34scarab

OK, one more time, as I'm sure it has been posted before, but I am trying to set up my Holley 830's on the Dart single plane intakes and I recall that Merc staggered their jets.
Anyone know what the stock jet sizes are for the 500 HP's?
I am running the MSD ignition too, so I'll probably start off a little higher.

Thanks

35/25

I am in the process of dialing in my rebuilt HP 500's. I put in the slightly larger Crane 168731 cams and did minor bowl porting to the heads. The first time out with the new motors I checked a few of the spark plugs and they were bone white. I richened the stock jetting a few steps and the motors definitely liked it and the plugs started to get a light shade of gray to them. So far I am three jet sizes larger than stock and I think it is very close to ideal. After a full day of running last weekend there was just a trace of soot on the transom.
I am mentioning this because it is likely the stock Merc jetting for these 800's could be too lean for your 830's and/or your engine combination.

To answer your question however, the stock Merc jetting on the HP 500 carb is: 81 on the port primary, 75 on the stb primary, 89 on the port secondary and 93 on the stb secondary.

I am not familiar enough with the 830's to know whether they have power valves in both the primaries and secondaries. The 800's have a power valve in the primaries but do not have one in the secondaries. That is why the secondary jets have to be so much larger than the primaries. If your 830's have power valves in the secondaries you would have to use about 6 jet sizes smaller than those mentioned above (for the secondaries) as a starting point.

Rich

Scott

I have the exact same combo. I did not check the plugs and still have a dirty transom. I know some of this is from rich idle and now you have me wondering about my WOT conditions.

How do you like the change so far?

35/25

Scott,
I checked my plugs after running at an easy part throttle cruise. They were totally white. I richened the front jetting and could feel an improvement in throttle response. I then did a WOT run and the motors felt strong but flattened out on the top end. I checked the plugs and they were still very white. I richened the back jets and the motors seemed to have more response everywhere but still flattened out on the top end.

The boat feels more powerful than stock, especially in the middle, but so far only runs the same top speed as the stock HP 500 set up. Next time out I am going to hook up a fuel pressure guage and see what's up. I am wondering if it is running out of fuel at WOT.

Also want to double check the ignition timing. I have heard conflicting recommendations on how to set the total advance. The merc book says to set it at 34 degrees @4500 rpm, with the pur/wht lead grounded. I read a Dennis Moore post that it should be 34 degrees @ 3500 rpm. If I do it Dennis's way, I noticed that the advance will go past 34 degrees (several degrees) if you rev it to 4500 rpm.

So you have the same set up as I do? Did you see a top speed gain? I have '99 35 Lightning and hopr to see a 2 mph, maybe 3.

Rich

Scott

I picked up a couple mph and a lot more constant speeds associated with air, water temp and weight.
I don't feel like the motors are flattening out at WOT they pull strong all through the RPM range.

The only thing I may have different is my heads had some exhaust relief and very mild porting. I also had a tad bit milled of the heads to make up for the bowl port keeping the compression ratio the same or a little bit higher. We also took some time dialing in the cams on the engines.
There has been an obvious difference in the way the engines run and as you can tell I am happy with the results. I need to check the plugs and see if I can improve it but never got too concerned since Merc sets them up so fat in the first place.

35/25

Scott,
my heads were bowl ported and milled .010". We did not do any porting in the runners themselves. The cams were degreed in exactly to the Crane cam card. I intalled Cloyes hex-adjust timing sets which makes it a breeze to degree the cams. Crane grinds their cams with 5 degrees of advance built in, so the intake centerline on these cams as installed is 107 degrees.
You say you took time dialing in your cams. Did you actually experiment with different cam settings after the motors were running in the boat?

Johno

On my Hp 500 I am at 85 pri/96 2nd. bored .30 over with the 731 Crane cam, 800Holley. Merlin single plane intake & CMI exhaust. 8-9lbs of fuel pressure. Motor ran way lean on std HP500 jetting. Timing full advance at 36 degrees/ 3500 rpm as per DUI ignition system.
It's always intersting to see what others are jetted a. I have very little soot at idle & she runs clean at cruise. She idles extremely well.
john

35/25

Thanks John,
I am also interested to hear other's results. You are jetted pretty rich by comparison, and you have high fuel pressure. If it turns out my fuel pressure is low (under 5 lbs) I will probably want to do something. Did you install different pumps and fuel lines? I see that CP offers an upgrade kit to boost the stock pump but kind of pricey for what you get. I guess a Mark IV-type high performance mechanical pump will not work on the GEN V/VI sea pump/fuel pump combo unit. May have to use an electric pump and larger -8 lines in place of the tiny 1/4" npt stuff. I see you also went to the Merlin intake in place of the Dart and you are no longer stagger jetted.
What type of performance gain did you see after all your changes compared to the stock HP500?

Rich

Out There

34 Scarab,
I have the same Holley 830 on a 509 and have checked with Holley.Stock: 85s in both primaries and secondaries. 6.5 power valves in both. I'm in the process learning how to fine tune mine as my mechanic is great but mostly on stock set ups. Good luck, Greg

Scott

No I am set up exactly the same including the Cloyes gear set. I meant that they were dialed in correctly instead of slamming them in and lining up the the timing marks.
The only difference that I can see is that I had some relief done on the heads (exhaust) and a little bit of work on the intake. Are you still running the stock ignition?
I will do some testing in a couple of weeks and check the plugs. I also should add that I have around 50 hours on this set up without any problems that were related to the rebuild (Knocking on the desk)