Carb question Options

[last337]

Hello everyone! I got my new EMPI 40s on yesterday and I have been going through the adjustment all day today. It has been a long time since I have messed with carbs and Im not sure if I am doing this correct.

Initially I got my linkages all set up and correct with the speed screw at about 1 turn in. I have all the air bleed screws all lightly seated and mixture screws about 1 1/2 turns out.

At this point it is very rich but runs well at an idle of about 900 and actually comes up really nice but is smoking and even spitting out fuel from exhaust. I figured at this point I could begin going in 1/4 turn at a time on each mixture screw to the point the engine starts to run rough then back a 1/4 turn. I did this on all and it was still smoking badly. I havent set timing or anything like that but I would assume the only electrical issue (am I wrong?) that could cause rich conditions at idle would be a fouled plug but it is running smooth and not as if it is missing with a fouled plug.

I am wondering if maybe I should go another half turn on the speed screw then see if I can go in further with the mixture screws. Is there anything I can do with the air bleed to adjust this? I thought they were only adjusted for syncing and not for a rich condition.

The vendor I got them from claims they have the following jets:
52 idle jets
115 main jets
200 air jets
28mm venturi
550 EX. pump jets
50 accelpump jets
F11 emulsion tubes

Am I oversized with that I have in there now? I have been reading the following link to troubleshoot and it says if I am over 1 1/2 turns in on mixture then my jets are too big. The problem is that I cant get it to run at under 1 1/2 turns on mixture. However, maybe I should try another half turn on speed screws?

Any help is greatly appreciated (IMG:style_emoticons/default/biggrin.gif)

[vw505]

Did you clean and adjust the floats before installing them on the car?

[last337]

Did you clean and adjust the floats before installing them on the car?

The carbs are brand new and vendor said floats set.

[Trekkor]

The only real adjustments are going to be with jetting.

The adjustment screws will only help balance the carbs at idle.

You will need an exhaust gas analyzer to properly dial in the jets/airs with the motor running under load. On a dyno for example.
13.1-13.5:1 is a safe target for an air cooled motor.


KT

[bperry]

What about fuel pressure?
The stock fuel pump creates way too much pressure.
--- bill

[last337]

What about fuel pressure?
The stock fuel pump creates way too much pressure.
--- bill

Nope, I have a new Facet fuel pump I just installed. I think it is about 3.5 psi. I had a weird single carb setup before and it didnt run near as rich as now.

Any other ideas?

[last337]

The only real adjustments are going to be with jetting.

The adjustment screws will only help balance the carbs at idle.

You will need an exhaust gas analyzer to properly dial in the jets/airs with the motor running under load. On a dyno for example.
13.1-13.5:1 is a safe target for an air cooled motor.


KT

Unfortunately I do not have access to a dyno anywhere around here. Should I try to decrease my jetting size to see if it clears up the smoke for now? What size should I try for a 2.0 liter stock with 40s? Where is a good place to buy jet kits?

[Wegeng_Haus]

The only real adjustments are going to be with jetting.

The adjustment screws will only help balance the carbs at idle.

You will need an exhaust gas analyzer to properly dial in the jets/airs with the motor running under load. On a dyno for example.
13.1-13.5:1 is a safe target for an air cooled motor.


KT

Unfortunately I do not have access to a dyno anywhere around here. Should I try to decrease my jetting size to see if it clears up the smoke for now? What size should I try for a 2.0 liter stock with 40s? Where is a good place to buy jet kits?

I've had great luck talking to the tech support at CB Performance. I can tell them my displacement, cam, exhaust and carbs and they tell me what mains, venturi's, etc. I need. They sell all the parts, too! Dave

[last337]

Thanks for the info! Today I started pulling apart the ignition system to see if poor ignition could have been the culprit. Sure enough, the plugs were as black as they can get. I am planning to go ahead and just change out plugs, wires, cap, rotor, to begin tuning process again.

I do have one question about the air bleed screw. What exactly does that do? When the carbs arrived they were backed out several turns and on first crank it didnt seem to run quite as rich. However, when I began my tuning the 'best lean setting' instructs them to all be seated. When do I adjust them and what will they do? Is that anything that could help with my problem?

Thanks!

[rhodyguy]

opening a air bleed screw allows air to enter that venturi beneath the throttle plate at low engine speeds and be can used to equalize the air flow thru the carbs during low speed idle. so when you closed by-pass screw, you richened things up. you'll need to confirm the sizes of venturis, the idle jets, [main gas jets, air corrector jets, and the emulsion tubes. these are all part of the main jet stack].

for 40s in stock form you should see a # on the top edge of a venturi. you might see 28.

i wouldn't bet that your facet puts out a consistent 3.5#.

[last337]

opening a air bleed screw allows air to enter that venturi beneath the throttle plate at low engine speeds and be can used to equalize the air flow thru the carbs during low speed idle. so when you closed by-pass screw, you richened things up. you'll need to confirm the sizes of venturis, the idle jets, [main gas jets, air corrector jets, and the emulsion tubes. these are all part of the main jet stack].

for 40s in stock form you should see a # on the top edge of a venturi. you might see 28.

i wouldn't bet that your facet puts out a consistent 3.5#.

So, should I open the bypass screws a bit to lean things out? I unfortunately do not have access to a dyno or a exhaust gas analyzer. Is it necessary for basic tuning or are there other ways to tell when I am going too lean? Wont the carb start popping when it leans out or is that when it is too rich?

I just edited this after reading the following link

It seems like what I am experiencing is most likely either a problem of poor ignition or a problem with my jets. If it isnt smoking at idle with everything okay I would assume my idle jets are fine? If it smokes only when accelerating where should I start? I suppose I can give CB a call at that point. Also, I still dont know if I have a stock cam or not. Is there any way to tell other than opening engine up? Id love to know what is in there.

The stock jets are as follows based on vendors doc's but you are right I should double-check if still have problems.

52 idle jets
115 main jets
200 air jets
28mm venturi
550 EX. pump jets
50 accelpump jets
F11 emulsion tubes

[rhodyguy]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

[last337]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

Thanks for the help! I realized two things. By backing out the air bleeds I was definitely able to lean things out a bit although at this point they are almost seating completely again. Secondly, I was trying to do my adjustments with the engine way too cold.

At this point I have a 'somewhat' smooth idle but I hear a popping/sucking sound from the carbs at times. Under the load there is a bad hesitation coming off idle and you can hear the carbs almost start to whistle as if they are starving for air after the hesitation goes away. Any ideas?

[FourBlades]

My brand new set up and shipped to my door carbs had one of the float levels off by 10mm and the other off by 5mm (which is way off).

I think they bounce around a lot in shipping with no fuel in the bowls to cushion the the floats and can be way off by the time you get them.

Setting them correctly helped me a lot.

John

[ThePaintedMan]

thomlinson (cb perform book) suggests setting the by-pass at 1/2 turn off closed for the initial setup. a 40 i'm looking has 50s for the idle jets. 52 might be a tad fat and you cut some air off the idle mixture when you closed the by-pass. open all 4 up 1/2 a turn and see what happens. if the idle circuit is rich to begin with and the engine is idling a lot when you're adj the carbs you'll be loading the plugs up with carbon. if your unregulated facet is over driving the fuel float needle valve you''ll in a rich condition all the time.

Thanks for the help! I realized two things. By backing out the air bleeds I was definitely able to lean things out a bit although at this point they are almost seating completely again. Secondly, I was trying to do my adjustments with the engine way too cold.

At this point I have a 'somewhat' smooth idle but I hear a popping/sucking sound from the carbs at times. Under the load there is a bad hesitation coming off idle and you can hear the carbs almost start to whistle as if they are starving for air after the hesitation goes away. Any ideas?

Kevin (rhodyguy) and John (FourBlades) have both been through this with me and I trust them implicitly. I'm still learning of course, but I also would suggest a few things. We don't know - did you do a good valve adjustment first before doing any of this? This can have a big impact. Make sure you do it with the engine dead cold. I was having issues with the carbs "coughing" the way you describe, but a lot of it went away once I did a good, honest valve lash adjustment.

Then I would ensure your timing is as good as you can get it. Depending on the distributor, you want it around 27 degrees before top dead center around 3,200-3,400 RPMs (again this varies with engine and distributor). Again, this seemed to help me get rid of some of the coughing.

Then, you can move back to the carbs to fine tune the idle. The stumble off idle probably has a lot to do with a lean condition, but can also be due to a crappy distributor (the Bosch 009 is often installed on these cars and is notorious for having a big "flat spot") or more often, not having the carbs synched left to right. Are you using the "hex bar" linkage or some version of it?

[Trekkor]

These are dual 2bbl's right? One throat for each cylinder?

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.hh-autoparts.com-1413-1357618923.1.jpg)


KT

This post has been edited by Trekkor: Jan 7 2013, 10:22 PM

[last337]

Thanks for all the input. I am on Pelicanparts today ordering everything I need to do a full and proper tune-up of the ignition system. I also need to do a good valve adjustment. I did read somewhere that not having the air filters on could also cause backfiring in the carbs because of the lack of flow restrictions. I guess for the time being I will just cough up the tuning I have done thus far to a learning curve (IMG:style_emoticons/default/sunglasses.gif)

I did find the following link last night which was really good info.

http://racetep.com/webjettune.html

Oh, and he mentions two books there for tuning but I have seen you guys mention other 'bibles' for tuning. I dont recall which they were. Which should I buy?

[rhodyguy]

Bob Thomlinson's Weber Tech Manual avail thru CB perfomance is the one i have. some after market VW parts shops carry them maybe amazon too.