Opel GT Forum banner
21 - 38 of 38 Posts

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
It was said at one time by RallyBob: "Almost every Opeler with a Weber could benefit from trimming the power valve spring."

It's a VERY weak spring, so small shortenings of it's length by trimming loops off only slightly affects how tightly/loosely it holds the valve closed. The first loop at each end of the spring is flat and does not rise, so trimming off the first loop does almost nothing, so I would say to cut off 1 1/2 loops for a start, put things back together and aggressively rev the engine from idle. You should see a decrease in the hesitation or stumble when you hit the gas. Trim off another 1/2 of a loop, repeat, and re-rev, you should see a further decrease in hesitation. You should not need to go past 3 loops(The 1st flat loop + 2 full rising loops).

I suffered from the hesitation/stumble problem for almost 25 years in my GTs. It got to the point that I reflexively flutter the gas pedal as I go off idle. The fluttering seemed to do something that lessened the stumble effect. Even after the spring shortening and moving on to side drafts and FI, I STILL have the habit of fluttering the pedal. The spring trimming works like magic and is so simple to do, it's a shame that the trimming wasn't common knowledge all those decades ago.
 

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
Thanks to everyone for the great information and visuals are always a plus. At sometime in the not to distant future I will open the top of the carb to see the hidden jets and check the float and will remove the carb to determine the porting match and at that point I will remove the Carb and the manifold again for porting possibilities but to also to install a new manifold gasket, making sure there are no vacuum leaks. And while I am at it I need to straighten out the part of my linkage that goes to the bracket mounted on the fire wall so I can install the new throttle grommet/bracket combination.Currently using a rubber grommet that is slightly larger than necessary but required because of the bent linkage section
The car has no stumble and the only noticeable issue, to me, I have low idle at first start 6 to 7 RPM's and after warmed up idle at around 13 - so something is not right. The car is running really well but since the 32/36 was right out of the box seems likely, based on what I have read, that it could use a little tweaking. Before I do anything I plan to reset the timing and adjust the carb as per factory settings and start from there.

Yup, sounds like a vacuum leak. One way to find out for sure is to spray electrical contact or carburetor cleaner at the carb-manifold join and the manifold-head join while the engine is running and cold. ANY change in engine speed or running is an indicator of a vacuum leak. A properly sealed system is impervious to anything sprayed at those gaskets.
 

·
Super Moderator
Joined
·
13,943 Posts
It was said at one time by RallyBob: "Almost every Opeler with a Weber could benefit from trimming the power valve spring."
No, please don’t misquote me.

I said any Opel with an aftermarket cam probably needs the power valve spring trimmed.

I have NEVER trimmed the power valve spring on an Weber downdraft with a stock or nearly standard camshaft. Absolutely no reason too.
 
  • Like
Reactions: kwilford

·
Registered
Joined
·
1,023 Posts
On the power valve spring Lindsay’s last post covers it, see post #15. Wii I Finish if your manifold vacuum is 14” or less at idle it would be spring trimming time. Of course fix all vacuum leaks first.
 

·
Opeler
Joined
·
3,106 Posts
Simple way to establish your power valve tuning. Get the engine running as well as possible, then measure the vacuum at idle. This means that your ignition timing and idle speed need to be correct for your specific combination.

Now, the stock power valves on a 32/36DG-series or 38 DG-series carb opens at about 14" of vacuum. If your engine idles at 15"-16" of vacuum or higher...leave the power valve alone!

If your engine idles at or below 14", you will need to modify the power valve. Cut ONLY enough coils so that the power valve opens 2" below your existing idle vacuum level. Example: Your big-cammed Opel idles at 9" of vacuum. Your power valve should open at 7" of vacuum. Using a vacuum gauge to test, cut the coils in small increments until that value is reached.

That's it.

This is the vacuum port to test the power valve 'cracking' point.
Using a vacuum tester held tightly to this opening, pump the tester slowly until the power valve spring just moves. Note the vacuum level on the tester's gauge. That is the cracking point when the power valve begins to open.
 

·
Opeler
Joined
·
3,106 Posts
Weber Carburetor Parts:

Full Power Valve Diaphragm/ Plunger, Weber 32/36
Certain Weber carburetors used a power valve to enrich the mixture only at at full throttle. This allowed the carburetor to be run leaner under all other conditions for cleaner emissions. Enriching the mixture at full throttle helps to avoid detonation and pinging under hard acceleration.
This is the diaphragm/spring plunger assembly, which gets installed into the top plate of the Weber 32/36 DGAV/DGEV carburetor (number 14 in our parts diagram). The Full Power Needle Valve (Part No. 1586-21), which this plunger operates, is sold separately. Sold individually, one required per carburetor. Mounting screws are not included.


Full Power Valve Seat Assembly
This valve seat screws into the bottom of the float bowl of 32/36 DGV and 32/36 DFV series carburetors. It is designed to richen the fuel mixture at full throttle, allowing a leaner mixture at idle and part-throttle conditions. This valve and the plunger that opens it are commonly removed and replaced with dump tubes in Formula Ford and Sports 2000 applications. 8 x 1.00mm (fine) threads. Sold individually.

The mating Full Power Valve Diaphragm/Plunger (Part No. 57804-097) is sold separately.

Emulsioning Tube for Weber
 

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
The vacuum gauge I ordered arrived today and I'm delighted to say that it's a great kit that is super simple to install. The BIG difference is that it doesn't use the super small diameter hose that previous gauges of this type I have bought had, it appears to be a 3/16" ID hose that is much easier to splice into your existing vacuum tree hoses. I would suggest using a brass T fitting from the auto store, this kit comes with a plastic one. I used the plastic ones for years with no problems, but a few years ago, during one of my mods, I put a hairline crack in my T and it escaped my notice and was giving me a slight vacuum leak until I discovered it.

This gauge is too small(2 1/16") to fit in an oem GT dash without some sort of shimming washer around the outside. Jegs does sell larger ones, but not necessarily this particular one. This one comes with a nice bracket that you could screw or velcro to your dash somewhere and has an illumination bulb that you could splice into your illumination circuit.

435096
435097
435098
435099
435100
435101
 

·
Registered
1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
Joined
·
791 Posts
Discussion Starter · #29 ·
Thanks Gordon for all of the great information on the Vacuum gauge - that is on my list to add to my GT in the near future .
So yesterday I did the carb spray exercise looking for vacuum leaks - hit a spot once around the carb, barely, but could not hit it again but never hit anything near the manifold, that makes me very happy. But since I want to port the manifold guess it does not matter so a new gasket is in the plan for this summer. During this vacuum leak search process I pulled the small plugs that I had placed over the vacuum connections from the distributor to the carb and pulling them off and putting them back on made no difference - that is the two connections on the passenger side fender of the carb. I had a tac/dwell meter attached and no change. Is that normal. Anyway when I pull the carb I will check the bottom to make sure it is flat, and install a new fat gasket, I plan to dismantle the carb and clean it, only around 2000 miles on it but it is 11 years old and has just sat a lot of that time in my garage. And at that time check all of the jets and flot and make sure that I am close to where I think it should be. I have a lot to think about prior to starting this project and I want to be sure that I address everything in that area when I have everything dismanteled as I have no plans to ever do that again. The car is running very well but I just need to get rid of that little blip so that it does in fact," purr like a kitten".

435103
 

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
New member JaysPA just informed me that he has a vacuum gauge in the fixer upper he just bought. Contact him, he might be willing to sell it to you cheaper than buying a new one.
 

·
Just Some Dude in Jersey
Joined
·
15,467 Posts
FYI: Someone also said that they gutted their GT clock and installed a vacuum gauge inside it. BRILLIANT! That solves the whole fitment issue!
 

·
Can Opeler
Joined
·
3,519 Posts


Here’s a digital clock with the original chrome ring and mounting ears added in the correct spots. This same idea could be used for a vacuum gauge. I took this out of my GT to put in a working original clock.
 
  • Like
Reactions: The Scifi Guy

·
Registered
1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
Joined
·
791 Posts
Discussion Starter · #33 ·
Great Idea. now just a matter of finding not only the best fit but also one that matches the other gauges as close as possible. Thanks, Carl
 

·
Registered
1970 Opel Gt - Purchased July 1972 - Chartreuse - restored - 3000 miles as of 02-16, 2021 -
Joined
·
791 Posts
Discussion Starter · #37 ·
And speaking of Carburetors and vacuum Gauges - the other day when I was checking for vacuum leaks I took the plugs off of the two vacuum ports on the carburetor and it made absolutly no difference. Does that sound right or am I missing something. I thought that would have an effect on the way the car ran at idle.
 

·
Registered
Joined
·
1,023 Posts
And speaking of Carburetors and vacuum Gauges - the other day when I was checking for vacuum leaks I took the plugs off of the two vacuum ports on the carburetor and it made absolutly no difference. Does that sound right or am I missing something. I thought that would have an effect on the way the car ran at idle.
Yes, that won’t effect your idle. You should only be utilizing one vacuum port, the “S” port should be the only available vacuum source on the 32/36. The distributor vacuum advance hose goes to the “S” port on the Weber 32/36. Of set up properly you should have zero vacuum reading at idle because the throttle plates are closed. It’s design is to advance the ignition timing once you hit the gas pedal and the throttle plates start to open.

The “E” port is typically plugged off at the factory with a long necked brass screw that a hose could fit on, located directly to the left of the “E” port about an inch to the left a tiny bit higher. It’s a delayed vacuum source if you were to remove the brass plug that isn’t needed on our engines. Some people just shove the small hose from the valve cover on there. I’m thinking that’s how you have yours set up? The small valve cover hose, by the book is supposed to go to a 1/32” tiny hole on one of the branches of the tee where your brake booster hose is. It makes little difference either way as long as the big hose from the valve cover isn’t restricted and is hooked up between the carburetor and air filter.
 
21 - 38 of 38 Posts
Top