RPM's & Prop

[Joker2]

Even if my tach is not accurate shouldn't I be going 40-45 MPH at full RPM with my setup. These are the numbers I have seen with similiar setups on this forum. I am running on all cylinders I just changed a bad ignition coil, so I have been through these checks, all butterflies open, compression is 120 on 1,3,5 and 100 on 2,4,6. I guess I can try the gas in the bottle thing. Thanks

[THEFERMANATOR]

Originally Posted by Joker2

Even if my tach is not accurate shouldn't I be going 40-45 MPH at full RPM with my setup. These are the numbers I have seen with similiar setups on this forum. I am running on all cylinders I just changed a bad ignition coil, so I have been through these checks, all butterflies open, compression is 120 on 1,3,5 and 100 on 2,4,6. I guess I can try the gas in the bottle thing. Thanks

Thos numbers are not very good to see. You want to see all of them within at least 15% of each other,b ut I prefer to see them within 5% of each other myself. I would expect to see 115-125 on all 6 for a healthy engine. Try and see if you can find a shop with a dyno and see just what it's making, I think this will show you your problem and upset you at the same time. Your speed sounds correct for your RPM's with that prop, so all that leaves is the engine or lower unit.

[tsubaki]

Just for the meanness of it, raise the engine up about an inch and a half and see how it does.
It's easily done without a hoist.
What you got to lose?

[spareparts]

have you tried a decarb of the engine? It might get those compression numbers a bit closer

[THEFERMANATOR]

Originally Posted by spareparts

have you tried a decarb of the engine? It might get those compression numbers a bit closer

this is supposed to be an overhauled engine that he just bought, so I wouldn't think a decarb is needed for it. I still think your mechanic isn't getting the job done for you from all of teh trouble you've had out of this engine from him.

[Genie Aye]

If I had 100 comp on any cylinder and it is more than 10% lower than my highest---bad cylinder/s.

With only 100lbs comp--I would wonder what type of freshen up your mechanic did--almost sounds like some ports may hooked the rings from burr's.

I can tell you with a injector out on my engine--I lost about 10 mph on the top end--that is a engine rated at 218 at the prop.

Good luck--but the news you are giving is NOT good.

Bummed for ya.

[Joker2]

You guys are scaring me, but I am not surprised with this guy. If it means anything, I did the test on a cold engine, only taking one plug out at a time, I did the test when I was troubleshooting my problem. At that point I had a bad ignition coil only firing on 5 cyl. I know this wasn't the proper way to do a Comp. test, but do you think it would make that much difference. I don't know. For what it is worth ( nothing ) he told me the engine was good when he got it, that he just changed the crank. Maybe now that it is running nice I'll do the test again. Thanks for all your input.