TheSamba.com :: View topic

Fri Jun 05, 2015 12:51 pm

Hi all,

I removed my h30/31 carb (with a 65 angled jet, 50 straight jet) and installed a professionally rebuilt solex 34pic3 (idle=55, main=127.5) on my 1600cc stock dual port, 034 SVDA distributor. The 34pic3 came with a 55 idle jet, but it runs like crap at low rpms and I constantly get a flat spot. I tried a Bocar 34pic3 with the same jetting. Same results. The solex was installed in another engine and it ran fine.
Today, I decided to try a 65 idle jet on the solex 34pic3 and it runs great, no hesitation at low rpms, flat spot disappeared. According to VW documentation, this carb should run with a 55 idle jet (and a 127.5 main jet) at sea level.
As far as I know, the engine is bone stock. No air leaks, valves are properly adjusted, as well as the timing.

Any ideas?
All opinions are welcome.

Fri Jun 05, 2015 4:27 pm

I had that issue... until I went up in idle jet size.
55 is a baseline.
I run a 57.5 idle jet and no flat spot on my car.
(1600 dual port with a new Empi 34 pict 3)
At what elevation are you? That plays a factor. I'm at sea level so a slightly fatter idle seem to be the norm here. (Shops all around regularly drill out jets to help with the same issue you have.)

In short, if EVERYTHING in your engine as far as tune goes is spot on, and the last thing that is left to do is mess with the idle jets, and a fatter idle fixes your issue, then do it.

But a 65 seems on the large side even for me.

Try buying a 57.5 and a 60 idle jets and see what happens.
(Remember to re-adjust your carb with every jet change.)
Good luck.

-Frank

Fri Jun 05, 2015 10:12 pm

Keep in mind as well the carb jetting you see in the reference tables dates from pre-ethanol days. When running ethanol blended gas you'll tend to run lean, hence the need for a larger jet.

Sat Jun 06, 2015 6:47 am

Exactly.

I've read that for today's common E10 the jet sizes typically increase two steps.... Apparently, for every step increased in size fuel flow increases about 2 %.

So, today's gas with 10% ethanol tends to run these engines about 4 % lean.

Two steps in jet sizing is therefore what would be called for in theory.

Having said that, I was able to get away with just a 1 step increase in the idle jet, and left the main alone. (57.5/127.5 and standard 75 air)

Another possible alternative that I will try today, is actually putting in normal gasoline without ethanol, and that should in theory work with standard jetting.

Just ideas thrown out there for the OP.

Sat Jun 06, 2015 8:13 am

What is a "step"? 1, 2.5, or 5?

If you have a 50 idle, and change to a 55, that's a 20% increase in fuel, FWIW. A HUGE change.

What this means is it's very possible for a 50 idle to be too lean, and a 55 to be too rich, because of the huge difference of the 2 sizes. Making changes in increments of 1 or 2 is a wise approach.

Sun Jun 07, 2015 9:28 am

Thank you all for your knowledge and advice. Yesterday I installed a 60 idle jet on the carb and it runs fine. The only strange thing I noticed was a occasional slow return to idle. I will try a 57.5 idle jet to see how it works and I'll post the results.

Sun Jun 07, 2015 4:24 pm

a slow return to idle is either a lean idle mixture, or a vacuum leak.

Mon Jun 08, 2015 10:15 am

Thanks for the advice, John. I adjusted the volume control screw and now the idle is fine.
I tried a 57.5 idle jet. Flat spot and hesitation at low rpms. I put back the 60 idle jet and it runs fine. I'll keep an eye on the mpg.

Mon Jun 08, 2015 10:31 am

I could never get mine to idle at 900 RPMs with the 55 idle jet. It was always in the 700s and it would die when I came to a stop sign. I put the 65 idle jet in and now it idles great.

Mon Jun 08, 2015 2:01 pm

You have to re-set idle mixture any time you change the idle jet.

Fri Jun 26, 2015 10:39 am

I've been running a 60 idle jet for a few weeks now. The engine runs great at low, mid, and high RPMs. No hesitation, and I get 26 MPG average. I haven't checked the spark plugs yet, but I'm leaving the 60 idle jet since the engine is happy with it.