Effects of fuel pressure on webers

[Carefree Carl]

For all I've looked, I can't seem to find a reason to run the fuel pressure regulator on my recently installed weber. I know the factory pressure and the weber pressure are different, but what effect does this have on the system as a whole.

For what it's worth, I'm having a hell of a time trying to get my car to pass emissions and I'm hoping it's something as simple as this putting one on. My more mechanically inclined brother (who supplied me with the weber) doesn't think this should have much if any effect on emissions. He ran the same carb on a 79 Corona without the regulator without any emission issues whatsoever.

[Petros]

The design of the float and needle valve in the carb are what determines how much fuel pressure it can handle. With too much fuel pressure it will overpower the ability to hold back the fuel supply, and it will spill over into the throat of the carb making it run rich, possibly causing it to stall out because it is getting too much fuel, especially at idle when it does not need much fuel. so it is possible the addition of a fuel pressure regulator might solve the emissions issue.

However, a number of other issues can cause it to fail emission because of a carb change, besides the fuel pressure. The fuel and air jets in the carb have to be changed to meet the needs of this engine. Displacement, cam shaft design, intake manifold length, operating temp, compression ratio, and a number of other issues all can change the need to change the mixture of fuel and air the carb delivers to the engine, if any of the jets or external adjustments are off it could fail emissions.

The way the carb works is a complicated thing relative to emissions. Most states will test for three things, hydrocarbons, NOx and Carbon Monoxide, running it too rich or too lean will cause one or the other of these emissions to be too high. So it is not enough to know it fails, but which one it failed, and by how much. Even a simple vacuum leak could cause a failure.

I would be surprised if you took a carburator from another car, just slap it on a totally different car, and have it pass emissions without any re-jetting or other adjustments at all.

So you have your homework cut out for yourself if you want to pass emissions with the Weber carb.

What state are you having to meet their emissions test? Do they test at idle only, or do you have to "load" test it with the wheels on a dynomometer running at a certain speeds? If you want some help you need to give us more information. Also, there are a number of threads on this forum about installing and jetting the weber for the Tercel. Go read all of those first, and than ask more specific questions.

[Carefree Carl]

Excellent points. I've read all I could find on jetting. We've tried 3 different combinations of jets and haven't given up yet.

Timing is at 8 dtdc, I think we're going to 13 next. We had the Idle passing with 135 pri idle. In UT they dyno the car... it dumps gas with 145 pri main jets. We then went to a 125 and 135 jets and the idle failed with no change while on the dyno.

The Cat needs to be replaced too, but I think it's effect will be minor (but still present).

[Petros]

You will want the timing to be a 5 deg BTDC for the test. But put it back to 10 or better afterward or you risk burning up your exhaust valve and possibly other engine damage.

If you did not burn up the cat by running too rich it should still be working. they do not wear out, but they can get damaged by running too rich.

[Carefree Carl]

It's been running rich since I purchased it (10k ago), so I'm not surprised if it's burned up.

Thanks for the timing tip.

[teranfirbt]

I've been running a 32/36 for about a year now with no issues with fuel overflowing the bowl or being overly rich... It passed the Oregon emissions test back in June, but I also had the idle tuned with a wideband O2 sensor.

[Carefree Carl]

I've been running a 32/36 for about a year now with no issues with fuel overflowing the bowl or being overly rich... It passed the Oregon emissions test back in June, but I also had the idle tuned with a wideband O2 sensor.

Without using a fuel pressure regulator?

Thanks.

[teranfirbt]

Yep, no FPR.
What jets are in it? Mine runs fantastic on 50 idle jets and a 145 primary main. I've got a 170 in the secondary main, but it makes it run rich when I open the secondaries.