Partially Blocked exhaust causing 4 bbl issues

[montyman]

HI, my 85 Riv bogs when I stomp on it, but accelerates smoothly if it stays on 2 barrels. Vacumns and electronics are ok. He says it is likely a partially blocked exzhaust system.
Has anyone had this issue? Where would I start before I take it to an exhaust shop.only 20k miles on it, and the exhaust system is clean and rust free on the outside!
any help appreciated
Thanks
John

 

[MelsRegal]

Did your mechanic check the choke pull off diaphragm?
In addition to cracking the choke open it slows the opening of the secondary air valve to prevent a bog.

 

[G-827858]

Did your mechanic check the choke pull off diaphragm?
In addition to cracking the choke open it slows the opening of the secondary air valve to prevent a bog.

Thanks, I will ask him!

 

[montyman]

Hi, it appears that my catalytic convertor is likely plugged, at least thats the opinion of three old timer mechanics.
Wrenchmonkey had one for 260 canadian$, which is about what I would pay to cut it out and replace it with a pipe. I have done this before and it makes a car louder and serious exhaust smell.
Thanks!

 

[Amanda Hugenkiss]

Did this issue ever get resolved? Did they check the choke issue before condemning the cat? Agree on keeping a cat in there, I can't stand that exhaust smell and don't like the thought of pouring unnecessary pollution into the air. It's amazing how much pollution reduction is done just by the cat. Far more than all the other controls combined.

 

[montyman]

Hi, it did not get resolved despite two mechanics looking at the carb. It does occasionally kick in, but the bog is still there. One told me to replace the carb, as it leaking and the electric choke is not working and there is damage to the front of the carb, where someone, not me, partially stripped the threads doing a feul filter change. I will make the decision to either live with it or replace the carb with a new reconditioned Rochestor - which I am told is way cheaper than adapting another make to the car.

 

[MelsRegal]

Hi, it did not get resolved despite two mechanics looking at the carb. It does occasionally kick in, but the bog is still there. One told me to replace the carb, as it leaking and the electric choke is not working and there is damage to the front of the carb, where someone, not me, partially stripped the threads doing a feul filter change. I will make the decision to either live with it or replace the carb with a new reconditioned Rochestor - which I am told is way cheaper than adapting another make to the car.

The mass rebuilder carbs do not have a good reputation. They grab whatever they have handy and slap it in. Find a local guy who does them and they the inlet can be fixed.

 

[Amanda Hugenkiss]

Yeah I would replace the carb before doing anything else since it has obvious problems

 

[02LTD2.0]

....or you could get a new Edelbrock and solve your carburetor issues. My '81 El Camino had one on it when I bought it nearly two decades ago and I haven't had to do anything to it besides adjusting the idle speed.

 

[MelsRegal]

....or you could get a new Edelbrock and solve your carburetor issues. My '81 El Camino had one on it when I bought it nearly two decades ago and I haven't had to do anything to it besides adjusting the idle speed.

Current Edelbrocks are square bore carburetors, so won't fit spread bore intake.

 

[02LTD2.0]

Current Edelbrocks are square bore carburetors, so won't fit spread bore intake.

I know that! They could change the manifold.

 

[MelsRegal]

I know that! They could change the manifold.

But they may not know that. Wouldn't be the first time someone bought a square bore carburetor and then unexpectedly found out it doesn't fit.

 

[HotZ28]

Another & better option for replacing the spread bore carb shown in the link below. I did this many times & never had a problem with the Holley!

https://www.summitracing.com/parts/hly-0-80555s

 

[LARRY70GS]

HI, my 85 Riv bogs when I stomp on it, but accelerates smoothly if it stays on 2 barrels. Vacumns and electronics are ok. He says it is likely a partially blocked exzhaust system.
Has anyone had this issue? Where would I start before I take it to an exhaust shop.only 20k miles on it, and the exhaust system is clean and rust free on the outside!
any help appreciated
Thanks
John

First, an easy check for clogged exhaust is to simply connect a vacuum gauge(they are cheap) to manifold vacuum. Bring the engine speed to 2000 RPM in Park. The vacuum gauge should read about 20". Hold the throttle steady. If the vacuum starts dropping off with steady RPM, you have an exhaust restriction. Most likely cause is a clogged catalytic converter.

There are other things that can make the engine bog. The #1 cause for a Quadrajet is the front choke pull off. It does double duty. It opens the choke a bit on cold start up. It also holds the secondary air valves up top closed until the engine needs the additional air flow. If it is bad, the air valves flop in creating a bog.

It's easy to see if the choke pull off is bad. Just look at it with the engine running. The plunger should be pulled in, and you should not be able to easily move the rear secondary air valves. The pull off should be holding them closed at idle.

Cheap and easy checks before you start spending money on another carburetor.

The Edelbrock carburetors are vastly inferior to the OEM Rochester Quadrajet IMHO.