Two Shops, Conflicting Opinions, Need some advice.

[ZForceRacing01]

Over the Summer I had a head replaced on my Sealed 1250 by USLC. I was told the car had been put on the Dyno and tuned up, but they only charged me labor for the replacement. We raced that weekend, the car was not magically faster and still did just didnt seem it was where it needed to be. We decided we may have a carb issue. Since we know Jack about these quad Mikuni carbs and the car had just came from USLC and was not at what we believed was peak performance, we decided to go to another shop. Keep in mind this is my first season, the car had a cracked head when I bought it. I have never driven a car @ peak perfromance.

We decided to go outside the box and chose a shop that does Drag and Track Bikes. Turns out he guy used to work on Legends and agreed to work on my car. He rebuilt the carbs and put a HSR jet kit in, in addition we went from a 122.5 to a 120 main jet. He tuned them up and we picked up .2 on the stopwatch of the bat.

Here is the issue. He did a leakdown and compression test before he touched the carbs. Cyl #1 160 @5%. #2 110 @ 30% Past Intake and Exhaust, #3 150 @5%, #4 160 @ 10%.

Since its a sealed motror I contacted USLC and informed them of the reults of the test. They said they would look at it at no charge and make sure there isnt an issue witht the head.

They did a compression and leakdown and said it pumped 172-178 and 6-8% accross the board.


So here I have two shops with very different opinions. I have never done a leakdown test , but have done a compression check. I dont see where this variation is soming from?

Atm, I plan to buy the equipment to do my own leak down and compression check.

Any advice on how to better handle this is greatly appreciated.

[DoubleZero]

Compression tests are just a quick way to find an obvious problem.   Leak down tests are the best way to find out what's really going on with the engine.  The testers are not that expensive.   Each tester will give you an acceptable leak percentage on their scale in green.   It takes time to run the tests but you can check your valve lash and change plugs while doing it.   

 If you have a cylinder leaking here is something to try.   If you have an old fashioned mechanic stethoscope you can listen for leaks while doing the test and pinpoint the issue.   If you hear noise thru the bore of the carb an intake valve is leaking.  If you hear noise from the header it's an exhaust valve.  Put it down the oil fill hole and if you hear noise you have blow by around the rings......all of this is easier said than done by the way.....and my hearing is not good!

I had my motor rebuilt this summer and put on the dyno at US Legends.  They do change the jetting in your carbs for pump gas.  We run MS98 so that really messed me up in the first race with the new motor.   Jetting is everything.   They sent my old jets and metering rods back in a bag. 

Also check valve lash.   After the initial break in your valves will need adjusted. 

[ZForceRacing01]

http://www.longacreracing.com/products.aspx?prodid=7635

This is the leak down tester I was going to buy. I says 14 millimeter connection for the sparkplug, is this correct?

[DoubleZero]

I believe our plugs are 12mm thread size.   Better check a plug before ordering.   The leak down tester I purchased had connections for different sizes.   

[ZForceRacing01]

They are 12 mm with a M 1.25 pitch. I had to order an adapter from Snap On. Cost me another $60.