Limited Engine Revs under load

S

Skigekco

Cadet
Joined
Aug 8, 2011
Messages
9
Hi all, back again for advice.:confused:
Background
I have a Wellcraft 175Sx Excel boat equipped with a 4.3GL Volvo Penta engine and SXCobra leg.

When I got the boat the engine was a bit lumpy and running very rich. I've fitted, new plugs, new electronic choke (old one not working). Got her running but seemed to miss and cut out when rev'd. Ive fitted a new coil, new ignition module (distributor cap looks new). I've also checked the timing which is ok by adjusting the distribution. The engine will rev to about 4000 rpm under no load (out of the water). However when under load I can't seam to get it above 3,100 rpm which I get at about 3/4 thottle range. After this there's no chnage on the rev's. There's plenty of fuel going down the carb barrels, plugs look a reasonable colour and its doesn't sound like its pinking or missing

The engine now starts fine.

The prop is new, marked 14 1/4 x 23.

Questions
Should I be able to get more rev's? could the prop be oversized ? if not any thoughts on cause of low revs or is this normal for this engine boat combination ?

My only other thoughts are new HT leads and a carb rebuild kits. :confused:

Suggestions/ advice/ help appreciated.

Thanks :)
 
S

Skigekco

Cadet
Joined
Aug 8, 2011
Messages
9
Re: Limited Engine Revs under load

Don, thanks I have reviewed the list you sent and added comments.

However, want I need to first establish is am I chasing Ghosts thinking I should get more than 3,100 rpm ? THANKS

1. Fuel condition. Type and Octane possibly old fuel - TANK DRAINED, NEW FUEL ADDED
2. Propeller pitch or diameter, damaged blades - ITS A NEW PROP - OLD ONE WAS A 14 1/4X 21 NEW ONE IS 14 1/4 X 23, WHAT DOES THE 23 SIGNIFY
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test - NOT DONE WILL CHECK
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse - FINE ON DIPSTICK
5. Marine growth on hull and outdrive - CLEAN
6. Wrong gear ratio in outdrive - NOT SURE HOW I CHECK THIS
7. Restricted carburetor air intake (clogged flame arrestor) - TRIED RUNNING WITHOUT INTAKE, NO DIFFERENCE
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive - NOT SURE HOW I CHECK THIS
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed. - BOAT TARED FOR 8 PERSONS THIS IS WITH 3 PEOPLE
13. Engine Overheating - DONT THINK THIS IS THE PROBLEM
14. Engine timing and ignition system operation - SEE PREVIOUS POST RE REPLACEMENT PARTS
15. Remote control cables and linkage for proper travel to open throttle plates fully. - NOT SURE HOW I CHECK THIS
 
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