I need a little help here fine tuning my boat. I plan on runing it in the 13-14 sec brackets. Its a flat with a 454BBC, roller cam (650lift/150dur),Holley strip dominator single plane intake with an 850 holley. Plugs are Champ.RV12YC. Timing 30 deg., Fuel 110 octane.
Stock jetting was size 78 for both primary/secondary.
First test runs had a plug reading that showed a very white insulator and a little soot on the base of the plug. I had a stumble off the line and a high speed miss and topped out at 5300 rpm's (my gears were too tall at 18%, 15% in now for next test run).
Now two weeks later at home:
On the trailer I bumped up two sizes on the shooters to size 37 to eliminate the stumble, it seems to have helped a little, but its still not completely gone. I went up to size 80 on the primary jets and 84 on the secondaries, too rich. The plugs were black. I'm back to 80's in both primary/secondaries. Any suggestions of where to go from here? I'm going out to the lake
again tomorrow, weather permitting, and test again at WOT. Thanks.
Fired up
Couple questions. If you are planning to run in the 13-14 second range, I assume this is a relatively stock engine, except for the cam? What compression ratio? I assume something in the 8.5-10:1 range. If so, why are you only running timing at 30 degrees? You should have no problem with it at 36-38 degrees. More importantly, why are you running 110 octane? It hardly seems to be called for if my other assumptions are correct.
More engine details would be helpful.
Check out this thread, if anyone here can help you, it's Ty.
TPC Racing Marine 850DP 4165 Sprd/Bore
On the carb side of the spectrum...
What number or color accelerator pump cams were you using? 50cc or 30cc pumps?
It might also be the your pvcr holes were too small. What I am trying to say is that you attempted to compensate a bog under acceleration with increaseing your jet size and shooter size which works for one but not the other.
You should try increaseing the duration of the amount of shot first. Maybe a 330 cam (red) with number 2 slot selected gives you well over 30cc's of fuel shot.
Another area you might look is the in the power enrichment area. Powervalve. Now you attempted to correct this with more jetting and it might have helped on the trailer but now you're fatter than a pig in the water. Rule of thumb would have been to increase the primary pvcr bleeds up .005" when you are 4-5 sizes above base calibration and nothing has cured your acceleration problem. This way you can run at a nominal Air-fuel ratio and have the extra shot from the powervalve.
What size powervalve are you running? IE 6.5in/hg etc.
[ February 17, 2003, 05:49 PM: Message edited by: Hotcrusader76 ]
Thanks for your replies. Here is some additional info: Compression is 10.5:1. Power valve is 125-65. (6.5in/hg). The pump cam is the stock one that came with the carb, no color. As far as the size accel. pump I really don't know. Strangely enough the Holley Carb tuning/modification book I have gives every other specification except that. Its holley model # 9380. It idles well at 850 rpm's with approx. 12 inches of vacuum. When I stomp on the throttle it drops to about 4-5 inches then pops back up. Will dropping the Power valve to a 5.0 or 4.5 be in the right direction? And I'm assuming just the PV in the primary side? Thanks for your help....keep the info/questions coming.
Put 36-38 timing in it and block the power valves and put 82 jets in it,and squirters around 40 that should get you in the ball park
Badboat1
Missed one also if the boat leaves real hard make sure you have jet extensions on the rear jets
Badboat1
Don't block the power valves and leave the stock squirters alone at this point! devil
Turn the accelerator pump cam to pump position number 2 identified on the primary acc.pump cam linkage (primary throttleshaft).
Try that first.
If that helps a little then you are in the right direction and might want to consider getting a higher in/hg power valve in the primary and more pump shot via the different cams. Most likely your secondary power valve is plugged already from the factory.
Remember even though it's a 30cc accelerator pump doesn't mean that's what it's pumping. Stock cams in number one only pump about half that number (over a 10 pump average). So by switching to a 330 cam in number 2 position will pump well over the 30cc amount, nearly 37.5cc to be exact. Kind of weird hunh?
Run the boat at cruise speed and see how she runs, rich or lean. If she runs perfect until you accelerate than the powervalve change should correct that (you're basically changing the time when it opens to be closer to your cruise in/hg reading).
Now if this still doesn't fix it then look into having some enlargement done to the pvcr bleeds inside the powervalve cavity. This isn't a Home Depot drilling operation, so don't just dive in there with the run-of-the mill drill gauges. You need precision here!
My best advice is that if you have come to a point where you are drilling then stop and give me a call first.
~Ty
(877)TPC-CARB
[ February 17, 2003, 08:08 PM: Message edited by: Hotcrusader76 ]
Great suggestions.....! Upon further and closer inspection my Accel. pump cams are both red. The primary pump cam screw is in the #1 position. The secondary pump screw is in the #2 position. So:
I will now move the Primary pump cam screw to the #1 position. Should I go back to the 78 jets (primary&secondary) it came with or stay with the 80's? Remember, it had a high speed miss I believe was from a lean condition.
Woops!....I mean I will move the primary pump cam screw to the #2 position!
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