Everything done but low rpm at WOT. Distributor spring?

[VancouverBoat]

Hi, Hi, I have an 89 OMC 460 and Cobra outdrive. Cannot get on a plane. Engine struggles at WOT but does not backfire. I can go 8 knots at 1900 rpm all day. In last year, engine has new cylinder heads, new manifolds and risers, new plugs, new plug wires, and leg was just serviced month ago with new gimbal bearing and boots etc. Prop is right size. for boat (bayliner 2858). Compression is all god at 150 each cylinder. Carb was professionally rebuilt. Timing is set properly I have older Mallory electronic ignitiion but mechanical advance. I noticed that one of the springs broke off and was rolling around inside the distributor so I bent the end to put it back on. Could that be the possible cause of this issue?

 

[kenny nunez]

If you cannot locate the correct springs you can get a complete distributor from Sierra Marine.
The carburetor is the original marine Holley ?
Is the electronic shift assist system still in place and connected to the distributor?
18-5481Flame Thrower
18-5482 Flame Thrower
Both are for 351-460

 

[VancouverBoat]

If you cannot locate the correct springs you can get a complete distributor from Sierra Marine.
The carburetor is the original marine Holley ?
Is the electronic shift assist system still in place and connected to the distributor?
18-5481Flame Thrower
18-5482 Flame Thrower
Both are for 351-460

Thanks for the info! Yes, the marine holly. The shift assist was replaced last summer with new by professional mechanics. The Mallory electronic breakerless ignition distributor YH that I have is wired directly to the coil and ground which is as per the instructions. Not sure if the shift assist is connected to the distributor but it is working. Do you know how to get the Mallory electonic ignition module off the top to get to the springs? There is no visible screws to remove it. I replaced the spring last time by rotating engine to expose part of the spring below and just barely was able to reattach the spring.

New item by Christian Saxvik

photos.app.goo.gl

 

[dubs283]

Need to verify proper timing advance

 

[Scott Danforth]

just call Mallory (now a division of MSD/Holley) and get new springs for your YH

 

[kenny nunez]

There might be a small wire spring retainer inside the top of the rotor shaft that has to be expanded slightly to lift the reluctor.
Also there is a shift override switch that by passes the shift assist module. After the drive is in forward disconnect the module and try to get the boat on plane.

 

[VancouverBoat]

just call Mallory (now a division of MSD/Holley) and get new springs for your YH

Thanks. Just tried that and they are no longer supporting that. I guess it is a new distribbutor, or lots of trial and error with springs.

 

[VancouverBoat]

There might be a small wire spring retainer inside the top of the rotor shaft that has to be expanded slightly to lift the reluctor.
Also there is a shift override switch that by passes the shift assist module. After the drive is in forward disconnect the module and try to get the boat on plane.

Ok thank you, I will try that.

 

[VancouverBoat]

Hi guys, to update, I put a new distributor from sierra and set the proper timing. Started right up. On sea trail it is slightly better but still does not get on a plane. What other issue could I have?. I have done everything as indcated in the first post. I might try just removing the air intake flame arrestor to see if better airflow helps but I am running out of options....

 

[jimmbo]

Compression, Fuel and Spark are needed.
What are the Compression Numbers?
Spark Issues and Timing Advance? New Distributor, should not be a Problem....
Is a Spark good enough to jump a 7/16" Gap getting to every Cylinder?
Fuel: That is a Holley 4bbl on there? Are the Primaries opening fully?
Can the Secondary Throttle Shaft rotate? I am assuming it is a Vacuum Secondary Model. Has the Carb been cleaned recently?

 

[VancouverBoat]

Compression, Fuel and Spark are needed.
What are the Compression Numbers?
Spark Issues and Timing Advance? New Distributor, should not be a Problem....
Is a Spark good enough to jump a 7/16" Gap getting to every Cylinder?
Fuel: That is a Holley 4bbl on there? Are the Primaries opening fully?
Can the Secondary Throttle Shaft rotate? I am assuming it is a Vacuum Secondary Model. Has the Carb been cleaned recently?

All 8 cylinders are about 150. Yes, new distributor. New spark plug wires and plugs. Yes 4bbl holly. Carb was professionsally rebuilt a few months ago.

 

[Scott Danforth]

base timing?
total timing?
fuel quality?
Carb size? Jetting? horn numbers?

 

[VancouverBoat]

Base timing is 12 and total is about 35. Fuel is mostly 89 octane but some 86 when 89 is outrageous price. Carb is 4bbl Holly 1850-5. Numbers on the horn are 1850-5 1692

 

[Scott Danforth]

that is only a 600 CFM carb. Big enough for a 4.3.

not big enough for a 7.5 liter.

 

[VancouverBoat]

Wow, that is significant. what CFM should I have?

 

[jimmbo]

The 1850 is not a Marine Carb, and is not Legal

 

[jimmbo]

that is only a 600 CFM carb. Big enough for a 4.3.

not big enough for a 7.5 liter.

Only if the 454 is spinning over 6000rpm. Otherwise it is plenty

 

[kenny nunez]

An Edelbrock Marine 750 from Summit or Jegs should do the job.
Summit’s #. EDL1410. @ $575.95.
Have you checked inside the exhaust system for any blockage such as any exhaust shutters or even a rag could cause this kind of problem.
Will the engine free rev in neutral? If so then that would rule out any blockage. I have seen autos with a internal exhaust blockage that would only rev to 1500.

 

[Scott Danforth]

Only if the 454 is spinning over 6000rpm. Otherwise it is plenty

Factory carb for Mercruiser 454's was always 850CFM Rochester's for a long time. The the Merc racing department ran 850HPs. Volvo put 715CFM on the small blocks and 800 or 850s on the BBC's. Everything I read was 830CFM on the Ford 460 Marine

 

[jimmbo]

454 engine spinning 5000 rpm can only inhale 660 cfm of air at 100% VE. At 78% VE the number is 515 cfm. Any Mercrusier Engine designated for Racing would certainly need a bigger Carb, and if the Class Rules stated the Engine had to use a carb that came from the Factory, then yes they would have had an oversized Carb. But for a 7.4 turning up to 5000rpm, a 600cfm is fine