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Old 09-01-2014, 12:45 AM   #1
wolffcub
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Dual carbs not working correct! Please try to help!

Ok i thought I would start a new topic for the issue I am having and not tuck it in with my other generic truck thread here. Thought this might get more replies.

My scenario is this.
Just recently got the truck on the road after 15 years of tinkering. Have a 1955 inline 235 that was fully rebuilt. Cam is still stock grind. Installed fenton split headers, dual Edebrock intake, dual 32 DFT carbs from Tom Langton, Pertronix ignition. The truck runs, it idles smooth in my opinion and runs only fair when driving around. It seems like something is lacking after hearing so may praise and talk about how good these 6's can be.

I have fully and properly set up the engine to my knowledge prior to getting it on the road about 2 weeks ago.

- Found TDC on #1 (yes I mm sure its not 180 out) Confirmed rotor position and valve positions.
- Set the octane selector to 0
- Started engine and set timing to stock setting using the ball bearing in flywheel.
- Got to running temps.
- Used vac gauge on intake manifold and found the needle jumping around so I rechecked my valves and found that some were set wrong. Corrected valve rocker gaps and vac needle was steady like a rock.
- Adjusted timing via the distributor to get best vac reading on gauge with the vac advance unhooked and blocked off at carb. 19 was the best it would do. It took a bit of timing advance to get the vac reading it to that number. Backed off the timing just slightly to get 18 vac reading after by using the octane selector so I can make easy adjustments later.
-Played ever so slightly with the idle mixture screws on the carbs but they were set perfect and the adjustments in either direction only made it run rougher.
- Set the RPM to 500 ish

Been driving it now for 450 miles and i have filled the tank 3 times. This cant be right. Accelerating moderately or aggressively it just slowly climbs, gets a bit more torque around the 2000rpm area and keeps moderately climbing after that. If I carefully let off the pedal as I am accelerating it actually for a brief a second accelerates with power. As if the second it leans out by me not applying and acceleration it stars to accelerate correctly. The smell of gas is so strong after accelerating almost every time I try to get up and go. Every time i also let off the gas and decelerate with it in gear the exhaust sputters and i get slight backfiring and pops.

Well I tested out the truck today with one carb at a time. All I did was disconnect the linkage arm but left it connected to the fuel line. The first try with carb "A" felt the same. Acceleration was slow and there was still a slight popping / backfire sound when letting off the throttle and letting it decelerate in gear. Truck still ran and never starved its self on the single carb like i thought it would.

Switched to carb "B" and the truck ran even smoother than what I thought was set up correctly before. You can't feel the engine running now but you can just hear it it's that smooth. It has sooooo much torque now compared to running both carbs together or just carb "A". When accelerating and getting to the point with the pedal travel that actually opens the secondaries you can feel it take off even more it and it starts to pull even harder!. The way it performs now is more what I was expecting form this inline in the first place.


The strange thing is with just one carb attached and working it should be too undersized in cfm to run the engine by itself but it runs it like it was meant to be. Something still bothers me about both of these carbs even though one works better than the other. It still seems like jetting is off or possibly its something else.

I have yet to call Tom and ask him what he thinks.

Thoughts?
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Old 09-01-2014, 01:07 AM   #2
dwcsr
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Re: Dual carbs not working correct! Please try to help!

If one runs better than two it may be a huge vacuum leak or more likely the original carb wasn't very big on cfm only 250 - 275, You now have 2 carbs between 330 and 400 cfm's each on there, 660 - 800 cfm total which is too much for the stock cam.
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Old 09-01-2014, 01:15 AM   #3
wolffcub
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Re: Dual carbs not working correct! Please try to help!

It sure seems from the events that are happening to me it is oversized carbs. However others running 216,235 and 261 are running them and are not complaining. Tom even swears by them and has been installing them for years and years. I'm sure if they were grossly oversized someone would have noticed by now.
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Old 09-01-2014, 02:09 PM   #4
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Re: Dual carbs not working correct! Please try to help!

The engine could handle that size its just that with a stock cam it may not. Give him a call and see what he thinks.
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Old 09-01-2014, 04:40 PM   #5
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Re: Dual carbs not working correct! Please try to help!

I would check the plugs and exhaust to see if all the fuel is getting burned. Usually more carb is part of a cam/intake/exhaust system. Might be simple as a jet change. I used this link to see what Summitt would recommend for a 235 CI engine at 3300 rpm. Came up with 190 cfm on a street engine (85% efficeincy) and 246 on a racing engine (110% efficiency). So sounds like you are trying to push too much fuel thru the stock engine.
http://www.summitracing.com/expertad...cfm-calculator

Also kudos on using the vac gauge, lost art for many.
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Old 09-01-2014, 06:01 PM   #6
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Re: Dual carbs not working correct! Please try to help!

Its even noted you can run 3 of these carbs on a stock setup and it should run fine. I honestly think its just way over jetted for some reason.
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Old 09-02-2014, 02:47 AM   #7
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Re: Dual carbs not working correct! Please try to help!

LS swap would fix it.


(Sorry. Born in '84. MPFI is all I'm good for)
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Old 09-02-2014, 09:49 PM   #8
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Re: Dual carbs not working correct! Please try to help!

Quote:
If one runs better than two it may be a huge vacuum leak or more likely the original carb wasn't very big on cfm only 250 - 275, You now have 2 carbs between 330 and 400 cfm's each on there, 660 - 800 cfm total which is too much for the stock cam.
Dual carbs often require careful setup to work well. Are you using a heated intake as the vendor recommends? Incomplete vaporization wastes fuel. Do those carbs use a power enrichment valve? You do not want power enrichment active in cruise. Are those vacuum secondaries? Are they opening? Do you use an electric choke? Is it getting power when it should?
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Old 09-02-2014, 10:01 PM   #9
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Re: Dual carbs not working correct! Please try to help!

Too much carb. You're not getting adequate velocity or fuel atomization with two carbs. Doubt it's a vacuum leak with that reading and idle.
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Last edited by imjeff; 09-02-2014 at 10:05 PM. Reason: Forgot a point
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Old 09-02-2014, 10:19 PM   #10
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Re: Dual carbs not working correct! Please try to help!

Quote:
Originally Posted by 1project2many View Post
Dual carbs often require careful setup to work well. Are you using a heated intake as the vendor recommends?
Yes i have the intake heated via coolant and always allow it to fully heat up prior to driving. It get nice and hot and stays hot during driving.

Quote:
Originally Posted by 1project2many View Post
Do those carbs use a power enrichment valve? You do not want power enrichment active in cruise.
Yes it has a PEV in each carb. What they are set at I do not know as I see no marking on them telling me what vac level they open at.

Quote:
Originally Posted by 1project2many View Post
Are those vacuum secondaries? Are they opening?
The secondaries are mechanical driven via the links on the carb. Once the predetermined primary travel has been reached they start to open. You can feel more resistance in the pedal as you start to open them when depressing all the way due to the additional return springs adding tension.

Quote:
Originally Posted by 1project2many View Post
Do you use an electric choke? Is it getting power when it should?
The electric choke is fully functional and will fully open after a few min after running. All blades remain open and do not go closed after the choke is open. Power is always to the chokes when the key is on and they stay open.

This is good......I like the questions as we might figure something out!

I phoned Patrick's today to ask his opinion. He passed me on to the guy he uses for all his carb setups and tuning. The first thing out of the guys mouth when I told him that I was that running 2 of them with the stock jetting was that they were grossly over rich. The stock jetting on these is 160 primary and 220 secondary. He even phoned Weber directly and discussed the setup and called me back to tell me that I should be running 115 for both the primary and secondary.

I don't know much about carb jetting as of right now but I am trying to learn fast. Not sure if this suggested re jetting has merit or not. I cant see tom suggesting something so far off.
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Old 09-02-2014, 10:40 PM   #11
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Re: Dual carbs not working correct! Please try to help!

Have you tried setting your fuel levels lower. At your elevation with less air pressure your carbs will run rich. Or use a fuel regulator.
Or have you tried running the carbs progressively. Have one as the primary and the other come in at 60% of the primary opening.
I ran a dual quad on a sbc and my carbs where float level sensitive and at that time I lived west of Red Deer.
I lowered my floats 1/4 inch, ran 4psi pressure and set my back carb as the primary.
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Old 09-02-2014, 10:50 PM   #12
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Re: Dual carbs not working correct! Please try to help!

I have not tried lowering the floats. I was not aware that would make a difference in how rich it would run. The linkage system used between the 2 barbs can not be hooked up progressively the way it comes. I would have to try to make something up in order to do that.
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Old 09-02-2014, 10:59 PM   #13
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Re: Dual carbs not working correct! Please try to help!

Not hard to modify your linkage.
I built mine from scratch using ready rod and some flat iron. Built my own air cleaners too!
I tried running my carbs in sync but was a no go. Ran good like yours with only one.
Went to tipping in the other at 60% and it flat hauled butt. Knocked down 22 mpg too.
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Old 09-03-2014, 07:58 AM   #14
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Re: Dual carbs not working correct! Please try to help!

Quote:
I don't know much about carb jetting as of right now but I am trying to learn fast. Not sure if this suggested re jetting has merit or not.
The engine ran well on one carb, performance is soggy, and you're using a fair amount of fuel so smaller jets may be in order.

[/quote]I don't know much about carb jetting as of right now but I am trying to learn fast. [/quote]

About the why or the how? The why is because the jets affect almost all fueling through the carb. The how is found in several online manuals:
https://docs.google.com/file/d/0B85S...Vjg/edit?pli=1

http://www.webercarburatori.com/?p=handbook&s=2

Jets are here:
http://www.carburetion.com/Weber/weberJets.asp
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Old 09-03-2014, 11:47 AM   #15
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Re: Dual carbs not working correct! Please try to help!

From others experience it sounds like you need to drop the jet size and use progressive linkage. If you are going to run both at once, I suspect jet size will need to be dropped even more. Carb guy reinforced that by saying the jet sizes were 75-100 percent over sized. Basically the jets determine how much fuel is released into the air stream, bigger=more. You didn't answer my previous plug, tailpipe question, but suspect both are running wet and sooty. I would also install a pressure regulator, it solved a lot of fuel delivery issues we were having with my daughters Mustang, they do not like more than 4 psi.
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Old 09-03-2014, 02:01 PM   #16
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Re: Dual carbs not working correct! Please try to help!

Did I see what your fuel pressure was at idle?
I remember Webers being sensitive to pressure above 4# and float level
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Old 09-03-2014, 02:50 PM   #17
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Re: Dual carbs not working correct! Please try to help!

Im going to have to look into making a progressive linkage I guess to help out. Will that be an issue feeding the engine from one side of the intake for the majority of the time and not from the center?

Strange thing is the plugs are never actually wet. They are crystal clean with no deposits or discoloration. Possibly a bit of white haze. I know that indicates lean but it cant be that way. If it is lean where is all this fuel going? how is it getting into the oil the way it is and why such crappy engine power?

The tailpipes are black and very covered in soot.

I have a fuel pressure gauge installed inline and it never goes above 3.75 psi. when the car is running.

I will also do a compression test again today. Wish I had a leak down tester.
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Old 09-04-2014, 12:26 PM   #18
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Re: Dual carbs not working correct! Please try to help!

OK as of last night im going to start again and look at everything i can to see why its acting like it is and using so much fuel. Met up with a nice gent yesterday and he has a 55 235 with dual intake and dual exhaust. He has rod original carbs and a 261 cam. Thing goes like a bat out of hell compared to mine and he is even running larger tires and a lower geared rear. Granted i have a stock cam but i don't think you can say it all gain from the cam.

I have been running it with both carbs on for the last few days and only one actually connected via linkage.

Started with a compression test. I do not have a leak down tester but i will start here.



Checked all the plugs. Will check gaps again. Im using a NGK BR6S. If anyone can comment or confirm im still good with those that would be awesome. Thats the number i got when not being able to find the AC delco ones.





Later today i will recheck the the timing. Also recheck im not 180 out but the engine would never run on the road the way it was if it was out. Will also get a new mechanical fuel pump to ensure its not the culprit and leaking into the block. I will reset my float levels a bit lower and then try driving it on both carbs again.
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Old 09-04-2014, 12:37 PM   #19
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Re: Dual carbs not working correct! Please try to help!

With compression like that, no need for a leakdown test.
Plugs don't look bad. If you where too rich they'd be sooty black on the porcelain too.
Got a pic of the motor?
With your carb set up?
What distributor you running?
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Old 09-04-2014, 01:25 PM   #20
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Re: Dual carbs not working correct! Please try to help!

I don't think its been ran enough for the soot to show up on the center, but they are definately sooty. Did the other guy say what jetting he was running, assuming same/similar carb?
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Old 09-04-2014, 01:27 PM   #21
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Re: Dual carbs not working correct! Please try to help!

Those plugs are showing rich operation. The outer shell is black and there are traces of carbon on the center electrode. The heat level and / or timing are causing the center and side electrode to get hot and burning off some of the carbon. Look at 2nd plug from right... is that a colored ring around center electrode? If so it should be further down the insulator. Ring position indicates plug heat range or timing could be an issue. If the timing is ok I might try looking for a BR7 plug, slightly colder.

Don't underestimate the difference a cam can make.
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Old 09-04-2014, 01:31 PM   #22
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Re: Dual carbs not working correct! Please try to help!

Distributor is original reman unit and i installed Pertronix solid state ignition. Im running the carter weber carbs from tom 2x 32dft units. Also know as the Motorcraft 740 unit found on 80's the escort. He is running stock 235 carbs with all stock jetting.

Motor pic as requested



I know the vac advance in this pic is on the wrong vac port on the carb. I was not driving it a year ago and its a old pic. It is now on the correct port.
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Old 09-04-2014, 01:36 PM   #23
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Re: Dual carbs not working correct! Please try to help!

The plug on the left is the second one in from the other overall picture.

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Old 09-04-2014, 02:16 PM   #24
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Re: Dual carbs not working correct! Please try to help!

Keep in mine the rich plugs you see are from only running one carb for about a week. Imagine what it would be like if i hook up the second carb.
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Old 09-04-2014, 02:29 PM   #25
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Re: Dual carbs not working correct! Please try to help!

Curiousity question!
What's the line that runs of the intake and runs towards the rear for?
The one with the black anodized connectors.
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