Disable secondarys?

Car is a '32 5 window, engine is a Chevy 350, stroked to 383, Edelbrock ally heads. I've got an Edelbrock street tunnel ram fitted along with the recommended 2 x Edelbrock performer 500's. It is idling oK but overfuelling when you get a few revs on it. I have jetted it down but it is still washing the bores. Fuel pressure is OK and not too high, carbs are new and have been checked that they are clean and floats not stuck.

It is street driven and not raced so what do you guys think if I was to disable the secondaries? I'm pretty sure the overfuelling is only when the secondaries open.

Am I way off base?

Thanks

 

That sounds like one for FlamedAbone. He's an Edelbrock carb guy.


Why don't you snag a couple of Holley wide base 2 bbls and try that to see if too much carb is really the problem or it is just a setup problem.

 

There's an L shaped link connecting the primary shaft and secondary shaft on the passenger side of the carb. They would be pretty easy to disconnect to check and see if that's where your problem is. I'm gonna guess that disconnecting the secondaries won't fix your problem. They don't come in until there is enough vacuum under the top set of butterflies to open them.

 

disabling the secondaries the the absolute wrong thing to do! with those vacuum operated secondaries, if you are using them, you NEED them. all best you'll lose power, at worst you'll lean it out at high rpms and cause engine damage.

have you got jetting recommendations from edelbrock for your application?

i don't recall ever hearing washing of the cylinders with fuel being a symptom of running too rich, if it's that rich, you should be getting smoke out the tailpipe and terrible performance long before washing of the bores is a problem.

how does it run? what kind of rpm does it see? and what exactly is tipping you off that you have a mixture problem?

 

If you're jetted lean, have the accellerator pump set at the lowest stroke and hit the throttle pretty hard you're dumping in a lot of air and not enough gas.

Accentuated by the large plenum of the tunnel ram . . . even if it is a street tunnel ram.

Big plenums give a weaker signal to the jets.

If you have some, stick in some smaller (richer) metering rods and set the accellerator pumps to the max.
That won't take much work and if the engine runs better when the secondaries come in the next step will be to get the right jets & rods in it and perhaps back off the accell pump shot.

A metering rod spring change may be required as well.

Go to the Edelbrock carb tuning site and see what they have to say.

I have yet to see their recommendations fail.

Take your altitude into account as well, but I'm guessing that's not too much of a problem in the UK.

 

How do you know it's "washing" the bores? What exactly are the symptoms? I'm wondering if you're mis-diagnosing it. If those carbs are with out of the box settings, it's not common to have a big/noticeable problem. Usually those things are pretty good. You might find improvements on a Dyno that you normally can't feel in the seat of your pants. But, a real problem as you state, not likely. My guess, you have something else wrong. Unless that puppy's got no compression (bad piston/cyl head chamber combo?)

 

Thanks for the replies, much appreciated. It all got very complicated as while setting up the carbs after the first short run we could smell petrol pretty bad but it didn't look as if it was pooling in the bowl. The plugs were black so suspecting it may be overfuelling when the secondaries opened we dropped the engine oil to have a look. There was some evidence of petrol in the oil, but not too bad.

Fresh oil and cleaned the plugs, started and idled fine. Ran a few miles and it was very responsive and good return to idle when stopped. Took it for a blast to open the secondaries and saw the oil pressure drop off. Clicked off and coasted.

Dropped the oil and it had a lot of fuel in it, the oil was like a load of puke, it had broken down totally.

Pulled the engine and it has screwed the bottom end and started to eat the pistons.

Engine is now being rebuilt, block is having a bore and hone and starting again.

I don't want to junk a new Tunnel ram set up and carbs but am wayyyyyyyyy scared of repeating the same thing.

It could be that something let go and it wasn't fuel related but there was a lot of fuel in the oil and we had only been out for 10 minutes and went about 5 miles total.

I read that disconnecting the secondaries or maybe disconnecting one of the carbs and using a progressive linkage may be an option.

I've emailed Edelbrock a couple of times but not had a response.

Thanks

 

Edelbrock home page:
http://www.edelbrock.com/automotive_new/mc/carbs_acc/carbs_access_main.shtml

Carb FAQs:
http://www.edelbrock.com/automotive_new/misc/tech_center/install/carb_faq.shtml

Carb Manual (PDF) can be downloaded from either page listed above.

 

As you continue to test that setup, allow the intake manifold to get up to operating temperature to evaluate your success. In the cold air the fuel wont atomize in a cold intake. Ran this setup and it ran great with two 450's

 

What kind of fuel pump and regulator are you using?

 

That much gas in the oil that quickly sounds like a leak, not a mixture issue. Mechanical fuel pump? bad diaphragm ? Needle and seat not?

Can't imagine great amount of fuel getting past the rings, when running for only 10 minutes.

 

Have you checked the float settings?

Float height and float drop.

Float height is obvious, but if there's too much float drop - defined as float hangs too low in the carb - the floats needle tang will be pressing against the needle sideways and it won't be able to close the needle.

Most times these carbs run fine right out of the box.
I've heard that the floats can be off, but I've not found that to be true with a half dozen new Edelbrock/Carters.

I ran two Carter 500's on a medium riser Offenhauser dual quad intake and the only changes required were swapping the metering rod springs to coordinate with the bigger cam.

Vacuum pulls the rods shut and the springs open them.
Big cams usually require a lighter spring.

 

i would definitely recheck the adjustments on those carbs...

working at a speed shop and doing carb work has put dozens of edelbrocks through my hands. EVERY one needed the floats adjusted properly. i also recommend changing out the springs based on altitude above sea level since that's what the carbs are set at. i've seen a total of zero run great outta the box, but the 4000ft altitude here has a lot to do with that. listen to what the other guys are saying though, it's good advice. i just wanted to share my experiences in hopes of saving someone else some trouble.

 

My brand new Edelbrock 500 poured fuel into the motor straight out of the box. I never noticed until after a couple dozen miles it got hard to start and smelt of gas. The sparklers were sooty black, so I pulled the air filter off and peered into the carb, with the motor off and the electric fuel pump still running, and could see the fuel overflowing onto the primaries. A quick tear down and a clean and it was good, but to have a leaky needle valve straight out of the box is piss poor.

 

Mechanical pump?

Bad diaphram, fills up the crankcase fast. I've had two do this to me in my cars.

Frank

 

Thanks for the replies, really helpfull.

It's running a Holley red electric fuel pump with a regulator before the carb. Pressure seemed OK.

Would 2 x Holley 390's be worth a try? ... I'm still waiting on Edelbrock to come back to me but it would seem mighty strange if they recommend 2 x 500 Performers if it over - carbs a small block.

I'll strip down the Performers in the interim. I've got about 3 weeks to wait for the machining on the block anyway ...