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Its a 800dp elec.choke. I have one on my suburban currently. Those jets sound about right. I think I went to a 73 or 4. I figured my 305 Merc motta in the burb could use a little less fuel. The cruise fuel ratio on my 305 is about 14 to 1. WOT is 13.4. I know this is apple and oranges but thats what it is. I would put a couple jet sizes in the Pri. just for grins anyway for your 502. Just because the plugs are white. Check a NEW set of plugs after WOT and an emediate shut down. Look for the smoke ring around the porcelin about a 1/16-3/32" down. The porcelin can still be white with this ring. It looks almost like a thin grey O-ring was rolled down it. And check fuel press. at WOT
 

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The stock HP500 800cfm DP came with the following jetting arrangement:
Star Prim 75 Star Sec 93
Port Prim 81 Port Sec 89
 

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I can't find that carb... do you know what was the stock jet???

do you think I can go up 2 jets and burn the reg gas thats in the tank with out pinging???
If you have the stock jets that I lsted above in there and correctly, jet size should not be causing the pinging. People have been running 87 octane in these motors for eon's.

You could have something in the carb blocking fuel (not uncommon today with the ethanol fuels...you should have seen the last 3 carbs I just rebuilt....yuk !) or bad fuel or your ignition has issues or wrong timing.

These are 8:75:1 motors with 222,230 at .050" cams with 110LSA. Not a detonation prone motor by any stretch.
 

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lean won't ping???... what about the 850... would that be a better carb??
If you have the stock jets that I lsted above in there and correctly, jet size should not be causing the pinging. People have been running 87 octane in these motors for eon's.

You could have something in the carb blocking fuel (not uncommon today with the ethanol fuels...you should have seen the last 3 carbs I just rebuilt....yuk !) or bad fuel or your ignition has issues or wrong timing.

These are 8:75:1 motors with 222,230 at .050" cams with 110LSA. Not a detonation prone motor by any stretch.
Lean will ping, a blockage in the carb would cause a lean condition. You probably will not get any gain by switching to the 850, none that you would notice anyway.
 

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Disconnect the fuel tank/s and run the boat with new (I'd use 87) gas from a portable gas tank and see what you get. If it runs better, put the gas from your boat in your car.
 

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could I just have bad gas???why the four different jets... and where did you get that info..???
Out my azz. LOL.

That is what Mercury lists...doubted way back too but over time took a couple of virgin carbs apart and they had those in it. So, that's what is supposed to be in there.

BTW: Not uncommon to find staggered jetting in OEM performance builds. The OEM has the resources and the willingness to go thru the type of testing that will lead to this.
 

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Look up jets for any HP500 in a Merc site or at your dealer and you'll see. They'll list them in orifice size but tell you prim/sec and which side port/starboard.

Are you thinking about an 850 ? Why ? The factory 800 is perfect/already set-up for your motor.
 

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wow.... I pulled the secondary jets..... stamped 93.... thats a 105????
A little concerned why you stated this like you did. On an earlier post you wrote 75=82. Not sure why you posted what youb posted what you did but you do realize that is the diameter of the jet. Holley jet #s do not follow the orfice size.

CFM is correct, that is the stock jetting, but he did leave out the 6.5 PV on the primary side only. Its called stagger jetting, and its done due to fuel distribution in the stock GM dual plane manifold. GM and Mercury spend alot of hours on jetting that engine. So if you feel inclined to bypass all their dyno time on one of the most well thought out engine packages built, go for it.
CFM is also right in that if it is pinging, its either running hot, running lean, or you have timing issues. That engine will on 87 octane all day with no problems.



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A little concerned why you stated this like you did. On an earlier post you wrote 75=82. Not sure why you posted what youb posted what you did but you do realize that is the diameter of the jet. Holley jet #s do not follow the orfice size.

CFM is correct, that is the stock jetting, but he did leave out the 6.5 PV on the primary side only. Its called stagger jetting, and its done due to fuel distribution in the stock GM dual plane manifold. GM and Mercury spend alot of hours on jetting that engine. So if you feel inclined to bypass all their dyno time on one of the most well thought out engine packages built, go for it.
CFM is also right in that if it is pinging, its either running hot, running lean, or you have timing issues. That engine will on 87 octane all day with no problems.
Are you sure about that, on an HP500 :D
 

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Merc has sent out many bulletins about fuel lines collapsing. The alc. content is killing normal rubber hose. CFM might correct me but wasnt Merc sayn to use the blue liner stuff for unusually high alc. content. HP 5 hundo is a single plane.
 

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I was running prem gas...motor say's 87 octain
went on the dam run, run it down to 1/4 tank
fill it with reg. gas 87 octain..
ran good till the prem was out of the fuel line and started pinging...
I'm slowly comming to the conclusion that maybe my timing is locked in at full advance.. or
maybe just adjusted with tooo much timing..

When something goes wrong, I personally do the same thing you seem to be doing. I get all caught up in all the possible answers and if I don't slow my thought process and concentrate on one thing at a time, I end up spending more time and money where it never needed to be spent. In most cases, the solution was way more simple than I made it out to be. Take my words for whatever value you wish. Slow down a bit.

It ran just fine on 91, all the way down to a quarter tank. You topped the tank with 87 and shortly thereafter it's pinging.
Same day/trip?
No other changes?
What was the engine water temp?

Given the circumstances, the first 3 easy things I'd do is:

Verify fuel quality, verify the cooling system (impeller), and if you have a timing light, verify the timing.


I'm going to do a cam and head upgrade, sooo..thought I'd step up to a 850 cfm..

I'm susposed to get my new carb to day..then I can check the timing..

should be at 34 all in??? anyone know what merc says???
JMO, check the timing before you change anything. It's easy and there's no reason to add more uncertainty to the combination by adding more variables. If "stepping up" to the 850 makes you feel good, so be it. Money not so well spent though. No need for it at all, even with cam/heads you'll not be able to outflow the 800. Slightly different story if you had a dual plane manifold.
 

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Bang for the buck the AFR305 are an excellent head for a 502 boat engine. No problem making 575 or so with a mild cam and keeping silent choice option.
 

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first off, I wanna thank everyone for the posts....

next,..

I'm slowly comming to the conclusion that maybe my timing is locked in at full advance.. or
maybe just adjusted with tooo much timing..

the carb on my motor is a 1996 that has never been touched...

I'm going to do a cam and head upgrade, sooo..thought I'd step up to a 850 cfm..

I'm susposed to get my new carb to day..then I can check the timing..

should be at 34 all in??? anyone know what merc says???
Nice 2nd picture :D I have the full size file if you want it. Let me know.

I failed to mention the fact that my motor (96 HP500, same as yours) has been altered slightly :D. Resulting in my need for more carburetor. If your going to get that far into the motor (heads and Cam), talk to Chris, cstraub here on the boards. You won't be disappointed.

Dave
 

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I put the new 850 holley,checked the timing....its at 37 degrees all in

starts and runs bitchen''' gonna put the timing at 34 I think... any one know whait should be???


heres the video..


‪100 1166‬‏ - YouTube
34 Degree's at 4500rpm's. Initial should end up around 14. The Thunderbolt ignition has a 20 degree advance built in to the module.
 

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Yup, heard it...just past 1:30. Detonation on the trailer (ie: no load) is near impossible.

Sounds like valvetrain to me. Earlier Hp500's where known to break valvesprings around the 200hr mark. Crane had supplied normal HR springs for them...which again, didn't hold up long. Just as a note, many that had broke a valvespring also beat up the valve seat and/or lifter and/or rocker arm.
 

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Only so much we can help with being behind a computer screen and not being there.

Have you ever heard a motor detonate when not in gear ? Miss....yes.....detonate....no.
 

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830 merc

heres what i got going.... My boat has a merc 500 hp

i was running prem gas...motor say's 87 octain

went on the dam run, run it down to 1/4 tank

fill it with reg. Gas 87 octain..

Ran good till the prem was out of the fuel line and started pinging...

The transon on the boat is allway perfect clean...

The plugs are snow white...

Also i took a few winds of the spark aresster out...might have leaned it....


Any way... Pulled the front jets....75s


did the carb come with 87s???


Also, ...weren't the early...1996, jet different sizes...75 was really bigger???
830 cfm marine holley
 
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