force 85 hp top end surging bog please help

[slx12001]

~~I have installed all new fuel lines. Tried 2 new tanks
Rebuilt all 3 carbs, Rebuilt fuel pump
I installed a new head gasket
Black coils and boxes.
135psi all 3 cylinders
The engine will idle all day and run up to about 4000 rpm without any issues. I can cruse at 25mph like it's should. It will jump out of the hole great any time. The problem is after about 4000rpm. If you go full throttle it will run up to 5000 rpm then surge between 5k and 4k back and forth. Back the throttle to about 4k and all is well again. I have a clear glass fuel filter at the fuel pump. I have a friend watch the fuel filter. It never runs dry. I have clear fuel lines to the carbs. They never run dry. The plugs look black and wet but never have fouled. I have read many similar posts about this engine but never have read a real fix. I checked the fuel recirculation system. It seems ok but I don't know much about it. Any help Please.

 

[slx12001]

Another thing to add is fuel economy is terrible. I ran 6 miles down river to the bay and back total 12 miles 75% was no wake and went through 8 gallons of gas or about 1.5 mpg.

 

[pnwboat]

Have you done a link and sync on all three carburetors? Make sure the butterflies in all three carbs are pretty much horizontal at WOT. Does your primer bulb get good and firm after you squeeze it four or five times?

 

[slx12001]

Yes new primer bulb gets hard. Yes carbs are perfect. Thanks.

Have you done a link and sync on all three carburetors? Make sure the butterflies in all three carbs are pretty much horizontal at WOT. Does your primer bulb get good and firm after you squeeze it four or five times?

 

[foodfisher]

Check the plastic parts at the top of the timing tower for cracks or stripped threads.

 

[mitchbuck]

Have you checked the timing?

 

[Jiggz]

From what I have read from this forum regarding surging or bogging downs at WOT are caused primarily by the following:
1. fuel starvation, i.e. faulty fuel pump, clogged pick up, clogged tank vent, leaky primer bulb, improperly set carb floats, clogged needle port, clogged fuel lines, etc.
2. Improperly set throttles
3. Improperly set timing, i.e. could have been set improperly or unknowingly adjusted the idle using the timing rod instead of the idle screw at the bottom of the tower
4. fouled spark plugs
5. High carbon build up
6. Improperly set carb floats
7. Clogged carb inlet port
8. Carb throttles not properly synch'ed
9. Worn insulation trigger wires or bad conductor wire on trigger wires causing short to ground in certain control lever position
10 Minor water intrusion into one or more cylinders which gets exacerbated by higher rpms. This is usually indicated by a cleaner spark plug after running at high rpm.

Now I understand you said the carbs are perfect after you rebuild them. Do you know for sure how the carb floats were set? Have you tried, spraying fuel oil mix into the carbs when the motor is bogging down above 4K rpm? If so, did the engine bog down further or did it increase in rpm? If it is the latter then (which ever carb reacted with higher rpm) the float is set incorrectly indicating the needle is not opening all the way to allow more fuel to come in faster into the bowl. Or it could be there is a restriction on the needle port.

For the carbs, to make sure they are properly set do the fuel spray test first and troubleshoot from there.

 

[slx12001]

~~SOLVED_____----_____
When I initially rebuilt the carbs float height was level. The float drop seemed to be less then I would say is normal, But I figured since all 3 carbs were the same it must be how it runs. Well that was wrong. The last guy in there made a mess of float drop and probably the reason I got the boat for a song. (Side note: Thanks to the fella who did not know what they were doing) I took all 3 carbs back apart after pulling out most of my hair and set float drop so it went all the way until it touched the carb. (it was half way there when I started) 16ft bay liner open bow Capri is running 37mph on gps and does not miss a beat. Rpm's are at 5200 17p MI wheel prop. Thanks for the replies.

 

[SkiDad]

that's awesome !

 

[Jiggz]

Outstanding! That took less than 8 posts to correct the problem and thank you for getting back to post the result. Enjoy.