Warm up regulator questions

[bkcbuilder]

79'SC Euro, pulled out of a barn after 5 years of sitting with a blown up airbox. I've had it 4 weeks now, replaced airbox, fuel pump, filter, accumulator. Will set CO when I can get the idle in spec.
Problem is that it lean idle backfires at startup like crazy, as soon as you give it gas it goes great and runs fine and pulls like crazy(except for the 12-1300 idle)
Startup pressure is 2.5 bars, warm is 75-80lbs, WUP ohms at 28, has power at plug of 11.8V. All lines have been checked for vac leaks.
When I unplug the WUP it will start cold just fine, a slight pop once or twice maybe and is good, replug in WUR and the thing starts popping again.

Would love to set CO but just can't get idle down, and the idle screw is on it's low stop.

I'd take the WUR apart and clean, but am worried about the gasket on the bottom, and screwing it up, then end up buying a WUR anyway, that and I hate being beat by something and refuse to be a parts changer.

Any clues or something I'm overlooking? I tested the thermoswitch. What else leans this thing out to backfire so bad???

Thanks..Brian

[ianc]

Startup pressure is 2.5 bars, warm is 75-80lbs

Why the difference in units here? Did you actually measure this yourself? If so, what (exactly) is the procedure you used? Where did you find the correct temp vs. press graphs for your particular model?

I'd try richening the mixture slightly if you're convinced it's too lean. Get a 3 mm allen and turn the adjusting screw CW about half a turn, see if there's any change.

The high idle does sound like a vacuum leak though. What makes you so sure you don't have a vacuum leak? How did you check this? When cars sit, rubber cracks and breaks, sometimes in spots you can't readily see until you've taken everything off and checked it.

Taking the WUR apart is not bad. Making it adjustable is not that bad either...

ianc

[unclebilly]

Spray Carb Cleaner on your intake hoses and see if the engine RPM changes. If it does, you've found a vaccum leak.

Don't be afraid t pull apart the WUR, it's pretty simple and hard to screw up.

[bkcbuilder]

ianc...

I used the procedure straight out of the bentley, the graph in the bentley used bar pressure for cold, and a bar and psi. pressure for warm from the tables, based on WUR model. There was a little variation in the procedure, one being to activate the pump by jumper at the relay, which I did, and then another from a CIS troubleshooting manual which said to hook up cold and start the engine(also which I did as a way to check my first way) both are identical.
I used carb cleaner, and propane as means to check for vac leaks, and also when I had the engine out(for the airbox change), I replaced all the hoses on the back that would be difficult to do with it in the car.
Turned the mixture screw on the venturi , ran it, made no difference, turned some more....same. Turned back to original so as not to screw up the baseline. Don't know who the last hack to work on the car was, but hopefully he didn't screw with this adjustment to bad. I mean the cracked airbox was screaming in his face, no amount of mixture tuning was gonna fix that crack.

Since it runs so well after a min. of driving, I'm wondering if the chambers of the WUR could be clogged and that is leaning it out. But I just don't know that much about them, and there isn't any good text out there help out...all they say is if it's out of spec..replace. I'll take it off and disassemble this evening...worst case is I have to buy one.

[ianc]

It's pretty easy to take the WUR apart and clean it, but it would definitely be worth the trouble to make it adjustable. Take a look at this thread:
Made an Adjustable WUR- Step by step, got Pics!

ianc

[cmonref]

These pressures ("Startup pressure is 2.5 bars, warm is 75-80lbs") are far enough off of the spec values that you really HAVE to correct them before proceeding. Your "cold" pressure should be around 1.4 or 1.8 bar, depending on the WUR, and the "warm" pressure should be around 43-49 psi. The total SYSTEM pressure should be around 70 psi. There are some good threads in the archives about how to adjust the WUR.

[bkcbuilder]

Are the Bentley specs off? I'm hittng dead center of the shaded area for my WUR , at the give ambient temp for cold, and on the high end of the range for warm....what gives here?

[ianc]

Are the Bentley specs off?

That's why it's difficult to comment when people post their pressures; each WUR has a specific pressure range for a given temp. Be sure the graph you're looking at matches the part # on your particular WUR, and that the WUR is correct for your model year and engine.

Making it adjustable allows you to set it where it works well though...

ianc

[klaucke]

I went adjustable and never looked back, its a mod I would highly recommend. If you have acess to tuning with a wideband A/F meter (i.e. LM1), that can help and is probably preferable to tuning with the CIS pressure guages.

The symptoms you mention are not out of the ordinary for CIS. My car backfires quite badly below about 3k until it warms up, then it is smooth over all RPMs.

[bkcbuilder]

All is right in the garage tonight! WUR was pretty bad inside, cleaned the 5 year old gunk out of the line/screen on top, didn't make adjustable maybe later. Still had a bad hunt but lean backfires(machine gun style)are gone, so I leaned it enough to get at least a small (200)rpm hunt. Used my new Gunson and found the CO was still 15%...last guy MUST have richened trying to overcome airbox crack. Kept at it adjusting idle and CO until I hit 900RPM and 2%CO. Took it out for a good romp, came back and retested..spot on. Timing needed a slight kick, another fast test ride, and all is holding and running smooth. AHHHHH! Thanks all for the help....Brian

[ianc]

Glad to hear it. Have fun!

ianc