Engine idles better with vacuum leak?

ChevyReb

Veteran Member
Lifetime Gold Member
Feb 4, 2003
4,499
SC
That looks like a 50cc accelerator pump cover. I think the stock 30cc ones are thinner than one in your pic. You may need a thicker spacer for clearance if that is a 50cc pump.
 

G72Zed

Veteran Member
Sep 8, 2015
3,917
Canada
Looks like the older styled 30cc, the 50cc REO body would not allow you to bolt on the carb.

Take a look at the Edelbrock spacer #9265. Will not disrupt the A/F distribution, and has some great insulating properties, use a little grease and no other gaskets required. Compresses approx. .275 and has insert limiters that prevents over tightening the carb.
 

Bentley

Veteran Member
Aug 14, 2020
252
If the vacuum hose was plugged into the side of the metering block, as in a ported source, I'm with 1980RS, your primary throttle is into the port just above the throttle plate.

If you are on manifold vacuum, and not over activating the primary trans slots, chances are you may in fact be a little on the rich side, and the extra air leans out and brings the idle afr's in check, so, the engine is not labouring as much and picks up rpm naturally, and that in itself picks up some timing centrifugally, and that pick's up more RPM.

In my opinion, get the primary and secondaries adjusted before you go drill some holes in those plates, that's the last thing to do, and more often than not it points to other underlying issues. I get some of these carbs in with holes in the butterfly's, they do not need them 90% of the time, heck, I take out the original ones with holes and put solids in.....and wow, things get better LOL.

To be really straight up forward, getting the idle mix screws "perfect" is not a walk in the park sometimes, 2 corner or 4 corner, and I'm on the pump every weekend, and soon to be at the track. Every one of these carbs I built are different going out the door, if you have a "tuners" secret, I'm all ears !!!! heck I'll pay for it LOL.

This is my "completed" carb waiting shelf.....always looking for tips.

View attachment 138843
Your shelf of carburetors reminds me of going to the Portland OR. Swap meet many years ago when there was nothing but neat stuff to see and buy...
Last time I went, probably 13 years ago, it was ALL junk and " model cars".....
 

Bikefixr

Veteran Member
Lifetime Gold Member
Mar 13, 2006
1,881
The idle speed went up because you idle mixture is very fuel-rich. So adding air by any means makes the final mixture more correct and increasing the idle speed. The engine doesn;t care where the extra air comes from. An air leak is no different that opening the throttle blades a little. Depending on what carb you have, the 2 idle screws may adjust just air, just fuel or an amount of the final air-fuel mix. On most Holley carbs, the only way to adjust the air-fuel idle mix is through the little air bleeds in the horn area and the 2 brass idle feed fuel restricters in the metering block. Those 2 in conjunction control how much air and fuel mixture goes to the 2 idle screws. The screws do not 'lean' or 'richen' the mix, they control the amount of fuel only. If you are very rich, (and most Holleys are), they were almost all designed to run a PCV valve which is a controlled air leak. Holley figures this extra amount of air into the final overall mix.
 

G72Zed

Veteran Member
Sep 8, 2015
3,917
Canada
Your shelf of carburetors reminds me of going to the Portland OR. Swap meet many years ago when there was nothing but neat stuff to see and buy...
Last time I went, probably 13 years ago, it was ALL junk and " model cars".....

Yep, I remember going to a few swap meets myself, I'd buy the crappy old Holley's for pennies on the dollar.

That "shelf" in the pic is worth more money then my first 3 cars LOL...all sold....some race teams have large budgets!!!
 




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