IDA3C Weber Troubleshooting Options

[Cfletch]

Hey there everyone, working on getting my 6 conversion going here and I was able to hook up a temp fuel system in place of my tank while I am waiting on a few parts. I wanted to get the car to idle with its new fuel pump (not yet regulated down to 3.5psi) rated at 5 PSI max. I wanted to get the carb bodies full of fuel and get some pressure into the system and as soon as the pump turned on with the ignition the carbs essentially started dumping fuel down my intakes. Almost as if there was an internal leak causing fuel to just enter their respective cylinders. I'm new to down draft webers so this confuses me. I popped the top off of one of the carbs and noticed the fuel level was extremely low in the bowls so it was not like the needle and seat were stuck or a float was stuck causing it to overfill. Kind of stumped here as these carbs are rebuilt. Really any suggestions are good here. the float level was set, the needle and seats are good and not sticking at all.

I read somewhere but not in much detail that the bowls are vented? I have these little plunger-esq things in each vent tube that I have not yet pulled out. Would that be the source of my problem? If the bowls couldn't vent its just pressurizing the changes and causing the fuel to just leak down into the engine?

[brant]

You should check and reset your float levels

Most likely reason

And they change. Even just from use or possibly sitting

You’ll need a float gauge to do this
And the different thickness of special washers they sell for this purpose
I like to use two of the float gauges at the same time, one per a bank

Floats are checked while the motor is running with this special tool

3 barrel webers are the most complicated and sensitive carbs I’ve ever had personal experience learning

You need to read the hundred pages of Paul abbot set up articles any time you have the carbs off. Lots and lots of tuning and linkage that needs to be done in correct sequence
There is an art to these carbs. Might be worth paying a guru for this job. It can take a lot of time as a beginner to learn this skill and still not come out as well as a guru can perform


And if previous rebuild time was very long.
Worth considering another rebuild, fresh gaskets all around if you don’t know the age of that last rebuild and gaskets

[mate914]

carb float needle not setting, Get extra because new ones fail


Matt

Hey there everyone, working on getting my 6 conversion going here and I was able to hook up a temp fuel system in place of my tank while I am waiting on a few parts. I wanted to get the car to idle with its new fuel pump (not yet regulated down to 3.5psi) rated at 5 PSI max. I wanted to get the carb bodies full of fuel and get some pressure into the system and as soon as the pump turned on with the ignition the carbs essentially started dumping fuel down my intakes. Almost as if there was an internal leak causing fuel to just enter their respective cylinders. I'm new to down draft webers so this confuses me. I popped the top off of one of the carbs and noticed the fuel level was extremely low in the bowls so it was not like the needle and seat were stuck or a float was stuck causing it to overfill. Kind of stumped here as these carbs are rebuilt. Really any suggestions are good here. the float level was set, the needle and seats are good and not sticking at all.

I read somewhere but not in much detail that the bowls are vented? I have these little plunger-esq things in each vent tube that I have not yet pulled out. Would that be the source of my problem? If the bowls couldn't vent its just pressurizing the changes and causing the fuel to just leak down into the engine?

[930cabman]

Hey there everyone, working on getting my 6 conversion going here and I was able to hook up a temp fuel system in place of my tank while I am waiting on a few parts. I wanted to get the car to idle with its new fuel pump (not yet regulated down to 3.5psi) rated at 5 PSI max. I wanted to get the carb bodies full of fuel and get some pressure into the system and as soon as the pump turned on with the ignition the carbs essentially started dumping fuel down my intakes. Almost as if there was an internal leak causing fuel to just enter their respective cylinders. I'm new to down draft webers so this confuses me. I popped the top off of one of the carbs and noticed the fuel level was extremely low in the bowls so it was not like the needle and seat were stuck or a float was stuck causing it to overfill. Kind of stumped here as these carbs are rebuilt. Really any suggestions are good here. the float level was set, the needle and seats are good and not sticking at all.

I read somewhere but not in much detail that the bowls are vented? I have these little plunger-esq things in each vent tube that I have not yet pulled out. Would that be the source of my problem? If the bowls couldn't vent its just pressurizing the changes and causing the fuel to just leak down into the engine?

Congrats with another /6 conversion

I would start by lowering the fuel pressure. I have run 2 - 3 psi maximum on Webers for many many years and have never run low on fuel. In this case, less is better. On my recent /6 conversion I found a couple 40 IDT carbs, spent a bit of time learning/rebuilding them. There seems to be a certain mystique with the 3C Webers, but my experience has been straightforward.

[Graydingo]

My vote would be stuck or faulty float needle. I noticed that occasionaly, an air bubble can form when you swap out the carb - take it off for cleaning or whatever, and to alleviate this, run the pump for a second, turn off the system. Remove the hexagon cap over the needle valves, and reseal. If you still have trouble, take a look at your needle valves and make sure they can close and open without resistance. There are a lot of cheap less than versions on the market. I've purchased brand new ones only to have them stick.

If the needle /valve doesn't close, fuel will pour into the float bowls and spill over the tops directly into the cylinders.

While your PSI is not ideal, 5 psi should still function. You of course want around 3.5 psi.

Agree that you need the float bowl gauge and to set them, but this sounds like the needle is stuck open.

Here's another really odd thing, but I'll mention it just in case. I kept having one of the float bowls low and gas was draining into the cylinder after power was turned off.

It turned out to be two tiny holes behind the chokes that came from the back float bowl. Fuel was draining out of the float bowl area directly into #3 cylinder.

Also if fuel is filling up the cylinder, you need to be careful about hydrolocking as you can cause some serious engine damage if that happens.

Pull the plug and make sure there's no fuel in there.

[Cfletch]

What would be an official test on the needle/seat? I pulled them both out of the carb body, lips to top and blew hard on them, used finger to press ball and that was my check. They were free, didn't get stuck at all and when closed, I was unable to blow through. I did an initial set of the floats on the bench. I have read that the final adjustment with shims and what not would be on a running motor, do not want to start the engine because with ignition on its just dumping fuel down the throats. Again if the floats/needle and seat were suspect, I would assume that my fuel bowls would first fill up in order for the bodies to start leaking fuel out of wherever it could escape, that is not happening in my case as the bowls are maybe 1/5 or 1/4 full.

I would suspect even the same result when/if my fuel pressure is too high, it would 'bypass' the needle seat valve because too much pressure and then fill up my bowls, then lead to a leaking situation. I'm stumped because my bowls are no where near full.

[Graydingo]

How are you verifying the bowl fullness?

What do you mean by "i have these plunger things in the vent tubes"

Did you set the floats correctly? You need to pin the float loosely to the inside of the carb body using a piece of folded up paper and check with a micrometer to see that the top of the float is adjusted to 12.5-13mm from the top of the carb body without gasket. Then you need to check the tab height relative to the carb body and that should be 18mm. The float tabs can then be adjusted and make sure there are no indentations where the needle touches it.

The second part is then using the float gauge to see where the floats fill. This can be done without starting the motor, just the fuel pump. If the bowls are not filling at that point, something wonky is up with your measurements or where the floats are.

Aftermarket plastic floats suck fyi. The brass ones are king imho.

Brass floats can become holy if you use compressed air in the bowls. Check their buoyancy.

Once you've set the floats, then you can do minor adjustments using the different washers on the float needles. But the bowls should still fill up as long as the floats are set pretty close to the above way.

Could your rebuild guy have messed up setting the floats so that they turn the needles off at 1/4 full?

Is fuel leaking out in both bowls by the time you take the tops off to inspect? (unlikely but possible)

Most likely it's the floats are wrong.

As for your needle test, yes you are good. They should move freely, Sometimes they will stick when holding them upside down.

[flyer86d]

I haven’t looked at mine but if your float needles have neoprene tips, modern gas with ethanol degrades them and they stick shut.

Charlie

[930cabman]

Pierce has a float gauge kit if you need one. Easy, simple and works well

[porschetub]

Hey there everyone, working on getting my 6 conversion going here and I was able to hook up a temp fuel system in place of my tank while I am waiting on a few parts. I wanted to get the car to idle with its new fuel pump (not yet regulated down to 3.5psi) rated at 5 PSI max. I wanted to get the carb bodies full of fuel and get some pressure into the system and as soon as the pump turned on with the ignition the carbs essentially started dumping fuel down my intakes. Almost as if there was an internal leak causing fuel to just enter their respective cylinders. I'm new to down draft webers so this confuses me. I popped the top off of one of the carbs and noticed the fuel level was extremely low in the bowls so it was not like the needle and seat were stuck or a float was stuck causing it to overfill. Kind of stumped here as these carbs are rebuilt. Really any suggestions are good here. the float level was set, the needle and seats are good and not sticking at all.

I read somewhere but not in much detail that the bowls are vented? I have these little plunger-esq things in each vent tube that I have not yet pulled out. Would that be the source of my problem? If the bowls couldn't vent its just pressurizing the changes and causing the fuel to just leak down into the engine?

Congrats with another /6 conversion

I would start by lowering the fuel pressure. I have run 2 - 3 psi maximum on Webers for many many years and have never run low on fuel. In this case, less is better. On my recent /6 conversion I found a couple 40 IDT carbs, spent a bit of time learning/rebuilding them. There seems to be a certain mystique with the 3C Webers, but my experience has been straightforward.

(IMG:style_emoticons/default/agree.gif) I run around 3psi with Zeniths ,before I set pump pressure with my regulator I checked the float levels with the PMO gauge .
What I found without the regulator screwed down just over 3.6 psi showed on the gauge and had fuel just starting to overflow ,regulated back and all was fine ,haven't changed it since then.
IMO 5psi is too high and will overcome the float valves ,I used the Holley 1 to 4psi LP regulator part # 12-803 with a qualiy gauge ,so far no issues .

[brant]

I run 4 psi on the race car

But bumpy and hard vibration
Plus curbs in the corners at high rpm
So works well for me

[Cfletch]

Ok team here is an end of day update.

My vents were the culprit for the initial issue I mentioned. The vent tubes were sealed with these little plugs for lack of a better term, causing the air/fuel to not have a place to go when the pump was turned on. It basically just created too much pressure in the float chambers and the fuel had no place to go but out the secondary venturi's and pool at the bottom of the carb and sit on the throttle plates.

Next issue I tackled was one of the float levels was too high, you all guessed it, but before I could not even get to that point because of the aforementioned reason. I then popped off the top and saw it was too high and so I messed with the tab and also checked my needle and that one was bad even though new like mentioned by one of you, so I put in the old and that solved that issue.

Now its onto tuning. My passenger side bank seems to be running really rich as that side is popping out the exhaust at idle quite a bit and the other side is not. I also checked the exhaust temps and that side is significantly less hot than the 'better' running side. I have the suggested jetting for my engine and that is all new. And want to reiterate that I do not yet have the recommended fuel pressure as well as float level set. Thats in the mail!
Would it be recommended that I get those 2 things resolved first before tackling any form of tuning? I assume the answer is yes, but would those 2 thing cause my funky poor running on 1 carb/bank vs the other?

Any info is most appreciated!!

[Graydingo]

Sounds like you are making progress.

Popping out the exhaust is rich. Reduce the idle by 1/4 turn. You can search best lean procedure and that should be your starting point. In a nutshell you run them in until it sputters then 1/4 turn out or maybe 1/8th turn. it doesn't take much. Some of the idle mixture screws on emissions carbs were stepped. Pull one out and verify it's tapered.

You can pick up a cheap laser temp gun. I use one to shine it on the exhaust header coming right out of the cylinder to verify that cylinder is firing.

If one is cold, but you have it set up correctly, it could be plugged in one of the hidden passageways. Even so called rebuild carbs dont always have the hidden passages cleared.

[Cfletch]

Sounds like you are making progress.

Popping out the exhaust is rich. Reduce the idle by 1/4 turn. You can search best lean procedure and that should be your starting point. In a nutshell you run them in until it sputters then 1/4 turn out or maybe 1/8th turn. it doesn't take much. Some of the idle mixture screws on emissions carbs were stepped. Pull one out and verify it's tapered.

You can pick up a cheap laser temp gun. I use one to shine it on the exhaust header coming right out of the cylinder to verify that cylinder is firing.

If one is cold, but you have it set up correctly, it could be plugged in one of the hidden passageways. Even so called rebuild carbs dont always have the hidden passages cleared.

Yup used one of those laser temp readers and saw a noticable difference in temps. 1 and 2 seemed to be lower than all others. I'm going to get new plug wires as mine as suspect to begin with and then ensure I have correct float level as well as pressure and use that as my starting point. My adjustments didn't see to matter much when I was running the engine so I'll do the above and get to a standard baseline per your lean suggestion and go from these in the coming days. Also need a muffler since tuning while its just headers kind of sucks