Edelbrock Carb Help - Idle Mixture Screws

Off Topic, I don't have an Edlebrock,
,,,,,but you're saying that the amount of vacuum/fuel pressure might cause idle mixture screws to be ineffective? I'm thinking that I won't ever want any 4barrel Edelbrocks, that is if the inability to adjust idle is inherent to all of the solutions suggested?

With me, adjusting the idle is the first step in tuning a covey of single-barrels. In all the carbs I use the idle mixture is actually changed by running the screw in and out, consequently the idle mixture will actually change, and that change changes the idle performance. All the way in/out will change the rich/lean and result in a definate change, rich or lean it runs rough, just right it runs smooth.

Not trying to convince anybody that my carb setups are the way to go, just observing, reminding myself (in writing) that should I be tempted sometime in the future that I probably should stick to my old-school multi-one barrel Rochester setups, (potbellys on the 250), (monojets on the 292). I can't imagine them running any better with fourbarrels anyhow since they run perfect now, which I attribute to the inherent design of the carbs, not necessarily my ability to set them up.

 

ALL carbs have a idle, off idle and a power circuit of some kind. MOST are vacuum operated and if the vacuum is low enough ( below the power valve setting) the they will open ( usually a spring action) and allow fuel to enter the carb at idle etc. At that point the idle circuits are kinda over ridden with excess fuel and have little if any effect.

 

Don't mean to hijack but this thread is looking familiar to my situation. Can you please elaborate on the vacuum leak please. Mine is performer 2101 with eddy 1405. Or PM me.......thanks

 

This is what he is referring to. It is slightly wider than the carburetor's base and helps to make up the difference in widths between the Q-jet and regular square bore secondaries.

http://www.summitracing.com/parts/EDL-2732/?image=large

 

Are you sure you have the right timing tab for your balancer?

 

I located TDC of the engine and marked the tab based on the balancer tape (0) and went from there. I've never found nor do I rely on the accuracy of the after market bolt on tabs. The one I did have was 4 degrees off.

 

That isn't how my single barrel, multi-unit setups work. At idle the vacuum is at it's maximum and I can adjust any one of them and get a definate response. Wouldn't have a carburetor system on a hotrod that worked otherwise.

 

You guys are mis interpreting what i said. I said :
Originally Posted by GMC BUBBA
ALL carbs have a idle, off idle and a power circuit of some kind. MOST are vacuum operated and if the vacuum is low enough ( below the power valve setting) the they will open ( usually a spring action) and allow fuel to enter the carb at idle etc. At that point the idle circuits are kinda over ridden with excess fuel and have little if any effect.

Your single barrels work the same way. IF you install a higher lift , higher duration camshaft on many applications the usual vacuum reading will be some what lower manifold vacuum, in this case the carb will need some adjustment to get all circuits back in sync and properly working.
Thats what Jeff has done here with the rear axle/transmission change. At highway cruise the power valve used to open at lets say 7-9 inches of vacuum and with the old gear ration ( final) the engine vac was lets say 14 at cruise. Then the power valve would be shut..
NOW with the 5th gear change the car vacuum will pull down at ( lets say) to 8 inchs ( which is below the power valve rating and now the power valve is adding unneeded fuel causing his first complaint of poor mpg.
I just went thru this with my GMC six and have done a few more this summer with Jeffs problem..

 

Click here: Volvord 784VC Edelbrock Caruretor Section 1

 

bttt

 

Hi there,
I'd hate to be another who hijacks this thread, but here goes.
I'm having some tuning issues with a similar setup and I'm hoping somebody here might be able to point me in the right direction!
I have a carter 9605s (Edelbrock 1405) on an edelbrock performer RPM 7101 manifold, on a new 350 which is in a ski boat. As the motor is mounted at an angle, there is a wedge shaped spacer between the manifold and carb so that the carb is mounted level.
The setup has the following symptoms:

• under load and WOT, the engine is down on power - the throttle needs to be opened very slowly to avoid bogging down.
• with the choke slightly closed, it runs perfectly with plenty of seamless power.
• the idle screws make absolutely no difference to the idle RPM.

Could the open-style wedge spacer that we are using cause the internal vacuum leaks that are mentioned above? It doesn't appear to be an issue to my untrained eye. A pic of the spacer is here: http://www.cassellmarine.com.au/p/334860/carby-wedge-1411---squarebore-to-squarebore-.html.
Unfortunately I don't have a vacuum gauge or fuel pressure gauge handy, but if there isn't something else obvious that is amiss then I'll get hold of one (or both) - but until then, do you have any suggestions?
Thanks,
Anthony

 

Hey Anthony - got my carb dialed in after all the good advice I got from the guys that posted on here. I went up one on the step up spring (#5) and also changed the metering rod to richen it up a little. Solved my stumbling problem off the line. The idle mixture screws are about a quarter out now. I did find that I had an ignition problem too which contributed to some of my problems.

 

I gotta say, this thread helped me sort out a problem with my Edelbrocks as well.

I have two 500 cfm carbs on a cross ram. It seemed to idle, cruise and run wide open pretty nicely, but it was still fouling plugs and sometimes just flooding out when idling and cruising around.

It was a step up spring problem. Made a HUGE difference to go to a much lighter spring.

I changed a number of other things as well to sharpen the tune once the new springs were in.

Thanks HAMBers.

 

Thanks for the replies guys!
Well I did make some progress over the weekend. I couldn't find any external vacuum leaks so I took a stab and went for a test run with the wedge shaped spacer removed and the carb at a fairly steep angle. There was a big improvement, which goes to show that the wedge spacer should at least have a left and right divider rather than be completely open. I haven't seen any of these available off the shelf so I'll probably need to fabricate something myself.
Interestingly the carb seemed to perform fine even through it was at an angle - I'm tempted to ditch the spacer idea alltogether and simply leave the carb mounted directly on top of the manifold. I haven't seen any skiboats run without the spacer, might need to look around the next time I am at the boat ramp.
We still have some experimenting ahead of us - I'll try going with 4% richer rods (it has 071x047 rods, 0.100 primaries, 0.95 secondaries), and I think the timing might need some more attention as well. But at least we are heading in the right direction.
Thanks again for your help!

 

Hey poida,

We do a lot of HP marine stuff. You'll want that spacer in place. If you have to buy a solid four hole spacer (or single divider) and have it angle milled to match the angle of your Cassell unit if its at an odd angle. Holley, Moroso, Offy and others seem to have the 5, 7 and 12 degree plates available but they are open type.

Glenwood marine has 4 hole spacers available.

http://www.glenwoodmarine.net/Catalog/CARBURETOR.pdf

Edelbrock also offers a marine version of that carb. Vents are rerouted, needle and seat are improved for the constant pounding they get in a marine environment and they are US Coast Guard approved (if that matters to you down under).

Good luck with it.

-Bigchief.

 

Is the car a street runner or racer?

Without vacuum advance the next problem will probably be overheating at idle and slow speeds.

 

one question,y would u run a square bore carb on a spread bore manifold?

 

I just purchased an Edelbrock carb (don't have the part number handy) for use on my 66 390 on top of the Performer RPM 390 intake. My idle is a bit high though and this mention of a plate between the carb and intake makes me wonder if I need something like this or not that perhaps I am getting a vacuum leak too. I still got a ways to go with the tuning though so we'll see. I was surprised that there was no mention when I purchased it that I needed a special bracket for the Ford kickdown and that it is only designed for 67 and up. I did manage to bend my linkage in a way that preserved the geometry and got it in line where I needed it.

 

Sometimes that's all you have and you make it work.