rs34's

the compression will rise, you probably don't have any valve train problems give the motor a bit of time and let the rings seat before you start freakin out.those compression numbers are quite good,what do you have for cams and what kind of overlap have they got.

If interested, here's a Simple Simon explanation of the leakdown test.

With the leakdown test, each cylinder is tested separately. Compressed air is pumped through the spark plug hole into the combustion chamber while both valves are closed. Usually you can actually hear where the compressed air from inside the cylinder is leaking out from.

A hissing sound from the exhaust indicates the exhaust valve isn't fully sealing, as compressed air leaks past the exhaust valve out through the exhaust.

A hissing sound from the carb intake indicates the intake valve isn't fully sealing, as compressed air leaks past the intake valve back through the carb.

A hissing sound from the crankcase vent indicates compressed air from the combustion chamber is getting past the pistons and compression rings and on down into the crankcase.

Even a perfect cylinder gradually loses the compression, but generally the longer a cylinder holds compression, the better. And of course, hissing sounds are unwelcome.

Good Luck!

That's a very good explanation Patton (did you call me simple?)

I'll keep that test in mind if it shows any other symptoms of engine issues. I'm only digging because I can hear carb "clacking" and and it was suggested that I test the compression. The clacking seems to be much better now that I have synched the carbs, but I have't been able to ride it because of snow! For right now, I don't have any reason to think I have any mechanical problems since it's a new build with only 42 miles. I plan to check the valve clearances after I get some miles on it. Hopefully the rings will break in and the compression will come up a bit too.

Judging by the black plugs I think I need to lean out the pilot circuit too. It really loaded up while I was synchronizing the carbs.

The cams are .425 web and I forget the overlap, sorry. I'm really bummed that I ran out of good weather before I got this thing dialed in. I'm hoping for a little break in the weather so I can try it out after synchronizing. I might have to lean out the pilot and the needles too (currently at 20 pilot down from 22.5).

79MKII wrote:

... did you call me simple....

Oh goodness no, not all all! As possible valve damage was mentioned, and a leakdown test suggested (in addition to normal compression testing), the post was aimed at affording a better understanding to someone who might be unfamilar with benefits of a leakdown test. And boo on me for in any way implying otherwise.:blush:

If clacking persists after synching, am wondering if it might be feasible to swap positions with another carb to determine whether the clacking follows the same carb or stays with the cylinder.

Good Luck!

My 34's are perfect for my ported head and 3x cams. I could not be happier with them. Very easy to tune.

Patton wrote:

79MKII wrote:

... did you call me simple....

Oh goodness no, not all all! ...

Just kidding with ya Patton - thanks for the good tips!

79MKII wrote:

mark1122 wrote:

I take it that those # are from a dry test.
Nothing outstanding there.There just a little low ,due to the rings not being seated yet.
Did u do a wet test?(with oil)Wet u should be around 225psi.The wet test can identify a valve issue. But your #'s look fairly even now.

Is that 225 for 10:5 - 1 compression ratio? Do you think the compression will rise much as the engine breaks in?

I have used caps In places below. Please don’t think I’m yelling at you.
Some times I over simplify things, but it is only for others who read this that may not have any experience. And I am no expert. Just hope i can help.

The compression will definitely increase as it breaks in.
It is better to do the wet and dry test back to back . also try to use the same amount of oil in each cyl. U must use enough to SEAL the rings so that it will help to identify OTHER issues. Think of all testing as a science experiment. U need to do everything the same way so u can compare YOUR test results , with your future test results. Other peoples #’s cant be taken as gospel..
The wet test tells u what your max pressure COULD be IF u had a perfect ring seal and only IF the valves are sealed.
Remember that we have to interpret the results and there are variables in every test, so keep the variables to a minimum. So if u do the test warm 1 day and cold the next, u WILL have dif results.

I got 170 dry and 225 wet on my worn out 1135 and 1327 motors.(aprox. #’s)
This only tells me that I have a large spread and that my rings must be bad since my valves are assumed to be sealing. If all the numbers are similar then the valves are LIKELY to be ok , especially in a fresh build if u have good shim clearances.
U also must keep in mind that the #’s that YOUR gauge provides, can be dif. than others peoples.
I did a leak down test and it showed 1 cyl to be worse but the air noise from the leaking rings was too loud to be able to hear the valve that was leaking.as it turned out i had 4 slitly bent valves.
As far as the clacking in # 1 . all u can do is continue to try to find out what is dif about that cyl as a whole(from carb to exht). I would check the valve clearances before going any further. Could there be a restriction in # 1 exht? Dent or gasket? Did u center the exht o rings and glue them in place? , air filter?
I hope this helps.

OK, got lucky today with the weather - sunny, dry and 40 degrees. Took the bike for a ride and the carbs are way better since they've been synchronized. I don't hear any clacking at all except at idle. I think I'm still running way too rich, but it runs pretty good now. I think I'm getting closer...

Sounds like you're on the right track. No clacking while cruising is good. Don't worry about the clack at idle. You'll drive yourself nuts trying to get rid of it. It's normal to have this at idle even if it's only one carb that's clacking. Your compression numbers are very good and consistent. I just did a compression test on my 1075 and it read 185psi across all cyliinders. The engine has about 3000 miles since installing the piston kit. It has loads of power, idles smooth and burns no oil.

Get the jetting close for now. 125 mains and middle clip position on the needles is a good place to start. Also, Now that the carbs are synched you might need to step back down to the stock pilot jets (17.5). Trying to fine tune the carbs before the rings seat is futile. Just keep an eye on engine temperature and make sure you're not running excessively lean. Give the rings a few hundred miles to seat then dial the carbs in exactly.

Good to here that its running good.
Just keep in mind that u did not see much of an increase in compression when u added oil. This may be nothing, but since there wasn’t a sig increase i wouldn’t wait too long before checking the valve clearance(just for peace of mind).There are only a few resons for the lack of increase. 1/ not enough oil added for the test, 2/ rings are already seated, 3/poorly seated valves.
also don’t forget to check the cam chain tension occasionally for the first while , as the chain will stretch just like the drive chain.Also , if u havent already ? u should retorque the head.
Happy riding .

sounds like one carb is out of synch. The comp. differences are probly just do to valve clearance and the amount of carbon on the piston tops and chamber roof. Dont worry about it they are close enough.