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Discussion Starter #1
Ok, so following the advice of some folks I hold in high regard in the engine world I removed the primary PV plug from my carb, re-jetted it and put a 6.5 PV in it. I did the whole vacuum gauge at idle, cruise, and the hit of the throttle. My boat ran like total shit. Backfiring through the carb, lost almost 5 mph, just not a good day. I put it on the trailer, took the PV out and reinstalled the plug, changed my jetting back to where it was. Boat runs perfect again.

My question is this, why the hell doesn't my carb like the PV? Holley HP950 choke horn milled & blended, worked by C&J engineering. I'd love a tad more economy but not if I have to deal with the headaches.

Help!
 

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just a ski boat with bark
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Ok, so following the advice of some folks I hold in high regard in the engine world I removed the primary PV plug from my carb, re-jetted it and put a 6.5 PV in it. I did the whole vacuum gauge at idle, cruise, and the hit of the throttle. My boat ran like total shit. Backfiring through the carb, lost almost 5 mph, just not a good day. I put it on the trailer, took the PV out and reinstalled the plug, changed my jetting back to where it was. Boat runs perfect again.

My question is this, why the hell doesn't my carb like the PV? Holley HP950 choke horn milled & blended, worked by C&J engineering. I'd love a tad more economy but not if I have to deal with the headaches.

Help!
Well you didn't give much to go off here so here's a couple questions.
  • what were your primary jets with the plug?
  • What did you change them to with the PV, or did you change them (if not it would be fat with a PV).
  • what was your vacum reading at idle
  • what was it while cruising?
Have you ever pulled a plug and read it after cruising? If not you might try that next time out to see if it can be safely leaned out any more.


JMO.
 

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The PV is part of the Cruise Circit. Theres no vacume , so it doesn't work. You don't need it on race app. or on a tunnel ram app.You are trying to expect vac. you're not creating vac.
 

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Discussion Starter #4
Well you didn't give much to go off here so here's a couple questions.
  • what were your primary jets with the plug? 86
  • What did you change them to with the PV, or did you change them (if not it would be fat with a PV).80
  • what was your vacum reading at idle10ish
  • what was it while cruising?7ish
Have you ever pulled a plug and read it after cruising? If not you might try that next time out to see if it can be safely leaned out any more. nice cocoa color on the plugs


JMO.
This is a 950 HP on a Team G intake. @ the hit my vacuum dropped to 5.75 so I went with the 6.5 PV
 

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just a ski boat with bark
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what was it while cruising?7ish

Have you ever pulled a plug and read it after cruising? If not you might try that next time out to see if it can be safely leaned out any more. nice cocoa color on the plugs

This is a 950 HP on a Team G intake. @ the hit my vacuum dropped to 5.75 so I went with the 6.5 PV
If your engine cruises at 7hg I would have probably started with 5.5 or maybe even a 4.5 to keep it leaned out longer. What do you mean by at the hit? When you mash it and leave it for a few seconds doesn't drop to near 0-2 on the vacum gauge? I'm not sure why it acted up with a PV unless that metering block doesn't have all the provisions for it. Have you tried calling C&J engineering since they reworked it? Maybe they changed some circuits and it won't work with a PV now, not sure just throwing it out there.
 

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just curious!...what c.u. is the motor?...perhaps the 950 is too big!...maybe a change to an 850 would be a better choice & better fuel economy :)...just sayin' my .02 cents :)

FastRat
 

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Discussion Starter #7
just curious!...what c.u. is the motor?...perhaps the 950 is too big!...maybe a change to an 850 would be a better choice & better fuel economy :)...just sayin' my .02 cents :)

FastRat
I've thought about that, but money is kinda tight right now so I gotta make what I got work. Motor is 10.5:1 468 BBC. It's funny, I went and pulled my plugs after I made the original post, the last time I ran it was last weekend, idled to the boat ramp, plugs are a tad too light for my taste, think I'm gonna back the timing down a bit and see what that does.
 

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just curious!...what c.u. is the motor?...perhaps the 950 is too big!...maybe a change to an 850 would be a better choice & better fuel economy :)...just sayin' my .02 cents :)

FastRat
I've thought about that, but money is kinda tight right now so I gotta make what I got work. Motor is 10.5:1 468 BBC. It's funny, I went and pulled my plugs after I made the original post, the last time I ran it was last weekend, idled to the boat ramp, plugs are a tad too light for my taste, think I'm gonna back the timing down a bit and see what that does.
The 950 is not too big. In fact the 950 has a smaller venturi, and the same base plate as a 850. Holley should have never called this carb a 950. It is so misleading it unbelievable.
My first question would be why your vacuum is 7ish. Just how big is the cam in the thing?
And you never did post the jetting. And may need MORE timing.
My gut says your lean, back firing thru the carb, loss if top speed. You LEAN!


Your going in the wrong direction.



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Discussion Starter #9
Jetting is 86 Primary, 88 Secondary, total timing @ 3000 RPM is 38* What do you suggest GN7?
 

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Another thing to take a look at is the power valve restriction size. This is the the size of the two small holes in the metering block directly behind the power valve. (you can see them when you screw the valve or plug out). If these holes happened not to be drilled, then the pv is not enrichening the circuit at all.

I have had a couple of Holley performance carbs come in thru the years that did not have the metering blocks drilled. We simply drilled them to size and added the cruise circuit.
 

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Discussion Starter #11
Ok, for now I'm going to leave the carburetor alone. I'll deal with the lack of fuel economy. My question now is my timing, my plugs looked a little light after my idle to the ramp last weekend. They're more of a dingy grey/white/tan. I'm at 38* total, all in by 3000 RPM. Should I back it down to 36? 34? I really don't want to shitcan a motor at the start of summer...
 

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Try 24* all in at 2,000 rpm. It'll elimenate the vac. adv. Then what ever you adjust the dist. at. add both for total * timming. It'll be real quick.:)hand
 

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Discussion Starter #13 (Edited)
Try 24* all in at 2,000 rpm. It'll elimenate the vac. adv. Then what ever you adjust the dist. at. add both for total * timming. It'll be real quick.:)hand
24* @ 2K ? That seems a little on the lower side of things, or am I missing something?


Here's what all of my plugs look like.
 

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Set your curve in the dist. at 24* at 2,000 rpm. Then adj. the dist.Add what is on the crank to the 24* you have curved in the dist. and you have your total. Yes it will be more than 24*. As long as it doesn't want to kick back when starting, then you're there.
24* + what is on the crank.:)hand
 

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Discussion Starter #15
Set your curve in the dist. at 24* at 2,000 rpm. Then adj. the dist.Add what is on the crank to the 24* you have curved in the dist. and you have your total. Yes it will be more than 24*. As long as it doesn't want to kick back when starting, then you're there.
24* + what is on the crank.:)hand
Ok, now that makes total sense. Thanks a bunch for your help :)hand
 

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24* @ 2K ? That seems a little on the lower side of things, or am I missing something?


Here's what all of my plugs look like.
Man , when you said the plug was a little clean , Uh , thats not real clean. Real clean looks almost like their right out of the box. Those appear to have been run some. The timing mark appears to be right in the bend of the strap which is fine. You'd need to put a new plug in and make a hard pass and shut it down then pull the plug and cut it to see if there is any color on the porcelain.
Also , what # are those plugs? Just from the pic it doesnt appear that any of the threads are discolored which may indicate that they are a little to cold.
 

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Discussion Starter #17
Man , when you said the plug was a little clean , Uh , thats not real clean. Real clean looks almost like their right out of the box. Those appear to have been run some. The timing mark appears to be right in the bend of the strap which is fine. You'd need to put a new plug in and make a hard pass and shut it down then pull the plug and cut it to see if there is any color on the porcelain.

When you say timing mark I'm assuming you're talking about the color variation on the strap?
 

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When you say timing mark I'm assuming you're talking about the color variation on the strap?
Yes, its pretty clear in the pic. Advancing it will move the mark closer to the body of the plug and retarding it will move it toward the tip. Its best right in the center of the bend. Which is were it appears to be. If you decide to try hotter plugs you will need to remove a couple degrees of timing and check'em again. Dont start chasing your tail with this, just get a good safe tune & have fun, Hass.
 

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Discussion Starter #19
Thanks Haas! I'm not changing heat range with the new plugs. I'm going to leave it alone, and just have some fun!
 

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Jetting is 86 Primary, 88 Secondary, total timing @ 3000 RPM is 38* What do you suggest GN7?
Well, that thing came out of the box with 89 all four corners, WITH 6.5 PV on both sides. Like I said, I think your lean. And it never hurts to go back to what Holley shipped it with. Unless CJs tweeked the air bleeds, the stock jetting should be pretty damn close.
If you insist on pulling the secondary PV, then jet it up maybe 6 sizes to start.

getrdone recommendation on the timing is fine so long as you TOTALLY understand what it is he is saying. I do, and it still confused the hell out of me.

Basically, if you at 12* at an idle, and 36* by 2000-2500 your where he was trying to get you. 12 initial+24 in the dizzy=36 total. But I hate having that much in the dizzy unless you bring it in real fast.

Personally, I would set the thing at 36* and do away with the advance all together. You don't need it, you can't load a boat hard enough to need the retard. It only effects starting. If it starts ok locked at 36, then lock it. Why "F" with a timing mechanisim that is fully advanced 1000 above idle. :)sphss



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