Major Engine Issues: Need technical help / advice

[Hutch998]

I have a 86' k20 with a built 350, th400 with a shift kit. Its got the standard axles with 4.11 gears in them. 35' inch tires and a 4 inch lift kit. As the details suggest, this is a big mud truck. I bought it with a freshly rebuilt engine with less than 300 miles on it. My issue comes in when I'm getting around 4mpg. The carb is an edelbrock 1405 manual choke (600 cfm). I've tried tuning it, which makes no change to how the engine runs, and I've tried adjusting the idle screw, which kills the engine if it goes any lower than 1100. Now obviously this isn't going to get the mpg of a 4cyl, but I'd be beyond grateful for 10mpg. I don't know if thats optimistic, or I'm missing an obvious reason for the mpg. This is the list of things that I recovered from the previous owners rebuild.

Block is bored .30 over- 355

Cam- Comp cam 12-231-2

Bored 30 over flat top notched pistons

crank bearings are -.10 approx.

heads are late model from crate motor. - never modified. Im not sure of the casting numbers yet.

Compression was somewhere above 10.x to 1

Given the little info I have, can someone point me in a direction that isn't going to break the bank? I'm at a loss for things to do other than buy a 500 cfm carb. Even with that I'm not sure if it will help much, if at all. Thanks ahead of time for any advice.

[rich weyand]

That all should work great.  Nice cam choice.  The carb is OK.  Should idle really nice.

My guess on first blush?  The carb and timing tune are both off.

What distributor is on it?  Let me guess.  Some "high performance" POS, right?

[travisr1988]

I would start with timing, find the factory setting and put it there, my truck was 8°, then tune the carb for best vacuum. Once you have it tuned it should run good and idle good. With the baseline established you can now increase the timing of you want and readjust the carb which should be easier with a base tune.

[Hutch998]

The distributor is a Delco Remy? Not sure if that is good or bad, and as far as the carb goes, should I try to make it work? Or switch to a holley? The guy I trust from napa said that a Holley is the only way to go for reliability and decent performance. Also this truck dies anytime it's going uphill, apparently another downside of the edelbrock 600? I appreciate the timing advice, I'll give that a try and see if it helps.

[timthescarrd]

I run an edelbrock 1406 on my DD (basically same but with elec choke and jetted slightly leaner)  with no real issue, get around 10MPG, regularly climb hills with 7-9 grade. 

Your truck should idle around 700 in park and 550 in drive.  Again, timing is probably your issue, and you are having to keep it at 1100 because the timing is off so it's overcompensating and running rich (thus the low MPGs)

The edelbrock only wants around 5PSI of fuel pressure and the mech pump on our engines can produce almost 14PSI, so if there isn't a regulator that could also be an issue.

Finally what altitude are you at? 

[Hutch998]

I'm at about 650 ft. So nowhere near an effecting altitude for carbs. And I knew the timing was likely the issue.

The regulator on the other hand, I had no idea existed? Not to say its not there, but where would it likely be located? I knew fuel pressure could be an issue, but have no idea where to start looking.

If I'm at 1100 in park, do I advance or retard the timing? (clockwise or counter) for simplicity. Or does it just need to be played with? Also when I turn the distributor, if I do it wrong, can it hurt the engine? or am I pretty safe? Thanks for all the input!

[travisr1988]

Ok, so to start off carbs are like cars, everyone has a favorite and says it's best. Now I've known people with edelbrocks who loved them and had no issues, same for holley, personally I use a quadrant which people hate on more so than the edelbrock, but I like it, it runs good now that it has been tuned and is capable of 2 barrel economy while still providing 4 barrel performance. Adjust what you have first then decide if you want to spend extra money on a holley. As for timing usually the rpm climbs as you advance so try regarding it a little, and when you turn the dizzy do so slowly, too much and the engine will stall, if you turn it something like a half turn it will stall and possibly cause damage, it only needs to move a hair at a time. The distance from too retarded to run and too advanced to run is only a few inches of that. That being said as long as you move it slowly and in small increments it is safe to do.

[gunrac]

If I'm at 1100 in park, do I advance or retard the timing? (clockwise or counter) for simplicity. Or does it just need to be played with? Also when I turn the distributor, if I do it wrong, can it hurt the engine? or am I pretty safe? Thanks for all the input!

This part of your question, I just read about this morn.
"Distributor"  Rear mounted, as Chevy is: counter clock for advance.
Front mounted, as Ford is: clockwise for advance.
This might interest you.   http://www.crankshaftcoalition.com/wiki/Timing_Tabs_and_Damper_TDC_Lines_SBC

[timthescarrd]

As travisr1988 said, you probably need to retard the timing some, but consider that your carb has been adjusted to run where it is currently, so you will need to readjust the carb (idle mix) when you adjust the timing.  Best bet is to get a timing light and see where you are at now.

Looking for a pressure regulator, start at the fuel pump, Is it a mechanical one on the block? then trace the line that comes off the fuel pump and goes into the carb, they come in different shapes and sizes so its hard to say what you're looking for, but factory would have just had a solid metal line from the pump to the carb.  When people put in aftermarket carbs, they usually splice into that with rubber hose and add an inline filter.  If you see anything else, it's probably a regulator.

Also, has the fuel filter been changed? it is running a filter I hope

[Captain Swampy]

I'm not familiar with this carb, what it available to tune it? Jets,pump cam, or what? Maybe the previous owner changed jets or something. Can you find out what it came with originally and compare whats in it now.

I also thought I read somewhere that high volume oil pumps can keep some hydralic lifters pumped up enough they don't let the valves completely shut. Try backing the rocker arms off a bit. Have you checked your engine vacuum at idle?

[Hutch998]

I know the carb is going to need to be retuned as is. I tried tuning to fix a high idle which in all likeliness is a vacuum or timing issue, not the carb itself. I got carb clean to find the vacuum leaks, and I think I can get a timing light from family.

Also as a boost in knowledge, I recently figured out my choke (manual) is fully closed, and must remain so to keep the engine running. Opening it at all results in the engine bogging or dying. I'm assuming this must mean there's a vacuum leak?

I will also check for the pressure regulator this weekend, and will get back to you guys. As for the fuel filter, yes I do have one, and yes its brand new. I will follow the inlet of that to see if theres a regulator. It is connected via rubber hoses, so I'm thinking there's a good chance it's on there, or it would be easy to hook one up. I really appreciate all the help everyone has been able to give me, as well as the validity your advice has had. I work at a chevy dealership, and talked to the master tech about this, he said basically the same thing you guys did. Check for vacuum, and he told me to advance the timing to 13 degrees at 3500 rpm. I'm going to try this all and will return with results! Thanks again!

[timthescarrd]

13 degrees at 3500 rpms? no way.

your initial setting should probably be around 10 BTDC at 700RPM
an SBC distributor should be all-in (mechanical wont advance any further) between 2500-3000 rpms usually around 32-34 degrees.  This should be done with the vacuum advance disconnected and the line plugged.

[rich weyand]

^^^ except you don't have to plug the line just to set timing.

If that is the 1986 distributor and the engine has been carbed with an Edelbrock and the pollution stuff removed, it has the wrong advance can.  Look down between the distributor cap and the advance can with a flashlight and read the numbers stamped on the arm of the vac advance module.  Report that back.

Best bet is to swap the vac advance can for an AR23/Echlin1853.