking on the petcock vacuum line will answer that question and might seriously harm you. So, use a hand vacuum pump to test it; or a jar with 2 well sealed lines coming out of it. One to the petcock vacuum, one for applying a vacuum.
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Post by magoconnor on May 21, 2019 14:56:42 GMT -5
Should the arrow on the 90cc naraku piston point up or down? Cause I have pointed it up towards the intake.
If so could this be the issue? I havent heard any bad sounds or any ticking.
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Post by KSR Moto on May 21, 2019 19:17:23 GMT -5
Should the arrow on the 90cc naraku piston point up or down? Cause I have pointed it up towards the intake. If so could this be the issue? I havent heard any bad sounds or any ticking. I would say that arrow should be pointing at exhaust, I never had a naraku bbk so I cant tell for sure
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Post by magoconnor on May 21, 2019 22:14:05 GMT -5
Could it be the cause? And if so, what kind of damage am I looking at ?
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