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Discussion Starter · #1 ·
First I'd like to apoligize for making my first post a "Help Me" post. Kinda rude but I to just get to the point.

I have a 89 chevy 4x4 with a drivibability issue, which is: The truck (5 speed manual) will pull good in first and second, but when I shift to 3rd and give it any amount of gas it falls on its face/backfires and has no power. It will do this in any gear above second, and even the first two gears seem lacking from what it should be. What I need to know is if my combination just doesn't mesh or if I have a timing issue, or anything else you guys can think of. The build is as follows:

400sbc .040over, speed pro 4-valve releif flat top pistons, moly rings, Comp Extreme energy 4x4 cam cl12-243-3 270deg/278deg @ .480/.498 lift, pro comp aluminum heads 2.05/1.60 valve 215cc runner cnc ported 64cc chamber strait plug, comp +.100 push rods .080 thickness, comp 1.5 pro magnum roller rockers, weiand action plus intake, edelbrock 750cfm performer carb, stock fuel pump(running around 5psi), shorty headers, jegs off road y-pipe into 3inch with a thrush vortex muffler, stock HEI

Trans is a NV4500 5-speed and has 3.73 gears with 33x10.5r15 tires.

We had the same setup minus the aluminum heads and pushrods(preveiously it had a set of 92 5.7 heads with 220k miles on them) and the truck ran fine as far as no backfiring it just blew smoke because of the crappy heads. My brother bought the heads with plans of changing to a more agressive cam but then gave me the whole set up for my truck.

I think we have a little over 12deg timing... but this is the first we have messed with aluminum heads and I think I read somewhere that that changes where you would want your timing?

I also know that the carb is probably a bit big for what we have but it was on the setup before with the crap heads and it would at least function without backfiring.

so with that wall of text i'm hoping someone can give me some insight on where to start to get rid of the backfiring and lack of power.

Thanks!
 

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Faith - Respect - Trust
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I'm not an engine guru like many guys here on the site but could you have a vacuum leak? Lack of power under load, back fire, do you have a vacuum advance on the distributor? That would effect your timing.

Ray
 

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Discussion Starter · #4 ·
Vaccume is in the green on the guage. Wires are good/no miss at idle and goes good in first and second. starts backfiring when it has to work a little harder because of the taller gears in third.

not hearing any lifter noise and I think tht would show up on the vaccume gage(?) and cause a miss.

Could be timing related possibly... Not sure where it should be set at with this set up.
 

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You could try advancing the timing, with the modifications I wouldn't know what to set it at, but, you could try this, put it in gear with your foot an the brake...get it to rev at at about 2000 RPM and advance the timing until it starts to ping, then back the timing just a little...this is by no means the proper way to set your timing for your engine but, if it works than you know that timing was an issue. Questions like degreeing your cam and things like that I'm sure will come into play when the guys that know try and help.

As I mentioned earlier, if you have a vacuum advance distributor and have a vacuum leak it could cause this effect...even though your vacuum is in the green, you would need to check the vacuum going to your advance and if it is , is your advance working as it seems to give you the problem under load
 

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Discussion Starter · #7 ·
Advance is hooked up, and the line going to it is hole free. We have messed with the springs in the distriburator a little trying to get better results. not much luck. There is no lock out installed... might sound dumb but is that something you buy or something you modify?

The carb is a manual choke and we have tried to richen the mixture... no wideband to test the air/fuel though.

The fuel pump was kickin out about 8 or 9 psi at idle so we put a regulator on it... not sure if that disproves anything or not, but it is a stock mecanical pump, not sure why it is putting out so many psi.I may hook up the eletrical pump again to make sure its not fuel pump related.


Thanks for all the replys! Hopefully we can get this thing figured out before we get too much snow!
 

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If you slowly accelerate and shift into 3rd gear,coast for awhile the hammer it,does it instantly fall down or is it ok for a few seconds?
I think hcompton is on the right track
 

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WFO
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First I'd like to apoligize for making my first post a "Help Me" post. Kinda rude but I to just get to the point.

I have a 89 chevy 4x4 with a drivibability issue, which is: The truck (5 speed manual) will pull good in first and second, but when I shift to 3rd and give it any amount of gas it falls on its face/backfires and has no power. It will do this in any gear above second, and even the first two gears seem lacking from what it should be. What I need to know is if my combination just doesn't mesh or if I have a timing issue, or anything else you guys can think of. The build is as follows:

400sbc .040over, speed pro 4-valve releif flat top pistons, moly rings, Comp Extreme energy 4x4 cam cl12-243-3 270deg/278deg @ .480/.498 lift, pro comp aluminum heads 2.05/1.60 valve 215cc runner cnc ported 64cc chamber strait plug, comp +.100 push rods .080 thickness, comp 1.5 pro magnum roller rockers, weiand action plus intake, edelbrock 750cfm performer carb, stock fuel pump(running around 5psi), shorty headers, jegs off road y-pipe into 3inch with a thrush vortex muffler, stock HEI

Trans is a NV4500 5-speed and has 3.73 gears with 33x10.5r15 tires.

We had the same setup minus the aluminum heads and pushrods(preveiously it had a set of 92 5.7 heads with 220k miles on them) and the truck ran fine as far as no backfiring it just blew smoke because of the crappy heads. My brother bought the heads with plans of changing to a more agressive cam but then gave me the whole set up for my truck.

I think we have a little over 12deg timing... but this is the first we have messed with aluminum heads and I think I read somewhere that that changes where you would want your timing?

I also know that the carb is probably a bit big for what we have but it was on the setup before with the crap heads and it would at least function without backfiring.

so with that wall of text i'm hoping someone can give me some insight on where to start to get rid of the backfiring and lack of power.

Thanks!
The carb has to have the correct step up springs to match the amount of vacuum the engine makes when it is under a load. Refer to the Edelbrock Owner’s Manual for that. Edelbrock sells a tuning kit w/the parts needed to adjust your carb to most any application.

The initial timing may need to be advanced from where it's at, but if you add initial timing you must be sure the total timing (initial plus mechanical) doesn't go too high or it'll detonate (ping) under a load.

More on timing can be read here.

I would try the vacuum advance on manifold vacuum (full time vacuum in other words). It may give too much advance. The use of a limiter device is in the link above.

I tend to think it's not the fuel pump, but it is possible. You can show good pressure on a fuel pressure gauge but still have a lack of volume. If you haven't tried this set up without the pressure regulator, try it- some regulators are very restrictive. If you have an electric pump that worked before, by all means try that.
 

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Read the article Cobalt327 provided a link for. To me it sounds like it is advance related. You say you changed springs in the distributor they might be too weak. Most of the time you can use 1 light spring and a medium spring. Get a Crane PN #99600-1 vacuum advance kit. Start with two blue springs. Unplug the vacuum line from the distributor and plug it. When checking, have someone hold the rpms at 3000-3500. Set the advance on the timing light to 36* and the mark on the balancer should align to zero. Then zero the timing light advance. Check the timing at idle. You will want your advance curve to start at about 800 rpms and to be all in by 3000 rpms. Make sure that the weights are not sticking, clean and polish them if necessary.
 

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Discussion Starter · #14 ·
Thanks for the links and other information guys! Looks like I have a lot of reading to do. I think i'll buy a limiter plate and the crane advance kit and try and dial in the timing.

"If you slowly accelerate and shift into 3rd gear,coast for awhile the hammer it,does it instantly fall down or is it ok for a few seconds?" I will have to try this and get back to you!

I will more than likely switch back to the electric pump also just to eliminate the fuel pump as the problem.

Fuel filter was one of the first things to get changed. =)
 

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Discussion Starter · #15 ·
The regulator that I am running now is a mallory 3 port competion regultor(return style) PN 4309. I'm going to hook up the electric pump when I get a chance and see if that cures some of my issues. The more I read on setting timing and what-not the more I think I need to address that as well.

Thanks again for the links and info! If you guys have any other helpful links on this stuff feel free to post em. I have no problem reading and I am new to the carburated world, and my brother works weird hours so it looks like if this truck is gunna get dialed in, its going to take effort on my part too. =)
 

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Cam has 226 int./234 exh. @ 0.050" lift and needs no where near 26 degrees initial. Start around 16-18 degrees initial and work up from there.

Generally it is better to get the timing worked out, then go on to carburetion- as long as it's running well enough to set the mechanical (should be all in by about 3K rpm).
 

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Discussion Starter · #17 ·
Well I finaly got some time and messed with the fuel system. Hooked the electric pump up and now I have a solid 6psi. Now when I drive it it still backfires in third and higher gears, but it has a LOT more power. I havent messed with the carb settings since changing the pump(it was 30 degrees outside) and I still think the timing is off, but so far there is marked improvement!
 

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Discussion Starter · #18 ·
I foregot that I had put a distriburator on it from e-bay. Not sure if that makes it better or worse

SBC BBC Chevy 65K Red Hei Distributor 6501 R | eBay

not sure how good of quality it is. It was in another motor and that one didn't have any problems other than being tired.

What am I looking for on the plugs? I had em out today and they were kinda black. They were new when we put the motor together.

are you thinking I have too much timing and that is why I am setting it a 10deg?
 

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Depending on the distributor that was on it, that could have made all- or none- of the difference. That's why it's a better idea to make ONE change at a time, so you know what helps and what doesn't.

In any event if it's running better, something caused it and that's a step in the right direction.
 

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Discussion Starter · #20 ·
oops, I was kinda unclear. I ment when we put the motor together we put the ebay distriburator in it. Its not a recent thing I have done while trying to troubleshoot the problem.
 
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