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Just got a 63 Sprite. Question about compression..

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pbrane

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Hi all. This is my first post. I bought a Sprite MK2 with the CG high-compression engine. It wasn't running and needs lots to get it on the road. I warmed it up and did a compression test:
1) 175/185 (wet)
2) 185/205
3) 182/195
4) 175/185

I was expecting much lower compression, as I thought it had a lot of wear and tear by the looks of things.. I'm wondering what the experts think of these numbers? And, if some of this could be due to carbon build-up (previous owner had wrong plugs and they and pistons look very carbon-fouled)..? Or did I get (sort of) lucky?

Thanks for any comments..
m
 
I think those numbers are great. Carbon build up is prob due to bad tuneing, ie too rich.
 
You probably already know this, but it's not so much the numbers, but the differences between the cylinders that are significant. I'm no expert by far, but your results seem to be pretty consistent to me. I wouldn't be concerned if it was my motor.
 
Re: Just got a 63 Sprite. Question about compression

Thanks for the replies..

Isn't the normal CR for the 1098 CG (in good condition)supposed to be around 160? So I guess this was rebuilt somewhere in it's history? How much can severe carbon build up in the combustion chamber elevate compression?

ALso..

If the float jets aren't sealing well, do you get flooding or over-rich mixture (or...??)? Can you tell if they're working by blowing into the inlet and actuating the float (with cover assembly removed)? Or is isn't that accurate enough? Mine "seem" to be working.. Or should I just assume they're bad and replace?

Thanks again!
m
 
Re: Just got a 63 Sprite. Question about compression

No no, assume they are not adjusted properly and go by the book.
 
Re: Just got a 63 Sprite. Question about compression

Apologies in advance if you already know this -- I didn't when I started this a couple years ago.

Compression readings can vary wildly between different gauges -- 2 different instruments can give you different numbers on the same engine. That's why one normally looks for a serious drop in the numbers across the cylinders.

In other words, if you had a reading of:

170 - 175 - 168 - 120

That would indicate possible issues with cylinder #4. Once you understand how your gauge reads, you'll have a better feel for what is out of range.

I would tend to agree with Jack on the float issue -- if the car's been sitting for a while, do a complete adjustment of everything first (heck, it's free to do), then look into replacement of some of the bits if necessary.
 
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