weber problems

gestalt1 · 11-20-2013, 09:02 AM

Hi, I am at my wits end. I built a 3.2 short stroke with weber 46 carbs that a freshly rebuilt. i got it running fine - not perfect but good enough to idle and throttle fine. today i needed to get the car started and running to pull it onto a transport truck to deliver the car to the new owner. I got it started and idling but as soon as i touched the throttle it dies. i got it better but once it is put in gear and the slightest load put on the engine and it dies. after 4 hours of tweeking i could not inmprove the situation and had to tell the trucker that i will need to re-schedule. any ideas? fuel pressure? mixture screws? the floats have gas in them and the accelerator pumps pump gas into the cylinders.
thanks

Joe Bob · Joe Bob's Garage

Fuel pressure, filter, jets...

gestalt1 · 11-20-2013, 12:07 PM

Thanks Joe, I ordered a pmo pressure regulator and a new filter. hopefully that will solve it.

911pcars · 11-21-2013, 12:20 PM

Weber carbs only need 3.5-4psi fuel pressure and enough volume.

Sherwood

gestalt1 · 12-01-2013, 08:04 AM

Hi all, I really need some help. it still will not start. here is what i have done:
replaced fuel regulator with PMO unit and set pressure to 3.5 PSI
new fuel filter
cleaned idle circuit/jet and accelerator nosels on carbs
adjusted mixture screws to 2 turns out, idle stops to 1/2 turn in from touching shaft.
replaced battery with high amp battery.
put fresh fuel in
changed all plugs twice
did compression test - 175psi average
checked plug wire routing, adjusted magnetic pickup gap

here is what it does: cranks fine, sounds like it might catch but never does. there is combustion happening but not enough. the electromotive hpv is set at 10 INIT, 10 3000k and 10 at 8000k.
i checked the impedence of the sensor and it is 7 ohm - where it should be. the one problem i see is that the plugs are getting fouled. any help would be appreciated.
also, the trucking company is coming to pick it up tomorrow morning and i must get it running today.
thanks.

gestalt1 · 12-01-2013, 08:09 AM

also, it starts for a brief moment on starter fluid. i also add that it ran fine a couple weeks ago.

GaryR · GaryR's Garage

Gestalt - Have you checked to see if you are actually getting spark? Gas-Air-Spark. Plugs fouled/wet points me to lack of spark..

gestalt1 · 12-01-2013, 08:50 AM

well, i would agree but it does try to spark. it could be a weak spark but i do have 12.5v getting to the ignition and the timing light does flash. would it make sense to take the plugs out and disconnect the fuel pump and crank it a little to clean out whatever is in the cylinders that might be fouling the plugs? if it is a weak spark how would i fix that?

thanks

gestalt1 · 12-01-2013, 09:52 AM

ok, i just hooked up a grounded spark plug and i did get a solid spark - certainly good to start an engine. at this point i thing it can only be a carb or ignition timing problem. i'm going to take one carb off and see if there is any gas dripping off the idle circuit. what timing should i use to have the best chance of starting - retarded or advanced?

jpnovak · 12-01-2013, 10:41 AM

I understand your frustration.

How are the carbs jetted? What size idle, main, air correctors, venturies?

Have you tried to open the mixture screws another turn? It will run rich but it will run.

Can you get it to fire and start on the accelerator pump circuit? i.e. feathering the throttle? If yes, then the idle circuit is not allowing enough gas - open mixture screws or try bigger jets.

Have you verified your timing with a light on the crank pulley? I would guess that 8-10 BTDC should be enough to get the car to fire and have a stable idle. I know you have spark, where does it occur in the combustion cycle. You will need someone else to crank the car while you operate the timing light. It is possible that you have an offset to your advance curve based on the position of the VR sensor and trigger.

gestalt1 · 12-01-2013, 11:14 AM

well, i was able to get it running last weekend before i swapped out the fuel pressure regulator by turning the idle screws all the way in so it was running on the accerator circuit. it died at any throttle application however. i did clean out the idle jets and mixture screws. i tried opening the mixture screws to 3 turns out and i set the timing at 5 degrees and it still will not start. it must be the idle circuit.

gestalt1 · 12-01-2013, 11:22 AM

i just took the mixture screws out and blew some compressed air in and then screwed them back in just a couple threads - seems like it is closer to starting. i will pull ot the idle jets and clean them again.

jpnovak · 12-01-2013, 12:55 PM

Did you blow out the passageways in the idle circuit in addition to the jets?

gestalt1 · 12-01-2013, 12:59 PM

success. after pulling out the idle jets, mixture screws and air screws and squirting carb cleaner and canned air through everything, it started. this goes to show just how important clean gas is. everything is new on the car and the carbs still got gunked up. thanks for all the help!

jpnovak · 12-01-2013, 03:03 PM

I run 3 fuel filters. A main filter on the inlet (DS) of the engine bay. And individual in-line filters right before each carb. It helps keep things clean.

jpnovak · 12-01-2013, 03:04 PM

Of course, now you need to pull the carbs and clean the bottom of the float bowls. There is likely some crud in there that will keep getting caught in your jet passage ways.

gestalt1 · 12-01-2013, 03:14 PM

There actually was't any visible crud really. I think it was gas sitting for too long in the carbs.