One cold Cylinder

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guyh

One cold Cylinder

#1 Post by guyh » Tue Jun 28, 2005 2:43 pm

Hi,<br> I have the #1 ( upper left cylinder ) running cold.<br>And when I start the motor cold that cylinder backfires out the exhaust pipe...usually just once.<br> With the airboxes removed ... covering either carb mouth of the lower carburettors I get noticleable vacumn on the palm of the hand and the motor begins to die .... the vacumn effect is not noticeable on the upper carby's unless I rev it up and blocking the either of the upper carb mouths does'nt seem to affect idle.<br>I have replaced spark plugs, the coil,The ignition box and the left hand carburettor bank with parts from a working motorcycle. The spark looks OK and swapping left and right plug leads makes no difference.<br> The new plug does not seem to be getting oiled up like the running cylinders so I think theres a lack of fuel.<br> I pulled out the reed block and it looks ok.<br> The piston looks ok when viewed through the exhaust and inlet ports and through the spark plug hole.<br> I think there must be an air leak for there not to be much fuel getting to that pot.<br> I have not yet checked the blind seal, done a compression test or pulled the head & barrell<br> Anyone have idea's on what is the most likely cause of the problem ?<br>
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guy_harper@yahoo.com.au

Jeff B

Re: One cold Cylinder

#2 Post by Jeff B » Wed Jun 29, 2005 1:24 pm

I'd do a compression test if I were you. If you can rule out piston problems then you know you have an air leak. On the other hand if the plugs aren't getting oiled up you could have oil delivery problems which may have caused a scored piston andor cylinder wall resulting in bad compression.
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beeks81@aol.com

guyh

Re: One cold Cylinder

#3 Post by guyh » Wed Jun 29, 2005 2:08 pm

Thanks for the follow ups .... and you are right... not having a compression tester I tried the thumb over the spark plug hole test last night and I get pressure on only one of the upper cylinders ( you can feel and hear it hiss past your thumb) whereas the other has seemingly no compression whatsoever. So next step wll be removing the motor and having a look inside. As everything still turns over nicely I'm hoping its just worn rings but with the total compression loss that seems unlikely.<br>regards,<br> Guy
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guy_harper@yahoo.com.au

guy

Re: One cold Cylinder

#4 Post by guy » Sun Jul 03, 2005 2:20 pm

Hi, <br>I removed the head and found the piston to be cracked right across the crown ... just the rings holding things together and the bore looks fine. <br>So that was the cause of the loss of compression and cold running cylinder.<br>I'll probably do an all cylinders rebuild now I've got the motor out. Hone or rebore & new pistons & rings. <br>regards Guy<br>
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guy_harper@yahoo.com.au

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