The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 01-12-2010, 03:21 PM   #1
vtwinsport
Registered User
 
vtwinsport's Avatar
 
Join Date: Nov 2008
Location: edmonton, alberta
Posts: 293
Carb tuning eh?

Hey all,
Got a question. Here's some background;
1. rebuilt 350 in in a 76 C10, th350 trans, edelbrock 2101 intake, edelbrock 1406 car, hedmann headers into new duals and pipes, msd streetfire diz with vac.
2. been tuning the carb, timing, and vac (ported and manifol) for months now.
3. have had timing as high as 14 down to 2 and was most recent at 12 btdc, at 12 and anything above 6, exhaust spits out water on ground and plugs read tan and clean, with vac at manifold and mileage is about 6-7 mpg
5. now is set at best operation with timing 4 btdc, vac at ported oulet and water from exhaust has stopped, plugs read mildly sooty but performance is all round better including pickup and mpg is closer to 10-12

First question, was that fuel coming out my exhaust? it didn't smell really gas like.

Second question, better mpg with mildly sooty plugs? Is that possible? Isn't it running richer with the soot?

Thanks in advance for all comments.
greg
__________________

76 Silverado, 2wd, long box, 350/th350, 3.42 posi, edelbrock performer 64cc heads, edelbrock 1405, 2101 intake, Hedman Headers, Comp Cam XE262
http://beerbreadbike.wordpress.com/

Last edited by vtwinsport; 01-12-2010 at 03:22 PM.
vtwinsport is offline   Reply With Quote
Old 01-12-2010, 03:41 PM   #2
Damien
Registered User
 
Damien's Avatar
 
Join Date: Mar 2007
Location: Farmington, MN
Posts: 928
Re: Carb tuning eh?

Water is a byproduct of the combustion of gasoline and oxygen, so that is fine. There is also some condensation in the exhaust due to temperature fluctuations.

With having the truck run a little rich, you are making more power as you stated. With the more power, you do not need as much throttle so you are saving gas. If you run the engine lean and it is struggling, you are going to need more throttle to get up to speed, and therefore need more fuel.
__________________
I can still count my vehicles on two... wait three hands.
Damien is offline   Reply With Quote
Old 01-12-2010, 03:44 PM   #3
ChevLoRay
Old Skool Club
 
ChevLoRay's Avatar
 
Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
Re: Carb tuning eh?

On my '69, there was a 1406 (manual choke, right?) atop an adapter on the OEM Q-Jet manifold. It had Hooker headers and an HEI with an RV camshaft. Beyond that....nothing out of the ordinary.

But, it ran rich....rich enough to bring tears to your eyes/nose if you were standing in the exhaust stream. Nr. 1 plug would gas-foul every few weeks. The oil was diluted from the the excess gasoline washing through the cylinders. Timing was set at 10BTDC, I believe. I did have to replace the vacuum advance because the old one wasn't working (used one intended for a Vette that was recommended in a magazine I read).

I finally bought an Edelbrock 2101 Performer intake and an Edelbrock Q-Jet. I had to add a heat shield to the starter because the new intake/carb ran so much leaner that the heat soak from the headers made hot starts a problem.

In my opinion, if you have it tuned and running like you like, it starts easily and gets decent mileage w/o oil dilution, you should be good to go. As for the liquid you see/saw from your exhaust system...it's condensation. As far as the exhaust system color goes, we used the term "chalkin' the pipes" to indicate a good, lean-running engine. It wasn't something you saw if you were driving in town, but would be apparent after some highway running.

www.edelbrock.com should have tuning technical help available if you have any questions.
__________________
Member Nr. 2770

'96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed.

'69 C-10 SWB; 350/TH400 - in limbo

The older I get, the better I was.
ChevLoRay is offline   Reply With Quote
Old 01-12-2010, 06:37 PM   #4
spinem
haha, ford guys...
 
Join Date: Feb 2007
Location: Visalia, CA
Posts: 576
Re: Carb tuning eh?

vacc leak.
spinem is offline   Reply With Quote
Old 01-13-2010, 09:50 AM   #5
vtwinsport
Registered User
 
vtwinsport's Avatar
 
Join Date: Nov 2008
Location: edmonton, alberta
Posts: 293
Re: Carb tuning eh?

Damien, I understand the water as a bypoduct of combustion but wouldn't there still be water out the exhaust even if it was richer?

Chevloray, yeah I have had to install a spacer to stop the heat soak and was replacing plugs regularly every two weeks due to white ash buildup on the plugs. May have a mild intake leak. Oil seems fine so yeah, I may leave it as is until spring.

Spinem, how do you think a vac leak is affecting things?
I do have some problems with idle tuning that make me think of a vac leak. For instance, when setting idle, has to be around 850 to keep from stalling in gear.
I was thinking this might be transmission vac modulator or torque converter issue or the possible intake leak I mentioned above, as I have checked for leaks in every other hose including brake booster.

thx
__________________

76 Silverado, 2wd, long box, 350/th350, 3.42 posi, edelbrock performer 64cc heads, edelbrock 1405, 2101 intake, Hedman Headers, Comp Cam XE262
http://beerbreadbike.wordpress.com/

Last edited by vtwinsport; 01-13-2010 at 09:51 AM.
vtwinsport is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 01:24 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com