Engine Bogs/Discharge Nozzles/ Manual Camaro

[badazz81z28]

Gents,

I have one of the new Holley 650 Ultra DP carbs. Bottom line the car bogs when you floor it. Its got 3.73 gears and a manual trans. I know I need to swap out the Accelerator Pump Discharge Nozzles, but these suckers dont come in a kit. What do I do? Guess?

Anyone here running a second gen camaro with a similar set-up? What size are you running?

[oestek]

You'll need to test several sizes to get it right, (along with adjusting timing.) Holley sells a kit, http://holley.com/36-184.asp - PM me if you're interested in a good price on one. Good luck!

[badazz81z28]

Please PM me a price. Thx

[Chevelle598bb]

What is your engine combo (cam, compression, manifold, ignition) and what is your base and overall timing? What squirters and jets are in the carb now.

[badazz81z28]

What is your engine combo (cam, compression, manifold, ignition) and what is your base and overall timing? What squirters and jets are in the carb now.


Its the 400 horsepower 355ci Vortec headed Yearone Crate engine. I'm running 36* total timing. What ever comes stock in the Holley Ultra Avenger Double Pumper 650.

[Chevelle598bb]

I just looked up the Holley avenger seres of carbs. None of them are double pumpers. They are 4160 double feed vacuum secondary carbs. Many people confuse them with double pumpers because of the duel feed line. Could you get the part number off of the air horn of the carb so we know what we are dealing with? Also I looked up the specs on the motor but it did not have can specs. Do you have the cam specs? If not no big deal we can still get you started tuning. Also what is your initial timing set at right now and also what is your idle speed. Your timing has to be dead on before you start tuning the carb. Every time you change the initial timing, it changes the overal timing and carb tune.

[anthonys 69]

You might want to check your timing and vacuum advance and mechanical advance spring rate. At idle your vacuum advance is pulling the advance up from say 10 deg to 18 -20deg. when you want to go to wide open throttle you lose the advancement and sometimes that causes a hesitation

[Chevelle598bb]

The intial timing at idle should be anywhere from 8-14 degrees depending on what gets the total timing to 36 degrees overall. The cam specs were not advertised on Year one's website but it is a hydraulic roller that I am sure is not very large. There should be no vacuum advance at idle, only base timing. Vacuum advance is only used at part throttle to increase timing. The vacuum advance line is connected to a ported vacuum source which only gets vacuum at part throttle, none at idle or wot. As long as the overall timing and base timing is correct, the op can start tuning the carb. Then he can attack the curve of the timing.

To the op, how many turns are the idle mixture screws turned out. And for grins, what distributor are you working with. Sorry for all the questions, but the more I know about your combo, the more help I can give.

[badazz81z28]

This is the carb I'm using. Ultra Avenger DP 650 http://www.holley.com/0-76650BK.asp

Timing is at 36* total, not sure what it is at idle. I set it to run best as when I first installed it, it would hesitate just reving the engine. Revs great right now with timing adjustments done, just hesitation with load on it full throttle.

The adjustments, I didnt mess with any of the factory settings, as the instruction say they shouldnt be required. The Bog is stated in the manual and says the nozzles and cams are the reason.

[Chevelle598bb]

With the timing set, you can move onto the carb. As far as the carb goes, you made a great choice for the engine and car. That carb will work great with that motor. As with any carb, the factory out of the box settings will get the engine started but still must be tuned to the engine. They must be checked to make sure they are correct before adjustments to the discharge nozzles and accelerator pump cams are made. The first setting to check is the float level. It is set from holley, but I have had to change the float level in just about every carb I have ever used out of the box. The float level should be set at just to the lower part of the sight glass. I believe your carb has glass fuel bowl sights for easy float adjustments. So check those first. Next thing is to check the idle mixture screws. The best way to set idle mixture is to use a vacuum gauge. A vacuum gauge is about 10-15 bucks at any autoparts store and an invaluable tool when tuning or diagnosing issues with carbs. Just hook the vacuum gauge up to a port that has vacuum at idle. First turn all four idle mixture screws in until they are fully seated. Do not turn them in too hard because the idle mixture screw will cause the passage in the aluminum metering block to become oversized. So just turn them in until they gently seat. Then turn all mixture screws out one turn. Start the engine and let the engine come to operating temperature. Note the reading on the vacuum gauge at operating temperature and regular idle speed. Start with one mixture screw and turn it an 1/8 of a turn in and note the reading on the gauge. If the reading goes down then turn the screw back out. If the reading goes up, move to the next mixture screw and turn it the same as the first. Then keep moving to the remaining two idle mixture screws. The point is the have all the idle mixture screws turned out the same with the highest reading you can get on the vacuum gauge. There is no way Holley can adjust these and have them right out of the box for every engine a universal (keyword) carb can bolt too. After the float levels and idle mixtures have been set, now you can move to the discharge nozzles and pump cams. First make sure accelerator pump arm has no play in between it and the lever. If it is very loose, adjust the nut on the arm until there in no play. Don't forget the secondary pump arm also. Next you can up the discharge nozzle size (the carb probably came with 25 or 28 nozzles) to 31. I would just change the primary first. As far as the pump cams go, the stock cams that came on the carb usually work very well and you shouldn't have to mess with them. Next make some full throttle passess and then read the plugs. Your 350 will pull really hard on that 650 and you may have to put some more jet in the primary and seconday. The last thing is to see if you have a stumble or not at part throttle or the transistion from part throttle to full throttle. Your carb comes with a 6.5 inch power valve from the factory. This means the power valve fuel enrichment does not hit until vacuum drops below 6.5 inches. For maximum driveability, use a power valve 2-4 inches less inches of vacuum under how much vacuum the engine makes at idle. I don't have your cam specs but I'm sure your engine should pull about 15-16 inches of vacuum at idle. So you would want to use a 12.5 inch power valve or a little smaller. 12.5 is about the biggest power valve made. Also get a dual stage power valve for smoother transistion with the power valve enrichment. That should get your motor running good.

Sorry for the long winded post but I'm trying to give you all the info you need to get that stumble gone. I have a feeling the stumble is being caused by either the float level being too high or idle mixture being off. Keep us posted with the tuning.

[badazz81z28]

I finally got around to play with the car a little. Well it turns out the stock nozzle on the primary is already a .031 and the secondary is a .028. I also checked/adjusted the pump arms, the secondary was WAYYYYY lose. The car has more power now ;), but still an slight off idle WOT stumple AND a part throttle ~2000rpm cruise transition to WOT stumble as well. I was thinking of trying the nozzle first. Does .035 nozzle sound too far out there considering I have a somewhat heavy car? I do have 3.73 gears and a manual tranny.

[oestek]

I'd try the nozzle, but a jump from .31 to .35 might be too much. Where is the timing set? It might want a little more initial. The correct answer is what it has when it's running right!

[badazz81z28]

The engine is at 36* total timing. The engine has never ran great, its a new engine with a new carb.

[badazz81z28]

I correct myself. The engine runs great and accelerates fine. Its the initial WOT that gives me grief.

[oestek]

Do you know what initial timing is, or how aggressive the curve is? (What RPM does it reach 36?)

[badazz81z28]

I will have to check, Last time I think it was 15* at idle, 36* at 3500 rpms

[badazz81z28]

Alright Gents,

Went through the carb, set timing at 32* total (as set for engine dyno), initial timing is 15*. Adjusted floats and idle screws. Still hesitates on WOT under load. Doesnt back fire nor black smoke.

Should I increase or decrease nozzle size? I checked out Holleys video and it says"

Heavy car/Low number gears = smaller nozzles
Light car/High number gears = bigger nozzles

What do you do when you have a "Heavy Car" AND "High Numbered gears"

Is there a sign if the nozzle is too big?

[badazz81z28]

I also have a green cam on the primary. From what I have read, green is the 2nd to most agressive. Would that cause a hesitation or Bog?

Please help!

[badazz81z28]

Good news, a .035 nozzle in the primary rid me of the off idle Bog. Still a very very slight bog from half throttle to WOT. I changed the secondary from .031 to .035 and really no change. I will play with the cams now.

[badazz81z28]

Gents,

The Bog is back. I just moved out of state and I did drop in elevation a little over 2,000 feets. The off idle slight bog cam back right when I started driving around here....should I start going up in nozzles again or something else?

I pulled the plugs and they look fine.

[TheJDMan]

As you drop altitude the air gets denser so you have to add fuel to compensate. From what I have been reading, the carb was jetted a little on the lean side where you were at previously. By dropping 2000 ft you have gone even more lean causing the stumble to come back. I suspect your shooter nozzles are fine but the jets are too small. What jets are in the carb now? I would venture to guess that you will need to move up 2 to 4 jet sizes. Also, the transition stumble is caused by the power vavle, you should try an 8.5 or 10.5.