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 YAMAHA ZUMA BUGEYE 50 - Athena BBK very low compression 
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Location: Castro Valley, CA
scooters and mods: 09 zuma 50
Post YAMAHA ZUMA BUGEYE 50 - Athena BBK very low compression
I just installed an athena bbk and it wont start. My HF compression gauge reads 38psi. I checked the stock bore prior to the tear down and got the stuck at 90 reading but it ran just fine. I'm stumped, it has spark, ignition is oem new, it's getting gas, the plug is moist but not saturated float bowl is full.

Here's the set up
09 zuma
Athena sport bbk single ring
Arrow pointed at exhaust (I disassembled to double check)
Bh9 plug
Head bolts torqued to 11ftlbs
2nd thinnest base gasket
Athena head hasket
Stock exhaust
84 main
Adjustable needle set one up from the bottom
Stock airbox/stock filter
Stock reds and new oem gasket
Throttle mod
Cleaned carb passageways
Put a smear of oil in the cylinder to try to create a seal
I put my thumb over the plug hole and cycled the piston via kick start and it felt weak,
I need a sanity check.

-kp-


Fri Jun 29, 2018 8:53 am
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Location: portage wi
scooters and mods: 08 zuma dual headlight tmod rally kit cutom red paint koso mirros red anodized trans bolts
Post Re: Athena BBK very low compression
If the gauge is right something isn’t sealed right or you have the wrong pistion or bad ring gap or bad pistion to wall clearance.

Stock reeds are asking for a choked reed and damaged cylinder when it eats the metal

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2008 zuma dual headlight mod koso mirrors liquid cooled polini corsa kit leo vince zx stage 6 variator rally kit custom red paintFUEL INJECTEDsoon to be 100cc
2008 stella olive custom ported 177 cc kit dechromed ford tear drop tail light alive and breathing and awaiting cosmtic surgery thanks to an trump cager
1985 elite 150 how long can i leave it stock


Fri Jun 29, 2018 3:37 pm
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Joined: Fri Jun 29, 2018 8:35 am
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Location: Castro Valley, CA
scooters and mods: 09 zuma 50
Post Re: Athena BBK very low compression
Carbon reeds are going in they had a a small gap in the seal so I swapped them to see if that caused a pressure leak. Its temporary. Ill swap back.

Regarding the pressure, I'll put a new base gasket on to see if that is the cause.

Bbk is brand new, can't imagine a bad ring grrrrrr..... Piston came with the kit. Both cylinder and piston came sealed and in original packaging.

I'll report back with a new base gasket + c reeds. Is there a spray or something I can use to really rule out leaking gaskets?


Fri Jun 29, 2018 4:49 pm
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Joined: Thu Mar 20, 2008 5:27 pm
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Location: portage wi
scooters and mods: 08 zuma dual headlight tmod rally kit cutom red paint koso mirros red anodized trans bolts
Post Re: Athena BBK very low compression
Just because it’s new and shipped together doesn’t mean it’s rght
That is why you check ring gap and pistion to wall clearance
They should check the pistion fit but I have seen many cases of them shipping an a pistion when you need a b pistion or however that brand marks there sizes because things happen and are never manufactured perfect

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2008 zuma dual headlight mod koso mirrors liquid cooled polini corsa kit leo vince zx stage 6 variator rally kit custom red paintFUEL INJECTEDsoon to be 100cc
2008 stella olive custom ported 177 cc kit dechromed ford tear drop tail light alive and breathing and awaiting cosmtic surgery thanks to an trump cager
1985 elite 150 how long can i leave it stock


Fri Jun 29, 2018 7:02 pm
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Joined: Fri Jun 29, 2018 8:35 am
Posts: 8
Location: Castro Valley, CA
scooters and mods: 09 zuma 50
Post Re: Athena BBK very low compression
New base gasket, Carbon reeds and no luck. I have an "A" piston on the label and the piston is stamped accordingly. Stock crank w 10mm shaft. If "A" piston is right I'll order a new ring and cross my fingers.

***just did some research, to clarify, they use the same ring but come with the piston that meets spec with the cylinder.


Fri Jun 29, 2018 7:25 pm
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Post Re: Athena BBK very low compression
I tore it down again.

Checked piston ring gap at the base of the cylinder and it was tight enough I couldn't get a feeler gauge in.

I don't have extra circlips to pull the piston but the piston w no rings was snug and wasn't sloppy in the bore.

Permatex the base and head gasket and torqued it back down.

Same reading 38psi. No start. I did leave it at TDC with the Guage hooked up and no pressure drop so the head gasket is legit.

I'm loosing patience fast, this is a top end on a two stroke not formula one. :gonk:


Sat Jun 30, 2018 8:52 am
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scooters and mods: 09 zuma 50
Post Re: Athena BBK very low compression
Did a leak down test, intake and cases held 8psi and the head held pressure so I think the piston is correct, the ring is within spec, and the engine is sealed. Something just ain't right. I tried to get some squish readings but my solder is 1mm so it's too thin based on my research.


Sat Jun 30, 2018 11:16 am
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Location: Castro Valley, CA
scooters and mods: 09 zuma 50
Post Re: Athena BBK very low compression
I took another stab at the kit and came up in the same spot. I put the stock top end on and it hit the stuck at 90psi HF reading. I've given up on this kit, something wasn't right somewhere and there are no PN#'s stamped in the castings to cross reference so it's back in the box.

Does Athena have any USA presence or am I stuck going international?


Sun Jul 01, 2018 8:03 pm
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scooters and mods: '03 yellow Zuma with Malossi 70 cc, rejetted stock carb and stock exhaust.
Post Re: Athena BBK very low compression
I strongly recommend a Malossi cast iron sport cylinder, especially since you're using the stock exhaust. Mine's been perfect for over 10k miles.

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Malossi 70cc, 82 main, 46 pilot and needle raised on stock carb, stock exhaust, air cleaner and clutch.


Mon Jul 02, 2018 11:13 am
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Location: Castro Valley, CA
scooters and mods: 09 zuma 50
Post Re: Athena BBK very low compression
After a few beers and a moment away from the scooter I'm back at it again. I got in touch with Athena USA and they'll check the the specs to make sure it's correct.

Anyone know if the 069301/1 is the correct cylinder for the sport kit? A quick search yielded different results.

I'll check out the malossi kit if my new found enthusiasm runs out.


Mon Jul 02, 2018 4:35 pm
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Post Re: YAMAHA ZUMA BUGEYE 50 - Athena BBK very low compression
Quick update:

Athena stood by their product and although there was nothing visually wrong with the kit, and Im sure they had their own doubts, they sent me a new one. Class act, big shout out to their customer service. I thought I was dead in the water.

Quick install and boom 137psi, started right up.

84 main jet and needle one notch up and wow! Impressive. Can't imagine what I pipe and carb would do.....and so it begins.

-kp-


Tue Jul 24, 2018 8:42 pm
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