Chasing down a high idle

Weblamer · March 21, 2015, 04:27 PM

Hello all.
I have a 1985 Winnebago with on a Chevy g30 chassis with a 350 5.7 engine. Rochester Quadjet carb.
I have been trying to chase down a high idle problem. The camper had been having engine run-on problems, so one of the first things I wanted to do was check the idle. I finally got a tach installed, and to my surprise the idle in park was well over 2000 rpm.
First thing i did was open up the doghouse and check for any vacuum leaks. I could not seem to find any.
So I went to reading up on adjusting the idle speeds. The first thing I noticed was there were two different procedures for adjusting the idle, one with an AC compressor, and one without.
Now, my van has an AC compressor. However, there is no belt hooked up to it. I cannot seem to find a diagram that corresponds to my engine layout. There seems to be a pully on the radiator fan that lines up well with the compressor. However the zit-faced teen at Autozone could not find the belt size in his computer, and I am having problems finding one online.
I am trying to figure out if there is indeed a single belt that leads to the pully, or if the previous owner somehow belted up the engine in a configuration that bypassed the AC compressor.
Now, if so, I can live without the AC compressor. However, I need to get my idle down. Honestly it feels like I should just be able to slacken up the throttle cable on the carb a bit. However, the linkage at on the carb does not seem to have any adjustment points to slacken it down.
Any advice?

Froggy1936 · March 21, 2015, 05:06 PM

First dissconect the throttle cable from the carb completly , Then start the veh (May have to open throttle slightly by hand to start) Let it warm up observing the choke operaton It should slowly open as temp comes up . After warmed up idle should be approx 600 RPM You should be able to see any problem that would not allow it to idle down . If the idle speed stop is up magainst the adj screw then most likely you have a vacuume leak . Can best be found by listening thru a piece of extra heater hose. Or use a flamable spray (carb cleaner) Have a fire extiguisher handy . When the idle increases spray has been sucked into the leak . After repair reconnect cable . If the problem is internal in the carb . With a quadrajet seek professional help. As they are very complicated , THey are the very best for all around use when working correctly . But they can have numerous problems . Incl leaking raw fuel straight into the manifold ! Frank

Weblamer · March 21, 2015, 05:56 PM

Did all that, sounds I like I need a carb rebuild.

Just to confirm, there should be no difference in idle speed weather or not the AC pump is connected to a belt?

Froggy1936 · March 21, 2015, 09:07 PM

No, Haveing the compressor operating will not change the idle setting, Though with the A/C operating the compressor will slow the engine RPM from the drag of the compressor operating The only reason for their to be 2 different speeds listed for W/WO A/C Frank

Rickf1985 · March 22, 2015, 12:16 PM

Just check to make sure there is not a high idle solenoid mounted on the carb above the throttle linkage. This was a Chevy favorite and they failed a lot, It will be a round solenoid mounted on the drivers side usually facing front/back with a rod that contacts the throttle linkage. Some were controlled by the A/C controls and they are adjusted with a small 1/4 inch wrench if I remember correctly. A lot of people do not know how to adjust them or do not realize what they are or that they are there. I usually just remove it if it is not working. When it is working correctly THAT is where the idle is adjusted, NOT at the normal idle adjusting screw.

Weblamer · March 22, 2015, 07:16 PM

Well, after fiddling with it some more today, I realized that I can just lightly place my finger on the choke plate and the idle will go way back down to normal.

There seems to be a lot of play on that linkage. Looking at the diagram, I should be able to adjust the fast idle screw to bring it down.

But ill be darned if I can figure out how to get to it. I cant reach it via the doghouse, and from the hood-side there is a big mass of hoses and cables blocking it.

Weblamer · March 22, 2015, 07:19 PM

Rick, I do indeed have one of those solenoids, and it is functional, but it does not come anywhere near my throttle when it pops up.

My throttle linkage seems to be really tight. With the throttle cable off and it totally at rest, it does not come anywhere near the adjustable stop screw.

circleD · March 22, 2015, 09:20 PM

I got tired of my quadra jet and waited on a deal for an Edelbrock 1411. That helped out everything.

Rickf1985 · March 23, 2015, 10:03 AM

If the throttle plate is not straight up and down then there is an issue with the choke adjustment or with the choke itself. If it is coming off most of the way but not all the way I would say the adjustment is off. Are there screws holding the black cover on the choke? If so then someone has changed it before, it originally had rivets and it was common to replace the rivets with self tapping screws so the adjustment could be changed in the future. If you try to just adjust the fast idle and run it that way your gas mileage will be horrific. Not to mention washing the cylinders down with gas, not good.

Weblamer · March 23, 2015, 03:56 PM

No, there are rivits on the electric choke.

I am just going to bite the bullet and buy a rebuilt one off of ebay.

cncsparky · March 23, 2015, 08:52 PM

My preference was to send my original in for a rebuild. That way I know I got the correct carb for my application. If you can do without if for a couple of weeks. Cost was around $200 at Sean Murphy Induction.

TerryH · March 24, 2015, 12:49 AM

There is a lot of info here regarding the difference between rebuilt and remanufactured items when buying over the counter. Suggest you read them. Also various posts that include some recommendations for companies that supply/ rebuild carbs. Starter, alternator are maybe not so critical as a carb. Sending yours in for a rebuild and receiving yours back may be a better alternative.
Search carburetor here and then expand on the search as necessary.
Suggestion only.
Terry

Froggy1936 · March 25, 2015, 10:08 PM

Weblamer read your PM i sent ya Frank

Rickf1985 · March 26, 2015, 07:07 AM

Quote from: cncsparky on March 23, 2015, 08:52 PM
My preference was to send my original in for a rebuild. That way I know I got the correct carb for my application. If you can do without if for a couple of weeks. Cost was around $200 at Sean Murphy Induction.

Second this. I have rebuilt a couple hundred Quadrajets and if it is not done correctly they are junk. I am actually going to buy one from SMI because I do not feel like dealing with the beat up core that I have.

legomybago · March 26, 2015, 02:04 PM

Quote"My throttle linkage seems to be really tight. With the throttle cable off and it totally at rest, it does not come anywhere near the adjustable stop screw.

Sounds to me like your choke fast idle screw is out of adjustment, or is getting stuck on the fast idle cam. Make sure your choke is disengaging and everything association with the choke moves freely. Doing this is a lot easier than replacing the entire carb.....and cheaper.

Weblamer · April 12, 2015, 05:25 PM

Hey all, just an updated.

I went ahead and bought a shiny refurbished carb. Bolted it in and it fired up great. idle is perfect and I do not get any more engine run on.

HOWEVER, it seems I bought a carb that was ever so slightly different from my stock on.

Can anyone tell me what this cable is? (note: not my image) Turns out the carb I bought did not have the linkage for it.

Engine seems to be working fine with it not hooked up.

M & J · April 12, 2015, 06:59 PM

I'd say either kick down for the transmission or more likely for the cruise control.

Weblamer · April 12, 2015, 07:16 PM

Oops, please disregard, saw there was a bolt hole for it so I took the linkage off the old carb and installed it on the new one. All set now.

jimitona · November 01, 2015, 09:43 AM

Quote from: Weblamer on March 21, 2015, 05:56 PM
Did all that, sounds I like I need a carb rebuild.

Just to confirm, there should be no difference in idle speed weather or not the AC pump is connected to a belt?

I have the same rv.
1985 chevy G30 chassis 350 with the same high idle problem.
the high idle problem is in the choke adjustment on the pass side of the 4barrel qjet carb.
loosen the 3 tiny chock screws.
the chock needs to be turned counter clockwise ( as you are facing it from the passenger side)
in order to adjust the fast idle cam between the choke & carb.
clockwise will advance the rpm.
Fast idle cam is the actual problem.
the adjustment depends on personal preference of how high of an idle you want during cold start ups.

Rickf1985 · November 01, 2015, 10:01 AM

What you are adjusting there is the time the choke is on and not the idle speed while the choke is on. There is a separate adjustment for fast idle speed. I am pretty sure they were having a problem with idle speed after the choke was off.