1slowta

This is going to be kind of long i'm sorry in advance especially because the information is a little scattered but i want to give as much information as possible. 1st the car is a 92 camaro rs with a 5spd. I had problems with it constantly loosing the fuel pump(if you've had to change one i'm sorry) after about the fifth time I decided to go to a carb with mechanical fuel pump. In fact I built a whole new engine. it's a 2pc seal 350 with an aftermarket vortec head, forged pistons, lunati voodoo hydraulic flat tappet cam roughly .500 lift. the distributor is a hei vacuume advance summit brand. carb is a 750cfm vacuume secondary quick fuel technology slayer series. Also to mention i am at 5000ft elevation. I am having major driveability problems. I had a wideband til it lost power and fried the sensor. o.k so the problem if i nail the gas it sneezes through the carb and falls on its face. The carb is brand new and was running extremely lean out the box. I jetted it up and changed the squirters to help this. My afr's are now still a little lean 13.1 under throttle need to get bigger jets still. I could have multiple problems but things i've noticed the gas tank still builds a ridiculous amount of pressure, sounds like the gas is boiling and after i shut the car off the gas in the fuel filter continues to bubble almost to the point of a rapid boil. the car also surges under power almost seems ignition related the way it comes in and out. I've checked for fuel leaks and i cant find any! There is a pinhole in the filler tube from taking the tank out so many times. I've eliminated exhaust heat as a culprit for the boiling tank as i just left it off where the y pipe came into the cat. vacuume guage reads a steady 11 inches of vacuume again 5000ft elevation. timing was set at 34 degrees total and i've moved it every which way. I've checked for vacuume leaks used brake cleaner not sure if that'll work but didn't make any difference. fuel psi is regulated at 6psi. Plugs is something i know nothing about I know they are autolights not sure of the heat range or gap to be honest dont even know what a good starting point is. i will pull 1 tonight to find out and see how it looks. My biggest concern right now is the sneezing through the carb. It only does it when i punch the gas and it's really bad if im in second going like 10 mph. actually throws flames out the air cleaner. When i 1st put the motor together I lost the cam due to the 6.5 power valve just flooding the motor. This problem doesn't seem the same and i prey its not another cam. The heads were set up by the machine shop for the cam bt the way! I will try and get a video tonight and post it on you tube. If I have confused you i guess my questions are what can cause the carb to sneeze when i nail the gas. Also always seems to lose power if i power shift it. If i roll into it seems much better but still surges at the 4-5k rpm range. This motor does not feel it has the power it should then again i probably have high expectations for it.. what things do you need to know to help diagnose this? Like I said i will try and get a video up might have to wait until this weekend but please help i'm about to just dump this thing for nothing and take my losses!!!!

zed-028

retracted all my previous questions - the flames shooting out the carb still indicate to me that the timing is off

what fuel are you running?

1slowta

i live in reno get 91 octane only. Altitude should help me with detonation at 5000ft! Not sure of the cylinder head chamber cc but if 67cc I should be at 9.7:1 compression. the chamber is a vortec design. Its weird you say that because when timing i just listened to it and turned the distributor until it quit adding vacuume on the vacuume guage. Checked the timing and it was 30 degrees initial timing but the motor seemed happy. I didnt really drive it that way seems sketchy. I played with the carb so i could make it idle when i set the timing down at 12 initial but the motor doesnt seem as happy. How much timing is to much when it comes to more performance but not boost. I really dont want to hurt the motor again.

zed-028

well the fact that this thing is modded out means you can throw any ideas of stock timing out the window. You will basically be incrementally advancing it until it pings then back it off until it stops.

am i right in guessing its American Spec 91 with 10% ethanol?

zed-028

if youre getting backfiring out of the carb that means that at some point of the duration of the stroke you are copping ignited fuel back out the intake, through the carb and igniting the fuel. try to work your timing into at least eliminating that flamethrower and youll be on the right track.

The idle might sound worse but with all the work done to it, its sure as hell not gonna sound like a stock idle

1slowta

also back to the carb bought new 6 months ago and i've just gone up in jetting and squirters for off idle and under throttle lean. I have the biggest squirter in the holley trick kit in it and it seems weird at my elevation with a small block and a 750 that im fighting a lean condition. Carb out of the box my afr were dropping all the way to 18:1 pretty much with medium throttle acceleration.

pancherj

Seems to me that you may have three separate issues:


1) Your timing is off. Make sure you set the timing with the vacuum plugged and the idle as low as possible with the engine warmed up. With a more aggressive cam, the car may want 12-18 initial advance. Start at 14 and then plug in the vacuum to a manifold source (so it is pulling vacuum at idle). See where the timing goes to. Something close to 40 degrees is not unheard of. Lastly, check to see where the full mechanical advances takes you to. I would keep it at 34 or less. YOU MAY NOT BE ABLE TO DO 14 INITIAL AND STILL MAINTAIN 34 MAXIMUM. It all depends on how much mechanical the distributer allows. There are ways to limit it.


2) The stumble when you step on it is most likely the timing and also the pump shot. fix the timing first and then check to see if the stumble went away. If it didn't, you need to make sure the pump arm is activating with even the slightest move of the throttle. A touch of the throttle should cause a squirt of gas.


3) Is there a disabled electric pump still in the stock tank that you are trying to pull through with the new mechanical pump?

MSgt Luttrell

I would suggest setting the total timing, to 34 degrees at 3400 rpms, with the vacuum advance disconnected and plugged. When you have it set to 34 degrees at 3400 rpms, it should drop back down to around 14 degrees at idle. After setting the timing this way, connect the vacuum advance to manifold vacuum, which will help that engine burn the lean mixture at idle, keeping the plugs from fouling so easily.

If after doing this you still have a fire ball coming out the carb when you hit the gas, you have a valve train issue that's causing an intake valve to hang open or you have a lean air condition because of improper squirter set up on the accelerater pump.

1slowta

Alright this weekend I will play with the timing and let you know how that goes. Also I did remove the electric pump in the tank that's why I don't understand why it's building so much pressure. I will get a video and let you guys know how it goes

pancherj

The tanks don't vent through the filler neck like they did on older cars. These cars had an EVAP system. Find the line coming from the tank and put a small fuel filter on it. This will let the tank breathe and also cut down on some of the fumes.

1slowta

Alright update. Timing was the spitting out the carb. Found a spark plug that was pushed closed also. Car is running way better but I still have a nasty miss when I power shift the car. Whether I lift on the gas pedal or not. It's worse in 3rd gear then 2nd gear any ideas on that. I was thinking the squirters in the carb but it does it if I no lift shift also. I now have timing set at 22 initial 36 total. I changed the springs in the distributor to the medium and light spring. I also ran a compression test and only have 120psi cranking. My Cam is. 500 lift I'm starting to think I should put a smaller Cam. My power brakes work and everything. I have vortec heads with speed pro flat top pistons. Shouldn't I have more cranking compression?

1987L69

Did you do your compression check with the gas petal floored? if not you will get lower readings like 120 ish. I would still pull more timing out of it, and the first thing I would do is put the heaviest springs in the distributor till you break the engine in, IE 500 or so miles, then worry about getting more timing in the engine. If you get a good, stable idle and can drive the car without it knocking, pinging, dying, or backfiring, after that your can tune it from there with timing and what not, dont expect a HUGE hp increase from a fresh engine, it has to break in and loosen up. do it right and conservative and you will have a very happy engine for many years

1slowta

I didn't hit the gas while doing the test so that's good news. I have no detonation with those springs just a bad miss after I powershift it. If I shift normal no miss. I'm going to have to make a video cause it's hard to explain and if I can't explain it how can anyone help diagnose it. I have the car at my apartment so maybe I can get one tonight. Depends on what time I get off work. I love Monday's

1987L69

Monday's huh, this was what I was doing a few weeks back........

pancherj

When you no-lift shift, the squirters aren't coming into play at all (because the throttle isn't moving). It is likely a lean miss. Do you have an O2 sensor you can watch? If not, I would go 4 bigger on the jet sizes to see if it goes away. This is just a test! If it works, we can tell you the correct way to fix it (and return the jets back to where they were).