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Can Opeler
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I'm back on this thread to ask a simple question. I did look for an answer but didn't see it.

First, I have a Weber 38/38 with electric choke and the choke opens properly. All tests were done with the engine warmed up.

When tuning idle, I know the adjustment screw can tell you if you need bigger or smaller idle jets.

I believe the starting point for tuning is around 2 full turns from seated.

My question is...

When tuning, if you have to go 3.5 turns to start to smooth, do you need a bigger or smaller idle jet?
On the opposite side, if you smooth out at 1 turn, do you need a bigger or smaller jet?

If I turn mine in beyond 2.5 turns, the engine really gets jumpy and wants to die. I can't seem to get a difference on adjustment past 3.5 turns but it seems to need more than 3.5 turns.
A lot of people will disagree, but I have found the Weber “best lean idle” adjustment to be a crock of crap. There are too many variables involved from engine to engine. That being said if you don’t have an AFR gauge it is helpful to start tuning. In my experience the “best lean adjustment” gives a too lean AFR of around 13.5 on the 3 engines I’ve tuned. The sweet spot for idle is 12.5-13.0 on my engines.

If you are not having any changes in engine speed at 3.5 turns you are already too rich approaching 11AFR.

If the engine is jumpy below 2.5 turns you are too lean (this starts at 13.2-13.5 AFR idle with a DGAS).

If you are below 1 turn out you need to go down on your idle jet

If you are above 3 turns (2 according to Weber, but I disagree) you need to go up on your idle jets.
 

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Über Genius
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9,401 Posts
So it looks like I need bigger jets.
I wish my sons car were here. I could just find his recipe and repeat it. LOL

I was hesitant to put 50's in there when I built the engine. i am pretty sure that's where I ended up though.
 

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Can Opeler
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3,486 Posts
So it looks like I need bigger jets.
I wish my sons car were here. I could just find his recipe and repeat it. LOL

I was hesitant to put 50's in there when I built the engine. i am pretty sure that's where I ended up though.
Yes I’d drill out your 50s if you have a pin vise. I aim for 2 turns out, but it’s ok to go over. Just get it where the car is happiest and then lean out the mixture screws a bit to compromise.
 

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Über Genius
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Yes I’d drill out your 50s if you have a pin vise. I aim for 2 turns out, but it’s ok to go over. Just get it where the car is happiest and then lean out the mixture screws a bit to compromise.
I might get a set of drills at CHinaFreight tomorrow. They usually have their dentist drill bits for cheap.
 
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Bikini Inspector
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my 2.0 and another guy's 2.0 from green bay I helped with had to go up to nearly 75s-80s to get it to best idle adjustments in spec.

it all depends on cam and valves.
 

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Super Moderator
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Important, Kyler!

Yes I’d drill out your 50s if you have a pin vise. I aim for 2 turns out, but it’s ok to go over. Just get it where the car is happiest and then lean out the mixture screws a bit to compromise.
If you haven't done so already, Kyler, you should go look at my "Understanding idle transition . . ." thread from many years ago. HTH :pat:
 

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Über Genius
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It turns out I don't have any jets between .50 and .65.

I had .50 in the carb as it sat so, knowing others have gone bigger, I am ordering a set of .55 and .60
I have .65 and even .75 but I'm sure I won't have to go that high. I even have a set of .45 but those are useless, I'm sure.
 

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If you feel like you're going ridiculously oversized on the jets or it isn't responding well to adjustment, I'd advise checking for vacuum leaks.

Harold
 

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Über Genius
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If you feel like you're going ridiculously oversized on the jets or it isn't responding well to adjustment, I'd advise checking for vacuum leaks.

Harold
Vacuum leaks are all bundled up.
I have been battling to get this car to idle since the first time I fired the motor. I finally, just recently, found the culprit. I had a crack in my brake booster hose. Now I can get it to idle every time but the carb needs adjusted. I had it "best idle" with the cracked hose but only on the transition circuit. Now that I've closed off that intermittent vacuum leak, I can start to jet the carb. Like I said, it idles now (at 800RPM even). I just want it to idle a little more smoothly and set it to 900-950 RPM.

I've toyed around with the idea of drilling a small hole in the butterfly but that seems a little drastic.
 

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Super Moderator
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...it idles now (at 800RPM even). I just want it to idle a little more smoothly and set it to 900-950 RPM.

I've toyed around with the idea of drilling a small hole in the butterfly but that seems a little drastic.
Factory spec for a manual transmission car is 850-900 RPM. You are using a more accurate tachometer than the factory one. I use to chide the previous owner of the Old Hag about his high idle setting. The factory tach says it's idling at 1100 RPM, my Snap On tach tells a different story.

Harold

P.S. Unless you have a serious performance cam I can't see the need for drilling the throttle plates.
 

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Über Genius
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My carb is weird.
It takes two different idle jets. It's probably not supposed to.

I forgot this little tidbit when I ordered new jets. Oh well, I'll have a spare.

I found a .60 in my jet collection for the one side and drilled out my .50 to match. So now I have .60 in both sides.

It seems to have helped. A little anyhow.

Some things that might add to the loping is that I have a combo cam and an aluminum flywheel. At 1200 it purrs like a kitten. At 900 it lopes a little. I can live with a little loping, I suppose.

With the .60 idle jets it seems to be a little smoother off the line. It used to hesitate ever so slightly.

I'm done for the weekend.
 

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Can Opeler
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3,486 Posts
It’s normal for the idle mixtures to be pretty different on either side of the carb. The Opel manifold delivers fuel pretty unevenly from each barrel probably because of the distance from each barrel to the engine, and further complicated by the different angles the air needs to travel from each barrel. That being said you do not want to have different sized idle jets on either side! It is better to have one of your screws very different instead. Having different sized idle jets is fine and dandy at idle, but you will have issues at low speed cruise. Mine ran like crap with two different idles even though the idle was perfect.

Edit: it’s been awhile since my DGAS was on, but I think I had a barely one turn out on the one closest to the engine, and 2.5 turns out on the other (or vise versa).
Despite the fact these were nearly 2 turns apart on some days the car drove beautifully with no flat spots or rich spots. (Except WOT being too darn rich at 12.3 on the dyno.)
 
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