Simple problem, or grenaded motor?: Sprockets forum: Grassroots Motorsports Magazine

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July 28, 2010 3:59 p.m. SlickDizzy UltraDork

http://appleton.craigslist.org/mcy/1855697376.html

I just found this today. I've always wanted an FZ750; I talked to the owner, and this is the apparent story:

He bought it from his brother, and rode it for a little over a month. It ran fantastically in this time period. He parked it for 2-3 days, and when he came back to it, it would not start. He claims to have done a compression test, with the results coming out like 30-30-30-110 (factory spec is like 175 on each cylinder). He seems to think that it could be a timing or valve adjustment problem.

What do you guys think? I'm wondering about a possible blown head gasket, or maybe the guy has no idea what he's doing. It looks to be a real nice bike and it's even the color scheme I'd want. Any tips on what to look for would be great.
July 28, 2010 4:16 p.m. triumph5 Reader

30psi? With no valves, I think one could get 30psi merely from the pistons moving the air in the cylinders. Spec is 175, and he's getting 30, more damage than a head gasket, me thinks,
July 28, 2010 4:45 p.m. alex Dork

This sounds like a job for Mr. Leakdown Tester. If you're willing to invest the time, I'd go and check that - you'll know a lot more that way. Kinda sounds to me like this guy may not be doing a proper compression test.
July 28, 2010 8:12 p.m. SlickDizzy UltraDork

I will probably be doing that. At this point, I'm just trying to hypothesize possible scenarios - I have a bit of a hunch that his CDI box burned up and made it quit running, so he's looking in all the wrong places for the solution.
July 28, 2010 8:30 p.m. Dr. Hess PowerDork

Uh, not the timing, except maybe VALVE TIMING. Not a head gasket (alone.) Not a valve adjustment, except for after the new ones go in, they'll need adjusting. Unless you want to tear that motor down, I'd pass.
July 28, 2010 8:44 p.m. 44Dwarf HalfDork

BUY IT! plastic is worth it if motor turns out to be junk double your $$ by parting it out.

44
July 28, 2010 11:16 p.m. alex Dork

SlickDizzy wrote:

I have a bit of a hunch that his CDI box burned up and made it quit running, so he's looking in all the wrong places for the solution.

I like this hunch.
July 29, 2010 10:47 p.m. 93gsxturbo Reader

Last time I checked a bad CDI won't contribute to low compression.

Save your pennies, son. I paid $2400 for a 2001 GSX-R1000 last spring. EFI, ride it anywhere, and hasnt needed anything but gas, tires, and typical maintenance.
Aug. 2, 2010 7:46 p.m. Streetwiseguy HalfDork

Bad ignition won't cause bad compression, but a flooded engine with all the oil washed off the rings will.

Just a suggestion. Its probably bent all the valves.