Air leak....

[skiracer]

I just put together my 250 MC 5 with a freshly rebuilt motor.  Upon completion, I have found that I have an air leak somewhere....  I tried spraying carb cleaner around the head and base gaskets, intake manifold, and the seal behind the ignition without creating any revs from the spray.  I replaced the head and base gasket again with new ones; no change....  The bike starts well, over-revs a bit while sitting still.  The bike runs okay at low RPM's in 1st-3rd gear.  Once I rev the motor more than 40%, it starts acting like it is running lean, along with additional revving when I turn the throttle off...  Any suggestions?

1976 MC 5 Original Owner
1976 Hercules 250 GS 7A
1982 Suzuki PE 175
1976 Penton 175 GS

[tomale]

I doubt that using carb cleaner will net you the kind of results you are looking for.  You will need to do leak test and a vacuum test.  The leat test will tell you if there is a problem with gaskets, seals and if you have a hole in a case.  Once you can hold 5 pounds of pressure for a few minutes, you need to do a vacuum test.  This will tell you if you seals will hold a vacuum. The main seals do both since both happen during the running of the engine.  To do this test right you will need to take the clutch cover off because the main seal on the left side is buried.
Things to look for, on the KTM it has a drain plug for the crank case, make sure it seals well, spark plug hole can get pretty chewed up, make sure it seals well, on one of my bikes it was giving me fits until I had it machined flat again.  The cases are made of magnesium so when you do a leak test check for leaks in the cases themselves. I had a bike with a leak in the transfer port, leaking outside.   Plug all the holes, add abou 5 pounds of pressure and spray it down with soapy water.  A trip to the plumbing section got me nearl everything I needed, that and valve stem and you can test most bikes.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74' 1/2 440 maico
70' 400 maico (project)
72' cr125 Husky (project)
93' RMx 250 suzuki
Honda TL 125
2004 Suzuki DL1000

[tofriedel]

You might also want to consider your exhaust pipe and air filter.  If either of these are restricting air flow you will get similar results that you have experienced.

Tony

[slvrbrdfxr]

Yes, its always a very good idea to pressure check the engines after reassembly. I've had a couple KTM engines that have given me fits chasing leaks and so I made pretty simple tester to pressurize the top end. I bought everything needed to make the tester with one trip to Lowes and Auto Zone. Email me and I'll be glad to send you pictures of the tester I made. Just use my screen name here and add @cox.net.
Dave McCullough

[skiracer]

Thanks Thom,  I appreciate the input.   James

quote:Originally posted by tomale

I doubt that using carb cleaner will net you the kind of results you are looking for.  You will need to do leak test and a vacuum test.  The leat test will tell you if there is a problem with gaskets, seals and if you have a hole in a case.  Once you can hold 5 pounds of pressure for a few minutes, you need to do a vacuum test.  This will tell you if you seals will hold a vacuum. The main seals do both since both happen during the running of the engine.  To do this test right you will need to take the clutch cover off because the main seal on the left side is buried.
Things to look for, on the KTM it has a drain plug for the crank case, make sure it seals well, spark plug hole can get pretty chewed up, make sure it seals well, on one of my bikes it was giving me fits until I had it machined flat again.  The cases are made of magnesium so when you do a leak test check for leaks in the cases themselves. I had a bike with a leak in the transfer port, leaking outside.   Plug all the holes, add abou 5 pounds of pressure and spray it down with soapy water.  A trip to the plumbing section got me nearl everything I needed, that and valve stem and you can test most bikes.

Thom Green,Still crazy after all these years!
76' 250 MC5 (orginal owner)
74' 1/2 440 maico
70' 400 maico (project)
72' cr125 Husky (project)
93' RMx 250 suzuki
Honda TL 125
2004 Suzuki DL1000

1976 MC 5 Original Owner
1976 Hercules 250 GS 7A
1982 Suzuki PE 175
1976 Penton 175 GS

[skiracer]

Thanks Tony!

quote:Originally posted by tofriedel

You might also want to consider your exhaust pipe and air filter.  If either of these are restricting air flow you will get similar results that you have experienced.

Tony

1976 MC 5 Original Owner
1976 Hercules 250 GS 7A
1982 Suzuki PE 175
1976 Penton 175 GS

[skiracer]

Hey Dave,  Thanks for the offer, but I have already made one several years ago.  I appreciate the offer.  James

quote:Originally posted by slvrbrdfxr

Yes, its always a very good idea to pressure check the engines after reassembly. I've had a couple KTM engines that have given me fits chasing leaks and so I made pretty simple tester to pressurize the top end. I bought everything needed to make the tester with one trip to Lowes and Auto Zone. Email me and I'll be glad to send you pictures of the tester I made. Just use my screen name here and add @cox.net.
Dave McCullough

1976 MC 5 Original Owner
1976 Hercules 250 GS 7A
1982 Suzuki PE 175
1976 Penton 175 GS