Another carb tuning question, Problem solved!! Options

[Cevan]

So I’m entering the wonderful world of carb tuning. (Please save all the FI comments. I couldn’t afford aftermarket FI and I’m using a cam not compatible with stock FI.) The engine is a recently built 2056.

I’ve sync’d the carbs using my STE meter. I adjusted the idle mixture screws per Aircooled.net’s website. It doesn’t appear to make a huge difference when I go from one turn out to all the way in, or from one turn out to two turns out. I adjusted them so that the engine ran the smoothest.

The engine seems to idles nice. So I go for the first drive. After puttering down my long driveway in 1st gear, I pull out onto the road and it goes nicely through 4th gear, maybe at half throttle. At some point (maybe ½ to 1 mile into the drive) it starts to get boggy on acceleration. Definitely a change, so I head back home.

This morning I started it back up. It’s still boggy, pretty much from 2000-4000. If I go WOT, it bogs worse. If I slowly increase the speed, it bogs less. And it smells like it’s running rich, like unburnt fuel (I did check for fuel leaks). I tried adjusting the idle screws some more. It seemed like I got it to run a little faster at idle. The engine revs fine with no load on it. I checked the carb balance again and went for another spin. Still boggy. Still smells like it’s running rich. For the next drive I need to pay more attention to any carb or exhaust popping.

I’m trying to diagnosis this problem in a logical order. I’ve already checked the dwell, timing and valves. The carbs were just rebuilt. The floats are set per the Redine website.

My plan is to pull a spark plug from either side and inspect them for signs of it running rich or lean. I’m also going to clean the idle jets as maybe something clogged the jets during the first drive. I’m also going to install a fuel pressure gauge so a passenger can see it while I drive (just in case it’s running lean), although the fuel pump is new.

If none of this helps, should I try a different size idle jet? I have 50s already. Any other suggestions?

Here’s the current setup:

Weber 40mm IDFs
Idles 55
Main 130
Air 200
Emulsion F11
Vents 32mm

[Root_Werks]

Sounds like you fouled the plugs. Runs good for that short while, then will only get worse the more you drive it.

(IMG:style_emoticons/default/agree.gif)

Pull the plugs, check for all that black junk. If they are clean, do a compression check, even if it's cold. Just to establish a baseline and make sure 1 or 2 cyl's aren't sitting bellow 100psig.

I did my 914 cold and the worst was still 120 if that helps.

Hopefully with just those, some answers will come.

I wouldn't think 55's to be too large or 130's either.

On the IDF's, I know there is a "Mixture" set-screw. But you mentioned those were in pretty far already.

Cold start enrichment? Is that done correctly? I've heard horor storries about those not being done right.

[biosurfer1]

One other thing you might check is for any air leaks around the base of the carbs to the manifolds and the manifold to the block. One of my gaskets wasn't sealing correctly and caused all sorts of problems, including making it so the mixture screws did very little to the running condition (similar to what you stated)

[VaccaRabite]

I have 30 vents on my 2056 with IDF 40s. Other then that they are the same as yours. My car runs like a raped ape. I would think with 32 vents you might be just a tad lean.

My carb venting (for 2056 with a Raby carb cam)
IDF 40s.
30 vents
130 Main
200 Air
f11
55 idle

IIRC you were having issues with thinking that your mix knobs were not bottoming out when the springs were fully compressed? I had that problem, and had to cut off the last coil of each spring to get them to properly seat. You may have too much mix going in.

Zach

[Cevan]

I took out the idle jets and cleaned them. They looked fine when they came out. Took it for another short run and the same thing.

I really got on it just before I shut it down. Pulled one of the plugs and it's black, but not wet. None of that light brown color I was looking for. It definitely seems like its flooding out when I get on the throttle.

[VaccaRabite]

I took out the idle jets and cleaned them. They looked fine when they came out. Took it for another short run and the same thing.

I really got on it just before I shut it down. Pulled one of the plugs and it's black, but not wet. None of that light brown color I was looking for. It definitely seems like its flooding out when I get on the throttle.

Clean the plugs, first off. Carbon makes it harder for them to do their job. Idling the car a lot (which you were doing when you ran in the motor and for most of the carb tuning) will foul the plugs.

My plugs started black after my initial tuning, and got nice and brown when I finally had a chance to really run the engine and get some miles on it.

Where are you timed? And with what dizzy?

Zach

[Cevan]

I'm using my L-jet dizzy with no vacuum advance. The timing is at 28 degrees all in. It's about 5 degrees at idle.

On a prior drive, I checked my plugs after the car idled for awhile and they weren't black. I think it's not fouling at idle.

Could timing that was too retarded cause this? Maybe I screwed up when I put the TDC mark on my fan.

[cgnj]

Hi,
Been there done that. Chassis dyno. Here is a link http://www.smokemup.com/utils/dynosearch.php

Carlos

[jmill]

It doesn’t appear to make a huge difference when I go from one turn out to all the way in, or from one turn out to two turns out. I adjusted them so that the engine ran the smoothest.

Doesn't sound right. Go out farther than 2 turns. You can go like 5 before fear of the needle falling out. I'm thinking you haven't gone out far enough. You'll hear and feel a difference. It's not huge but you'll know when your passing through the sweet spot. If that spot is more than 2 1/2 turns out increase idle jet size.

If your not advanced enough it will be boggy.

[Cevan]

It doesn’t appear to make a huge difference when I go from one turn out to all the way in, or from one turn out to two turns out. I adjusted them so that the engine ran the smoothest.

Doesn't sound right. Go out farther than 2 turns. You can go like 5 before fear of the needle falling out. I'm thinking you haven't gone out far enough. You'll hear and feel a difference. It's not huge but you'll know when your passing through the sweet spot. If that spot is more than 2 1/2 turns out increase idle jet size.

If your not advanced enough it will be boggy.

It does make a difference. I just thought it would be more pronounced.

I will advance the timing and drive it again.

[VaccaRabite]

It does make a difference. I just thought it would be more pronounced.
I will advance the timing and drive it again.

Advance one degree at a time.
Do you have a copy of the weber tech manual?

Zach

[r_towle]

Which screw are you turning?

Rich

[Cevan]

I'm adjusting the idle mixture screws. The air bypass screws are all the way in.

Zach - I don't the Weber manual. I presume you will recommend getting copy.

[VaccaRabite]

I found it very useful, but there are some issues with it. I know that they have the float height wrong. but for tuning, it does help zero in on your issues.

Zach

[jmill]

I found it very useful, but there are some issues with it. I know that they have the float height wrong. but for tuning, it does help zero in on your issues.

Zach

(IMG:style_emoticons/default/agree.gif) I have read it cover to cover several times. You'll reference it often if you have it.

[Cevan]

I found it very useful, but there are some issues with it. I know that they have the float height wrong. but for tuning, it does help zero in on your issues.

Zach

I set my float height to 10mm closed and 32mm open

[jmill]

Make sure you set it with the gasket in place. If not it'll be too high

[r_towle]

The air bypass screws are all the way in?
Why?
They should not be.

Rich

[Cevan]

The air bypass screws are all the way in?
Why?
They should not be.

Rich

I read it here that the airbypass screws should be closed. I'll be the first to admit I'm a complete idiot when it comes to carbs.

I tried advancing the timing but no change. It just completely falls flat under load. The frustrating part is that it idles perfect. Not sure where to go from here.

[jmill]

Air bypasses should be all the way in unless you tweaked them to equalize the flow at idle with the butterflies closed.

Do you get lean popping through the carbs or does it just bog down. If it just bogs I'd say your too rich. My guess is you set the float level too high. Did you set it with the gasket? You needed to. If not your float will be high. If it's too high it will give you an overly rich mixture as soon as the carb tries to go on the main jet. The ET, main and AC jet all work together. They do that correctly only if the fuel level in the main wells is at the right height.