ScottCLo

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About ScottCLo

  • Birthday 01/10/1996

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  • Website URL scottclo.com

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  • Gender Male
  • Location Califonia, San Diego

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  1. And maybe miss-aligned throttle plate is the wrong term. It seems to suggest the throttle plate is installed incorrectly. I mean the position the throttle plate sits relative to the progression holes. This is set with the idle speed screw. When you turn the screw clockwise the throttle plate is opened and the top of the plate moves down in my diagram. This lets more air into the engine and increases the idle speed. On some engine/carb combinations, the desired idle speed leaves the throttle plate in a sub-optimal position relative to the progression holes.
  2. This is the procedure I use. The final tune does not have to be at lean best idle. I do this before checking the throttle position as a baseline, it ensures the engine is at the maximum rpm per throttle position and is not suffering from an over rich or lean idle that can affect throttle position. If the throttle position is fine, or very close but still suffers from a lean condition off idle, minor compensation using the mixture screws is certainly a good option. It's not the only option though. That lean condition is caused by the progression circuit not acting soon enough or strong enough and can be fixed by modifying the throttle plate or progression holes. Doing so is tricky, often not worth it, and can cause more problems if not done right but is sometimes the only fix, like, on that 240z. No amount of mixture compensation could solve that problem. That's why I posted, if op, or anyone else this kind of problem, they at least can identify and understand what a miss-aligned throttle plate is and what the common fixes are. I don't expect anyone to go out and start punching holes and griding on their throttle plates after reading this. Well.... I really just wanted to make a pretty drawing and talk about carburetors.
  3. I suggested starting a new topic as this is OP's topic not the Chris vs Scott carb debate topic, haha. Anyway if you are still open to the discussion and want to continue here... I'm just speaking from experience. I'll give an extreme example. A Datsun 240z with a set of triple 45DCOE webers installed on it. It idled poorly and was backfiring through the carburetors at cruise/light throttle. It was idling off 2 carburetors. I balance the carburetors to get the engine running on all 3. I then set the fuel mixture to lean best idle. This took the engine rpm from around 700 to 1500 without adjusting the idle speed screws due to it being so rich. I rebalance the carbs at 800 rpm lean best idle. If I tried to drive the car at this point the problem would feel 10x worse because the rich idle was only masking the real problem. I then inspected the progression ports. The throttle plate is not even visible through the first progression port. If I checked this before setting the engine at lean best idle at the desired idle rpm and proper balance I would have seen the throttle shaft through the port and may have picked fix A. Instead since I had the car at the target idle rpm and at lean best idle I could accurately judge that I needed to proceed with fix B. The carburetors were then modified with an additional progression port. I then tune the diameter of the progression ports and jetting without having to enrich the idle screw. A smooth transition was achieved with 36 chokes on an engine with a lower cylinder displacement than a 2002 ~400cc vs ~500cc. A proper step by step procedure should be used to avoid wasting time in the wrong area. I also always check the health of the motor by Inspecting the ignition system, adjusting the valves and performing compression and leak down tests. I have seen people spend hours fiddling with carbs just to find a broken rocker arm, tight valve, or improper dwell. Also when talking about balancing I'm talking about removing the throttle linkage and balancing each cylinder to draw the same amount of air at idle. Once this is done I reattach the throttle linkage and synchronize each carburetor to act in unison.
  4. I was not quoting the book, if I had it on hand or I would have posted pictures of the pages, haha. But I agree, this whole back and forth is probably not going to help him. The carbs should be set to lean best idle before checking throttle position because often carbs are enriched to the point the rpm drops and the idle screws are adjusted to compensate to try and mask a problem in the progression circuit. If you want to discuss this further, start a new topic and we can get the whole forum to chip in, it might be an interesting discussion.
  5. Balancing is required when sitting idle speed, I'm shocked if you think otherwise. The carbs should be set to learn best idle before checking the throttle plate position this ensures you are at the maximum rpm per given throttle position. If your engine requires running rich at idle to get a smooth transition your progression circuit is not tuned correctly. it needs modification or different jetting.
  6. I would suggest reading the book Weaber Carburetors by Pat Braden. It gives a whole rundown on carburetor theory. At idle, manifold vacuum draws fuel from the idle mixture screw. As you open the throttle the progression ports are exposed to manifold vacuum and additional fuel is drawn into the engine. Once the throttle is opened sufficiently you lose manifold vacuum and fuel stops being drawn from the idle progression circuit. By this point air moving across the Secondary Ventri, the little tube that sits before the choke, creates a vacuum, drawing fuel from the main jet. The function of the primary venturi, or choke, is to create a high-velocity, low-pressure zone after the secondary venturi to help atomize the fuel. At light throttle fuel not draw from the main jet so the venturi has nothing atomize and the venturi effect is not strong enough to anyway. All the fuel entering the engine is below the throttle plate. If the venturi is too large at low-mid rpm wide open throttle the fuel will not atomize and you will lose horsepower. If its too small you restrict the amount of air able to pass through the carburetor at med-high rpm and you lose power there. So its a tradeoff between low/mid range power to mid/high range power.
  7. And just to clarify you must make sure the ignition is all squared away before looking at carbs. Then the idle needs set including balencing carbs. Once it's purring like a kitten at lean best idle inspect the throttle shaft alignment. If that checks out then you can move on to idle jets.
  8. Well since he already has the carbs worrying about venturi size before checking the throttle plate alignment seems like a waste of time. The venturi size does not affect the throttle plate position. A smooth transition should be achievable with 36mm choaks. Chokes don't have much effect at cruise, if at all.
  9. Yes, the main venturi should be selected before doing anything, before even buying the carburetors in fact. They should be matched to the engine size/rpm and then the carburetor should match the desired venturi size. Venti Size * 1.25 = throttle plate size. Stock size for a 45DCOE is 36mm and should be fine for a 2.0L up to 6000rpm. The idle jets should be selected after making sure the throttle plate is possiond correctly as described by my previous post.
  10. The first thing I do when tuning webers is set the timing, idle mixture and speed then inspect the progression circuit. Big carbs on a small engine can cause problems in the progression circuit. Unscrew the progression port cover and look down it with a flashlight. You should be able to see the brass throttle plate covering the hole closest to the mounting flange. If it looks similar to #1 You are okay. If it looks like #2 or #3 the progression circuit will not work as intended and you will have problems at idle and cruise. When you use oversized carbs you often end up with #2. No matter what jetting you use and no matter how much you fiddle with the timing it will never run right. The job of the progression holes is to create a smooth transition between closed and open throttle. As you open the throttle it uncovers the holes allowing more fuel to be drawn into the engine. If the holes are not uncovered soon enough the engine will run lean. The correct fix would be to chamfer the throttle plate so that the hole is uncovered sooner, fix A, or drill an additional progression hole above the throttle plate, fix B. This will need to be done by a machinist as the holes need to be drilled precisely and uniformly on each throat of the carb. To correct #3 you will need to drill a small hole through the throttle plate opposite of the progression port, fix C. I recommend reading Weaber Carburetors by Pat Braden. You need a solid understanding of how carburetors work to be able to tune them properly.
  11. I can see what appears to be rust bubbles on image 29/95, so assume the entire car suffers from poor bodywork unless you view it in person. https://cdn.bringatrailer.com/wp-content/uploads/2018/12/1971_bmw_2002ti_1547578792cb2dc8f93IMG_0603.jpg
  12. ScottCLo

    WTB hood center stop

    Thanks but they are NLA. I still need a good used one.
  13. ScottCLo

    WTB hood center stop

    I need 1 hood center stopper. P/N 41 61 5 480 193
  14. ScottCLo

    WTB Center console ash trays

    I need 2 center console ashtrays. I also need the housing and green "button". I know everyone is pulling them out and tossing them in junk piles for shiny VDO gauges and fancy 2 din radios. Why not toss them my way?