Sidewinder looses power around 15-20mph

[maxwedge]

I have a 1976 Sidewinder SS with a 455 olds that I took out today. The boat seems to run fine at idle and speeds up to about 15-20. If you try to go any faster the boat looses power and feels like it's going to stall but it picks back up after a few seconds. Almost like it's running out of fuel except the problem seems indepedent of throttle position and more speed related. The motor doesn't misfire or anything just feels like you pulled the thottle back to idle for a second. I thought something might have gotten sucked into the pump but I pulled the inspection plate and looked in the both ends and didn't see anything unless it's deep in the bowl side (is that possible?). Almost seems like a carb or fuel pump problem except it runs fine with no load out of the water and at lower speeds. Mostly stock motor, Berkeley pump, Q jet. Last time out, this boat was running 65-70mph with no problems. Anyone got ideas?

[SmokinLowriderSS]

Fuel and ignition requirements unloaded are like night and day for an unloaded versus a loaded engine, doesn't tell you anything of value IMO. My first suspect is a coil failing as I had mine start failing hot under hi-rev load 3 years ago, severe missfire would correct at lower RPM. Ran fine when first cool untill coil heated up from use. Other suspect is fuel level (meaning fuel pump suply volume). I developed a weak fuel pump that would suply idle but anything above about 2,000 would suck the Holley faster than the pump would fill it. I finally determined this taking a sight plug off the side and reving the motor a bit (while in water) and watched the fuel level drop, higher RPM, faster drop. $175 mail order later and my 454 was happy again.

[Red Horse]

Fuel Delivery issue or carb way out of adjustment

[maxwedge]

Yeah I am kinda leaning towards the carb or fuel pump myself. Is there a good way to test this theory out of the water? I'm 30min each way from the nearest lake.

[Danhercules]

Is there a good way to test this theory out of the water? I'm 30min each way from the nearest lake.
Dyno. Check you fuel pressure. Get yourself a gauge to put on your lines permantly. It will help with future problems.

[maxwedge]

ok so the pump is barley putting out about 2 psi while running on the hose in my driveway, which leads me to my next problem. Where do you get a marine fuel pump for an olds 455. The local marine shop told me nobody makes a marine pump for the Olds anymore and that I should just run an automoive style pump. Is this safe? Isn't there suppossed to be an extra vent line going to the carb with the marine pump? I wouldn't mind running the automotive pump because it's only $15 and in stock at the local Auto Zone, but I would rather not blow myself up in the interest of saving a few bucks.

[Cas]

you can go with an electric marine certified
Marine Fuel Pumps (http://www.rexmar.com/page206.html)

[SB]

auto pump is fine. I don't know about Olds, with Ford you should be able to change one at the lake in 15 min.
1. You might have something stuck in the jet. With my jetski, I used to put it on the trailer and rev it up and blow the junk out.
2. You have a carb issue, such as back barrels not opening, linkage stuck, choke on.
3. You have problem somewhere in the line, filter, water in gas, venting, dirt at bottome of tank. Take a remote tank with you to the lake or drop your fuel line into the tank from the top.
4. You are spraying water on the coil.
5. Your ignition timing advance is not working.

[maxwedge]

If I buy a new automotive style pump and put it on, do I just block off the extra line to the carb? Leave it open? Run it someplace else? I've gotten conflicting answers as to what exactly it does. Is it the bowl vent line? Because if so, I would think blocking it off would be a bad idea. Or is it just an emergency return line incase the pump diaphragm ruptures, like somebody else told me? If it's the latter, I won't worry to much about it because it's an Olds, and it will likely throw a rod or something long before that happens.

[jtmarten]

Or is it just an emergency return line incase the pump diaphragm ruptures,
Thats what its for. If you have an open engine bay I wouldn't worry too much about using the automotive one. If you're going to go with an electric make sure you use a very good quality one. I went through 2 Holley's, got tired of being stranded on the lake and went back to a mechanical.
Jeff

[Wicked Performance Boats]

You can use the auto one. If it concerns you, you can usually find a vaccum fitting in a real auto parts store to tap into the fuel pump hole that will adapt to the hose going to the carb. Then boatcop won't have to put a post on here about using auto parts on a marine appication :D and it will be safe. Budlight

[maxwedge]

Thnaks for all the help guys. I got the new pump installed, seems to run a little smoother at idle anyway and the fuel pressure is up to 4.5lbs. I guess I'll take it out on the water tommorow and see what else I can break.

[Wicked Performance Boats]

Personally I don't think 4.5 psi is still enough, but tell us what it reads at wide open throttle. I like about 7.5 to 8psi Budlight :D

[SmokinLowriderSS]

Agreed Wicked. At idle I consider 4.5 to be good but it needs to come up at higher revs. My 454 runs just about 5 or a tad below at idle after being started, runs about 7 (and very solid) WFO.

[Boatcop]

You can use the auto one. If it concerns you, you can usually find a vaccum fitting in a real auto parts store to tap into the fuel pump hole that will adapt to the hose going to the carb. Then boatcop won't have to put a post on here about using auto parts on a marine appication :D and it will be safe. Budlight
That's what I was going to do with my 455.
Had the same problem with mine, and it turned out to be the fuel filter(s). Ran all new lines and a Mercury spin-on fuel seperator/filter and and it's running like a top.

[maxwedge]

Holy crap! What a difference a new fuel pump and some clean filters make. I just ran 73 MPH according to my admittetedly highly optomistic speedo. I would guess it's probably more like 60-65 real MPH or about 16mph on a GPS (ha,ha). Still, it's the best this boat has run since I've owned it. There was also probably a lot of drag from my dogs head sticking up in the breeze. Does anyone know the formula for calculating drag on a labrador head with 8 inches of tounge sticking out in the breeze?
Anyway the boat is fixed. Thanks for all your help.