fine tuning guidance requested

[michaedo]

Hello listers,
Well, I've got probably better than 200 miles on the wagon now. (Hard to
tell, speedo doesn't work.)
Pulls like crazy from idle up to 6000 and beyond. Looking at some people's
various problems with stalling, stuttering, bogging and such I shouldn't
complain, and I'm not.
Just little pesterations I'd like to take care of and it'd be a peach of a
car. I drive a ways, diddle, drive a little further, and diddle a little more.
Now for some guidance on the final diddle.

It pings on acceleration beyond about 4600rpm. I'm using mid-grade this
last tank. Should I quit being cheap and go for the high priced spread?

It doesn't idle down coming up to a stop, or between shifts like I think it should. It'll like hold the revs up at about 2-2.5K before dropping off to
idle.

It diesels for about 10 seconds after shutdown all the time except when
still cold.

Do all these symptoms point to one problem or am I still in the final tune
stage and need to continue to fine tune the timing and carb? Right now
dist. is set right at 0*, the idle mix screw closest to the engine is set at
about one turn out, (maybe a tad less) and the outside screw is between
1-1.5 turns out.

Other than the problems noted above I couldn't be more pleased with the
way it's running. Thanks in advance.
Don.

[BQS4]

I don't know if you have one problem or several, but, I do know that the 38 weber carb is not as forgiving as the 32/36. The 32/36 can be used straight out of the box, but, could be better with fine tuning of jets. The 38 on the other hand DOES need to be tuned for your particular motor/driving.

[tekenaar]

First thing I'd "fiddle with" on your next outing is your ignition timing . . . sounds like too much advance to me. Different distis have different mechanical advance curves, the earlier distis have a lot of allowed adavance, the later ones less . . . which year disti are you using?

And like Gene already said, do a search here on "38 DGAS jetting" and get that carb rejetted before trying to "adjust" it any further . . . it's been said before, can't "fine tune" an "improperly jetted" carb, don't even try!

[deaner]

I was just looking at a picture of your engine, looks like you have your carb mounted backwards.

[michaedo]

thanks folks,
The carb was jetted as to what others on the website with like engine
had done.
The dist. is a 75 unit and more than likely needs to be backed off a tad.
It's just that the redline carb guide said webers like a little more advance
than stock. I'm starting at the 0 degree and will work from there.
Just a little bit ago on a vacant stretch of road I ran it up, kicked it in
to neutral, (it stayed at about 2000rpm), jumped out to see what was
up. Danged if the throttle return spring wasn't up to the task to bring
the revs back down. That may cure a lot of my ills. I'll let you know.
Again, thanks for everyone's rapid response. Ya can't beat this group
for helping out.
Don.

[kwilford]

Originally Posted by deaner I was just looking at a picture of your engine, looks like you have your carb mounted backwards.

http://www.opelgt.com/forums/175173-post20.html

[RallyBob]

Originally Posted by michaedo thanks folks, The carb was jetted as to what others on the website with like engine had done. The dist. is a 75 unit and more than likely needs to be backed off a tad. It's just that the redline carb guide said webers like a little more advance than stock. I'm starting at the 0 degree and will work from there. Just a little bit ago on a vacant stretch of road I ran it up, kicked it in to neutral, (it stayed at about 2000rpm), jumped out to see what was up. Danged if the throttle return spring wasn't up to the task to bring the revs back down. That may cure a lot of my ills. I'll let you know. Again, thanks for everyone's rapid response. Ya can't beat this group for helping out. Don.

In truth you may need *more* initial timing, and perhaps just need to slow the rate of advance. A 1975 distributor has only 25 degrees of advance, so at 0° you end up with a total of 25°. A stock 1975 Opel is set at 5° BTDC, for a total of 30°. Don't idle the car too high either. Depending on your camshaft, this will contribute to the run-on problem. To slow the rate of advance a set of stiffer advance springs and/or lightening the advance weights will accomplish the same thing. If the total timing comes in too soon in conjunction with the low octane fuel, it'll certainly ping.

I'd also suggest upgrading to CA's best 91 octane piss water...uh, I mean gasoline. I've messed with a few CA Opels and the quality of the gasoline leaves a lot to be desired, it's requires a different mentality than in other parts of the country in terms of tuning.

Bob

[bgdowski]

I would bet its a combination of your throttle return spring, carb jetting, and ignition timing. Hope it gets figured out... If you still get some knocking, head over to your local airport and throw in some 100LL

[RallyBob]

Originally Posted by bgdowski I would bet its a combination of your throttle return spring, carb jetting, and ignition timing. Hope it gets figured out... If you still get some knocking, head over to your local airport and throw in some 100LL

I'm pretty sure he can't pump any into his car, but if he knows someone with a pilot's license he can probably put some into a gas can. Most states with strict emissions standards don't allow this practice. But I do like the performance of mixed pump gas/aviation fuel in an Opel, a friend of mine used to run it in his circle track car with good results. Burns very cool, so you need to bump the timing a bit to gain any power. We actually lost power running straight aviation fuel.

[bgdowski]

What was the mixture ratio that he ran?!

[BMWonly]

Originally Posted by RallyBob I'm pretty sure he can't pump any into his car, but if he knows someone with a pilot's license he can probably put some into a gas can. Most states with strict emissions standards don't allow this practice. But I do like the performance of mixed pump gas/aviation fuel in an Opel, a friend of mine used to run it in his circle track car with good results. Burns very cool, so you need to bump the timing a bit to gain any power. We actually lost power running straight aviation fuel.

The Riebes car parts stores in CA sell racing fuel to anyone !!! 108 octane unleaded, and 110 leaded. $10 a gallon !!!

I recently rebuilt the motor in my 71 GT, with high comp 60 over pistons, 2.0 valves, combo cam, some mild porting and a 38 Weber. No matter how I would retard my ignition, it pinged. Mixing 91 (the CA premium) with the race fuel worked fine. Based on the mixture I probably have about 94-95 octane. Not sure what my advance is, but I played with the timing until it ran best. Also, replacing the emulsion tubes and the main jets (135) helped.

Dieter

[bgdowski]

Dang, $10 a gallon?! The going rate for 100LL is about $5.50 at an airport...

[RallyBob]

Originally Posted by bgdowski What was the mixture ratio that he ran?!

IIRC we used 3 gallons, mixed with 5 gallons of 93 octane. Fuel cell was 8 gallons.

[michaedo]

Throttle return spring solved a lot of the ills. Pinging almost gone.
Once I cycled through the gas in the tank, (some probably better
than two years old) Also won't be getting anymore gas down and
the mom & pop station at the corner. All is good. 'cept it still runs
on after the ignition is turned off. Monkeyed with the dist. but it
has a sweet spot just a tad CCW of 0*. Going to leave it as is.
Thanks for the advice ya'll. Sunny day here in Sacramento, think
I'll head down to the drag strip and watch some domestic iron
go at it. Have a nice day folks.
Don.