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Discussion Starter · #1 ·
Just installed the Holley 870 street avenger on my 496. It runs super rough and can't get it to idle. I tried to adjust the idle/mixture screws but that didn't help. It won't run smooth under 3,000rpm. Could it be the electric choke or float levels?? It's running pretty rich too

Any help would be appreciated.
 

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I have never worked on the new Avenger Holley carbs, just the ol 4150/4160 models, but should be the same. On new Holley cabs always check to make sure the floats are not hanging up, tap the fuel bowls around the float adjustment screws, then with the car running check the float levels. For the electric choke, set it on the lean side to start. IMS screws adjust both out 1 1/2 turns as a baseline setting. I always like to have an air cleaner on the carb while adjusting it. If after this it is still running rough, check you initial timing to see where it is, you should have 16-20 degress initial timing, you may need to limit your mech. advance to run this much initial advance, you need to play with it to get total timing in the 36-38 degree range. If it is still rich, put a couple of numbers leaner jets in the primaries, you may need to change the pump shooter size also. Find out what power valves you have and hook up a vacuum gauge, if you have 10" vacuum you need 5.5 valves, if you have 12-14" vacuum you can get away with 6.5 valves.
 

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make sure you're primaries (and secondaries) aren't too far open, also. You can do a quick search here using the words "transfer slot" and should get a lot of help for the correct setting.

Float levels too high can also flood the engine with extra gas, as can excessive fuel pressure.
 

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make sure you're primaries (and secondaries) aren't too far open, also. You can do a quick search here using the words "transfer slot" and should get a lot of help for the correct setting.

Float levels too high can also flood the engine with extra gas, as can excessive fuel pressure.

get her running yet/ dont believe changing the primary jets leaner, won't matter? as the jet's don't have anything to do with just idling.
 

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Sorry, bad wording there - I wasn't talking about the jets - I'm referring to the primary and secondary throttle blades. If open too far, you WILL pull from the primary circuit and the idle screws won't do anything for you. The basic adjustments need to be in line before jetting, etc changes.
 

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And let me clarify what I mean, he said the engine was running rough under 3000 RPM, you are into the primary metering system at this RPM, and the accelerator pump system to get to that RPM. So the primary jets may be on the rich side and need to be leaned down, and the pump shooters changed as well to smooth out the transition from the idle system to the primary metering system.
 

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Is there gas dripping out the boosters? If so it is a stuck needle and seat. It runs good at 3000 plus, because it is using all the fuel that is dripping in the manifold. under that it is flooding it out.
 

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Discussion Starter · #9 ·
I unbolted the carb from the manifold and the carb gasket was soaking wet with gas. I looked inside the manifold and it seemed like a lot of fuel was getting dumped into the manifold ports.

As of now I put the 800cfm EDL back on until I get one of the Holley tuning books and gather more info from all of you guys about tuning.
 

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I've had several (have obe now actually) and all ran great.

Just a quick FYI, the 870 have 78/82 jets, and 4.5 F and 3.5 R powervalves.

Did you check the float levels? Should be even with the bottom of the sight hole while engine is running. I like to bump the car w/my leg and then see the fuel slosh a bit. Keep a rag handy in case fuel shoots out - if that's the case it was too high or a stuck needle/seat.

Next, is your vacuum line where it needs to be? If you were running full manifold vacuum before on the otehr carb, you would probably want to do it on this carb. The connection for full man. vacuum is on the front of the carb t the very bottom. There's 2 connections there: a large port for pcv, and a small one for manifold vac. The other small port thats up high (its horizontal above the mixture screw on the metering block) is the ported vac. You could of easily lost at least 10-12* of timing, hence rough running, which in turn caused you to crank the idle screw in too far, which caused the transfer ports to be open too far, etc.

Take your carb back off and adjust the primary throttle blades via idle screw till these slots (called transfer slots) till they are kinda squared. here's a pic:



Your mixture screws, if turned all the way in should kill the motor, If not its getting fuel somewhere else. Mixtures should end up around 1 to 1.5 out usually.

Good luck
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