Alfa Romeo Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
3,489 Posts
Discussion Starter #1
This no doubt should be in carbs, fuel injection, etc. but to the best of my knowledge these carbs are only used on 750/101 Normales.

I installed this (new) carb on client's '62 1300 (now 1400) Giulia transition Spider. I've just started making test runs, but I'm having trouble getting a combination of advance/retard and (completely rebuilt Lucas distributor) and fuel. However I set both, the engine dies if the rpm drops to about 1700. If you're not familiar with this set-up, the tach starts at 1000.

I've found virtually no difference if I have the Idle Mixture Screw at a half turn or two full turns. However, I'm somewhat at a loss as to where the Throttle Adjustment Screw comes in. I'm assuming it is a version of the center adjusting screw on dual throat side draft Webers.

If you turn the TAS In (for instance) does this start to open the Primary Throttle Valve? And how can you tell if (another for instance) you turn it a full turn and nothing happens? I'll add that I can't tell if there is a bypass for the Primary Throttle Valve or not. I assume not.

I'm going to take a test run in a few hours and would like to have a better idea as to how and when to adjust the TAS
 

·
Registered
Joined
·
3,489 Posts
Discussion Starter #2
I assume there must be at least one person (out of 36) who has installed a 36 DCD in their Alfa. If so, did you never need to adjust the Throttle Adjustment Screw?
 

·
Premium Member
Joined
·
1,163 Posts
Here's a page out of the John Passini Weber book with beginning specifications for a 1300/1600 Alfa using the Weber 36DCD.Just my opinion,but I'd check that new Weber.Sorry for the quality of my photos of crappy copies. PT#29 is the throttle adjustment screw.Good luck
 

Attachments

·
Registered
Joined
·
3,489 Posts
Discussion Starter #4
alphil, thanks for the effort, but I have that information. Should you come across a detailed description as to how the Throttle Adjustment Screw works, I would be more than happy to have that info.
 

·
Registered
Joined
·
116 Posts
The throttle adjustment screw only operates the primary valve. It pushes against the small notch (close to #42 in the picture) on the primary shaft. One turn should definitely be noticeable.

Jeroen
 

·
Premium Member
Joined
·
1,163 Posts
Thanks Jerone,I thought I was missing something....Simply put,#29,the throttle adjustment screw,pushes on a small flat on the throttle shaft(inside the cover)that rotates the throttle shaft and opens the primary throttle plate. In the photos,I removed the adjustment screw spring,and then replaced only the screw.It took appx.9-10 full turns before it touched the throttle shaft lever(throttle plate still completely closed,pic.#3). Only another 1-3/4 turns opened the primary throttle plate enough to fully expose the small primary progression hole(pic.#4). The last picture is maximum plate opening,screw bottomed out with the spring in place.
 

Attachments

·
Registered
Joined
·
3,489 Posts
Discussion Starter #7
I apologize for not replying sooner but got caught up with an Alfa 2600 Spider coming into the shop.

Alfa-Jerone, thanks for replying. I hadn't noticed the flat until you pointed it out.

aphil and also a big thank you for taking the trouble to pin down what happens at various turns. Good information. But I still have to wonder how it actually works. If the screw is turned in fairly far (but not all of the way) won't that stop the throttle shaft from moving? And if you back the screw out so that the rounded end no longer touches the flat - aren't we back to the Primary Throttle Valve remaining closed?

I'm at a bit of a loss as to what the lower hole (next to the bottom of the carb) is accomplishing. I assume the upper one is bypassing the throttle when it's closed.
 

·
Premium Member
Joined
·
1,163 Posts
Biba, Sorry if I've misled you;the screw pushes on the throttle shafts' lever,which is part of the shaft(#42).This lever is "inside" the cover and appears to the left of the #42 in the parts diagram).This lever also has a tab that fits inside the slot of the primary toothed sector(#49). When the primary shaft rotates that tab to the end of the slot,any further rotation will act on the secondary sector(toothed gear)and cause the secondary to open.Hope this helps
 

Attachments

·
Registered
Joined
·
3,489 Posts
Discussion Starter #9
alphil, I should have known the lower opening was for the Idle Mixture Control Screw. Again thank you for going to the trouble of opening up the throttle control section. It almost appears as if the end of the screw is pushing on both the Shaft for Primary Duct and the inward bent arm. In any case this is making a lot more sense.

Thoughts on initial adjustment: Leave throttle plate 'just' closed or opened slightly?
 

·
Registered
Joined
·
116 Posts
Try to leave them as closed as possible. The DCD carbs tend to keep the engine running for a couple of strokes when shut off.
The best way to prevent dieseling is a low idle speed.

Jerone
 

·
Registered
Joined
·
106 Posts
Nice to know the DCD causes running on, (dieseling). I have really been struggling to try and stop this happening. The problem being that the idle at low revs is rough. The head has been ported,as best I could and the valves cut at 30 & 45 degrees. It has a 10548 inlet cam set at 99.5 and a 105020320001 exhaust cam set at 102.
The 123 distributor is set on 'E' at the moment, although I have tried a few other settings. Because the idle is rough it is hard to set the timing, so I have tried to set it at max advance at 4000 revs. At idle, the idling mark on the pulley is jumping around the timing arrow, but not possible to get exact. The 36/36 DCD has been set up according to the chart earlier in the thread.
Has anyone tried any different jetting, or made any improvements to the carb which could prevent running on.
Thanks
 

·
Premium Member
Joined
·
220 Posts
Nice to know the DCD causes running on, (dieseling). I have really been struggling to try and stop this happening. The problem being that the idle at low revs is rough. The head has been ported,as best I could and the valves cut at 30 & 45 degrees. It has a 10548 inlet cam set at 99.5 and a 105020320001 exhaust cam set at 102.
The 123 distributor is set on 'E' at the moment, although I have tried a few other settings. Because the idle is rough it is hard to set the timing, so I have tried to set it at max advance at 4000 revs. At idle, the idling mark on the pulley is jumping around the timing arrow, but not possible to get exact. The 36/36 DCD has been set up according to the chart earlier in the thread.
Has anyone tried any different jetting, or made any improvements to the carb which could prevent running on.
Thanks
Antony,
Please see Richard Jemison's post in the thread I started titled "Cam timing 1300N with 36DCD below in this Giulietta and Giulia forum.

Jim
San Antonio, TX
 

·
Premium Member
Joined
·
220 Posts
Thank-you. If I am reading that correctly, doesn't that mean the cam timing is right, or does it need adjusted?
The cam timing you've set is appropriate for twin DCOEs. The DCD and original Solex do best with a cam timing of 111.5. See the cam timing specs in the Centerline Tech Tips section, a reprint from the original Shankle catalogue. I get a good under 1000 rpm idle with Normale cams and original Lucas distributor, no dieseling on shut down. You're even better with the 123.

Jim
San Antonio
 

·
Super Moderator
Joined
·
11,555 Posts
This is a variant of the Webers used on 60's Ferrari V12's but Ferrari had 3. Each throat can be balanced by air flow to the other. The procedure for the V12 is complicated, yet simple if you have done it enough times, and THAT I have. The single DCD for the Alfa it set up similarly. Maybe contact me with a PM or e-mail and I'll try to get it into the written word. Actually easier to do than explain. Drop by my house, and I'll set yours up in about 5 minutes....
:)
 

·
Premium Member
Joined
·
220 Posts
Gordon,
I don't have your email address so I've sent you a PM.
If you'd like to reply here for all to benefit, that's good too.
Thanks,
Jim
San Antonio, TX
 
1 - 17 of 17 Posts
Top