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Post by fixit1958 on Jan 14, 2012 14:12:53 GMT -5
 Hey guys, I'm new to this board, but looks like one of the BETTER ones out there for scooter info! Anyway, I have a Jonway 50cc wide body scooter that I just put an 80cc big bore kit on. After installing the kit along with a "NEW" Walbro carburator the engine cranks very slow and extremely hard. I checked the piston ring clearances before assembly....007" on top and .009 on bottom compression rings. Everything went GREAT during assembly. I have set the valves to .003 on the intake and .004 on the exhaust. The engine has GREAT compression around 215psi. I have been fooling around with trying to get this bike to start for over 3 days! Last night I pulled the carb from the intake and the engine cranked as normal...smooth and steady. When I reinstall the carb, the engine cranks very slow and hard. Don't get this one! I've got good spark and suction through the intake when cranking. ANYONE HAVE THIS PROBLEM BEFORE.....AND WHAT DO I DO TO GET THIS BIKE TO RUN? PLEASE HELP!! :sos:
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Post by 90GTVert on Jan 14, 2012 14:26:38 GMT -5
:welcome:
I think that 215psi might be the problem. That's a lot more compression for your starting system to act against. Your battery is gonna need to be tip top, charged up and all connections will need to be secure. Some of us move up to larger battery/starter cables and battery upgrades to be sure we're moving as much juice as possible. I'm not so sure your compression isn't gonna prove to be too much even when it's running.
Can you kickstart it? I hate to even ask that since I find the kickstart gear on these to be shotty and easy to break. I know some members have said they kick start on the first start of the day and afterwards the e-start will handle it.
If you do end up needing to lower compression, an easy way is to add a 2nd base gasket. If you're using a stock cylinder head and this is a 50mm or bigger kit, you may wish to consider a cylinder head that matches the bore or machining the existing head to match.
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Post by fixit1958 on Jan 14, 2012 14:37:49 GMT -5
I have fully charged the battery and checked all connections. All look good! I was guessing on the compression based upon the scooter repair manual and my guage could also be off. I will check again, but YES I can kick it and turn the flywheel by hand with no problem. It will still not start. Question....Why would it crank smooth and steady with the carb off and hard and slow with the carb on? I have also placed my thumb in the intake while cranking and it cranks smooth and steady! This thing is frustrating me beyond frustration!
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Post by fixit1958 on Jan 14, 2012 14:39:33 GMT -5
I do have the 80cc head on it that came with the bore kit!
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Post by jmkjr72 on Jan 14, 2012 15:19:31 GMT -5
i have found that it helps to upgrade to a battery with more cranking amps when you kit the scoots
many of the 50s come with batteries that are 80 cca or less and that just doesnt cut it
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vvtr
Scoot Enthusiast
Posts: 243
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Post by vvtr on Jan 14, 2012 18:46:04 GMT -5
yup 215psi is like 14 bar = 14:1 compression ratio..... definately theres your issue. while that might be great on a race engine, i think before long you will bust the head gasket and break down miles from home! are you sure you have set the valve clearance correctly?  is the exhaust valve opening at all? did it fire up? you have to be carefull with these 4Ts when adding thicker gaskets or jacking up the cylinder etc as you will find the cam wont seat properly due to the chain being stretched. you can force it down but this puts excessive force on the camchain and cam bearings... i think you may end up cutting the head deeper? what kit is it btw??? and are you absolutely sure that compression reading is correct? i'm wondering if you have the valve timing set corectly - can you go through step by step what you did - maybe take a picture of the position of the cam gear at tdc? *btw - on these chinese scoots, a lot of owners will remove the kickstart for security reasons..... it is extremely easy to steal a scooter that has a kickstart.
i wont post how for obvious reasons, but just bear that in mind, if you have a chinese scoot, it may be wise to remove it and store it under the locked seat just in case you need it.
(and a spanner to fit it obviously) |
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Deleted
Deleted Member
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Post by Deleted on Feb 11, 2012 22:14:19 GMT -5
an extra base gasket or 2 would help plus larger battery cables and a high cca battery like 190 cca or more will help. a stock qmb scooter battery is a pathetic 70cca.
My 50mm bbk has 2 thick hoca base gaskets under the jug and still has 190 psi. I went to massive automotive #4 ga starter cables and a 90cca battery and it did the trick but barely.
I have seen 235cca batteries on ebay for good prices.
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Post by usmcdoc on Feb 12, 2012 18:56:08 GMT -5
215 psi??? I have done over 15 BBK's for myself and others...even with the stock head on an 80cc BBK...145 psi is as high as compression gets..if the starter won't crank it....it is obviously too high...are you sure it was not one of the 100cc kits they sell?...with a stock head I see them pushing 225 psi...add 2 base gaskets and it goes away...but 215 on an 80 kit...is actually 72cc....which the GY6 50cc was actually built as....just sold in the U.S. with a 39 mm piston....to meet our 'moped' laws..
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Post by vegaslightsss on Oct 18, 2012 18:18:07 GMT -5
52mm Kit from scrappy with stock head is at 225 psi no BS on a 1P39QMB 2012 Tao Tao ATM50 A1 ,cant ride until I find a suitable big valve head.Vegas
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Post by vegaslightsss on Oct 19, 2012 22:36:33 GMT -5
Could be this 30.00 Harbor Freight Compression Tester I suppose,this thing reads like a Diesel ...
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Post by Corrosion on Oct 20, 2012 8:26:50 GMT -5
Try Cranking with the Ignition - OFF or kill Switch engaged. If speed is normal or better, Possibly Ignition Timing is to advanced. PS the HF compression gauges are JUNK... MightyVac, has a very nice kit for a reasonable price, And it is accurate. www.tooltopia.com/mityvac-mv5530.aspx |
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Post by stepthrutuner on Oct 20, 2012 9:41:41 GMT -5
I'd check the piston-to-valve clearance with some modeling clay. There should be a post on this in 90GTVert's Sunl 50 build. Could save you a bent valve, etc.
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Post by scooterscott on Oct 22, 2012 19:30:55 GMT -5
im having the same problem i have to kick start it and sometimes the battery has the stuff to get it going but not all the time
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Post by prodigit on Oct 28, 2012 22:51:38 GMT -5
Talking about kick start, can the kick starter be used together with the electric starter?
If so, problem solved!
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Hey guys, I'm new to this board, but looks like one of the BETTER ones out there for scooter info! Anyway, I have a Jonway 50cc wide body scooter that I just put an 80cc big bore kit on. After installing the kit along with a "NEW" Walbro carburator the engine cranks very slow and extremely hard. I checked the piston ring clearances before assembly....007" on top and .009 on bottom compression rings. Everything went GREAT during assembly. I have set the valves to .003 on the intake and .004 on the exhaust. The engine has GREAT compression around 215psi. I have been fooling around with trying to get this bike to start for over 3 days! Last night I pulled the carb from the intake and the engine cranked as normal...smooth and steady. When I reinstall the carb, the engine cranks very slow and hard. Don't get this one! I've got good spark and suction through the intake when cranking. ANYONE HAVE THIS PROBLEM BEFORE.....AND WHAT DO I DO TO GET THIS BIKE TO RUN? PLEASE HELP!! :sos: 
is the exhaust valve opening at all?
