850DP Tuning

[Fired Up]

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

[Oldsquirt]

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.

[twistedpair]

Check out this thread, if anyone here can help you, it's Ty.
TPC Racing Marine 850DP 4165 Sprd/Bore (http://free.***boat.net/ubb/ultimatebb.php?ubb=get_topic;f=5;t=001322)

[Hotcrusader76]

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 :D . 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 ]

[Fired Up]

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.

[Badboat1]

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

[Badboat1]

Missed one also if the boat leaves real hard make sure you have jet extensions on the rear jets
Badboat1

[Hotcrusader76]

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 ]

[Fired Up]

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.

[Fired Up]

Woops!....I mean I will move the primary pump cam screw to the #2 position!

[Fired Up]

Done. Primary pump cam screw in the #2 position of the cam and linkage. We'll see.

[Blown 472]

If this is a drag boat why would he need power valves?? vac goes right past the usefull point of power valves, idle to wot?? why tune for cruise??

[78Eliminator]

Blown 472:
If this is a drag boat why would he need power valves?? vac goes right past the usefull point of power valves, idle to wot?? why tune for cruise?? I agree. Why the hell would you ever want to hassle with power valves in a frggin drag boat?

[Hotcrusader76]

What model number are we talking about on this 850 carburetor?
A single power valve will help in on that stumble if there isn't one installed. Never assume that all carburetor set-ups are indentical in nature. IE tunnel rams with no pwr valves, blowers with boost referencing, etc.
If the accelerator pump tuning doesn't correct the problem and you are already running a 664 brown cam with a 50cc pump, then look into the pwr valve and the pvcr bleeds.
Let me how she ran.
~Ty

[Fired Up]

The carb is holley #R9380. It does have the red pump cam and after changing the primary cam to the #2 slot it ran worse. Much bigger stumble off idle. I readjusted the timing to 34 degrees. Looking down the throat of the carb the squirters seem to delay a great deal before shooting. Thinking a higher PowerValve at this time. Being that my vacuum reading is at approx 12" at idle would a 10.5 close that gap? It has 6.5 now.

[Hotcrusader76]

Please give me a call. You might have some other less obvious problems with the basic operation of that carburetor.

[Fired Up]

Okay,
So none of the accel. cam changes worked. Still stumbles when I punch it on the trailer. Everything is back to square one now. 78's in the primaries/80's in the secondaries. 34 degrees of advance.Accel pump cam (red 330) back to #1 position. 31 squirters back in. I put the 8.5 PValve in. Idle mixture screws are all 1 turn out.I flipped the carb over and set the opening to .045 inches on the transfer slot. In closer inspection it appears I have a 30cc primary accel pump and 50cc secondary. The housing is much smaller on the primary which leads me to beleive this. Since I'm at work today I won't have a chance to run it until tomorrow. While I was running the engine yesterday I noticed a small wisp of smoke coming from the small gap on the side of the (HEI) distributor cap where the ignition wires go through.I'm thinking crankcase smoke at this point. It seemed strange to me, but thought it must be leaking through the dist. shaft. Vacuum leak ??? I don't know...the vacuum gauge BOUNCES at about 12 inches, but I assumed it bounced because of the cam design. The vacuum drops to 4 inches when you punch it then bumps back up after. At higher RPM it increases to over 15-20 inches. What are you thinking?
Fired Up

[Fired Up]

Okay,
so I'm getting closer to figuring out the stumble on my 850. I adjusted the transfer slot and the idle mixture. Put a larger pump cam and bigger squirter in the primary side. It was sounding better as I was revving it on the trailer when suddenly...........a large pool of dark liquid came oozing by the v-drive as I stood next to the boat. At first I thought the v-drive sprung a leak. Nope...Then I thought my oil filter may have come loose...nope. A large amount of oil was pouring from the bottom of the block behind the bell housing. I instantly shut the motor down. I did notice moments before that my oil pressure was up to 100 psi as I revved the motor. I ended up with about 3 quarts of oil in the bottom of the boat. It was my last test of the day and getting dark so I didn't spend any time trying to find the source other that eliminate holes in the pan or block. I'm suspecting the rear main blew out. Not good with 3 weeks to race day. .........one step forward two steps back.

[Dragboat Dad]

I hate when this sort of thing happens. Sorry to hear that, hope it's not too big a deal.

[Fired Up]

Okay,
I'm back. What we found out was the oil filter adapter was cracked. When we went to remove it the adapter broke. Bought a billet adapter from Rex and the oil leak/filter blow out problem went away. The carb off idle stumble went away also. I want to thank everyone for the good suggestions. Based on that I eliminated possible causes. I ended up putting a larger squirter (40) and the big accel pump cam on the linkage. Stumble is gone. Rain and work has kept me from making it up to the lake for some under load tuning runs. We'll see monday.

[Hotcrusader76]

Great!
I am glad to see you are on the right track. Hope all is well in the water under a load. Funny how a simple problem turns out to be a little more involved than one might think.
~Ty

[Fired Up]

Thanks Ty,
Here is what resulted from yesterdays testing at the lake. On the trailer it revs good without the stumble off-idle.Under load when I give the boat a smooth quick full throttle acceleration it takes off great, no stumble, strong acceleration. but, if I just stab it to the floor the stumble is back. Top end still had the miss and I only pulled about 5000rpm's. Plugs were as white as porcelain. Ground strap on the plug was clean. I bumped up the secondaries from 80's to 82's and made another pass. Picked up 300 rpm's. Sounded better, but still had some top end miss. Bumped up the secondaries again to 84's and gained still another 300 rpm's. Still sounded better again, ran faster, pulled harder with miss top end to a total 5600 rpm's. Got late and couldn't run anymore. Quick review of what I have in the carb set up. 40 primary squirter with the black cam, 31 in the secondary. Primary jets are 78, secondaries are 84. Timing 34 degrees. Primary power valve 8.5 secondary is 6.5. Will bumping the primaries up a step or two help on the big end? I'm running RV12YC champion plugs. My other thought is maybe the plugs may be a step too hot. They are running very white clean. Thoughts.......?

[Hotcrusader76]

I tried to reach you tonight, but it seems that whoever answered the phone didn't know you. :D
E-mail me your number for the record. Thanks.
~Ty

[Jetty 468]

Hotcrusader76:
I tried to reach you tonight, but it seems that whoever answered the phone didn't know you. :D
E-mail me your number for the record. Thanks.
~Ty By god keep me posted on this ! I want to see what clears this up . 300 rpm's each time , is that normal ??

[Fired Up]

Ty,
I've sent you my numbers to contact me.