SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: 86caribbean on October 02, 2013, 01:15:12 PM
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Hi everyone, new to this forum. I just finished a three month project, it's a 1986 Caribbean 18' jet boat. I stripped it down to the bare hull and went from there. I built a fresh 467ci BBC, Scat 4340 4.0" crank, ZL1 con rods, JE pistons full floating pins 23cc dome, compression is 9.97:1. G.M. 049 heads 118cc open chamber, 2.190 & 1.880 valves all Comp valvetrain lift .578 and dur. @ .050 in 244 & 246 110 LSA. Edelbrock tunnel ram with two Holley V/S 600cfm on top. I have added Quick Fuel metering plates for secondary fuel delivery. Secondary's are opening fine under load, I have the light spring silver with a yellow paint swatch. I began with 69 jets in the primary and 77 in the secondary and all is great accept WOT, I think I was hearing a lean miss, so at Parker last weekend I bumped it up to 70/80 and still had a miss at WOT. Plugs are showing color, looks normal. Now I'm thinking it's a fat miss, I had a few people tell me that they think it's too rich, go back to a jet size close to origional like 65 up front stay with the 6.5 P/V and 70 in the rear...Timing is @32 total, manifold vac. is 10-11" at idle..any thoughts?
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I have a similar set up but haven't run 600's with a rear plates. The one thing I see right off is I'm running 36 degrees total advance.
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Your total timing needs to be 36 to 38 , no less make a run and then check your plugs you should be around right with the 70 and 80s you night tyr around a 72 in the primarys and 78 in the secondarys 8)
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Thanks, yeah I'll bump up the timing to about 36 deg. Also trim back the fuel delivery.
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Still having an issue with the engine having a miss at WOT. :banghead: I've taken the boat out for testing the last three weekends and I feel that I made an improvement yesterday. I bumped up the timing to 36deg. and found that it loved #69's up front so crusing at 3 to 4,000rpm it's totally happy and hitting clean on all 8. But I'm still only on the primary's, my problem is when I stuff it and the secondaries open and yes they are opening all the way and staying open, manifold vac. is at 0-1 hg @ WOT fuel pressure is 5 1/2 to 6 psi and I have #81's in the rear. When I put in the 81's my rpm went up 500, and it pulled harder to 5,500 and it cleaned up a bit, but the pop isn't completely gone, it still feels like it wants more fuel. I opened up the (pvcr) holes in the primary metering block from .041 to .050 to richen up the primary circuit at WOT, so by looking at total jet area at WOT I'm flowing fuel as if I had #73 jets up front. My plugs look nice, a light tan, is it just me or does this engine really want/need that amount of fuel? I still believe I have a glitch with the air/fuel delivery, I can't see it being anything else, but i'm open for other options.
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Still having an issue with the engine having a miss at WOT. :banghead: I've taken the boat out for testing the last three weekends and I feel that I made an improvement yesterday. I bumped up the timing to 36deg. and found that it loved #69's up front so crusing at 3 to 4,000rpm it's totally happy and hitting clean on all 8. But I'm still only on the primary's, my problem is when I stuff it and the secondaries open and yes they are opening all the way and staying open, manifold vac. is at 0-1 hg @ WOT fuel pressure is 5 1/2 to 6 psi and I have #81's in the rear. When I put in the 81's my rpm went up 500, and it pulled harder to 5,500 and it cleaned up a bit, but the pop isn't completely gone, it still feels like it wants more fuel. I opened up the (pvcr) holes in the primary metering block from .041 to .050 to richen up the primary circuit at WOT, so by looking at total jet area at WOT I'm flowing fuel as if I had #73 jets up front. My plugs look nice, a light tan, is it just me or does this engine really want/need that amount of fuel? I still believe I have a glitch with the air/fuel delivery, I can't see it being anything else, but i'm open for other options.
i would keep going up on the fuel. My 461 eats every bit of an 1150 dominator with 92f 96r jets
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I ran 72 in front and 74 in rear in a similar set up but you are way retarded on timming you need to be 38 to 42 all in on the timming
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I wouldn't think that 36 deg. total timing would be retarded, I've spend a fair amount of time in a dyno with BBC engines and I have found that timing in that area makes good power. There has to be something else just stupid that I'm not seeing that's causing this miss at WOT.
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Your vacuum numbers are trying to tell you something.
The problem you are having is venturi velocity.
Two things I would try.
Put a little more timing into it, just a couple degrees at a time.
Try some carb spacers, like one inch..
Also, are you running a scoop or flame arresters?
GT
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Just another random thought.
Try raising the float level a tiny bit.
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I know I have great velocity through those 600's a good signal at the booster. I'm not using any flame arresters, I ran the boat last weekend with nothing on top, just for saving time of removing the Mr. Gasket butterfly scoop that I usually run, but again no air cleaners, I have a pair of K&N stubstacks on the 600's that I also use to hold the scoop assembly down. I had the carb's off last night again and opened up the PVCR holes up to .051 from .041 and kept the 69 jets up front and put 82 in back. Looking at the math (total area of fuel flow) when the powervalve is open the primary's are getting the amount of fuel as if 74's are in and accounting for the PV add another 6 numbers. So in the end I would be flowing equil to 80's up front at WOT. I'll try that in a few weeks at Parker Strip during Turkey Day weekend. But deep down I still think there is something else that is causing the problem.
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I know I have great velocity through those 600's a good signal at the booster. I'm not using any flame arresters, I ran the boat last weekend with nothing on top, just for saving time of removing the Mr. Gasket butterfly scoop that I usually run, but again no air cleaners, I have a pair of K&N stubstacks on the 600's that I also use to hold the scoop assembly down. I had the carb's off last night again and opened up the PVCR holes up to .051 from .041 and kept the 69 jets up front and put 82 in back. Looking at the math (total area of fuel flow) when the powervalve is open the primary's are getting the amount of fuel as if 74's are in and accounting for the PV add another 6 numbers. So in the end I would be flowing equil to 80's up front at WOT. I'll try that in a few weeks at Parker Strip during Turkey Day weekend. But deep down I still think there is something else that is causing the problem.
It its my humble opinion that at minimum you need a velocity stack on the carb tops to keep them from fluting.
The air going across the inlets can cause bowl pressure issues.
Seen it a hundred times.
Run it again with the scoop or something.
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What ignition are you running on this deal?
What you describe almost sounds like coil breakdown.
Only seen it once before, but thinking about it, it is plausible.
The 500 rpm gain makes me really think there is a problem with the set up.
Hmmmm
Good one.
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As far as ignition, it's a brand new GM set up, an OBD 1 mid 90's style V6-V8 and GM coil. It's all electronic but no PCM to control timing. It's almost locked out, but still has a small curve. Initial it's 24 and total is 36. The boat came with a Pertronix ign. system and coil, on the very first outing with my new engine combo with that system it did the same thing. So, I know anything could be possible, but both ign. systems bad?, prob. not.
I hate to sound like others, and I know how this sounds, but a good friend of mine who is VERY knowledgeable with engines and boats has more of an engine than I do and he is running the same set up and has no such problem with his BBC. I choose this system because of trying to keep it simple, because of a possible parts failure at the river, or out in BFE, where can I go to find MSD parts and such, any auto parts store or maybe even a Wallmart would cary a GM part...LOL...thanks for all your input, just trying to keep all doors open to look into.
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As far as ignition, it's a brand new GM set up, an OBD 1 mid 90's style V6-V8 and GM coil. It's all electronic but no PCM to control timing. It's almost locked out, but still has a small curve. Initial it's 24 and total is 36. The boat came with a Pertronix ign. system and coil, on the very first outing with my new engine combo with that system it did the same thing. So, I know anything could be possible, but both ign. systems bad?, prob. not.
I hate to sound like others, and I know how this sounds, but a good friend of mine who is VERY knowledgeable with engines and boats has more of an engine than I do and he is running the same set up and has no such problem with his BBC. I choose this system because of trying to keep it simple, because of a possible parts failure at the river, or out in BFE, where can I go to find MSD parts and such, any auto parts store or maybe even a Wallmart would cary a GM part...LOL...thanks for all your input, just trying to keep all doors open to look into.
It's my humble opinion that there's absolutely nothing wrong with those ignition systems.
They do however require a lot of current at a minimum of 14 volts.
Just food for thought.
What plugs and what gap?
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Sounds like a ignition problem.
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I'm running AC Delco plugs R43TS gap is .035 Moroso wires. For the up comming river trip I'm going to bring the the origional Ign. that was from Pretronix, just to give it a try. It's an easy swap just to compare, after I have 4 days to try things.
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I would also try a bigger gal on those plugs. I'm. Running stock he I and same plugs with .45 gap. Worked well on my chevelle and could tell a big difference from .35 to .45
Just my opinion but sometimes its just the little things
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Thanks for all your opinions and suggestions, I'm going to look at everything very closely. For sh*t's and giggles I called Holley yesterday and spoke to a tech. Gave him the whole rundown, he was even stumped. I can try a larger plug gap, but that's not the problem. I know HEI's run fine @ .035-.050 even in my 565 14.2:1 alcohol engine I only run .035, with an MSD 7AL, the more cylinder pressure an engine has, you close down the gap. Hell, being behind the sceens at NASCAR years ago, they don't even bother gapping their plugs, because flexing the ground strap weakens it and it could break off. Is anyone going to Parker Strip for turkey day this year, if so give me a shout out and maybe we could hook up and have a few drinks and shoot the sh*t.
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Did you make sure the ground strap is in that hei dist?
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Not running an HEI dist, it's a late model mid 90's GM truck system with the factory coil.
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Ive seen the ignition control module in those style distributors do all kinds of weird shit! Might be worth a try to throw a new one in it, theyre cheap, and its a good idea to carry one as a spare anyways.
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Yeah, all true, I try and bring as much stuff (sprare parts) as I can just incase. I'm having the Pertronix dist gone through as we speak, I'm going to install it at the river later next week just to see how the engine responds, I'm actually starting to lean towards a possible ignition issue, I have run out of options as what else to do or try with the fuel system.
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If this is an ignition issue, U might wanna look for carbon tracking down a spark plug, or other signs of arcing. Spark could be jumping to ground under load. There's endless possibilities of what could be the problem.... Have u checked for a vacuum leak? Valve could be sticking at higher rpms? I know it's a new motor, but I've seen new valve guides a little too tight and cause intermittent sticking... All just options here....
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Since I'm the only one that builds my engines and set's all the clearances per the engines duty, I have ruled out any mechanical issues, am I or the parts I use perfect?, no, but at this time I will still tend to look at some of the external possibilities, but again keeping other options in mind.
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So I take it you think he might have a weak valve spring ? what about fuel volume ? I no the presure sounds good but what size fuel hose and pick up in the tank ? is a fuel line internally collapsing ? there is a lot of things it could be. :screwy: