Jet sizes for 351 and power valve size

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   I have a 1980 with a 351 commander engine.  Boat is equiped with a holly 4160 carb, mallory electronic ignition ylm554cv, epoxy coil, 8mm wires, plat plugs gaped at 36 and just about everything else is new including battery and alternator.  Primary jets are 66, secondarys are unknown and power valve is unknown.  

My question is what # jets should I use at 5,000 ft and at 0 elevation.  In the past I have ran 64 on the primary side at 5,000 ft and works fine.

When I increase the idle at this elevation does this effect the accelerator pump?  Meaning as the idle screw is turned in I believe the accelerator pump arm begins to pivot.  Should I be adjusting the accelerator pump arm linkage?  Mine has a spring in it with a bolt and nut on top.  Should there be clearence between the arm and pump diaphram base?

I have read the past post on power valves and vacuum.  I'm not sure which power valve I have in currently but would like to replace it.  Which # should I get?  I have installed the blow out kit by my carb guy which are hard to find!  His name is Michalobe Dave.  Yes like the beer.  $80 and a 12 pack you got the carb rebuilt.  Only the thing has had a rough idle for as long as I'v owned it.  Runs great off idle.  

The boat has hesitation upon nailing the throttle.  I'm thinking the accelerator pump, power valve or accelerator pump cam of which there is different colors.  What the differances are I'm not sure.  What color do you have?  Timing is perfect, voltage is good, no vacuum leaks, all new seals.

In general the motor has 740 hrs and has neck snaping power.  Boat does 48 mph on a gps with a 13/13 4 blade prop and velvet drive 1:1 tranny.  The motor has always had this rough idle though.  Another person suggested to crack the secondarys from a screw on the bottom of the carb which I did. Didn't help.  It just sounds like it has a frog in its throat at idle.  Not dry and poping like others I'v heard.  Help!!!!!!

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gordonw Members Profile Send Private Message Find Members Posts Add to Buddy List Guest	Post Options Post Reply Quote gordonw Thanks(0) Quote Reply Topic: Jet sizes for 351 and power valve size Posted: June-29-2005 at 5:59pm
	I have a 1980 with a 351 commander engine. Boat is equiped with a holly 4160 carb, mallory electronic ignition ylm554cv, epoxy coil, 8mm wires, plat plugs gaped at 36 and just about everything else is new including battery and alternator. Primary jets are 66, secondarys are unknown and power valve is unknown. My question is what # jets should I use at 5,000 ft and at 0 elevation. In the past I have ran 64 on the primary side at 5,000 ft and works fine. When I increase the idle at this elevation does this effect the accelerator pump? Meaning as the idle screw is turned in I believe the accelerator pump arm begins to pivot. Should I be adjusting the accelerator pump arm linkage? Mine has a spring in it with a bolt and nut on top. Should there be clearence between the arm and pump diaphram base? I have read the past post on power valves and vacuum. I'm not sure which power valve I have in currently but would like to replace it. Which # should I get? I have installed the blow out kit by my carb guy which are hard to find! His name is Michalobe Dave. Yes like the beer. $80 and a 12 pack you got the carb rebuilt. Only the thing has had a rough idle for as long as I'v owned it. Runs great off idle. The boat has hesitation upon nailing the throttle. I'm thinking the accelerator pump, power valve or accelerator pump cam of which there is different colors. What the differances are I'm not sure. What color do you have? Timing is perfect, voltage is good, no vacuum leaks, all new seals. In general the motor has 740 hrs and has neck snaping power. Boat does 48 mph on a gps with a 13/13 4 blade prop and velvet drive 1:1 tranny. The motor has always had this rough idle though. Another person suggested to crack the secondarys from a screw on the bottom of the carb which I did. Didn't help. It just sounds like it has a frog in its throat at idle. Not dry and poping like others I'v heard. Help!!!!!!

skyhawkflyer Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February-08-2005 Location: Zimbabwe Status: Offline Points: 275	Post Options Post Reply Quote skyhawkflyer Report Post Thanks(0) Quote Reply Posted: June-30-2005 at 11:12am
	If your having problems with a rough idle, it's got to be in the idle circuit. How are your idle screws? any burrs or damage? Are you running a wedge plate? It sounds like you may be having a problem with your forward metering plate. Try blowing it out with an air compressor and look it over closely, making sure it's not warped. My accelerator pump cam is pink (although this may be discolored from years of service). I would be cautious changing the accelerator pump curve, unless your thinking that you need more or less fuel sooner (or delivered later). If you change the cam, remember which one you had in it in case you need to go back if the condition worsens. Chances are though a bad power vavle will give you the same conditions. I think the #65 power valve works best for me. The #25 has been in lots of carbs and kits and is undersirable and for the most part gives the performance results your describing. Your accel pump should be adjusted after making your idle adjustment. Now there's 2 adjustments out there. You can use either. Holley say's adjust the pump so their is zero clearance between the pump arm and the bolt. That's all they say. Performance books say this is incorrect because the slightest movement of the throttle causes drips in the venturi from movement of the accel pump. They recommend .010" clearance, making sure that the diaphram does not bottom out when at full throttle (still more movement available). I use the .010 adjustment and it has been working well. As for the jets, Holley should have an altitude conversion chart. Have you tried their website? They also have a tech line that should be able to tell you the jets you need for the altitude your running at, but you'll have to be able to tell them which jets you currently are running. I can't remember well, but I think I had 64's and I'm running at sea level. hope this helps

skyhawkflyer Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February-08-2005 Location: Zimbabwe Status: Offline Points: 275	Post Options Post Reply Quote skyhawkflyer Report Post Thanks(0) Quote Reply Posted: June-30-2005 at 11:12am
	My 351 has 731 hours......

gordonw Members Profile Send Private Message Find Members Posts Add to Buddy List Guest	Post Options Post Reply Quote gordonw Thanks(0) Quote Reply Posted: June-30-2005 at 1:54pm
	Thanks so much. I'll tackle the meetering block and replace the power valve, idle screws and accel pump. Adjust the linkage too. I think my pump cam is black and I do not have a wedge plate. I know that their is also three holes in each pump cam.Holly site says to drop one jet size for every 2,000 ft. of elevation. I just don't know what jet size to start with though. It will run good. It's more for my wife than anything. She'll throw it in gear when it begins to clog up at an idle and then try to get me up and it dies! Of course you can't tell them how to drive right? I sware it's this damm idle circut or my marriage! Does holly offer counseling or anger management courses with each carb sale?

skyhawkflyer Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: February-08-2005 Location: Zimbabwe Status: Offline Points: 275	Post Options Post Reply Quote skyhawkflyer Report Post Thanks(0) Quote Reply Posted: June-30-2005 at 3:40pm
	Nope, Holley doesn't help much with anything unless your willing to write a check for it. I don't know what to advise you in the driving dept! Look closely at your primary metering plate, thats where the fuel emulsification takes place for the idle circuit. Warps, cracks, poor sealing surfaces or gouges from cleaning, loose power valve, cracking of the rubber in the power valve, power valve sealing washer not seated correctly..... (fuel getting sucked past the power valve). As for jets, changing jets won't help a bad idle. If you think your too rich take your boat out for a run at mid throttle for a few minutes and then shut down and pull a few plugs. Read your plugs and you can see which way you need to go with the jetting. On your set-up the forward plugs tend to burn a little leaner than the rears. Hope this helps

jameski Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: May-18-2004 Location: United States Status: Offline Points: 368	Post Options Post Reply Quote jameski Report Post Thanks(0) Quote Reply Posted: July-02-2005 at 1:48am
	gordonw, you said "timing is perfect", does this mean set to the factory settings? I had the same problem with hesitation off idle when I set my timing by the book with a timing light. I advanced my timing about 4 degrees and it took care of the problem. When these engines get high hours on them, the timing chain and gears are not as tight as when they were new and the timing can't be set to the factory setting. Their are a lot of articles online about timing by ear, and with an old engine, or a modified engine, that is the only way to set it "perfectly".
	current boat 94 Sport Nautique previous boat 78 Martinique

Jet sizes for 351 and power valve size

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