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Mercruiser 5.7l bogging / lagging at WOT

R

randolf

New member
I have a newly aquired Maxum 2400 SCR (2001) with a reman. merc 5.7l, only 3-4 hours. On the sea trial it bogged at WOT on hole shot. Last time I had it out i had 5 parents, 4 kids, could not get on plane without moving everyone to the galley, (slightly embarrasing). I haven't been able to find much info on the carb, there is a sticker on the upper housing 9780s, Weber. Any of the Holley forums seem to lead to the accelerator pump or secondaries.

My question is how do I know if the secondaries are opening? and squirting gas? They seem to have just a couple of weighted ends, that in the yard on a quick WOT dont move whatsoever.
Im well aware that many people consider this boat to be underpowered, but it serves my needs just fine, and I can reach 50mph fairly easily, just have to sort of take my time getting there.

If it makes a difference, WOT responds beautifully when Im already on plane.
THANKS!!!
 
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I don't think you are using the correct words. WOT means wide open throttle.

That means the throttle is fully forward and you are turning max rpms. So say WOT is supposed to be 4200-4600 rpms . You will find recommended WOT on the valve cover or some other sticker on your motor.

So here is a great checklist. Copied and pasted here, from another website

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
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.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.
__________________
Don S.
 
Alrighty, from a stop, when I open the throttle 1/2 way I accelerate just fine, but I cant reach plane depending on how loaded the boat is (gas, water, people etc..). At that point if I open the throttle all the way, wide open?? the engine bogs.
My understanding is the carb should be using the primary's under normal light acceleration, when I push more throttle the secondary's should kick in, to deliver more fuel/air the engine needs to increase speed quickly.
I suspect the secondary's may not be opening or getting extra fuel.

I know Holley 4bbl's have different springs with different tensions in order to adjust the accelerator pump, this Weber doesn't appear to have any sort of adjustment other than idle/air mix.
Maybe Im barking up the wrong tree here, but thats why Im looking for advice from all you experts out there;)
 
You should be able to hear the secondaries open up and feel the power surge. The carb is 9+ years old. Rebuild it or have a professional do it for you. I think chiefalen knows of a good rebuilder you can send the carb to for rebuild.
 
The carb is brand new, its on a GM factory reman. engine installed in Nov. 09 and used for about 3 hours. (sorry a fairly big detail to leave out!!) Anything to do with break in? I am taking it easy on the throttle for sure, but am still concerened things aren't the way they ought to be
 
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In all due respect to you sir, did you even read the checklist ?

See who says da Chief ain't a diplomat. I'm working on being nice.
 
A "brand new carb" only means what the words state; new. Look carefully at the linkage parts on the carb. Painted pieces will bind at the connecting points. Scrape those points clean and lube them w/a very light oil. See if the choke is working properly; check for 12 volts and feel the side of it to see if it is heating. It doesn't take long for electric ones to open.
 
It's all good chief. In regard to the checklist, I dont think its applicable to my situation. I am reaching operating RPM, alot of the items in the checklist would be showing alot of other symptoms that aren't occuring.
This is my first experience with a 4 bbl carb and mostly Im wondering if the secondary's are to blame for a carb lag on hole shot that is preventing me from getting on plane quickly.
With all due respect chief, you may have misundersood my question.

Thanks guy I'm out on the water tomorrow I'll see what choke and secondary's are up to
 
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