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-   -   new rebuild sbc runs great in the driveway but... (http://www.hotrodders.com/forum/new-rebuild-sbc-runs-great-driveway-but-41375.html)

gawdzilla 06-12-2004 12:12 AM

new rebuild sbc runs great in the driveway but...
 
as soon as I take it out it starts acting up.
I'm really frustrated with this thing. I rebuilt the carb. seemed ok sittin in the driveway. Idles fine, revs fine. Real smooth. take it out- goes about a mile and starts stumbling again. Then it idles rough. So I come back and look for vac leaks. find w/my starting fluid it seems to pick up around the carb base - but this is a new gasket. so I cinch it down just a bit. Still revs w/fluid but not as much. Also I noticed the bolts on my intake mani were a bit loose too- so I cinched those down "wrist tight" since apparently my cheapo torque wrench lied to me. Tomorrow when I start it up again it'll probably act fine.
checked the fuel filter, it's clean. Thought maybe it's the fuel tank solenoid actin up and causing some fuel starvation, so I bypassed that. Still does it.
I'm out of ideas, and don't even know what else could be causing this.

DoubleVision 06-12-2004 12:29 AM

Sounds a whole lot like my car a while back, which was a fuel pressure problem, what is your fuel pressure set at? A test you can do is this, remove the air cleaner, start the car and let it idle, as soon as it starts running rough, shine a flashlight in the carbs throat and see if fuel is coming out of the boosters, if you have a site view float type carb, check the float level and see where it`s at.

gawdzilla 06-12-2004 12:34 AM

it's a manual pump and an edelbrock 1407. I checked the fuel volume and it pumps good, but I'll try what you suggested tomorrow. I was wondering the same thing actually which is why I bypassed the other tank/fuel switch completely (didn't help). My floats are set to offroad specs (7/16" above gasket). Accelerator pump is on the shortest throw.
would that problem still exist though if after it starts running rought it continues to do so at idle for severa minutes?

DoubleVision 06-12-2004 12:44 AM

What my car would do first is the idle would start fluctuating up and down, and right afterwards, fuel would pour out of the boosters, the car would still idle, but real rough. Eddy carbs don`t like over 5.5 psi fuel pressure. When the car goes to idling bad, if you see no fuel flooding out of the boosters, check the exhaust for black smoke, the clue is the same. once my car got to the point it flooded it didn`t stop, I got a gauge for it and the fuel pressure was 14 psi, and with a STOCK pump, never seen anything like this, I later traced the problem down to the gas tank vent line that used to be connected to the carbon canister, I had blocked it off, and once the pressure in the tank built up, it would jack up the pressure since the air had no where to escape to.

gawdzilla 06-12-2004 12:49 AM

well you definitely gave me somewhere unique to look! I did have quite a bit of pressure in the fuel line when I disconnected it before I rebuilt the carb. I just redid the gas tank (pulled it, pool acid wash) and I know the vent line is free and clear. I'll look for black smoke too...my gut still tells me it's trying to run too rich or somethin. Right now it's 2 turns out both sides.
Before I rebuilt the carb I remember now that when it did this I messed w/the idle screws and it settled down- when I had them about 3.5 turns out each. Then when I went to start it again it did the same thing later.

tresi 06-12-2004 11:44 AM

Several things. I don't think your torque wrench lied, it's normal to have to retighten the manifold bolts after a few heat cycles. Are your step up pistons and metering rods able to move freely. If you have a big cam and stiff step up springs there may not be enough vacuum to pull the metering rods down ito the jets at idle. Did you ever completely fix the vacuum leak? If not you may have the same problem as the big cam problem. By the check for vacuum leaks with WD-40 instead of starting fluid. The engine will thank you for it.

gawdzilla 06-12-2004 05:04 PM

it's all a very stock build. stock cam. HEI dist. Edelbrock 1407 750cfm carb. about 2 turns out each side. Last vac reading after tuning was 17 steady, almost rock steady. Somehow my timing had worked it's way pretty advanced too so I made sure my dist was tighter this time. vac leaks using WD 40 (thanks!) showed no leaks.

I THINK I'm on to tracking down a fuel line vacuum issue, as in 1) return line was blocked off- I replaced all filters and ran a return to the solenoid port (dual tanks). Runs better so far but I ran out of gas around the corner. D'OH!
I have rubber line to metal line (about 1') then 4' of metal line then 4' of rubber line from there. How much rubber line is too much? I'm wondering if it's sucking the line shut.
at this point it seems better, in fact when I put more gas in after running out around the corner it seemed real happy, but haven't been out again yet.

tresi 06-12-2004 06:38 PM

It's always best to limit ruber fuel line but even if you had 15' the fuel pump shouldn't suck it shut as long as the the fuel pick up isn't blocked. Have you tried to lean the idle out yet? With a stock cam you should be pulling a little more vacuum. Unless your living at a high altitude you should be able to get more than 18" of vacuum.

gawdzilla 06-12-2004 07:47 PM

I just changed out the fuel vent line...the vent lines were switched on the solenoid. I have 17" of vacuum right now at 9* advance (w/the vac advance connected).
if I lean it out it doesn't like it - gets a little shudder-ey.

the return lines were it. straightened those out, made sure they were all in the right places and fixed a too tight bend.
thanks guys. Now I'm hoping adjusting the accelerator pump will solve the stall off a stop.

killerformula 06-12-2004 07:51 PM

Does the shaft for your throttle plates go through the body of the carb? Lots of rebuilt carbs suffer from air getting through that hole in particular-

K

gawdzilla 06-12-2004 11:23 PM

solution
 
yeah it does go thru.
problem solved- combination of adj. timing, fuel/air mixture, and proper return venting.
I'm on to locking hubs and DIY exhaust....

thanks again all!


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