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Post by dexameth on Sept 5, 2018 14:11:23 GMT -5
So, not often am I stumped with these little motors but after my fresh rebuild of my GY6 I have an issue where it backfires when I take off hard. It will start and idle just fine, and take off good with quarter throttle but the minute I open it up it starts popping and banging till I lessen the load on the motor. Here's the rundown:
-Brand new stock stroke crank
-Brand new 61mm piston/cylinder kit
-Stock head, cleaned up
-New intake, gasket, insulator
-New carb, 26mm, 115 main 38 idle with Uni Filter
-New high tension coil, CDI and iridium plug
I broke in the motor just fine, and rode it a few times with some distance without issues. The other day as I rode it around and it warmed up, the backfiring got worse and worse, but not too bad to where it's non-driveable (just somewhat annoying).
To me, it seems like a bad timing issue. I pulled my flywheel and inspected TDC with the mark and all is good. Gap on pickup is good.
Next I thought, maybe rich, since only at WOT pulls... so I removed the air filter and it didn't change anything.
Valve lash is .004 for both, so that's good. Timing holes on cam line up pretty much perfect.
Tonight I will try to install my OKO 26mm carb with a 24mm intake and new throttle cable and see if that helps any, maybe my "new" carb was a defect. That, or the CDI is a defect, my only two guesses at the moment. If anyone has any ideas feel free to chime in... thanks.
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Post by atlantamods on Sept 5, 2018 15:36:04 GMT -5
do you have a after market muffler on it ?
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Post by dexameth on Sept 5, 2018 16:00:03 GMT -5
do you have a after market muffler on it ? Always. I made a muffler myself using one of those eBay shorty mufflers, but using a different header. I had been using it with my stock setup for a while before I did the big bore upgrade with no issues. I also used a brand new SSP-G premium exhaust gasket when I finished the build. |
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Post by atlantamods on Sept 5, 2018 16:04:13 GMT -5
i have a after market muffler my self and it will back fire from time to time i have tuned my carb and it still back fires
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Post by dexameth on Sept 5, 2018 16:17:34 GMT -5
Mufflers are known to backfire if you re-use your crush style exhaust gasket or if you just fail to use one at all. Any air leak within an exhaust system will cause ignition inside the muffler when the throttle is closed... I've made mufflers do it just for fun, blowing foot-long blue flames out really gets people fired up when cruising the beaches at night.
This issue is not a leaky-exhaust backfire issue. It only happens under heavy load past half throttle and more at WOT.
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Post by lilpinny on Sept 5, 2018 22:47:31 GMT -5
my 170 will pop a little bit when coming off of WOT out the carb.
my valves are at .004 intake .007 ex. i was always told to bump up the ex by .003 from the intake.
The generic CDI's are cheap enough that you could see what swapping that out does.
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Post by dexameth on Sept 6, 2018 8:46:46 GMT -5
... .007 ex. i was always told to bump up the ex by .003 from the intake. The generic CDI's are cheap enough that you could see what swapping that out does. Holy crap! I always do .003/.004, .004 both, and on a stretch I've done .004/.005. That seems like way too much exhaust tapped slap... But as for the CDI guess, I'm with you on that. Could have been one of the bad ones, but we'll see. I got some OFF! this morning so I can actually work on the scoot outside my place and not be devoured by mosquitoes. Tonight I'll finish the carb swap and see what happens, it's a 26mm OKO, should be better than the stockish 26mm CVK alone. |
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Post by lilpinny on Sept 6, 2018 16:51:45 GMT -5
I was told that by the guy from martin mopeds and drowsports. Never had any problems... but it is a complete taida top end. maybe its different.
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Post by dexameth on Sept 6, 2018 17:02:43 GMT -5
lilpinny nahh nothing different with Taida... Taiwanese performance is all the same for the MOST part. Most NCY, Taida, SSP-G parts come from the same foundries believe it or not.
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Post by lilpinny on Sept 6, 2018 17:03:21 GMT -5
ya i didnt think so
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Post by dexameth on Sept 7, 2018 12:40:53 GMT -5
Swapped to the OKO 26mm carb. Did a 115 main, had a 48 idle. Got it running first thing this morning then rode it the 1.6 miles to work. The only way it would start was with blipping the throttle pretty much WOT and it would not idle at all. I limped it to work by intermittently blipping wide open throttle over and over. I just swapped out the 48 pilot which seemed WAY too big for a 35. No change. Did a few test rides and it acts just like this morning. Turned the air/fuel screw all the way in, same results; then 3 full turns out, same results.
When I'd get it to start up with all those settings I would basically drag-race myself and make a mental note of the performance. At WOT the scoot PULLS SO HARD but then once it started getting up to speed I'd here the backfiring. IDK, seems weird that no matter what I did with the A/F screw there was no change.
I did pull over and moved the needle position from the bottom notch to the top. Did a self-drag-race and the backfiring at high rpms went away a little.
I might need to back down to a 112 main or even a 110, but until then I just want this thing to start and idle. The choke lever did nothing but make starting harder... so does it seem right that I need a SMALLER than 35 idle jet?
I have such good luck with building my Scootie, the 139QMB platform and I've had nothing but issues with this stupid GY6 platform. I'm almost over it... I feel like I'm wasting my time just trying to get this thing at least rideable when I could be out making money fixing other scoots or just riding my other ones.
I'd prolly take 400 cash just to get this shit out of my hair.
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Post by lilpinny on Sept 7, 2018 12:43:38 GMT -5
GY6 1 -- Dex 0
dont let it beat you! Everyone has issues with it at first.
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Post by lilpinny on Sept 7, 2018 12:44:42 GMT -5
i think i have a 38 idle.
but maybe you have an air leak if the airscrew isnt doing anything.
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Post by dexameth on Sept 7, 2018 13:54:15 GMT -5
i think i have a 38 idle. but maybe you have an air leak if the airscrew isnt doing anything. I am honestly thinking the same thing. But, a new gasket went on during lunch when I swapped to the smaller idle jet so I can rule out gasket. Intake is a metal one, no rubber to crack. So I'm kinda lost... |
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Post by lilpinny on Sept 7, 2018 15:34:08 GMT -5
intake leaks are very common. many clocking flanges bump up againt the metal on the head and need to be filed a little to sit flush. then black rtv the heck outta it. they say dont use black on those parts but everybody does and it works great.
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