Fix my Whizzer!

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The cylinder can not get enough air for an accurate reading when the throttle is closed. Even removing the carb will be better for an accurate reading.

Jim
 
Yes, that makes perfect sense!

Wide-open-throttle, choke off, is 55psi, as hard as I can kick start it.
 
Wow.
At this point I don't know what else to tell you. I hope you don't have a bent valve. It may be time to pull the head and look for obvious damage or failure of the valves, head or piston.

Jim
 
Yup, that's my next step tomorrow.

For my reference, what is the compression of a stock Whizzer with a 22mm carb, choke off, wide open throttle?

Can someone perform a test for me? Thanks in advance.
 
I don't have a compression tester so I can not answer that question for you. I know someone will chime in with the info.
 
Hi go-rebels,

Wide-open throttle and motor turned briskly should range from 80 pounds [stock] to 165 pounds [not stock]. The numbers will vary depending on the stage of break-in your motor has achieved. I would suspect you should see numbers above 110 pounds with a similar motor.

It is important that I explain the term "briskly" in more detail......... with bike on stand, and serious pedal movement with the throttle wide open. The pedals should at least make 3 swift complete revolutions. Or simply connect a belt from an electric motor [like the one attached to my shop floor] and let the power company supply the needed "muscle"

Possible causes of low compression would most likely be head gasket or valve problems.

A possible detail to consider is the clearance between the head and the valves. It isn't always the same on new edition Whizzer motors. The height of the head of each valve can vary greatly from motor to motor, and depends on how centered the valve seats are in respect to the valve guides. I have only witnessed a few that were in "center", and the vast majority were off. If the seat is in center the valve seat doesn't require as deep of a cut. In other words some valves sit much higher in the cylinder and therefore reduce the area between the valve and the top of the head.

If the compression checks low, a quick look inside the head would be my suggestion.
Just give me a call, and I will supply solutions and answers.

Have fun,
 
Hopped on the bike with the kickstand down and got 65 psi compression.

A teardown indicated that I blew out a portion of my copper head gasket behind the intake valve. I have another gasket and will install that over the weekend.

I checked my cylinder head using a 6" metal ruler and it appeared dead flat. I check the top of my block in the area of the blowout and that looked good too. I suspect that for whatever reason I did not have good clamping force at the back of the head. The cylinder head mounting holes appear a bit small for the standard bolts and I plan to drill them open another 1/64" to get a little more clearance before reassembling with a new (larger) copper gasket.

I'm still perplexed why I couldn't get the bike to fire one using starting fluid, but that point may be moot with the compression restored.
 
The location of the head gasket failure would very likely cause the no fire situation. The fuel charge is escaping out the head gasket failure point so I can see why it didn't fire. I hope everything will be good to go with a new head gasket. It goes without saying but make sure you torque it down correctly. Sorry but I had to say it.

Jim
 
Yup, I had torqued all the bolts to spec but remember, this is a one-off custom copper gasket. The cross section was a little small behind the valves and the new copper gasket I will install this weekend is the standard (larger) type used with the stock head. After adding a little clearance to the mounting holes in the head, I don't expect another head gasket failure, even with the high compression head.

Just a word of caution too... when installing the custom head, I needed to cut 5mm of thread from the two front and rear left 8 mm cap head screws so as to prevent a bottoming-out condition. Apparently, the holes are tapped only slightly deeper than what is absolutely necessary when using the standard head. A slightly thinner head will result in the bolt bottoming-out in the blind hole and result in little or no clamping force on the gasket. I'd double check any new installation after milling the head 0.060".
 
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