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

[Mark Henry]

I'd look to see if I could find a brass tube to fit, maybe off of an old carb.
If you have a vac advance dizzy that's the first place I'd try to pull vac from. I'd also tee it with the one from the other carb.

[98101]

If you have a vac advance dizzy that's the first place I'd try to pull vac from. I'd also tee it with the one from the other carb.

Yes, good idea. I have a 123 Tune+ (Bluetooth), currently not using the vacuum advance. In the 123 group buy thread I've discussed hooking it up, and no one there seems to understand why I think it would be a good idea.

My one reservation is that I think I'd rather have the manifold vacuum signal, as I've read the port vacuum signal won't be strong at idle. As I understand it this was done to make combustion hotter at idle to reduce emissions. But this is probably still better than no vacuum advance at all + two carbs with 3.5mm vacuum leaks.

There's also an inop vacuum gauge in the dash. I haven't investigated what it's connected to, if anything. I'm assuming it would be difficult and painful to run a vacuum line from the engine compartment to the gauge.

[914_teener]

If you have a vac advance dizzy that's the first place I'd try to pull vac from. I'd also tee it with the one from the other carb.

Yes, good idea. I have a 123 Tune+ (Bluetooth), currently not using the vacuum advance. In the 123 group buy thread I've discussed hooking it up, and no one there seems to understand why I think it would be a good idea.

My one reservation is that I think I'd rather have the manifold vacuum signal, as I've read the port vacuum signal won't be strong at idle. As I understand it this was done to make combustion hotter at idle to reduce emissions. But this is probably still better than no vacuum advance at all + two carbs with 3.5mm vacuum leaks.

There's also an inop vacuum gauge in the dash. I haven't investigated what it's connected to, if anything. I'm assuming it would be difficult and painful to run a vacuum line from the engine compartment to the gauge.

Yes, good idea. I have a 123 Tune+ (Bluetooth), currently not using the vacuum advance. In the 123 group buy thread I've discussed hooking it up, and no one there seems to understand why I think it would be a good idea.



Never said it wasn't a good idea, I was wondering if it was necessary or worth the trouble porting a bunch of hoses around the engine.

If there are vaccum leaks in FI or carburetors, fixing those would be first order of business.....linkage....sync....jetting.....timing. More or less.

I'm just wondering that with a programmable dizzy....why augment the curve with vaccum when you can put it on a dyno and program it with your phone.

Am I missing something here?

The 123 I have has the vaccum advance port hooked onto the dizzy and it does work. There are two ports for the stock throttle body that were discussed. The model for D-jet is switched only so I can't use blue tooth to change it. Basically it is pre-programmed.

Do both and see what happens.

[98101]

I'm just wondering that with a programmable dizzy....why augment the curve with vaccum when you can put it on a dyno and program it with your phone.

Am I missing something here?

If a distributor ignores vacuum, the only information it has is RPM. This will work, but not as well as possible for street use. The best time to fire the sparkplug cannot be determined only from RPM because an engine running at 2000RPM at cruise benefits from an earlier spark and an engine running at 2000RPM at WOT -- with more stuff going into the cylinders -- benefits from a later spark. Manifold vacuum can give the distributor additional information it cannot get otherwise. Turbo guys take this even further by retarding the ignition sensitive to boost pressure.

The phone app cannot tell the distributor how much load the engine is under, but through the programmable MAP table it can tell the distributor how to respond to that load.

I have to do *something* about these open vacuum ports on the carbs, so running them to the distributor and setting up a MAP curve seems like an interesting experiment. I'm off to the hardware store with the carb to make sure they give me the right size.