Engine Bogs at almost WOT. Can only reach 4200 RPM.

I have a new engine with an edelbrock 1409.


I finally got around to getting a new tach because my old one was bad and not accurate.

Now that I have a new one I can try to figure this out.

At about a little over 3/4 throttle I can hear what sounds like the secondaries opening. But there is barely any throttle left to push before I cant push the throttle any more (WOT?)?

Problem is 1, Right when it sounds like the secondaries are opening sometimes it will bogg but if I feather or let off the throttle then push it again it will stop.

2, is that I have a 15 pitch prop. Donzi told me the boat was supposed to come with a 17 pitch prop. It will only get up to 4200-4300 RPM's at WOT.


It should be 4600-4800 I think. With Donzi saying that the boat come originally with a 17P prop and me needing more RPMs doesn't make sense.

I have checked the timing, fuel pressure, new fuel filter, fuel pump is brand new, flame arrestor is clean, manifolds and risers are brand new and rest of exhaust is in great condition, rest of engine is new.

I don't know what else to check. The throttle / shifter seems a little loose.

Is there a way to adjust the throttle so I can push it more? Is there anything else that could be causing this low WOT RPM?



Thanks so much

Re: Engine Bogs at almost WOT. Can only reach 4200 RPM.

are we talking mercruiser?

Re: Engine Bogs at almost WOT. Can only reach 4200 RPM.

and what size/make motor with what drive? If a 4.3L the air valve may only begin to open near wot. What was the performance prior to engine change?

A quick check:
Remove throttle linkage from carb. Push 2ndary air valve open and advance throttle to wot and make sure 2ndary butterflys are full open. Do same with linkage attached. 2ndary butterflies should start to open when Primaries are about 50-60% open.

Re: Engine Bogs at almost WOT. Can only reach 4200 RPM.

It's an OMC 5.7 350 with Cobra drive.


I don't know what the WOT RPM was with the old engine because the tach was broke when I had it.

I only had the boat with the old engine for a little while so I forget if it had more throttle after the secondaries opened or not.

I will try what John says when I get back in town Monday.

Re: Engine Bogs at almost WOT. Can only reach 4200 RPM.

When you do the above checks, mark the throttle position where the 2ndary butterflies begin to open. Once you are back on the water, bring the throttle up to just under that point and let speed stablize. Then push the throttle to just past this point. On a 5.7, the air valve should be openning.

Re: Engine Bogs at almost WOT. Can only reach 4200 RPM.

Ok went to the boat today.


I checked with the throttle off and on and both ways the secondaries are completely open at WOT.

they also do start to open when the primaries are about 50% open.

The bogg is gone now. I dunno why only thing I have done recently was change the fuel filter which wasn't that old anyways.


The Maine surplus store near me told me that the fuel water sep filters don't filter that good and that I should put an inline filter on too.

I tried that today but it only would fill up about halfway with fuel. The other half was air. I tried letting it run for a while but it wouldn't fill.

Then I could hear the engine like it wasn't getting enough fuel so I unhooked it.


But anyway the bog is gone and it still won't go over 4200 RPM at WOT.

When you say the air valve do you guys mean the part on top of the secondary butterflies?