Author Topic: tunning 350 c-10 and choke?  (Read 2899 times)

Offline Metal Man

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tunning 350 c-10 and choke?
« on: May 26, 2014, 10:39:38 AM »
quadrajet ID #17080204 (not original to truck)
I am running stock exhaust system with a catalytic converter.
EGR
Stock iron intake. (one crossover port blocked / one open crossover port.)
"high performance" ignition curve in HEI. 36° all in by 3000 RPM. Limited vac advance to 16° . Manifold vacuum
4.5 PSI
350 engine
Cam is a stock truck cam. (photo attached on cam)
350 automatic trans
2:73 rear end gears
31" tall tires.

I seem to have it tuned correctly for the most part but I seem to be a little lean coming off idle. I say lean because at idle I am reading 12.5  A/F  on a edelbrock narrow band meter. I have tuned idle with a vac gauge and tachometer.
When leaving a red light I get a VERY SLIGHT hesitation and the lights on the meter go out then its fine and smooth and the meter lights come back on. Then I am reading about 13.5-14 A/F at 70MPH. No black soot in the pipes.
Any ideas?

I also need to set up my choke correctly. Is the choke supposed to work in the summer also? With temps in the 70-80° area. I press the throttle to the floor and turn the ignition on and the engine turns on at idle RPM.

I want to tune for maximum fuel economy which is basically STOCK. I believe I am pretty close but dont know if my ignition curve is asking for some thing a little different.
Thanks


Offline ejowrench

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Re: tunning 350 c-10 and choke?
« Reply #1 on: May 26, 2014, 03:21:27 PM »
I saw a dyno test session where the power level and economy improved greatly with a good low restriction dual exhaust with stock manifolds.  If you have the pellet type of converter, get rid of it and get two honey comb type with some stainless steel Flow masters 50 series mufflers.[my preference]. Do you have a good timing light?

Offline Metal Man

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Re: tunning 350 c-10 and choke?
« Reply #2 on: May 27, 2014, 05:33:31 PM »
I dont think its a pellet type , looking down it it was like a honeycomb see thru. I am not really looking for loud exhaust so that out of the question. Yes the timing  light is a dial back light .

I did get the choke working correctly

Offline Cliff Ruggles

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Re: tunning 350 c-10 and choke?
« Reply #3 on: May 28, 2014, 02:26:03 AM »
Are you using an electric choke, or hot-air?

What jets and metering rods are in the carburetor?

Did you install one of our kits?  If so, what float height?

Why is the exhaust cross-over blocked on either side?  A cold intake will require a LOT more fuel from the carburetor for best engine performance, and it will take a LOT longer for the intake to warm up so the engine runs efficiently......Cliff

Offline Metal Man

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Re: tunning 350 c-10 and choke?
« Reply #4 on: May 30, 2014, 03:22:43 PM »
Are you using an electric choke, or hot-air? Electric choke . Choke is working correctly now.

What jets and metering rods are in the carburetor? Main jets are #75 and the metering rods are #41<

Did you install one of our kits? No , should of started there If so, what float height? Float height is set at 1/2"

Why is the exhaust cross-over blocked on either side?  I was having issues with the fuel bowl boiling over to the point of lowering the float to 1/2" and installing a 1" phenolic spacer. I left the side furthest from EGR open ( plate with 1/2" opening) to still allow heat to pass under carb. I am in TX and summers here are 110+ also.  I do realize NOW most of the heat issues I was having was do to running the engine on the lean edge creating the hot exhaust. I am going to remove the 1" spacer and go back to the 1/4" factory gasket. At this point also the intake has burned off the paint on the intake furthest from EGR at crossover area so there is still some heat there.

Offline Metal Man

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Re: tunning 350 c-10 and choke?
« Reply #5 on: May 31, 2014, 09:11:33 PM »
Some extra info :
84 c-10 short bed
350 "hecho en mexico" low compression crate engine Heads: Cast Iron, 76cc
Valves: 1.940” / 1.500”



I am also looking at getting rid of the spacer if it will help with fuel economy and will need to purchase those parts and gaskets for that from you also.

Offline Metal Man

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Re: tunning 350 c-10 and choke?
« Reply #6 on: June 01, 2014, 10:59:24 AM »
I adjusted the float level to 3/8" to see if it would make a difference but did not see any change.
I also disconnected the EGR and took it for a drive. Heres what I came up with while using the narrow band meter.
12.5 @ WOT
13. @70MPH slight load, uphill on highway
13.-13.5 @70MPH no load, but the meter is "fluttering" off and on also. I am thinking the metering rods are going into jets at high vacuum(leaning out at no load)

Meter goes lights out at cruise, 45 MPH, but at the slightest movement of throttle the lights come on( seems on the edge of lean)

This is reading the meter no complaints with engine operation through power band. Engine runs smooth, at idle, cruise, and WOT. Off idle acceleration is now smooth also. 

Offline Cliff Ruggles

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Re: tunning 350 c-10 and choke?
« Reply #7 on: June 02, 2014, 04:07:25 AM »
Those engines have had open exhaust crossovers in the intakes for decades with no negatives anyplace.  Most like flooding in lieu of "boiling over".  That comes from using over the counter parts, which are low quality and never the right parts.  Compensating with a low float setting is not the answer, as fuel level in the bowl effects the fuel delivery to the engine (tune).

Blocking off the crossover(s) also create tuning issues, as the intake will eventually heat soak anyhow, but it just takes a LOT longer, and in really cold weather it will run very poorly, and even "ice" up.

Tuning should be done to achieve best results in all areas, instead of chasing a meter around.  I'd put a piece of tape over it, tune for best idle, off idle, light/heavy/full throttle, then take a gander at the meter to see where your "base" settings are at.  A little fine tuning either direction from there and watching the meter is OK.  These engines have a pretty broad range of A/F they will tolerate, want and need, as some as just a LOT more efficient than others.

Don't forget distributor tuning, it is equally as important as the carburetor, and will allow for leaner mixtures at light throttle cruise, etc.....Cliff