It's Not Fair.............

[Clams Canino]

I'll ask a question to meet the rules. How this happen - to me???<br /><br />Brand new NOS powerhead, fitted with ceramic coated hi-dome pistons - and I got the dreaded #3 melt-down at 5800 rpm. I removed the #3 plug and was greeted with a wall of aluminum. <sigh><br /><br />I'm thinking there is a vacuum leak in the fuel lines ahead of the pump somewhere as right after the failure I could pump the ball 5 times till hard. So it was sucking air somewhere and prolly ran lean. <br /><br />This performance motor uses about 12% more fuel at WOT than my last (stock) powerhead and I bet the fuel problem was there all along but the system wasn't really taxed till I opened up those .082 main jets for a long burst.<br /><br />/sigh /whine<br /><br />-W (ordered a new #3 already)

 

[walleyehed]

Re: It's Not Fair.............

I gotta ask...are the .082 jets for that powerhead????<br />If so, what was the jet size before???<br />If it was running "that" much leaner to burn it up, how do you know it really only burns 12% more fuel???

 

[Clams Canino]

Re: It's Not Fair.............

The motor (which was a propshaft rated 115) was retrofitted to spec out like the 1500XS. <br /><br />Used the 10/10 reed blocks, high domes, and jetted the carbs from .074 to .082 which is the correct jet for the 1500XS the vanilla 1500 was .080. The propshaft 115 had the same size ports as the 150/140 series.<br /><br />Only #3 burned up... typical failure.<br /><br />I'm investigating now.... and have a new piston on order. I have a set of true 1500 carbs laying around somewhere, I'm gonna see if there's any other differences that matter. BUT from the air in the glass fuel filter and all the ball pumping I could do... I'm stil betting on a vaccum leak at the bottom of it all.<br /><br />None the less..... I'm gonna ramp it up more slowly next time and watch for stuff in 500 rpm increments.<br /><br />I might also check the timing not just at #1 but index the flywheel and check #3 too. <sigh><br /><br />-W<br /><br /><br />-W

 

[Laddies]

Re: It's Not Fair.............

Clams, do you have to run extra oil in that powerhead? On the 44 and 25 XS s as well s the older inline race engines we have to double mix oil ratios, I don't know that it woud apply to your I/6 though we run a lot of spark advance on our engines--Bob

 

[Clams Canino]

Re: It's Not Fair.............

Not under 6000 rpm at normal advance. <br /><br />I run it 40/1, but at that point it time it WAS still on double oil from the break-in tank. It had about 4 hours on it when I decided to try a quick test of the warp drive. <br /><br />I suppose if anyone can track it down, that would be me. <sigh><br /><br />-W

 

[Dhadley]

Re: It's Not Fair.............

Did you actually change jets or drill those out?<br /><br />What brand pistons did you use and who ceramic coated it?

 

[rodbolt]

Re: It's Not Fair.............

clams<br /> years ago I think there was a venturi size difference in the 150 carbs. also the 150 ran the wide transfer port covers and the ports and boost porting was a tad different. next time if you think it was a lean out, try starting with .90 or 95 jets. we always tried to calculate jet sizes then added .010 to .015 more . same as setting up a 6-71 on a big block. we set the blow off valves very light and worked towards our boost goal. the half full fuel bowl is about normal if its on the pump suction side. we also eliminated the back draft circuits in the carb. seems it would lean the carbs out way to much, that happened even on stock 1500's the back draft circuits were designed to lean out the fuel mix. sometimes they worked to well. next time tee in a fuel vacum gauge at the pump inlet. should see 2-3"Hg at or near wot,if you use clear tubing you can check for air bubbles as well. anything over about 4-4.5"Hg will indicate a restriction in the fuel system, we also found the fuel line quick connect cannot support a high flow motor so we eliminated them. gasoline can boil at ambient temps someplace around 6"Hg. so its possible to lean out and have no air leaks.<br /> sounds like a fun project. wish I remembered more. I do remember the 150 tower of power were tweaked to about the limit from the factory. most the racers I knew ran them on a 25/1 mix. a few went a bit heavier.

 

[Clams Canino]

Re: It's Not Fair.............

Yes, the ports were a *tad* different but that depends on if it was the short shaft 1500 or the "fishing motor". But if anythign they were less agressive - so as not to contribute to my problem. I already eliminated the back-draft - that's an SOP here.<br /><br />I was on a 25/1 mix when it let go - and 5800 RPM isn't even real high for a 1500, if I had a problem at 6500 - then OK it's time to look for wierd stuff, but 5800 is at the high end of normal paramaters.<br /><br />The jets were factory .082's and the pistons are Vertex with the 2 ring semi-keystone design. - coated by some guy in Fla.<br /><br />The damage was totally *confined* to #3, the eyebrow melted down and slashed all over the rest of the dome. I have it all cleaned up inside and await the new piston to get here.<br /><br />Now that it's apart (again) I don't like the sound of the upper ball bearing (slight chatter)- of course this one is the tough one to get off. <br /><br />LOL.<br /><br />-W