Solex Tuning

[gr_diver]

Ok this is it, I have been fighting this for over 3 years and it is still there, even after changing carb...

My car has a poor performance below ~2200rpms. If I accelerate in 3d gear, where it is more obvious, the car slowly accelerates from 1500rpm, and when it reaches the pre-mentioned spot (2200rpms) it suddenly gets a burst of power. It reminds me the feeling of my friend's turbo engine, with less power of course...

Considering that valves/compression/ignition is in order, and that a "new" carb has brought the "power boost" 300rpms lower (it used to be 2500rpms with the old carb), what else should I try?

In addition, if I suddenly open the throttle below that very same spot (2200rpms) the car would hesitate momentarily, pick up and accelerate as usual, and again when it reaches the 2200rpms it will go like hell. Secondary enabled/disabled does not make a difference, as it open above 2500/3000rpms....

I have tried a one size bigger idle jet with a 2 sizes bigger main (both at the same time and in turns), and there was no big change (appart from emissions )... I have tried all possible idle settings (from lean to rich) and no real change. It's driving me nuts!

But lets leave the sudden throttle, and focus first on the "little power under 2200rpms" subject, which I think is the real case.

Please don't tell me to toss the Solex, I am sure it just needs some help, not replacement!!



Something more: all manuals state emissions should be less than 2.5% CO at idle. What should it be at higher rpms, say 3000?

[deaner]

Solex's are very tempermental carbs. first you must make sure that all the setting are as factory spec's. Make sure you adjust the pump circuit diaphram and check for .001 clearance between the diaphram and the pump lever from the linkage. Any gap there will cause a hesitation. Also I've found that most stock pump jet's are too small. Try going up one size on this. For the other power problems, plug readings can help you figure out if your lean or rich. What was the jetting in the old carb? Start with matching these. Make sure the carb is "blueprinted". No air leaks. Solex's can be made to run correct, just takes a little work. I can't stress enough how important it is that all the settings are correct.

[gr_diver]

The previous Solex was a mess, so I started with a "fresh" one. I miled it flat, cleaned it completely, installed rebuild kit, corrected jetting to Opel specs, set primary with vacuum tool at 6" , set secondary to specs, everything in general...

Plugs tend to get a bit whitish, but with the unleaded SuperLRP we use here colour is of less value that with Super Leaded fuel...

With stock jetting, using a exhaust gas analyzer I got 2% CO idle, 0,7%CO at 2000rpms, and a 0,2CO% at 3200rpms, with 6%CO during "revving" from one speed to another (upwards)... The guy there confirmed that the lean 0,2 at 3000 was due to the lack of the secondary kicking in, as the car was stationary...

Eliminating the gap at the accelerator pump does not improve any condition... I have a #55, maybe I will swap it with the #45 currently in, and see what happens...

[gr_diver]

deaner:
when you say "stock pump jets" do you mean the shooter itself, or the small jet screwed at the main body, at the mating surface with the air-horn? Because in the previous post I meant I have a bigger shooter...

[deaner]

Originally Posted by gr_diver With stock jetting, using a exhaust gas analyzer I got 2% CO idle, 0,7%CO at 2000rpms, and a 0,2CO% at 3200rpms, with 6%CO during "revving" from one speed to another (upwards)... The guy there confirmed that the lean 0,2 at 3000 was due to the lack of the secondary kicking in, as the car was stationary... Eliminating the gap at the accelerator pump does not improve any condition... I have a #55, maybe I will swap it with the #45 currently in, and see what happens...

You can change the rpm the secondary opens, by cutting or changing the vacuum diaphram spring.(considering you have vacuum secondary) When I was racing with the Solex we used both methods. If you've changed your Engine, you will need to tune your carb accordingly. As we were talking about in an other thread, some time on a dyno is well worth it when tunning for specific power ranges.

[gr_diver]

Thank you for your time and advice! Yes, I have the vacuum secondary!

I cannot perform dyno testing, because not only it is very expensive for my budget, but most important, people with dynos here do not have experience on such old cars. They mainly work with new cars, EFI/ Turbo/ ECU re-programming etc.

I'll propably buy some more jet's, and make changes upwards and see what comes up...

Thanks again!

[deaner]

Originally Posted by gr_diver deaner: when you say "stock pump jets" do you mean the shooter itself, or the small jet screwed at the main body, at the mating surface with the air-horn? Because in the previous post I meant I have a bigger shooter...

The shooter itself.