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tamburello
08-21-2007, 07:14 PM
My 18 seems to be down on speed and RPMs since starting the season. My carb'd 350 Mag 250 PSHP can usually spin my 24" Turbo 2+2 four blade to 4,700 RPM and my 23" Laser II to 5,100 RPM. Since the start of the season I am only able to spin the four blade to 4,400 and the three blade to 4,800. I'm usually running in the low 60s with both props but now I max out at 53 with the four blade and 54 with the three blade.

The engine sounds like it is running fine although it has a slight irregular miss that I notice when idling. I had to have a cylinder head taken off at the end of last season to chase out the threads after a plug was cross threaded during installation. Also, I was a slacker and didn't put in a new cap/rotor and plugs this year. Any thoughts and theories as to why I've lost RPM's?

- Jeff

98shovel
08-21-2007, 07:36 PM
the slight irregular miss

mrfixxall
08-21-2007, 07:47 PM
My 18 seems to be down on speed and RPMs since starting the season. My carb'd 350 Mag 250 PSHP can usually spin my 24" Turbo 2+2 four blade to 4,700 RPM and my 23" Laser II to 5,100 RPM. Since the start of the season I am only able to spin the four blade to 4,400 and the three blade to 4,800. I'm usually running in the low 60s with both props but now I max out at 53 with the four blade and 54 with the three blade.
The engine sounds like it is running fine although it has a slight irregular miss that I notice when idling. I had to have a cylinder head taken off at the end of last season to chase out the threads after a plug was cross threaded during installation. Also, I was a slacker and didn't put in a new cap/rotor and plugs this year. Any thoughts and theories as to why I've lost RPM's?
- Jeff

throw a new set of plugs in it first and pay attension on what plug came out of what cylinder and number them with a sharpie marker,,if that doesnt work then look at the plugs again and pick out the blackest one..then look at the number on that plug and go back to that cylinder,it the new plug is black then recheck your rocker adjustment..you may have over tightened the exhaust valve..if you hear a popping through the carb then the intake valve is to tight..

BUIZILLA
08-21-2007, 07:53 PM
timing or valves too tight...

tamburello
08-23-2007, 04:57 PM
I took the boat out for a run yesterday. Gotta love a weekday afternoon with no boat traffic and calm seas. I listened to the carb and couldn't hear any popping sound. I made a couple of WOT runs and all of the runs except for one had the same results as before where I am topping out about 300 RPM off of where I should be. On one of the runs I opened it up and it seemed to be running stronger and sure enough my tach was at 5,000 RPM and I was running in the 60's where I should be. After that run it was only hitting 4,700 at WOT. I was wondering what could explain the momentary improvement in performance. :confused:

- Jeff

farmer tx
08-23-2007, 05:27 PM
Recheck the fuel system fittings. I had the same problem and had a leak on the suction side of the fuel pump. I have seem hose fittings that would not leak fuel but would suck air. Also if someone overtightened the line going into, or out of the fuel seperator the cast aluminium seperator housing threads could be cracked. That was my issue,very arriated fuel in the carb. Would run good sometime and wouldn't run off the secondarys at other times.

Rootsy
08-24-2007, 06:14 AM
make sure your battery cables are tight....

ITTLFLI
08-24-2007, 07:47 AM
Check to make sure the choke opens all the way. You will also have black soot on the transom if it is stuck closed or partly closed. It could have bounced open explaining the one good run.

smokediver
08-24-2007, 09:11 AM
probably a 30 -40 degree difference in the weather as well ...

tamburello
08-24-2007, 08:41 PM
Thanks for the suggestions, I'll check into the things that all of you mentioned.

- Jeff

tigweld
08-24-2007, 08:58 PM
I go with change in the weather allso...