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#1
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pinging
Hey guys, I have changed carbs to a Holley 950hp on my 500ci motor, and found that when the revs climb under full throttle,the motor starts pinging.
No problems when loading the motor, just in the upper rev range. Is this a leaning out problem? Timing is set at 35 deg, new msd 6AN, Unilite dissy, no vacuum advance. |
#2
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Maybe, but what cfm carb was on before?
I remember a milled head & block slnt 6 i built that never pinged till I put a bigger carb and manifold then it was ping city at wot. For a 500 950 is on the small side still but a smaller carb on there would be like a cork and if you remove that cork in comes a lot more air. But what was the cfm of the previous carb and what do the plugs look like and what compression? Does the carb have stock jetting? |
#3
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I would say that you need to rejet the carb. The secondaries are running lean.
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#4
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Agree.........
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#5
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950 cfm small for a 500 cu in? I don't know about that. The 850 DP on my 496 seems to do the job great! And an 850 hp NASCAR engine uses an 830 cfm carb.
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#6
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Maybe the secondaries are running too rich also?
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#7
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I ran a 1050 dominator for a while,being a race carb it was too rich for the street. I posted on this forum, and it was suggested that it was too big, try a barry grant, so I did with a 850 mighty demon, which was disappointing. The carb I have now is a Bigs stage 5, with 79 primary jets, 87 secondary.
I haven't checked plugs for color. compression is 10.5:1, I use premium gas, and never had pinging with other carbs. The carb is as they sent it, and much better alround than the BG, I just need to know whether I should try the jets, or is it timing? Is the unilite a good distributor? I also have a MSD programmable timing computer. Is that worth putting on and playing with? |
#8
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I would richen up the secondaries first, before spend cash on that.
If the primary jets are close, your spark plugs my not show the LEAN condition. I would say put a set of 89 secondary jets and go from there. When you pull the plug, look for consistence in color between plugs............Maybe one of the 4 barrels is not breathing right |
#9
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Quote:
For instance on my j headed 410 will eat and make use of 830-850. 451 likes 850 344 works 750 but will get 800-[830annular] All of those motors see 65-7000rpm on the street. |
#10
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Does your fuel system deliver enough pressure and volume for that carb ?
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#11
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It seems to me that your secondaries are too lean, you might also think of going with a stage colder plug.. just a thought.
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#12
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I have a BG hot rod electric pump mounted low at the tank, they are rated at 220gph, or something from memory. No mechanical pump.
I run a 1/2" line to and from the carb, and 5 1/2 lb/" pressure. Maybe pressure too low? That's what the regulator was set at from new. |
#13
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That low of pressure my not keep enough fuel in the bowls.
Turn it up to at least 7 1/2 psi........If it was mine i would set it a 9 psi. Start a 7 1/2 and see if it helps your problem............................ |
#14
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7 PSI maybe. 9 PSI will blow past the Holley needle valves.
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#15
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thats the way i us to fill.........decide to put a fuel pressure gauge in-line, as i was about to put a electric fuel pump that pushes 15 psi and knew i needed a adj reg to keep the pump in control.
My carter Hi flow (Mechanical pump, on the block) was holding or pushing 9 psi and had been for years. This same pump fed a TQ for several years and has been feeding a 600 Holley for many years sence. No problem, works grate. My Elec pump i installed has the regulator and pump next to the tank and is set at 7 pounds BUT! 7 PSI PUSHINING ON THE MECHANICAL PUMPS SUCTION SIDE...................make 12 psi( this is no B.S.) at idle. there is still no flooding of the carb, But Creates a rich condition. I now, only turn the Elec pump on just before i do my burn out. The mechanical pump will pull fuel thru the off elec pump just fine unless full power is demanded...........then i run out of fuel halfway thru 3 gear The elec. pump I'm using is a Carter Super Pump. This is why i said if it was me i would run 9 psi.....because i do |
#16
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Ok, thanks. I will try 7 1/2 lb as a start point and work up. If this doesn't do it, then I will try bigger rear jets.
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#17
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heck anything 6 psi or better will supply enough fuel.........
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#18
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As long as there is any fuel pressure at the carb the pump is keeping up with demand.
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#19
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dodge440, 7-1/2 is what Holley recommends for fuel pressure.
If the fuel system was factory, probably would see more in the 3 or 5 psi. Quote:
But, if you have your fuel bowl set up to be at "spec level" w 7 1/2 psi pushing on the needle and seat. The pressure drop to 1 psi under full load, the needle and seat will stop the flow of fuel in to the bowl sooner, causing the carb to lean out at full load conditions........ that is why i added a elec fuel pump to supplement my mechanical pump. |
#20
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has anyone ever noticed that when you increase the pressure with the regulator it decreases the flow or amount of fuel?
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#21
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Quote:
I'm up for a new theory!!!!! |
#22
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Its the pressure before the reg. that's important.The faster you go the more pressure you need,when your fuel tank and pump is in the rear of the car.
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#23
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when holley flows a pump ,they do it without a regulator.The free flow rate will be more than regulated flow.Its like putting your finger over the hose.The hose shoots a little stream ,but it won't fill a bucket faster than a open hose.
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#24
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then add the weight of the fuel and g-force to the mix.
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#25
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Quote:
Quote:
Quote:
I do understand you first statement now thow |
#26
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OK, I upped the rear main jets 2 sizes, and hooked up an Autometer analyser.
On hard acceleration, it showed immediate lean out, but also was blowing what looked like rich smoke. I am running NGK plugs, heat range to equivalent to Champion N9YC, the cam is a MP .528", I had been cruising, so maybe cleaning up fouling on the plugs?? I then put 2 sizes up in the rear main jets, and 1 size up in the front. No different. Went from 6.5 to 4.5 power valve, no again. In case it was the rear squirter too small, changed from a 31 t0 a 35, still lean. retarded the timing a touch, side of road tuning, still pings. Checked the plugs rh side, color ranges from dark brown at 1, to white at 7, and left hand side white at 2, to dark brown at 8. Any suggestions? maybe manifold, but idle is smooth, nothing shows on the vacuum gauge. |
#27
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Get a spray bottle and spray water along the intake....If the idle changes........You need to remove the intake and find the leak.
If not, there is something wrong inside that carb!!!!!! Are you using a carb spacer? The plugs should all be the same same....all brown..... white(White is way toooooo lean) I think you need to try a different carb. |
#28
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Yellow would be worse.
Are you running only 1 power valve in the front? If you are you need to be 8-10 jets bigger in the rear/secondary than the primary. Make sure there is no junk in the air bleeds, I say this cause recently a friend of mine was running one of those eddelbrock foam air cleaners and a back fire upon tuning sent bits of that foam into the air bleeds and took a few to figure it out..... If it was the shooters it would only be a momentary leanness or even stumble. Gas/mixture does not show on plugs like it used too, the most visible part of the insulator will show whitish while it's way down at the base that will show true mixture, and thats hard to see with out good light. So after it stops pinging don't worry if the plugs are a lil whitish, as long as your air fuel gauge shows 12.1+ a/f @ wot and around 14.5 cruise. |
#29
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I like what cudafever said on the vac leak, it could be.....
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#30
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Dodge 440,How do you set your timing?
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