Author Topic: Heavier throttle (mostly) issues  (Read 2209 times)

Offline MP81

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Heavier throttle (mostly) issues
« on: August 26, 2019, 08:29:29 AM »
So, I'm pretty sure most of what has been suggested to me thus far for this is probably the correct answer (that being: rebuild carb), but I figured I'd pose the question here just to be sure.

Earlier this year, I noticed that the car doesn't seem to like heavy throttle anymore (that said, this has happened on a few occasions of light throttle applications - I will detail below). If you get on it, it just doesn't go anywhere for a good few seconds - it's hard to describe exactly what it sounds/feels like, but it's almost like a rough/grating sound, mild sputtering (without actually sputtering). It just sounds "rough", and it just sits there not really accelerating, until it suddenly smooths out and pulls way harder (relative, given you were just not going anywhere the second before).

I'm sure not coincidentally, this seems to have also come at the same time as the vehicle starting to a rather low idle. The car starts (right up if it's been run in the last couple days, after the usual long cranking if it's been more than a few days - car has always been that way, probably the bowls draining or something) and idles at roughly 500 RPM, so you have to give it a rev or two to keep it from stalling. Those revs sound very "broken up". After a few seconds, it goes up to ~700 RPM where it should be, and sits there just fine.

Driving the car like a normal human being seems to be mostly fine, but as I've mentioned earlier in the post, sometimes you can notice it. One time that stands out in my mind was really the first instance where I noticed this all happening, leaving my spot after a car show back in June. Car started up right away, since I had driven it there in the morning, and then I went to pull out of the spot, but I looked like a total rookie with the car hopping up and down like it was trying to stall (4-speed car)...but I was driving it like I normally would, it's just that the gas I was giving it didn't seem to be doing anything at all. Then suddenly, that "smooth out" hit and the car took off, since now my foot was in it far more than normal, trying to get it to go.

I'm thinking maybe something to do with the accelerator pump, but I've really got no idea.

Made sense to post here before I go rebuilding the carb, in the event that maybe this is something else. For what it's worth, it did not do this at all last year, nor did I notice it the few times I started the car and let it run up to temp over the winter.
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #1 on: August 28, 2019, 09:19:44 AM »
I did some quick investigation yesterday:

First what I did was play with the throttle before even starting the car - last time it was started was a week or so ago, so the main bowl wasn't full. What I noticed were slight "fuel bubbles" coming from this kind of "crevice" here in the corner between the gasket and the raised area around the choke flap. You could hear it and see it "lightly" bubbling there when you'd open the throttle.



With the car running and the choke flap fully warmed up, it looked like I was getting a good solid spray in the primaries:


After revving it, the car seemed to only want to idle at like 500-600 rpm, lower than it should be, but it stayed there and didn't stall, but it was a little odd.

I noticed that this rod was a bit wet where it goes into the carb body:
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline tayto

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Re: Heavier throttle (mostly) issues
« Reply #2 on: August 28, 2019, 02:01:39 PM »
the "fuel bubbles" is normal with throttle movement. it should actually be a small stream, this is from your accellerator pump. the rod in the last picture is the stem from the accellerator pump. most likely time to order a kit from cliff and rebuild. make sure to check primary throttle shaft for wear (most likely) and also make sure primary & secondary well plugs are not leaking. you can check them with shop air and soap water.

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #3 on: August 29, 2019, 04:32:31 AM »
The fuel bubbling in here is normal? Didn't seem like the other side did that, but I could be wrong. I don't recall it doing that in the past, before all this started happening.
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline tayto

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Re: Heavier throttle (mostly) issues
« Reply #4 on: August 29, 2019, 07:10:32 AM »
it should be squirting fuel into the other side. sounds like airhorn gasket and/or the airhorn is warped slightly. cliffs airhorn gaskets are thicker than stock and generally allow for a slightly warped airhorn.

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #5 on: August 29, 2019, 08:12:25 AM »
It does - but yes, I was wondering if it was something like that.

Ultimately, necessary action aside, what is likely the root cause of the issue? It seems odd that it'd be too rich or too lean for a few seconds, and then suddenly be okay - but maybe it is! I'm an engineer, so I just like to know things, for my own personal knowledge.
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline tayto

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Re: Heavier throttle (mostly) issues
« Reply #6 on: August 29, 2019, 09:59:37 AM »
your accellerator pump seal is probably worn and failing from age and is probably not ethanol resistant.

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #7 on: August 29, 2019, 10:24:56 AM »
And then putting in too much fuel initially, causing it to bog, then when it stops adding fuel it goes back to being a better AFR which is where it actually accelerates?
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline Cliff Ruggles

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Re: Heavier throttle (mostly) issues
« Reply #8 on: August 29, 2019, 11:29:56 AM »
The "bubbling" at that location indicates a plugged hole in the partition past the accl pump discharge hole in the airhorn.  You need to remove the carb, remove the top and clean it out.

While it's apart get one of our kits and replace all the internals to get it up to par for this new fuel.  It looks like it's been a while since it's had any TLC anyhow.....Cliff

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #9 on: August 29, 2019, 01:30:34 PM »
It looks like it's been a while since it's had any TLC anyhow.....Cliff

If my assumptions are correct - 38 years! I have to confirm with my uncle, but I'm pretty sure this thing has never been off the car, haha.

Thanks for the feedback guys, looks like I will be placing an order here for the rebuild kit shortly!
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline Cliff Ruggles

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Re: Heavier throttle (mostly) issues
« Reply #10 on: August 30, 2019, 04:10:22 AM »
Those are actually excellent units, and after that many years for sure it needs a good cleaning and some modern components for this new fuel......Cliff

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #11 on: September 03, 2019, 07:03:39 AM »
Good deal! I just placed the order for the rebuild kit.

I also have the book (my buddy had a copy he let me borrow), but haven't had a chance to dive into it too much (we're on vacation this week) - but it looks like it's a pretty good breakdown on how to rebuild the whole carb. Does it mention any "performance tweaks" that are worth doing while I'm in there?
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline Cliff Ruggles

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Re: Heavier throttle (mostly) issues
« Reply #12 on: September 04, 2019, 04:11:19 AM »
Thanks for the order.

The CCC carburetors respond to all secondary performance mods same as any non-CCC unit.

The ECM only controls part throttle A/F, so heavy and full throttle is same as any other unit.

Always do the "basics", all throttle plates adjusted to 90 degrees, index the throttle plates if/as needed. 

A quick release choke pull-off helps, and some will need a little material ground off the stop on the secondary air door to get a little more CFM to them........Cliff

Offline MP81

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Re: Heavier throttle (mostly) issues
« Reply #13 on: September 05, 2019, 07:59:55 PM »
I assume all that is detailed in the book?

Do I need any fancy tools? I've seen that I need certain Thexton tool kits, but I've heard from others I don't? I totally forgot to order any, so "not" would be the preferable answer, haha.
-1981 Camaro Z28 - 305 ci LG4 V8 - Headers, Dual Exhaust, GW U/LCAs, Hotchkis Springs/Swaybars, DD HDX Cluster
-2007 Cobalt LT - 2.2L L61 I4 - M62 SC, FE5 Suspension, Much More
-2014 Cruze Diesel - 2.0L LUZ I4 Turbodiesel - MSR Wheels, UR Rear Bar
-2017 Volt LT - Voltec Gen 2 + 1.5L I4

Offline Cliff Ruggles

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Re: Heavier throttle (mostly) issues
« Reply #14 on: September 06, 2019, 06:20:35 AM »
No special tools required.  I like to slot the M/C solenoid adjustment screw with a fine hacksaw blade so I can turn it with a tiny flat tip screwdriver.   Pretty easy to make a special tool for it was well from an old screwdriver.  Cut a "slot" in the screwdriver shank pretty much like a tire valve core tool.

The upper metering rod limit screw can be done in similar fashion.  I'd tap and install set screws instead of driving in the tamper proof plugs so any adjustments needed can be done with the carb on the engine......Cliff