Low Idle, DVG adjusting = no dice

[pjsmetana]

So I've asked about the idle question before, and I've adjusted, and adjusted again... and again... and I can get the idle to go up for a while, but when the car is up to temp it really wants to stay around 600rpm, which means when the strong Moss Motors Electric fan kicks on my idle drops to about 400 and starts to shut the engine down. 600rpm is already too low, as it shakes the you-know-what out of me. I turned that main idle adjust screw about as far as it will go.

So what do I do now? New Idle jet? Stronger Alternator? Both maybe? Are there other screws on this carb I should play with as well? I don't have any other jets for my Weber DGV as it came with my Spit.

Thanks guys!
Pete

 

[kodanja]

I sent mine out to have re jetted since then I havent had a problem with them....

 

[71MKIV]

Um, make sure you are adjusting the screw that pushes on the throttle linkage. The mixture screw is adjusted at idle, then the idle stop screw adjusts the rpm. It would be the equivalent of you pushing on the accelerator. Follow the accelerator cable to the carb, the pivot back to it's center, then around the pivot is a cam, on the outside of that cam is a screw. The cam is your fast idle, the screw that sits on the outside of the cam is the idle speed. Tweek that screw in 1/2 turn and try that.

I don't mean to sound like I am impugning your mechanical skills, but if you are adjusting at the correct place, the idle should be fine.

 

[DrEntropy]

If it really IS a condition related to alternator draw, chase this thread around and maybe you could adapt the same rig to the Weber linkage with some MacGyverin'.

Here's another thread with pix... ZS linkage is different but the rigging will be similar.

 

[pjsmetana]

Wow! Darn good Idea Doc! Where did that come from? Any links to where I can buy this thing? It might be hard to hook up on a single DGV vise twin SU's but I sure am willing to give it a shot if this carb rebuild I started today don't do it for me. I'm all for playing McGyver... maybe I can even find a kids 'Big-Wheel' in my size too!

 

[DrEntropy]

TR6Bill had the problem, the first thing that came to mind was TR7/8 & Rover cars with A/C and the rig for idle compensation. Most A/C equipped vehicles have some sort of compensation scheme... new (read any ECM controlled FI) ones do it electronically. Back-when, it was gizmos like Bill rigged on his car.

 

[aeronca65t]

I have to agree with Steve S.

Although I am not a fan of the DGV, my MGB came with one and it has been easy to deal with.

The DGV has two "idle" screws.

Your description of the reaction makes it sound like your turning the idle <span style="text-decoration: underline">mixture</span> screw and not the idle <span style="text-decoration: underline">speed</span> screw.

 

[pjsmetana]

TR6Bill had the problem, the first thing that came to mind was TR7/8 & Rover cars with A/C and the rig for idle compensation. Most A/C equipped vehicles have some sort of compensation scheme... new (read any ECM controlled FI) ones do it electronically. Back-when, it was gizmos like Bill rigged on his car.

Where do I get one of these gizmos?

The DGV has two "idle" screws.

Your description of the reaction makes it sound like your turning the idle <span style="text-decoration: underline">mixture</span> screw and not the idle <span style="text-decoration: underline">speed</span> screw.

I was playing with both, I guess maybe I didn't mention that.

 

[DrEntropy]

Yeah, Nial, that's why I posted: "If it really *IS* a condition related to alternator draw".

The mixture screw "start point" would be: one to one and a half turns from "closed" and use the idle stop screw to set speed... "goose" it sharply and let go. If it revs and then stumbles and chokes returning to "idle", turn the mix screw in (leaner) an eighth turn and try again until it returns a steady idle. if it gets worse, go the other way (enrich). You may find you need to tweak the idle stop screw to maintain an 800-ish RPM as you go thru this drill.

Once you have a good steady return to idle see if the "alternator draw" issue still exists. If so, then consider the compensator "cheat".

 

[pjsmetana]

I did not turn these screws in any relation to each other... Maybe I'll try that as I have it back together and attached to the engine again. Not gonna drive it today though as its raining right now. I'm hoping this clean and rebuild did the trick though.

 

[aeronca65t]

......The mixture screw "start point" would be: one to one and a half turns from "closed" and use the idle stop screw to set speed... "goose" it sharply and let go. If it revs and then stumbles and chokes returning to "idle", turn the mix screw in (leaner) an eighth turn and try again until it returns a steady idle. if it gets worse, go the other way (enrich). You may find you need to tweak the idle stop screw to maintain an 800-ish RPM as you go thru this drill.

Yes. Exactly.

 

[DrEntropy]

*blush*

:smirk:

 

[71MKIV]

Nicely said. Good job posting the pic of the carb too. One of the idiosyncrasis (other then not being able to spell) I have, and frustrates me no end, is that I can see something in my head, and know how I would do something, that has worked in the past, but to explain it? If I can't get it across the first time, I'm out of luck. I can't think of another way to look at the issue at hand. That's one of the reasons I never went into teaching. Makes for some interesting fathering too.

Another point would be that a bigger alternator won't fix the drag down on the engine. It will always take x HP to make y amps. x HP as a percentage of total engine HP is always bigger on our little engines and comparitivly light flywheels than on the big carburated iron of our youths.

My two coppers