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Webber carb runs out of fuel

Old 11-05-04, 03:38 AM
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Webber carb runs out of fuel

I have a Webber 48 dco on my street ported 4 port 13b. Its using a one piece manifold that puts the carb pretty close to the fender. It also puts the carb 180 degrees to how rotaries generally run them. This one runs the float bowl empty after several moments of hard acceleration. Do you think that this could be the floats getting picked up and closing the needle? Or is it a simple case of not enough fuel supply. It has a universal fuel pump. not sure an the rating but it pumps like a garden hose. well ok maybe like a kitchen faucet. I got a higher pressure universal pump tonight to see what effect that has in the morning. Do you guys think that will be enough or do I need to go all out and get the holley?
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Old 11-05-04, 11:35 AM
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Lake City sidedraft - sweet! Some people swear by those intakes.

I have no idea, somebody help this guy out!
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Old 11-05-04, 12:03 PM
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I had fuel supply problems using a Mikuni until I used two facet fuel pumps run parallel. Rig up a temporary fuel pressure gauge taped to the windshield wiper and do a pull, if the fuel pressure isn't maintained then its a supply problem.

If supply is good, it is possible you need a larger neddle and seat assembly in the carb.

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Old 11-05-04, 12:38 PM
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Cool Jack. I was thinking of using 2 pumps as well haha. I am po and dont want to spend that much money on my junk yard special.

Brian
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Old 11-05-04, 03:49 PM
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Sounds like you are fuel starving. A higher capacity pump, or dual pumps should fix the problem. I had a similar problem on the race track with my dual weber setup. Two pumps did the trick
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Old 11-05-04, 07:35 PM
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A Facet pump only costs about $40 or 50 each plus some fittings and hose. Ya gotta pay to play.

A friend of mine with a Weber 48IDA used to use a stock pump at the rear and a Holley pump under the hood with a switch so he'd only use it when needed. Been a long time so I don't remember the model Holley pump.

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Old 11-05-04, 11:40 PM
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Originally Posted by xrotaryguy
I have a Webber 48 dco on my street ported 4 port 13b. Its using a one piece manifold that puts the carb pretty close to the fender. It also puts the carb 180 degrees to how rotaries generally run them. This one runs the float bowl empty after several moments of hard acceleration. Do you think that this could be the floats getting picked up and closing the needle? Or is it a simple case of not enough fuel supply. It has a universal fuel pump. not sure an the rating but it pumps like a garden hose. well ok maybe like a kitchen faucet. I got a higher pressure universal pump tonight to see what effect that has in the morning. Do you guys think that will be enough or do I need to go all out and get the holley?
you need big flow on weber Rotary. and this happend to me too my is 13B PP. but in my case. the needle seat is not flow enought fuel. so I upgarade my to 58 IDA and it solve the problem
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Old 11-06-04, 10:54 AM
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Im running 2 pumps as of this morning and the problem persists. I think i need a bigger needle and seat
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Old 11-06-04, 11:07 AM
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Sorry for the short post. I was having some sort of virus mess with the window. Any how... the needle and seat could be too small. I do however have a second "parts" webber lying around and I installed the top off of it. The car died at idle and so I went take the top off and when I did the thing sucked in as soon as the seal was broken. The vent for the float bowl must be in the body of the carb right? cause it sure doesnt seem to be in the top. Where the heck is the darn vent? can I drill a hole in the top of the carb and jb a tallish brass tube into it for the vent? :-D
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Old 11-07-04, 08:10 AM
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Originally Posted by xrotaryguy
Im running 2 pumps as of this morning and the problem persists. I think i need a bigger needle and seat
I was thinking that fuel pressure was not the issue. Most of us run a pressure regulator. I have mine set at 3-3.5 lbs. The similar to stock fuel pump is capable of much higher pressure. Did you check the filter that is in the carb. Its inside the fuel inlet. Check your float's as well. What are you running inside the carb.
idle jet
emulsion tube
air bleeder jet
main jet

I've been trying to get some help on the above as well. Im running a similar setup on a 12a street port. My setup
idle jet 65
emulsion tube F2
air bleeder jet 210
main jet 190

I think this might be too rich but I have having other issues and my egt's were a little low.

This is the best site I've found for weber's, thanks to someone in the first gen section. http://www.teglerizer.com/dcoe/webertune.htm

Good luck
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Old 11-07-04, 09:42 AM
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Another thing you might try is getting bigger fuel lines, then adjust the pressure to what it should be. That way you get the same line pressure but more fuel.
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Old 11-07-04, 10:42 AM
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Dude,
You're problem is a typical common issue with that set up !, The syst. works great on you're first run, them problem manifest it self,........If You were running the bowl dry, them it would happen as soon as You hit 3rd gear. on your first attempt to go fast. The problem is "Fuel Percolation" , the carb sits right on top of the headers and as soon as the exhaust get really hot, the RADIANT HEAT from the headers "BOILS" the fuel inside the bowl, and the fuel turn into gasious vapor and the "FEELS" like it's running out of gas. the issue here is Heat Convexsion, and no matter what fuel pump You deside to use, You will still have the same problem. Solution : build you're self a heat shield separating the headers from the carb, with a duct for cool air either from the flow of the radiato's fan, or even beater, from a small electric fan axial fan like what is used for race car oil coolers, and duct it to the carburators fuel bowl. This will create a breeze draft and take the Radiant Heat away with it. Good Luck !
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Old 11-07-04, 08:16 PM
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GT1-20B

I had dual webers that sat right above the header, and never had the issue you are bringing up. I doubt that it is the problem you are describing. When the car is in motion, a lot of air is moving thru the engine compartment, making what you have described nearly impossible. That being said, a heat shield is always a good idea in that location.
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Old 11-07-04, 09:36 PM
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the heat shield will help, but i think he has fuel starvation problems..... use a good aftermarket pump designed for high flow (holley, mallory or carter).....
also make sure the needle valve is a 300... anything less and the carb will starve for fuel....
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Old 11-08-04, 11:37 AM
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i actually made a little heat shield out of sheet steel when i was installing the carb. So its been there all along. I also have a #300 needle and seat. Come to find out that this is as big as they get. So I think that im back to getting a high flow pump. I guess I need to get my money back from auto zone on the second water faucet pump. Heck why not try and return em both lol. They, or rather we ( I work for auto zone ) stock a holley blue so I can get it for about $80 with my discount. I think its about that time.
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Old 11-08-04, 01:36 PM
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Ditto 680rwhp, root of the problem is low fuel volume. I use a holley 110gph fuel pump, lake cities manifold, 48 dellorto @ 2.25psi and it does not run out of fuel with that pump. The stock pump couldn't handle fuel flow in 3rd or 4th gear at higher rpms.

Regarding the carb being over the header, definately get a heat shield in there.

Actual data: I jet hot 2000 coated my stainless headers, put a 2 layer heat shield around the top and side of header with opening in the front to duct air inbetween header and heat shield to cool off header. After 40 minutes on the dyno @ 6000rpms the bottom of the carb was 105 - 110*F.
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Old 11-08-04, 03:32 PM
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Originally Posted by DriveFast7
........ After 40 minutes on the dyno @ 6000rpms the bottom of the carb was 105 - 110*F.
Maybe I am not understanding correctly, but I think you just said that you ran your car for 40 minutes at 6000 RPM on a dyno????

Is that right?
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Old 11-09-04, 07:42 AM
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The Holley b.ue will definatly work ( if you can put up with the noise !), reduce your air corrector specially in cooler weather, check You're Ventury size, the main jet should be the mm. size of the Ventury X 5 as a factor. This will give You a good starting point, if You're Ventury diameter in anything larger than 38 mm. based on you're main jet size you stated, then You dont have enough fuel (main jet). Normally most 48's come stock w/ 42mm., and the larger the Ventury, the lower the preassure differential, therefore the smaller the air correction jet must be.
Besides the tunning, I still think You got a "Heat Soak" problem, specially if its running LEAN.
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Old 11-09-04, 08:03 AM
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xrotaryguy: Do you have a fuel pressure gauge? You did not say you did in any of your posts.

It is very, very difficult to diagnose a fuel supply problem without a fuel pressure gauge that you can read while driving your car. The guage must tee into the fuel line as close to the carb as possible; after all filters, regulators, etc.

Without a gauge, you can make wrong assumptions, which will lead you down the wrong path.
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Old 11-09-04, 09:20 AM
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No I have no pressure guage as of yet but I do have the largest needle and seat that there is and its not enough. Im sure its not heat soak. The problen is too predictable. It acts the same in all weather condirions and no matter if the car is hot or cold. Plus I do have a heat shield. I knew I would want that with the carb like RIGHT THERE over the header. Maybe I'll pick up a cheap one next pay check pefore I splurge on the pump. I dont suppose it needs to be accurate to see the fuel pressure drop as the car dies lol. And thank you gt1 for the jetting advice. This carb actually runs really well until it runs aut of fuel. It only hesitates for a fraction of a second when being slammed straight to full throttle. Thats my only complaint aside from the starvation issue and I can definately live with thatt one. Especially when compared to how my pos holley setup acted.
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Old 11-09-04, 11:55 AM
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Originally Posted by adam c
Maybe I am not understanding correctly, but I think you just said that you ran your car for 40 minutes at 6000 RPM on a dyno????

Is that right?
Yes. Engine break in.
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Old 11-14-04, 01:47 PM
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If the car hesitates momentarily when You slam the throtle WOT, then You can try 2 different approches: 1) try a larger accelerator pump discharge jets (pump shots) w/ also a NO-Bypas vent valve at the bottom of the bowl, see if it picks up Rpm. quicker, but if the bog comtinues, or is still prominent, the 2) go to a larger idel jet setting.
Increase the idel jet but make sure You dont see traces of black smoke just when You crack the throtle, thios means You whent too far, & it will constantly fowl you're spark plugs.
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Old 11-15-04, 01:27 AM
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Awesome!!! you guys are definately helping. I am going to save all the advive on what to do with the idle jets and and accelerator pump jets in an email lol. Not to mention all of the advive gt1-20b gave me about air bleeds etc. Because by the time my wallet catches up to this fuel starvation problem I'll have forgotten.

Brian
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Old 11-16-04, 12:18 AM
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Well I got the holley blue in there and it still does it. Its totally proportional to what i set the fuel pressure to. if i set tit to 2 lbs it does it right away. like i can barely get to use second gear before it runs outta gas. if i set it to 5 lbs it happens much later like half way through 3rd gear. I have felt the heat comming off the header while cracking the throttle open in the garage and its miniscule. likewise i dont feel any heat in the bottom of the carb after runs. do you guys think i should install larger fuel lines? do you think it could be a restrictive fuel pressure regulator?
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Old 11-16-04, 04:58 PM
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What does the fuel pressure do while you are driving the car???

Fuel pressure readings at idle are not the same as fuel pressure while driving!
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