COMPRESSION

[MOUSETRAP]

hey all, got an 04 fatty, with the SE big bore kit, 203 cams, and SE high compression forged pistons. The bike is now running great, but a couple of weeks ago I had it in my buddies shop for a new rear tire and a starter rebuild. I asked them to do a compression test and he said the the compression was 150 LBS even on both cylinders. I thought that was kind of low . And that was cold cranking. Does this sound right? I would have done my own check, but do not have   32MM adapter, but I think I will put out the cash just to see for myself. Like I said bike is running the best it has since I purchased it. Thanx guys.

[Y2KRKNG]

Don't want to insult your buddy and his tools, BUT.....when my bike CCP'd at 150psi I crossed checked it with my Uncle's gauge...150psi. Long story short, bought a new Lisle gauge bike is at 200psi!

Don't know why 150 seems to be the magic faulty reading, my WAG is that when the small valve seal gets damaged(prob from alcohol in gas) that 150s all itll pass.

[aswracing]

Did he hold the throttle wide open while testing?

[86fxwg]

Did he hold the throttle wide open while testing?

86

[Matt C]

I've done comp tests both ways and there wasn't THAT much difference.
(Not 50 psi worth anyway) It's 'prolly' the gage!

[Don D]

Me too, 25 lbs is ballpark.

[a2wheeler]

What is your altitude  - 150 might be normal for where you are.

[86fxwg]

With & without open throttle 95" 203 came 030hg

[1FSTRK]

That has always been my finding as well.

[Matt C]

Hummmm, ok... Last time I did one, I forgot to open throttle and it was about 20# difference, but hey, roll with it.

[BUBBIE]

You saying that "The bike is now running great" and Nothing has been changed since the Check.... Faulty LOW pressure... 

I would Not worry about it.

Get your own Fitting (12 mm) and check it your self... Might be at 200# and that motor is Happy and so are You...

All Is Good...

NOW IF it ran Badly and then Goodly

signed....BUBBIE

[BUBBIE]

Another thing that WOULD cause the LOW pressure:

If the compression releases were Open... Equal footing from front to back and might show 150# each.

Does it have compression releases?

I can't see that engine NOT having them... Looks like a  build...

AND What is your Elevation? Above sea-level?

signed....BUBBIE

[Y2KRKNG]

I don't have any comp releases. Running 202CCP F&R. 3.15:1 ratio helps along with a 600ca battery. I'll still tap the starter on a hot gas & go before firing it up.

[BUBBIE]

In my 103" I Need the manuals on a HOT start... Especially over in the Parker/Bullhead Az. area... It is Low and very HIGH compression.
A real treat to Twist the wick

My bike runs good Down there BUT I'm set at 4000 feet for Just a Little above Average Performance... 

signed....BUBBIE

[FLTRI]

hey all, got an 04 fatty, with the SE big bore kit, 203 cams, and SE high compression forged pistons.

That cam is designed for flattop pistons NOT high compression but you may be able to get away with it since you have a softail rather than a big heavy Bagger.
Bob

[Y2KRKNG]

Update?