Keep Dellorto DRLA 45s and Bosch 009? Options

[98101]

I suddenly find myself owning 1970 4-cylinder 2.4 with Web hot street Cam idles nicely and pulls hard at WOT. Part throttle response is not great, often with carbs coughing and even backfiring on trailing throttle. My use is mostly street, so I'd like to get this part throttle stuff sorted.

Here's pictures of the stuff that's in there now. I guess that's the infamous Bosch 009 with no vacuum advance and a PerTronix 1847A. The carbs are Dellorto DRLA 45s with short velocity stacks and these tall foam things that don't seal against the air cleaner housings. I'm willing to learn about the carbs but I don't have much confidence in the 009 for running nicely on the street. Please correct me if I'm wrong about any of this stuff.

Also from other threads I gather that switching to EFI such as MicroSquirt would cost $5K or so ... though I'm not ruling this out completely. Correct me if I'm wrong about that.






Is this kind of linkage OK?


Here's the idle you may have seen in another post:

https://www.youtube.com/watch?v=-AC53RRrXOU


Any help you can provide is appreciated!

--Michael in Seattle

[98101]

The Road Test

VW shop owner asked me to drive around to test the new carburetors in action. At first it seemed great. It drove smoothly out of the parking lot and pulled hard when I floored it pulling onto the street. A few blocks later I noticed popping sounds and sneezes! But only in some conditions, typically cruising around 3000RPM. Not wide open. And much less often than before. Idle was still perfect. He looked really sad and confused when I told him. I suggested we call it a day.

Today (Tuesday) I wondered how to find out what was in the exhaust at cruising speed. I don't know how hard it is to run the wires for a wideband air-fuel meter, or whether I'd like a gauge that doesn't match the others. I called a local dyno shop (with a sniffer) and found out they weren't very busy. I suggested I should drive the car on the dyno because an ordinary person cannot operate my linkage and worn syncromesh. The car was backfiring even while driving onto the test stand. While setting up, a technician noticed that the left carb's main jet stack was just flopping around in its holder, not screwed in! They screwed that in properly, and I don't think I've heard a backfire since. That was the problem I'd gone there to solve.

We did some dyno tuning, as you can see here (or in the other thread I started). Air/fuel ratio was lean on the first run and OF COURSE they didn't have Dellorto jets, so I asked him to ream out the existing 165 main jets. (I see that CB Performance sells them.) They had never seen a Bluetooth tunable distributor before. We advanced the overall timing a bit from what I had, which improved the bottom end but detracted from the top end. So we backed down just the top end. I really like the 123 distributor. We didn't explore using vacuum advance to improve drivability... still think there's a lot of potential here since this style of dyno run is only optimizing for wide open throttle.

Car ran fantastically while driving home. Unfortunately it's really raining here so didn't get to play with it.

According to another thread, this dyno result isn't impressive and now it's time to fix the clutch.