• From: San Diego, CA
  • Registered: 2011-08-31
  • Posts: 7

Topic: Carburetor Tuning Help (H30/31)

Hello all,

I am in need of some dire help with my Brosol H30/31 carb.  I cannot get it to tune for the life of me, and was wondering if any of you all have some ideas as to what may be causing it (or how I COULD tune it). Please bare with me as I am a relatively new to VWs- I inherited the car a few years ago, but haven't been driving it much until recently. It was driving fine however the gas mileage was horrendous so I had to sit down to try and lean it out/tune it.

SO, I have a 1974 stock 1600 beetle setup. I understand that with the H30/31 carb, that the mixture screw is the smaller one on the drivers side of the carb and the bigger one controls the idle. That being said, whenever I try to tune it after setting the mixture screw at the standard 2.5/3 turns out, it wont really adjust. There isnt a noticeable drop in engine RPMs until I loosen it up drastically. Interestingly though, whenever I tighten the screw, the engine continues to run rather than die out.  In fact, the RPMs will continue to rise as I tighten the screw! WHAT THE!!!! How am I supposed to tune such an uncooperative thing!!!....Similarly, when i adjust the idle screw,  there isnt much change in the engine RPMs as I loosen that screw either (at least not a very noticeable one). The only real difference I can hear is when I start to bottom it out (in the other direction of course) and it starts to run like crap...

Should I just try adjusting it when the screws are further out oorrrrr....? Or try driving it around at the recommended settings to see what happens?

Suggestions or thoughts? Any help is extremely appreciated. Thanks.



-Nick

  • From: Cincinnati, Ohio
  • Registered: 2005-09-10
  • Posts: 2,336

Re: Carburetor Tuning Help (H30/31)

nickmantee wrote:

Suggestions or thoughts? Any help is extremely appreciated. Thanks.

Three quick thoughts:

1.  Do you have an Air-cooled VW repair manual?  If not, and you're going to be doing a lot of your own maintenance/repair work...this will come in handy many many times.

2.  One thing about carburetors in old VW's (or old vehicles in general)...is they wear out.  So the adjustment troubles you're having could simply be to things being out of adjustment, the carb. being worn out, or a combination.  Just throwing that out there to consider.

3.  A rough running engine can also be due to vacuum leaks, needing a full tune-up, valves needing adjustment, engine timing, etc.

Hope this helps.  smile

1979 Super Beetle Convertible
  • From: San Diego, CA
  • Registered: 2011-08-31
  • Posts: 7

Re: Carburetor Tuning Help (H30/31)

Thanks for the reply Bug In My Nose...

I suppose I should have given a bit more information as to the engine and car itself. When I inherited the car, I received a folder of old records (and manuals - Chilton and Muir) and discovered that the car got a new 1600 engine in it before it sat and fell into disarray. Since then, I have already put in new plugs, fuel filter, cap, rotor, wires, vacuum hoses, air filter, and set the timing. It seems that the engine is OK despite the fact that it sat for so long. As far as the carburetor itself goes, I did have a friend who is ASE certified rebuild it -thus I dont know why it is being uncooperative.

I was thinking about trying to set it with the mixture screw initially set at maybe 4 or 5 turns to see if that helps at all....

Thanks again BIMN

  • From: South Africa
  • Registered: 2004-11-11
  • Posts: 46

Re: Carburetor Tuning Help (H30/31)

Seeing that you mentioned that your engine is in good condition , I must ask if you have overhauled the Carb recently. There are needles, o-rings and injectors inside the carb that need to be replaced from time to time. Also when adjusting the carbs it is generally better to do at normal running temperature , in other words take the car for a run before you start with adjustments and adjust in small increments . Also what helps is a CO tester which you connect directly to your exhaust and this should help with fuel consumption adjustment.
Hope this helps :-)

'Keep on Rollin'
  • From: Austin, TX USA
  • Registered: 2004-03-30
  • Posts: 240

Re: Carburetor Tuning Help (H30/31)

Hi Nick,

I ran into the same issue some time back with my 30/31 after rekitting it (a.k.a. rebuilding it), and ultimately the culprit turned out to be the mixture screw O ring. After adjusting it by bottoming the screw out and then adjusting out 2.5 turns out and getting no response (several times….. grrrrr……), I swapped the old O ring back on, and UREKA, back in business. Upon comparison, the new O ring was just oversized enough to keep the screw from seating properly when bottomed out, so I was adjusting nothing, basically. I got a new rebuild kit from Wolfsburg West, redid my work, and the issue was resolved. Just something to consider, as many aftermarket parts these days are “less than exact”.

Good luck!
-David

  • From: San Diego, CA
  • Registered: 2011-08-31
  • Posts: 7

Re: Carburetor Tuning Help (H30/31)

Hey guys,

Luckily my friend saved the original o-ring from the rebuild (for the mixture screw), and put that bad boy back in there, but it did not fix my problem. The engine continues to run, and idle faster, when I bottom the screw out. I guess I will have to try jonnomans suggestion and see if I can find someone who has a meter I could use...I'd just do it myself by smell, but I have no idea what a lean mixture smells like!

Thanks for all of the input. I really appreciate it.

-Nick

  • From: Cincinnati, Ohio
  • Registered: 2005-09-10
  • Posts: 2,336

Re: Carburetor Tuning Help (H30/31)

nickmantee wrote:

Hey guys,

Luckily my friend saved the original o-ring from the rebuild (for the mixture screw), and put that bad boy back in there, but it did not fix my problem. The engine continues to run, and idle faster, when I bottom the screw out. I guess I will have to try jonnomans suggestion and see if I can find someone who has a meter I could use...I'd just do it myself by smell, but I have no idea what a lean mixture smells like!

Thanks for all of the input. I really appreciate it.

-Nick

Just so we know...and can eliminate as a possibilities:

- is the engine fully warmed up
- is the accelerator cable installed correctly (check the manual if not sure)
- is the choke fully open (not stuck on any of the choke "cams")

If any of these is not correct...idle adjustment won't be possible.

1979 Super Beetle Convertible
  • From: San Diego, CA
  • Registered: 2011-08-31
  • Posts: 7

Re: Carburetor Tuning Help (H30/31)

Hello Volkswebbin world!

After a long hiatus of not working on my bug, I finally have some spare time again to tinker with it and try to get it in acceptable condition. So back to this carb adjustment issue....I successfully got the carb/engine to perform as it is supposed to when I bottom out the mixture screw- it does in fact die out now. So my first question is, are the number of turns for the initial setting supposed to be 360, or 180, degree turns? It seems if I go three 360 degree turns, the engine runs too rich (due to the large black plume of smoke I get when I rev the engine). On the other hand, if I go three (or even 2) 180 degree turns, i dont see any noticeable black smoke. Is this correct? Should it be running richer as I loosen the screw? What do you guys have your settings at? I also noticed that at the two/three turn 180 degree interval, the exhaust has more of a machine gun sound (or as if you are rolling your Rs) than a normal free flowing feel.

I am trying to describe the engines behavior as best as possible so I can get the best advice. Any help is appreciated! Thanks!