tunning question

[broncnaz]

well as long as the engine is not pinging your timing is probably close to what it needs to be. Might still have a little to much. But the rich carb is probably also causing the issue. I'd get a whole rebuild kit for the carb and swap out the power valve it could be blown or loose. A blown or loose power valve will cause a rich mixture all the time might be why the idle screws have to be turned all the way in. Once that is swapped out see if anything changes. if its better then you can probably move on to rejetting.
If the power valve was bad or loose then you may not need to play with the accelerator pump. Although you can try changing the cam position on the cam you currently have. I've had way more luck just changing squirter size than I have changing pump cams. but some people have had good luck with just cam swaps as well.

 

[sicaz66]

You mentioned msd. Did you supply voltage through a "good" 12volt source. I had a problem where I wired mine using the old power for the coil not realizing it was a resistor wire. And was not supplying 12 volts.

 

[aliensecretion]

Going to pull the carb tomorrow and go through it. Will check the pv too.
I did confirm my power for the msd was good when I wired it up.

 

[aliensecretion]

Pulled the carb last night, everything seemed good to go. Accel pump set correctly and the diaphragm appears to be fine. The jets didn't match what was advertised to be in the carb. Was supposed to be 66 and 72 but in actuality they were 70 and 73. Went through and cleaned everything and will reinstall tonight.

I think the power to the MSD is the key.... When I originally ran it, I used the red/green wire from the ignition. I thought it wasn't a resistor wire but maybe I didn't check it right. Tonight I'm going to double check that and find out if it's right. If it is, i'll move onto getting smaller jets. If not, i'll fix it, run it, and see if it solves the problem. Sound logical?

 

[broncnaz]

the red green wire is a resistor wire. You may get a near full 12volts when you first check it leave it on a little while (a minute or two) and you should see voltage drop

 

[aliensecretion]

Is it the whole wire or just the part in the dash?

 

[broncnaz]

There's about 12-16 inch of it in the dash that is the actual resistor part. Really I'd just run a new wire from the switch

 

[aliensecretion]

Sorry this is long but I've been out of town for work and am finally back able to work on this. Here's what I've been up to.

First, I fixed yanked out that resistor wire. Now I'm set at a solid 35 total advance. It runs much cleaner and smoother with no pops when I shut it down. Learned something new there... didn't know the resistor wire could read 12 at first then go down. With this done, I'm up to 9.5 mpg over 50 mile highway trip. Still had the problem with idle screws being in farther than normal and the hesitation on start. Replaced the accelerator pump valve with a new one just to be sure. Only choices are 30 and 50cc. 30 came with it and that's what i put back in.

Now I drop down 2 sizes on the jets to 64 and 70. Also bump up the air bleeds slightly at QF's recommendation (don't have the number on me). Least hesitation of all, most vac and slightly less power than before. idle screws didn't really change from the 3/4 out position. Gas mileage drops to 6.5 mpg over the same trip.

Now I swap out the jets with 62 and 68. Power is fine at speed but can barely keep the thing running at low speed. The idle screws are even further in.

So before I swap the jets again, was looking for input. Thinking about putting the originals ones back in. Should I move up to the 50cc accel pump? My accel cam is already at the most aggressive position so I'd have to go find/order a more aggressive cam to replace it. Still not sure why the idle screws have to be so far in. I'm tuning with the timing light and a vac gauge hooked up shooting for 900rpm and highest vac possible.

 

[Broncobowsher]

The accelerator pump (cam, pump, squirter, etc.) are just for tip in. when you aggressivly go from idle to power. When you open the throttle a lot of air goes in fast, but the fuel is sluggish and takes a moment to get up to speed. The accelerator pump squirts in a shot of fuel to cover that response time. It has nothing to do with idle, cruise, fuel economy, etc. Only when you hit the gas. Doesn't sound like you have problems there, no need to mess with it. Even if it is off you need to fix the bigger issues before you bother messing with that specific circuit.

start the engine and let it idle. Look down the carb at the venturi boosters. Is there any fuel dripping off of them? If so you have a bad needle and seat.

It is hard to tell if you are too rich or too lean. Both will kill gas mileage. I am a modern tuner. I will weld in a bung (or a cheap M18x1.5 half nut from the local nut and bolt store) into the exhaust. Screw in an O2 sensor and watch the readings with a cheap DVOM wedged into the dash. Heater wires wired to a simple switched source. fairly cheap and wonderfully informative tuning aid. Not as nice as a good wide band O2 sensor, but cheap and very nice at getting into the ballpark.

 

[rustbucket]

Have you checked for vacuum leaks?

 

[aliensecretion]

Doesn't sound like you have problems there, no need to mess with it. Even if it is off you need to fix the bigger issues before you bother messing with that specific circuit.

That's kind of what I thought. Thanks for confirming.

start the engine and let it idle. Look down the carb at the venturi boosters. Is there any fuel dripping off of them? If so you have a bad needle and seat.

Will check this tomorrow.

Did check vac... no leaks.

 

[broncnaz]

How much vaccum are you pulling at idle how much at cruise? You should be able to idle less than 900 RPM but thats your choice.
I'd go back to your orginal jets and air bleeds. Your issue is mostly with idle maybe you need different idle air bleeds(bigger) or smaller idle feed restrictions.

As for jetting I probably wouldnt be changing jetting and air bleeds at the same time. air bleeds will work with quite a range of jetting. changing both really screws up things because its to big of a change all at once. So just mess with the primary jets for now mybe try the orginal air bleeds and the 64 jets see if there's any improvement in power and mileage. if so go 2 jet sizes smaller see what happens then.
Also wouldnt worry much about the secondary side of the carb until you get the primary side running right just cruising around you wont be into the secondaries anyway and its better to have them a bit rich anyway IMO.

Ditto on the acclerator pump you dont need to mess with it. If anything I'd go to the next size up squirter before changing the pump CC. but still your not having acclerator pump type issues so leave it alone.

 

[aliensecretion]

Thanks broncnaz. The too much at once logic made sense so I took it back as close to out of the box as i could get. Also took a different approach and just tried doing it by ear and actually got it running fairly smooth. Getting about 15 vac and idle about 650 in gear. Don't know about vac at cruise. Going to drive it a bit more today and see how it does.

You were talking about focusing on the primary first... I'm a little confused how to do that because when I'm adjusting it at idle, it takes a combination of both the primary and secondary adjustments to get it smooth. If the secondary doesn't kick in until you're on the throttle, why would adjusting it at idle make a difference?

 

[broncnaz]

I was just meaning on jetting about the primary side. as the primary's are were you do most of your driving and thus the jetting on that side is more critical to mileage and power. Its not until your running high RPM's and really getting on it that the secondary's come into play.
With idle mixture you have no choice both sides need adjustment. Vaccum at idle sounds a bit low but that depends on what cam you have. Ignition timing also affects vaccum you might be able to use a bit more timing. but again it depends on the camshaft. Its good to know how much vaccum you pull at cruise RPM as that can help with power valve choice.