Engine bogs at full throttle or when rpms pass 3200

[chesapeakeclassic]

I recently repowered my boat (24' chesapeake classic side console crab boat with full canopy) with a volvo 230B with a sp-c drive that came from another boat (18ft glastron bass boat style). I previously had a 250B/aq151 with 2 carbs with a sp-c drive. With the twin carb setup I could run 20-22mph with no problem at approx 3800rpm. New setup my top speed before engine starts to bog is 17 mph at best. All compression checks are 150psi, carb has been rebuilt and set perfect. The new engine and drive run great at idle and while under way with one exception. When I accelerate hard to full throttle past 3150 RPM, the engine starts to bog as if flooding or starving for fuel after approx 1 mile of full throttle. If I leave the throttle at full, the engine eventually slows and starts to backfire through the carb. If i back off the throttle to below 3200 RPM the boat continues to run strong but will not go past 3150rpms without bogging. Also with no load running the engine at the slip the motor will easily rev to 5000rpm. I recently replaced all rubber fuel lines, and checked the anti siphon valve to try to address the problem with no success. Has anyone had similar problems, or can anyone give some ideas to help troubleshoot. To help, ignition components such as wires, plugs, dist cap, rotor and points are new or in like new condition. Any help appreciated.

 

[Maclin]

Re: Engine bogs at full throttle or when rpms pass 3200

The fact that it will run for a short time at full throttle and higher rpm without the problem sure makes it sound like fuel starvation. Could be clogged fuel filter, may be one somewhere you don't see up in the carb. Could be fuel bowl float setting too low. Could be fuel tank venting plugged causing a vacuum lock at the fuel pump, could try running without gas cap to check that.

 

[chesapeakeclassic]

Re: Engine bogs at full throttle or when rpms pass 3200

I just took it out again after I changed my prop back to my original one. Speed potential is back, I hit 20mph before the engine began to bog. I did try to run with gas cap off, to no avail. I have changed the fuel filter and water seperater, still no improvement. Also when i rebuilt the carb, it was soaked over night in chemdip and at this time the in carb filter was cleaned. I agree it does sound like a fuel starving problem. My next step is to get another person to drive the boat while i have the carb cover and spark arrestor off to view the fuel spray or lack there of. On a side note I also thought a weakening alternator might be sending low voltage to coil, that might result in weak spark after running, but I am holding 14volts at all times(tested with multimeter). Maybe improper jets some how, i dunno. Still scratching my head.

 

[Bondo]

Re: Engine bogs at full throttle or when rpms pass 3200

I just took it out again after I changed my prop back to my original one. Speed potential is back, I hit 20mph before the engine began to bog. I did try to run with gas cap off, to no avail. I have changed the fuel filter and water seperater, still no improvement. Also when i rebuilt the carb, it was soaked over night in chemdip and at this time the in carb filter was cleaned. I agree it does sound like a fuel starving problem. My next step is to get another person to drive the boat while i have the carb cover and spark arrestor off to view the fuel spray or lack there of. On a side note I also thought a weakening alternator might be sending low voltage to coil, that might result in weak spark after running, but I am holding 14volts at all times(tested with multimeter). Maybe improper jets some how, i dunno. Still scratching my head.

Ayuh,.... test the Fuel pump for pressure, 'n flow,....

 

[Maclin]

Re: Engine bogs at full throttle or when rpms pass 3200

"Carb filter was cleaned"" Not sure how well that would work, needs replaced in my book.

Taking the carb apart and then dipping the metal parts is preferable to just lowering the whole carb into a chem bath. After each part is clean they need to be rinsed with carb cleaner or similar, than all holes and passages blown thru or wire-gouged. Please excuse this part of my post if that is what you did when rebuilding the carb.

 

[chesapeakeclassic]

Re: Engine bogs at full throttle or when rpms pass 3200

Thanks for the relpies, I should have added more detail on the carb rebuild. The in carb filter on the SOLEX 44pa1 carbs is a copper mesh tube that was also dipped and replaced, looked brand new, the carbs were completely disassembled dipped, rinsed in hot water, dried and reassembled with new gaskets O rings and fuel float stop valve. I am confident in my carb rebuild. Could an incorrect Points Gap, cause my problems, I replaced the points, did ingnition tune up. I am also going to use a dwell meter ASAP to check that out when I have some time. Another weird symptom I found today was what my timing light told me. When I checked the timing I read almost 40deg of timing, MIND BLOWING, if the timing light and marks are accurate, 40deg of timing would not allow this motor to run. Moving the Distributor to retard advance only brought it to 20deg as shown by the light, but the motor started to run bad when retarded to this point so I put the distributor to where the motor was audibly running best. OMG

 

[Maclin]

Re: Engine bogs at full throttle or when rpms pass 3200

Improper dwell (points gap setting) would not let it run ok for a while then deteriorate. Having typed that, dwell and condition of the points are all factors along with fuel delivery.

And Good On Ya for the carb rebuild. I would still want to replace the incarb filter though, but that's me :eyebrows:

By the way, what do the sparkplugs look like? Hopefully dark tan or brown. Lighter could indicate lean running at speed, not good for engine longevity.

 

[chesapeakeclassic]

Re: Engine bogs at full throttle or when rpms pass 3200

UPDATE

After some more troubleshooting and testing fuel pump and anti siphon valve, I had a breakthrough with my motor. I lost all spark for no apparent reason at all. So I began troubleshooting the lack of spark. Moral of the story, My new points were defective. I was losing voltage across the points gap at random times as tested with my voltmeter. Replaced the points with a spare set I had, set the gap, and i have never heard this motor run so good. I also hit my highest speed for this boat, 25mph in a head wind! Thanks for all the help!