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Discussion Starter · #1 ·
Having problems with engine bogging at 4200 and up. Running an Edelbrock marine 750 on a built small block spinning a Panther jet drive. Had a popped head gasket late last year, pulled both heads, had checked and reinstalled with new gaskets. Ever since (only had boat out 3 times in past 9 months) then, engine does not want to spin beyond 4200. It bog and surge but acts like something just isn't working as normal. Compression good on all cylinders, checked timing, DUI ignition seems to be working as normal felt I adjusted all valve train properly. I'm plain out of idea's. Help
 

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The Man
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1,788 Posts
I had a similar problem a few years ago. The fuel filters wouldn't flow enough fuel above 4k or so.
 

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Boat Nut
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5,131 Posts
Check the secondary air plate on the carb. If it is not moving fully open and exposing the secondary veturie, you will get all kinds of surging. The newer carbs have adjustable balance weights, the older ones needed to be taken apart and weights drilled accordingly.
 

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Angry American
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here are a few things to check

1. Put an inline pressure gauge on it to see what the fuel pressure is, Edelbrock/Carter, 5-1/2 lbs
2. a plugged fuel filter
3. a plugged tank vent - open the filler caps and go for a ride
4. float levels set too low
5. bad check valve on the tank
6. crimped fuel line
7. collapsed fuel line
8. Plugged pick ups in the tanks
 

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Jet Boat addict
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143 Posts
i had one do that years back it had a casting blockage in the carb where the passage goes from the fuel inlet on one side to the second bowl of the carb. i took off the top removed the needle and seats there was a fine mesh screen above the seats and looked through the passage to find the problam.
 

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Head Janitor
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690 Posts
What is this motor supposed to spin up to, as in before this issue what was your peak RPM? Maybe I missed it, but is this a mech or vac secondary carb?

An old SBC engine I had did this when I went past the capability of the fuel pump.
 

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Discussion Starter · #9 ·
X's 2 on the fuel availability ! Just curious is the boat in your Avatar the rig in question?
jetboatperformance, Yes, that is the boat in question.
To all others, sorry for not responding quicker, had to hit the road for a week without much warning. On the fuel delivery and pressure, actually just replaced the orginal fuel pump (24yrs old) with a new Marine Holley 110 gpm, new inlet side and outlet side fuel filters and new fuel hose from fuel selector valve to carb. Have not determined actual fuel pressure as of yet (will be getting a fuel pressure guage) but with a new fuel pump, I'd be thinking there should not be a delivery problem. On the bogging, this will happen off the line or cruising when nail it or try and get beyond 4200.
 

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Discussion Starter · #10 ·
What is this motor supposed to spin up to, as in before this issue what was your peak RPM? Maybe I missed it, but is this a mech or vac secondary carb?

An old SBC engine I had did this when I went past the capability of the fuel pump.
FormulaZR, was getting a solid 5600 last year before the head gasket replacement. Started this year late getting it ready to run. Performed all the prerun item then tried starting. Cranked for awhile and not firing at all, poured a shot of gas in carb and she fired right up. Bottom line was the old fuel pump gave up the ghost and I thought by replacing I was going to fix the problem from last years bogging problem, o well that's what I get for thinking. Keep the idea's coming. And carb has vac secondary system.
 

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Doubtfull that the replacement of the headgaskets has any real relationship to your bog ,IF all else is equal/unchanged (timing etc) I'd be looking ,for kinks , collapsing/spongey fuel lines, restrictive filters (like the tiny glass ones) and checking the tiny pickup screens (if so equipt) that many of these boats saddle fuel tanks have at the base of thier full tank pickup tubes (small funnel shapes and screened device) Many of those (tubes) were incidentally hard plastic line below the brass fitting and can easily be dislodged when removing and inspecting (especially if shop air is blown back thru them ) Good Luck Tom

PS just curious , when is "bogs" if you stay in it will it eventually die out ? and if so and it dies how quickley can you get a re- lite? or if you back down on the throttle opening when its bogging does it seem to recover
 

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i'd find some parts to borrow just to figure it out.swap a carb,any thing that fit,see if it's different. \then swap dizzy,maybe it's siezed (seen that);)
 

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Discussion Starter · #13 ·
Doubtfull that the replacement of the headgaskets has any real relationship to your bog ,IF all else is equal/unchanged (timing etc) I'd be looking ,for kinks , collapsing/spongey fuel lines, restrictive filters (like the tiny glass ones) and checking the tiny pickup screens (if so equipt) that many of these boats saddle fuel tanks have at the base of thier full tank pickup tubes (small funnel shapes and screened device) Many of those (tubes) were incidentally hard plastic line below the brass fitting and can easily be dislodged when removing and inspecting (especially if shop air is blown back thru them ) Good Luck Tom

PS just curious , when is "bogs" if you stay in it will it eventually die out ? and if so and it dies how quickley can you get a re- lite? or if you back down on the throttle opening when its bogging does it seem to recover
Engine starts right up and idles at 650rpm and will hop to 4200 with no problem. Once I try to get the engine beyond that it acts like way too much carb and if I feather the throttle it will try and climb but falls off. Up to 4200 no problem, push it and it stumbles, hold there or push futher and it only goes downhill. Ease up on the throttle back it where 4200 would be, no problem runs great at that point.
Same carb that I've had for 5 yrs so I don't think it's too much. During the start up this year, after the fuel pump replacement I tried starting only to have the floats stick and totally flood the motor (pulled plugs and had gas running out). Pulled carb, popped top off cleaned all internal parts, floats, needles and seats and reassembled put on engine fired up and idled great.
Carb swap is a quick check, I'll see if one of my locals can help me out. Other than that, will replace fuel lines from fuel selector to tank pick ups. Have to check clearance to pull tank pick ups to see what is involved.
Thanks all
 
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