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What should Gordo do?

What Should Gordo Do?

5K views 41 replies 17 participants last post by  The Scifi Guy 
#1 ·
I've taken my willingness to tune the new side draft I put on my car as far as I'm willing to go and I'm willing to accept the idea that it might need to be rejetted or new gizmos in it swapped out. I'm also willing to accept that the original problem, phantom shutdowns and phantom stumbling that would completely disappear and the car would return to normal, may have been caused by a simple vacuum leak. Side drafts in general react very quickly to slight changes in throttle/air/fuel and my particular set up may be super sensitive. The small vacuum leak I discovered after I installed a new carb and how radically it reacted to a little spray and the fact that 2 of my all-steel lock nuts weren't doing a good job of holding the carb and intake together, have me thinking that that was my problem all along.

The old carb was a more primitive DCOE 9 and the new carb is a DCOE 152. The 152 has extra progression holes and idle bypass features that my previous carb didn't. I just found a mention in my Weber carb book that says the DCOE 9's are easier to tune because they don't have those extra features. I think the new carb may need new hardware and professional tuning as a result of that comment.

Getting my car to a tuner is difficult in it's present state and I may have botched the initial diagnosis that a simple carb spray test would have revealed. Who would have thought that a vacuum leak could do nothing at all for 20 minutes and then totally kill the engine for 2 seconds and then totally disappear?

So, I'm making a Poll asking:

1) Should I put the old DCOE 9 carb back on and try to tune it myself before throwing in the towel and taking it to a tuner dude?
2) Keep the DCOE 152, throw in the towel, take it to a tuner.
 
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#32 ·
#33 ·
When I purchased my DCOE carbs from Pierce Manifolds, they asked for all engine information (displacement, compression, cam specs, etc) and provided carb jetting to meet those specs. It could be worth a call to them to see what they would suggest for your engine. You wouldn't have to buy anything, but it could give you insight on how close or far away your jetting may be.
 
#37 ·
OK, tnx... just wondering where the total advance is and when; don't want you to 'splode any pistons. I can't say if the light and Pertronix multi-spark 'like' each other or not. Plenty of info out there about incompatibilities found between MSD and dial-back.... just throwin' that on the 'food for thought' pile.....

When things don't make sense, it is time to question all assumptions....I am going further and further 'back to basics' on our '75 EFI oddities as we sort that out.
 
#36 ·
Wow. Between this thread and the Pissed thread you have gone nuts trying to figure out these carbs. A long time ago lots of people told me that trying to EFI my engine was too complicated. Seems to me that trying to carb your engine is more complicated than the EFI. Just fuel inject the sucker and get it over with!
 
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#39 · (Edited)
I'll be receiving a 2.2 with Motronic "someday" from Charlie. We'll see if I ever get around to installing it.

Guys, understand that there are essentially zero comprehensive write ups about single side draft set ups. My 125 page Weber and Dellorto side draft book has about 4 scattered sentences about SSD's. My 400 page Haynes Weber Carburetor Manual doesn't mention them at all. None of them say that you can have a vicious vacuum leak and the car will start normally and run just fine at idle. I only found a one sentence mention that said that DCOE 9's are easier to tune than 152's because of the extra/different progression holes and that DCOE 9'ers simply run their set ups a little richer. That's it. I only found the last sentence this past week.

But then consider how much is written about DUAL side drafts. Hundreds of pages of info and detailed information and charts for all sorts of different engines.

And then consider that my set up is for low speed daily driving a stroker engine in a city with a single side draft and an automatic on a car with a limited gear range and an intake manifold with one runner 3 times longer than the other one and a split profile cam that lifts very quickly, but closes slowly/normally. Go ahead, tell me what the timing and fuel mix should be on a set up like that.

I'm virtually certain that my whole problem was a small vacuum leak that would only manifest itself when the engine warmed up. The default limp mode feature in side drafts may have masked the leak at start up. The very rapid response of side drafts to rpms and throttle, plus the leak only happening to one runner/two cylinders, may have also masked the leak and gave me the false indication that my ignition turned off when my engine would be idling in the driveway for 20 minutes perfectly and then abruptly turn off or suffer bouts of stumbling. Wait 2 minutes and everything back to normal. My engine was the envy of the Opel world. How many Opelers can walk up to their cold engined car, at any time of year, and just reach in the window and turn the key to start it? Not many.

Assuming I'm right about the vac leak and the symptoms fooling me and every other Opeler and engine expert I talked to or who chimed in on the subject in various forums, any engine dude will tell you that a smooth running engine that just turns off without warning has an electrical/ignition issue. Most will also say that a stumbling engine is caused by fuel delivery or vacuum leaks. What do almost all Opels do when they have a vacuum leak? They are usually hard to start and have erratic idle. My engine started like I had a Saturn rocket booster under the hood and idled like a dream for 3 years. Then I had my recent problem and followed all the wrong paths and then tried a replacement carb that, although the same size and same manufacturer and the same jetting and set up, refused to run properly or use the same settings as the previous carb, all because it has a couple of extra pin holes in the barrels.

:veryhappy
 
#42 ·
Charlie drove up here on Friday and he whipped out his guns and gauges. We experimented with the timing at various points from 0-35 degrees, we eventually settled on around 18 degrees and about 2.5-3 turns out with the mix. Then we went for a long drive of about 45 minutes all through my neighborhood, downtown traffic, my torture test roads, etc. We were at full operating temperature the whole time and none of the shut offs or stumbling occurred. I floored it and spun tires and did everything I could think of to detect a glitch like pinging, etc. The car ran really great, just like it used to.

Except at stop signs and red lights. Basically, it had trouble when in Drive and stopped. It would drop out of normal running and go into "side draft limp mode". So we went back to the house and tried various experiments and fiddled with the timing to knock out that problem. The car ran fantastic running in Neutral in the driveway and passed every rev test with clean powerful running, but put it in Drive with my foot on the brake and maybe idle forwards and backwards and the limp mode would kick in. We made it worse, we made it better, but we couldn't kick out that last glitch. We had good results with ridiculous high idle at 2000, but you can't have your automatic car getting enough throttle for 2000 rpm and then put it in Drive and have the torque converter squash it down to 800. That ain't right. No matter what idle you set your auto trannied car to, the tranny will squash it to 8-900rpm when idling in Drive. If the carb goes into limp mode, that rpm will drop to 3-500rpm. A side draft is designed to run at 1000-1200rpm at idle. We couldn't get it to behave but we got it really close at points. Actually, having an automatic and putting it in Drive with my foot on the brake was a great way to simulate load at low rpm. It's kind of like having your car on a dyno with simulated load. If I had a stick I would have to do endless drives lugging around at 800rpm in 1st gear.

We got the car close enough to normal driving behavior where I should be able to get it to the Dyno dude's shop for fine tuning. We both kind of agreed that getting the timing EXACTLY right, within a degree or less, is the answer. But, man, is it hard to find that one perfect degree or fraction thereof! I might try fiddling around myself with it a bit, but I'm inclined to not touch it and just let the tuner dude zero in on the best setting for me. I'll ask him if he can change a jet or something to make the car easier to tune myself.

It definitely seems that my whole problem was a simple vacuum leak.

:veryhappy
 
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