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I need tuning help guys and gals. I have a new Holley 670 CFM Street Avenger Carb. Now it SAYS "ready to race out of the box" ...like I believe that. Anyway, when I am crusing around at 2500-3000 rpm's, the car surges, or jitters slightly. Also, it has a stumble when accelerating SLOWLY from a start. Now I haven't done a thing to the carb... So where would you suggest I start? I plan on adjusting the Idling circuits, but I don't think that is the problem. I have checked all vacuum hoses and even done the "cover the carb up and see if it dies" trick to make sure that I at least didnt't have a big vacuum leak.(It did die).

Not sure if this is related or not, but the car seems to be running hot, even with the Aluminum radiator, and 2850CFM electric fan. Could the carb be so lean that it is causing both problems? I plan on pulling the plugs and inspecting them tonight.

Is it difficult to change the jets on this Carb? I only have experience with Edelbrock carbs.

Thanks,


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I've ever had any luck with Holley carburetors. In my opinion, they are garbage...

I would suggest turning the air-fuel mixture up a little bit... Of course, do not rule out TIMING ISSUES... I had surging/shuddering happen to my Mustang also, and it turned out that the timing was set to 27 degrees TDC when it is supposed to be 12 degrees TDC.. The spark plugs were also gapped wrong...
 
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Finally, someone else that hates holleys. I'd go with a quadrajunk any day. Not as much power but great reliability and ease of repair. Agree with the air/fuel mixture and timing. Do you have any black smoke out the exhaust? You may be running too rich of you do? Does it miss at higher RPM's? If so, you could be running too lean. Does it backfire any or keep running when you turn it off? If so, you probably have a timing issue.
 
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Timing is set at 14 degrees BTC. No black smoke at all. At medium to full throttle it pulls STRONG without any miss.

I have an oxygen sensor and an air/fuel ratio gauge that I am planning on hooking up to do fine tuning with...I just haven't gotten that far yet.

any more ideas??

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Hi Mike...

Don't let these guys get you down...Holley carbs (and their design permutations) account for the vast majority of racing carbs extant today....

The beauty of the Holley design is it's flexibility...

Your two problems are likely unrelated.....

Go through the following procedures (regardless of what the packaging says..."ready to race my a**"....

Set float levels
Set idle mixture and speed
Set accelerator pump arm clearance
Check accelerator pump operation
Verify jetting, power valve, pump cam and pump nozzle settings
Get a Trick Kit for this carb if it didn't come with tuning extras (unless you already have extra Holley parts...sounds like you don't...

Questions...
Did the carb come with a 50cc pump stock?
What happens if you rev the engine up in neutral to around 4K
Is this carb a DP or VS? I'm not familiar with the Avenger series...
Is the surge rpm or speed dependent? IOW, does it occur at the same rpm in each gear or only at a certain road speed in high gear?
What happens if you power-brake the car to around 2700 rpm?....do it in 2nd gear....
Does this carb have 4 corner idle?
Did the engine surge before installing the carb (or is this a new engine combo)?

That'll do it for now....
Once you get the carb dialed in, it'll only require routine maintenance....you'll forget all about the last couple days...

Oh, yeah....let us know what the plugs look like...do a hot shutoff WOT run...no extended idling before shutting off....


Pat
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The surge could be a lean condition. Stumble probably a pump rod adjustment. If you can't solve these two problems with a minimum of time and effort, do Pat's laundry list.

65 FB "J" 302 lots of mods. 94 GT K&N only.
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Discussion Starter #7
Hey Pat,


Let me try and answer your questions;

1) Did the carb come with a 50cc pump stock?

A. I am not sure. On the Specs. page in the instructions it lists the following; Primary Jet 65 Secondary Jet 68 Pump Discharg Nozzle .031 Power valve 65. Nowhere can I find if it says what the cc's of the pump are.

2) What happens if you rev the engine up in neutral to around 4K

A. It seems to rev fine.

3) Is this carb a DP or VS? I'm not familiar with the Avenger series...
A. It is a Vacuum Secondary. the avenger is SUSPOSED to be ready out of the box and wet flow tested and yadda yadda yadda You know the sales hype. :)
4) Is the surge rpm or speed dependent? IOW, does it occur at the same rpm in each gear or only at a certain road speed in high gear?

A. it is RPM dependent. It seems to happen at low RPM's, any gear. It stumbles badly upon first acceleration.
5) What happens if you power-brake the car to around 2700 rpm?....do it in 2nd gear....

A. I haven't done this ....

6) Does this carb have 4 corner idle?

A. I have no Idea, but I doubt it.

7) Did the engine surge before installing the carb (or is this a new engine combo)?

A. It is a new combo.... Different Intake and Carb. However, I did have a slight surge before all of this.

Whew <G>


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You can identify a Reo pump (50cc) by its thickness...it's about twice as thick as a normal 30cc pump body.....I'd have to get one out of the shop and measure it to give you a precise dimension...usually if a carb comes with it there is a pink pump cam installed...

4 corner idle means you have two metering blocks and 4 idle mixture screws...much more adjustable with a performance camshaft...

Do the power-brake test and get back to me...

You may just have an adjustment problem on the pump cam/lever or you may need more pump capacity...

I've used 50cc pumps on all my racing engines...it just works..

If you can strap in a vacuum guage for a ride, try duplicating the surging problem and note the vacuum readings when it happens...

That's it for tonight...*G*

Pat
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You have described a classic lean condition. I would up the primary jets. You can also adjust the squirter, loosenen up the spring a turn or less and see the results. You can fine tune it, to much squirt is a waist of gas. I do not think you need a 50cc pump. 30 and some tuning should be ok
 
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