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Post by normybiy on Jul 8, 2012 17:09:10 GMT -5
hi can anybody offer any advice on this one ....my 125cc gy6 engine idles perfectly but as soon as i give it any kind of throttle the engine pops and bangs ..then as soon as you let off the throttle it idles again perfect....i am at a total loss......since owning the bike i have changed the carb...spark plug ..fuel just to get it started......any help gladly recieve
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Post by justin010304 on Jul 8, 2012 17:13:56 GMT -5
Have you checked your valve clearances? Tight valves could cause this. Have you ever had this bike running well or did you buy it like this?
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Post by wile on Jul 8, 2012 17:17:49 GMT -5
If it is popping when your execelerating it to to RICH. Did you put in a bigger carb or re-jetted and if so what size carb did you put on and or what size jets? Wile
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Post by normybiy on Jul 25, 2012 6:26:08 GMT -5
Hi thanks for replying .. The carb was a direct replacement as the diaphragm was torn and missing the auto choke .. Can u advise me were the mixture screw is on the carb??.....I'm sure the valve clearances are ok but I'm going to double check them to make sure ..
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Post by rks on Jul 25, 2012 11:31:38 GMT -5
Just because it was a "direct replacement" doesn't necessarily mean it is jetted the same. I recently replaced my factory 24mm carb with a new 24mm carb just so I could adjust air/fuel mixture. With new carb installed, I couldn't even use 1/2 throttle and scooter would bog badly. Back out of the throttle, engine would smooth out and run fine. Pulled carb apart, replaced main jet with a smaller one...scooter runs great.
Don't really know what size jet the new carb came with, it was not marked.....replaced it with a 115 because I had a K&N filter ordered
If you still have your old carb, you can just swap out the main jets, and your problem will probably be solved....Bob
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Post by petrol42 on Jul 26, 2012 1:03:03 GMT -5
I agree with rks.
I bought a carb off ebay to replace the one I had but it wasn't until recently that I had a look to see what jets my new carb had and what jets my old one had.
The new one had, I think a 28 pilot jet and a 103 main jet. My old carb had a 35 pilot jet and a 107 pilot jet. If you have the know how, take a look at the jets from both carbs.
The pops and bangs you're describing, are you talking about backfire? And if so, is it backfiring when you give it full throttle or when you let off the throttle?
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Post by normybiy on Jul 26, 2012 11:55:36 GMT -5
Ah ok guy thank you I'm going to check the jets now and maybe change them just to see...... The popping and banging only happens when full or half throttle is applied when I let off the throttle it goes back to running sweet
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Post by geh3333 on Jul 26, 2012 18:52:14 GMT -5
wow , popping and banging !!! thats some hell of a backfire, lol . i would lean more towards the jets and the valves, how many miles on the scoot? you bought it used right? after so many miles the valves usually need adjusted . any smoke from the exhaust ? when you give it throttle are you moving or just sitting there ? by the sound of it you are just sitting there giving it gas, i don't see it running to sweet and not being able to give it gas ( if you are moving ) ,lol .
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Post by petrol42 on Jul 26, 2012 22:58:20 GMT -5
Ah ok guy thank you I'm going to check the jets now and maybe change them just to see...... The popping and banging only happens when full or half throttle is applied when I let off the throttle it goes back to running sweet I had the same symptom recently before I tore my engine apart. Before I offer you some suggestions, I gotta ask if you did anything to your scooter before this started happening or did it just start to happen? Now my suggestions: First, check to see that your intake manifold hasn't come loose. My scoot would still run even though the manifold was extremely loose. If that's on tight, then try turning out your Air/Fuel mixture and then close the idle screw a little if your RPMs start to go up. Somebody on a different forum had popping like you and this fixed his problem. I also read on another forum about backfiring and this one guy said he replaced his ignition coil and it stopped the backfiring. If that doesn't fix your problem, the last two areas I could think of would be to check your spark plug gap (0.023 to 0.027) and your valve lash (.004 intake and .005 exhaust) Try these suggestions but please tell us how your backfiring issue started.
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Post by OverReved on Jul 27, 2012 3:30:09 GMT -5
when you give it throttle are you moving or just sitting there ? That's an important question I was going to ask if it hadn't been asked by someone else. That would help a lot to know.
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Post by normybiy on Jul 31, 2012 10:41:55 GMT -5
hey thanks for all the suggestions guys .....firstly its on a quad bike but its the gy6 engine on it so i have no clue as to what milage on it sadly.....when i bought it used i was told that apart from the auto choke it ran fine ...i replaced the carb and spark plug and got it running ....when i took it out i realised it was popping and banging under throttle either moving or stationary.....following some of the advice already given i changed the jets to the old ones and checked the valves....i have set both valves to .05 which combined with the jet change has made a very small difference but the pops and bangs are still there when throttle is applied ... maybe as i got it used there is a more serious problem causing it to not run right ... thanks for all the advice guys
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Post by normybiy on Jul 31, 2012 10:44:33 GMT -5
sorry the valves were set to .005 a wee typo there
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Post by normybiy on Jul 31, 2012 10:54:22 GMT -5
hey just a thought would having a wee vac fuel pump pumping fuel into the carb be too much for it??? should i remove this and put the fuel line straight to the carb?
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Post by petrol42 on Jul 31, 2012 17:02:25 GMT -5
hey just a thought would having a wee vac fuel pump pumping fuel into the carb be too much for it??? should i remove this and put the fuel line straight to the carb? That won't work. Without the fuel pump, fuel wouldn't get into the carb.
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Post by geh3333 on Aug 1, 2012 21:24:42 GMT -5
if its gravity fed with a vac type pump " valve" removing and running the line straight to the carb will work , and if its a stock vac pump " valve" removing it will probably be better. i did the same and added a shutoff valve instead.
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Post by geh3333 on Aug 1, 2012 21:29:45 GMT -5
is the fuel pump an actual electric pump ? and was it added or did it come with the setup ? if it was added and was originally gravity fed then you can take it out and run direct .
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Post by normybiy on Aug 4, 2012 9:29:06 GMT -5
hi no the fuel pump is a wee vacuum operated one think i will try removing it just to see if it helps my situation out any ......just ordered a new ignition coil to see if that helps any too ....fingers crossed it will
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