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Discussion Starter #1
As I continue with my DSD project, I've finally gotten to the the point where I can start tuning the carbs. I have the carbs synchronized and have started driving it around the block to see if there is any troubles. One thing that I have almost immediately run into is a throttle lag between about 2500-4000 rpm, after which the engine continues to increase rpm normally.

My thoughts on this are as follows:

1. The accelerator pump is not effectively delivering fuel when the throttles are opened

2. There is too much fuel pressure and the carbs are flooding when the gas pedal is pressed

3. The timing is set too low, and therefore the rpm doesn't advance as it should in this range

4. The jetting is off. (Although this seems unlikely based on another post in the forum.)

Any thoughts?
 

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Discussion Starter #2
I pulled the plugs to get more information. I'll add it here as well

Cylinder 1 - rich
Cylinder 2 - lean
Cylinder 3 - rich
Cylinder 4 - rich
 

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Can Opeler
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What is your tuning. What do you mean by throttle lag. Does it fall on its face and you have to let off the throttle for it to recover and accelerate, or do you hold the throttle and make it sound likes it’s struggling for minute before it gets up and goes.
 

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Opel Rallier since 1977
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As Knorm indicates, the exact nature of the bog or delay is important. If it is of very short time duration, then it may well be the accelerator pump circuit. But if it is prolonged for several seconds while the RPM's slowly build, then it is most likely in the tuning: main and/or air correction jets, or emulsion tubes.

Can you list your jets and all variable parts for everyone's consideration? And how is your ignition timing set up, in terms of initial advance and total and at what the advance comes in? Or your distributor, if stock?

Your plug readings are vague; the exact conditions under which they are taken has to be known. Was the car driven at slow speed, or idled for a while, before shut off and the plugs pulled? Then that will only tell you the mixture in the idle/progression circuit, not the main circuit.

Plug readings of the mains has to be done in a certain way. You have to accelerate at or close to to full throttle, and then cut the ignition and then let off the gas, and drift to the side of the road and pull the plugs.

And just know, that with the modern fuels, reading plugs has changed from what it was as you get to the fine levels of readings. In other words, it is a lot harder than it was a few decades ago. For example, a good mixture at heavy loading will look lean on the plugs compared to what the older fuels would look . A modern air-fuel meter (AFM) is a real boon in this work.
 

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Just Some Dude in Jersey
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14,402 Posts
Nathan has my RallyBob modified dizzy that was made for early advance for an aggressive cam, if that's any help. It's adjustable to a certain extent. It also has a Pertronix III in it.
 

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Opel Rallier since 1977
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OK, that is good to know. So it does not sound like a slow advance curve is part of the problem. The initial timing (base timing, or timing at idle with no vacuum advance connected) needs to be set somewhere near right. And with the Pertronix, it sounds like the spark ought to be solid.
 

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Just Some Dude in Jersey
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Hmmmm.....what size venturis do your side drafts have? Smaller ones develop more air velocity at the lower rpms and, I think, better power and drivability at the low end.
 

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I had a 45 DCOE in an SSD configuration, with the angled Steinmetz intake, when the motor was 2.0. It took a while to get it dialed in, but eventually worked well. Two things helped me a lot:
The book:
428107


And the fact that a PO had put in a wide-band AF gauge. It makes tuning a whole lot easier.

Then, recently I've gotten the motor running again, as a 2.2l, with a modified (Rally Bob, Gordon, Charles) midi intake. I started out with a fairly bad lean bog on off-idle acceleration---maybe similar to what you saw. I was thinking accel. pump, and changed the accel jets, and changed the accel spring, and actually got some different rods to alter the pump shot. Before I went too far, I pulled the carb off the car, to test the accel pump squirt, as shown on some YouTube videos. What surprised me was that the squirt did not start immediately; it seemed like it took a bit of rotation on the linkage (maybe 10-15 degrees) to get the squirt to start; and then when the rod dropped, it worked fine; it seemed to me that my problem was not accel pump driven. So, I think the first question for you, is do you get the bog right away, on first movement of the linkage, or later. Because if you get it right away, I don't think you can help yourself by fussing with the Accel pump.

Then I got to reading the book a bit more. I think there were a few sections that were relevant; the more important ones were on p. 70 and 71.

One quote:
"If the throttle is opened too much at idle the first of the progression holes will be in operation: this should never be necessary and is not desirable. The engine has to idle without any progression hole assistance (extra air/fuel mixture).

Another:
The point is that, if the engine is to accelerate smoothly, the air/fuel mixture that goes in through these holes has to be exactly right. This is why the idle jets have to suit the progression phase perfectly. The air fuel mixture for idling has a degree of adjustment via the idle mixture adjusting screw but the progression mixture can only be altered by changing the CHOOSING THE COMPONENTS FOR YOUR CARBURETTOR/S jets for an overall mixture change.

Since I had decided, my issue could not be Accel pump related, and I was getting the bog at first movement, I started again, trying to make sure the trottle stop screw setting put the blades at a point right before the first hole got uncovered. And then sort of worked backwards from there, fussing mainly with the idle jets so I got rid of the lean bog I'd seen on first tip-in. And also fussing with the idle mixture screws, but trying to keep those at 7/8 out from a light seated position (per "The Book"). I think I've now got that initial lean bog cured now, although it idles at 1k, while I had the 2.0 idling around 700, which I liked better.
 

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Opel Rallier since 1977
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You have found a big secret to good off-idle carbed throttle response, Mark1. This happens all the time over in V8-land too.... too much throttle opening (often on the secondary throttle blades of a 4 BBL), and it throws off the whole progression calibration. Did the same thing as you for my son's 340 with 600 cfm 4 bbl; closed down the secondary throttle stops to make the primary progression work right.

I am a bit surposed that you still have that much throttle shaft angualr rotation before the accelerator pump action starts. Sounds like something is not quite right.
 

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It may be that my numeric estimate is off. I did not have a degree wheel on the shaft; just holding the carb in one hand and turning the shaft with the other (and aiming away from the BBQ). When I had the carb off, I pulled the plate to examine the mechanism for the pump. Everything seemed in order, with no obvious way to adjust, and pretty smooth operation. I don't see anything wrong; but initially the amount of shaft turn before the pump kicked in surprised me; I had imagined it would be almost instantaneous.
 

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Just Some Dude in Jersey
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Bog, bog, bog, the Bane of all Opel engines. We've all had it. On my last downdraft set up, this was cured by trimming the accelerator pump spring. After that, punch the pedal and it roared with no bog. But, I had driven for so many decades with the bog prior to that, that I just couldn't/can't stop the habit of fluttering the gas pedal as I transition off idle. This defeats the bog.

On my single side draft, that car was tuned by a tuner dude with one goal: Extreme low speed drivability, especially in traffic. Unbeknownst to him or me, the engine had been made with too much compression and I really should have been using race fuel. I was always using the recommended for a 2.4 premium grade fuel. He was wildly successful. The car drove like a fuel injection car. Hit the pedal and the wheels spun like a blender(I may have fluttered the pedal a bit at tip in, due to force of habit). I could punch it from a dead stop and roar to 100mph with no flattening of the acceleration between the almost imperceptible shifts of my automatic. It was like how I guess an electric car drives. No sense of gear shifting, no flattening of acceleration as the gears wound out. It was the most perfect and ferocious engine I have ever had. I didn't want to change one thing about it.

Two year later engine trouble stated. The head was never milled flat enough and there was a chronic coolant leak into #1 and carbon deposits built up like a muthafluffa. The tuner dude had apparently made it run really rich. But, gosh dang that was a great engine.

My new FI engine is boring as schitt, in comparison. Yeah, reliable. Yeah, smooth boring acceleration. Not nearly as fast. Feels like a budget passenger car.

Does this help you? Probably not, except for the bit about fluttering your gas pedal. If fluttering your pedal works for you to get past the bog, then I'd say live with it. It's an Opel.

:)
 

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Discussion Starter #12
Dang, I posted and then forgot all about it. The lag I was having seemed to be in between either the idle curve and the acceleration curve or the acceleration curve and the main curve. The annoying thing was if I went from idle to flooring it(for example) or a similar abrupt power change, the engine would fall flat on its face and stall. As for jetting it has the same jet setup as noted in this post from 2017. Interestingly that's what the carbs had when I bought them, so I think they may have been used on another Opel 1.9 previously. I'm running a mostly stock 1.9 aside from the dizzy and DCOEs. Not surprisingly I'm having another issue that I will post in a separate thread, perhaps this and the other are related, perhaps not. I'll throw a link in here when it's up. Thank you all for your replies, if I can get it working correctly again I'll try to apply your advice
 

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Just Some Dude in Jersey
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There's a possibility that you don't have your floats adjusted properly and that your fuel bowl is chronically low. Adjusting the floats is a maddening process. Your problem seems to occur when you need a sudden surge of fuel to accelerate. Low fuel in the bowl can cause this. I think that one way to check this is to remove your main jets, possibly while the engine is running, but maybe not, and stick a paper match or paper down inside the jet hole until it stops and then pull it out real quick and compare it along side your jet. The small emulsion holes on the side of your jet MUST be emersed in fuel. The wet part of the paper or match must extend high enough to cover all the holes.
 

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Discussion Starter #14
There's a possibility that you don't have your floats adjusted properly and that your fuel bowl is chronically low. Adjusting the floats is a maddening process. Your problem seems to occur when you need a sudden surge of fuel to accelerate. Low fuel in the bowl can cause this. I think that one way to check this is to remove your main jets, possibly while the engine is running, but maybe not, and stick a paper match or paper down inside the jet hole until it stops and then pull it out real quick and compare it along side your jet. The small emulsion holes on the side of your jet MUST be emersed in fuel. The wet part of the paper or match must extend high enough to cover all the holes.
Could this also contribute to the problem I'm having here?
 

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Just Some Dude in Jersey
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All I can tell you is that the float setting is unbelievably CRITICAL. I've read that it's the #1 thing that people screw up. Just a 1/8" height change can make a car run completely different. It's not just a toilet bowl float, it's a major component of how the carb works. It sets the height of the fuel going to the jets and their emulsion tubes. Your problem clearly sounds like a fuel starvation issue right when you need to have extra fuel. If any of the emulsion holes are exposed to air they will suck in air instead of fuel. Fuel good, air bad. I have screwed up my float heights incredibly bad and gotten a full spectrum of weird engine behavior that made no sense. I finally took it to a side draft tuner dude in Philadelphia and he beat it into my head that the float height is super critical.
 
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