SBC, down on power

[chpthril]

You unhooked it from the trailer, right J/K

Symptom with both props eliminates slipping hub? Fuel pressure/volume as suggested?

Week coil/poor spark would be another thing to check. Restricted exhaust is still a possible cause based on the symptom.

[mneal]

Yea since it acts same with both props pretty much rules out prop hub spinning or beat up leading edges etc.

I have not checked fuel pressure/volume yet but since electric typically they either work...or not, plus does not act like it fuel starves, in other words it will pull (with reduced power) all day consistently, typically it would change power as the float bowls empty and it goes leaner.

I didn't think about a weak spark but could that reduce power and still idle/run well, perhaps a dying coil?

I agree, the exhaust restriction had me most excited because how it behaves (runs well, just low power) but I am out of places for a restriction right?

Please keep suggestions coming, all ideas are welcome.

You unhooked it from the trailer, right J/K

Symptom with both props eliminates slipping hub? Fuel pressure/volume as suggested?

Week coil/poor spark would be another thing to check. Restricted exhaust is still a possible cause based on the symptom.

[chpthril]

Yea since it acts same with both props pretty much rules out prop hub spinning or beat up leading edges etc.

I have not checked fuel pressure/volume yet but since electric typically they either work...or not, plus does not act like it fuel starves, in other words it will pull (with reduced power) all day consistently, typically it would change power as the float bowls empty and it goes leaner.

I didn't think about a weak spark but could that reduce power and still idle/run well, perhaps a dying coil?

I agree, the exhaust restriction had me most excited because how it behaves (runs well, just low power) but I am out of places for a restriction right?

Please keep suggestions coming, all ideas are welcome.

The most load is put on the ignition while accelerating. Idle and steady speed put much less strain on the coil.

[mneal]

I will throw an Ohm Meter on it tomorrow and see .

[kpond57]

I have a carbon copy

Mneal,
was it your coil?
I have same power issue, could use some help.
KP

[mtnsmith]

I am a friend of mneal and am actually going over there in a few minutes and will ask him to respond.

[kko]

Yea since it acts same with both props pretty much rules out prop hub spinning or beat up leading edges etc.

I have not checked fuel pressure/volume yet but since electric typically they either work...or not, plus does not act like it fuel starves, in other words it will pull (with reduced power) all day consistently, typically it would change power as the float bowls empty and it goes leaner.

I didn't think about a weak spark but could that reduce power and still idle/run well, perhaps a dying coil?

I agree, the exhaust restriction had me most excited because how it behaves (runs well, just low power) but I am out of places for a restriction right?

Please keep suggestions coming, all ideas are welcome.

The statement about fuel pump is not true. my MP eng. was down about 7-800 rpm and i chased it for a month i finally found it when i took my high pressure pump out of filter housing and found the bottom had broken loose an was blocking off some of the hole on the bottom where it takes in fuel. i understand you have a different fuel pump all together but my pump would run the boat ok but not a 100% but now it will hit 5300 if i let it. when i first got the new pump i had to remember to back it off full throttle or it would bounce off rev limiter at 5300 rpm. good luck i hope you get it fixed.
Or better yet bring it on down and trade it for a TIGE!!

[mneal]

I chased it for a while and actually kinda quit chasing it. In the meantime (since I last posted) I did some more stuff. I got really exicted about Doms suggestion about the exhaust flapper because about ~ 3 yrs ago I broke a raw water to cir pump hose and got it hot...really hot and I loved his idea and thought maybe there was flapper piece left in the Y pipe. Pulled drive off and searched it really well and no luck.
I made a setup to measure/verify the fuel pressure remained constant and in the proper range under WOT. (it did).

KKO, your statement is sorta right, bit not totally, you gotta remember carbs and EFI are as different as night and day. Since in your post you talk about high pressure pump, that means you have EFI correct? In EFI stuff the AF ratio (fuel mapping) is function of the fuel pressure, injector size and injector duty cycle. Carburated things are differerent, the fuel ratio is a function of pressure differences in the carb but from a a fuel prospective , if the bowl is full (and proper level)...it is full. (I know, I am over simplifying things, but basically that is the basic idea) .
The trade it in idea, nah, I still like the old beater boat good enough, especailly the 1st of the month when I get nothing in the mail requiring a check. I actually always look around at boats (new and used) as a hobby , as well as attend a fair amount of boat shows a year because I like boats and nearly everything associated with them. Me and my wife are fortunate enough to have enough dispensable income (DINKS) that if we truly fell in love with the "perfect boat setup", I would buy one.....but that has never happened......not yet anyhow. But I am still looking. :-)

I actually swapped the carb over to a 4 barrel, got a good deal on a new one and figured could not hurt. (Volvo uses a 4 barrel manifold and an adapter plate with their factory 2 barrel so was easy/cheap to do). And that helped power some but still not 100% what it used to be. Actually helped the cruise economy because the primarys are smaller and uses less fuel at cruise. Not a great deal less but less is good. I can't remember how much info I have now vs. when I started this post, but I now think the distributor advance curve is wrong, the initial advance is dead on. Llike Dom said , electronic ignition typically does not move much ,short of chain stretch or something goofy happening. Anyhow, my advance curve follows the factory spec exactly right to ~2500 RPM which is 21 degrees BTDC, then that is it, no more advance. The factory curve continues up the curve to about 28 BTDC (if I remember right). The weights/springs are free and lubed so I dunno why the curve stops advancing early. If I ever get really bored or find anyone to re-curve the advance I might pull distributor out. Not too many places mess with mechanical distributor advance curves any more so I am not sure where to take it that might have a Sun distributor machine. Or I guess I coule mess at the lake for a day, but the way the dist. is set in the boat it is not super easy/fun to remove so the trial and error approach is far less then apealing.

OK, KP, as far as your situation. It could be a coil, but I doubt it. If I understand you right , it runs fine, just down on overall power? IMHO, typically when a coil is bad they cause high speed misfires and and are somewhat temperature dependent. (worst when hot). I dunno what power plant is in your boat and what one costs, but you could try one if they are cheap enough. What are the compression numbers? Leak down numbers if possible? I assume the easy things are done already (recent tune up etc.?) Like KKO said, if your boat is EFI, fuel pressure and flow is a great place to start, no chance you have a great dealer or any access to a scan tool to verify no codes?


Keep me posted, I am far from a regular here, but I will stop back to see how things are going. Good luck.

[kko]

i have still seen fuel pumps that dont keep up with demand wether it be carb or efi. not saying its your problem but it can happen.

[FIC]

Normally when distributor advance is down the engine will pull more top speed and be sluggish on the low in , because the cylinders run a bit richer when timing is retarded, when we wanted more top speed on our race car we would restrict total timing. Still sounds like you have another problem. We had a 454 mercruiser that the timing was to far advanced and it lost about 20mph.