Speed Issue
#11
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I've been personally helping with this engine and the Crane ignition is set to 34 degrees advance at WOT, it is firing on all 8 and the wires are properly seperated and routed away from excessive heat and abrasion. the four barrels do tend to "stick" at idle and I suspect the base gasket is interfering. The outdrive is a Bravo. ALL speed checks are done via GPS this boat has a sweet Livorsi GPS speedo. I will hook my fuel gauge up to the fuel rail and monitor the psi at WOT...This power issue is only present with the 25 pitch the less demanding 21 has no issue with power but this engine should be spinning way more prop than a 21. ALL fuel lines are 3/8" and the check valve outlet from the tank has been replaced with a straight through version and all elbows are radius type tube and not restrictive "street elbows".
#12
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I suspect the 25 is a little too much and won't let the engine get into its real power band. The 21 is probably a little light and the engine torque is starting fall off hard in the 5500rpm range.
The thing is, all these numbers may change once the bottom is back to 100% and then the 25 may be the right prop.
The thing is, all these numbers may change once the bottom is back to 100% and then the 25 may be the right prop.
#13
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He bought that prop from me....and in our old boat ( a heavy '89 Chris Craft 245 Limited..with a slightly warmed up 502 ), we turned that prop 5200 rpms @ 66.7 mph on the GPS with a half tank of fuel and two 250 lb guys on it. I think hes running outta fuel on the top end. We had a bigger Holley mechanical pump on the 502. He indicated that it seemed to be running out of power at 2/3 throttle. As an example..drag cars that seem to "lay down" about 3/4 track are notorious for not having enough fuel volume AND pressure. I would definately get a fuel pressure gauge on it. In my opinion..that carb seems a bit large. We had a 9022 800 Holley on our 502. What jets are you running ? Any black soot (at all) on the back of the boat ? Could be running way rich too. Just things to consider.
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#14
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sounds like fuel and carb might be to big for the small heads, bottom paint = 3 to 5 mph my friend has 550hp in a superboat 24 with trs and bottom paint that combo costs him about 6 to 9 mph he gets 76 at 5600 and would break 80 easy with b1 drive and no bottom paint. also when I BUILT MY 585HP WE WENT TO 1/2'' LINES EVERYWHERE AND THE BIG KE gen 5 fuel pump which worked on the 595hp motor and 650hp motor carbs were 850bg with 84 jets the 670hp motor ran1050 .
#15
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Thanks for all the info and opinions on this..... I'm currently stripping the bottom paint off the bottom. Hopefully I'll have most if not all the paint off the bottom tomorrow and report what results I get. As far and the heads and carb go, the AFR's I'm running may have small ports but they flow similar to a Dart pro 1 310. The carb was custom built to the flow of the heads, intake, ect. I think the carb is fine but i do feel that the fuel pump is to weak for my combo. I'll check the pressure when i get the boat back in the water.
#16
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The bottom is 98% stripped which added another 5 mph. So I'm now at 62 mph @ 5900 rpms, which is where Bob told me to prop the engine. Prop slip dropped to 21% but its still a little high. I haven't checked the fuel pressure yet but I think that is part of issue. When I was at WOT the engine hit 5900 and then started dropping rpms at which point I backed off the throttle. However I wasn't able to replicate it again. All of this was at max trim and tabs up with the old 21 mirage.
Last edited by endeavour32; 08-07-2010 at 09:05 AM.
#17
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The Mirage prop will slip a lot. Sometimes it's still the fastest on top end but it is a fuel waster in the midrange. See if you can borrow a 22 or 24 Bravo 4 blade from someone.
#18
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The last time out I was having issue with running out of power at 3/4 throttle agian. I could get up to 5000 rpms and then the boat would loose power, as I pulled back on the throttle the engine would come back to life. What i don't understand is why does it do this from time to time and not all the time?
#19
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When was the last time you changed your fuel/water seperator? Maybe you have some Sh!t in your tank that keeps cloggin your seperator ???
#20
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I have 16 hours on the engine and everything was new when the engine went in. I did run the old fuel out through it so its quite possible the old gas had sediments in it that is clogging the filter. I'll try a new seperator and see what happens.