Post by brianjenkins on Jul 16, 2015 19:53:05 GMT -5
I used a 1/4 NPT with a 1/8" hose barb on my vacuum gauge to get a better reading.
Using your guide...
I was able to get a steady 21 hg on the dizzy, backed it off 100 RPM on rotating the dizzy CCW. Steel idle screw was 3 turns in after touching (1100 RPM - 100 = 1k)...adjusted the brass idle mixture screw, and the only change was all the way in. It would read around 850 RPM here.
When I rebuilt the carb and set the metering rod - was the screw supposed to be out or in? I may not have set it correctly.
When doing the initial set up of the Accelerator Pump and the Metering Rod, (in that precise order) the steel Idle Stop Screw should be backed off and not touching the throttle plate when fully closed. Both settings are done with the throttle plate fully closed. If I read your post correctly, the Idle Mixture (Brass) Screw is all the way IN at 850 RPM?
Last Edit: Jul 17, 2015 4:24:20 GMT -5 by Scoutpilot
Post by brianjenkins on Jul 17, 2015 23:20:35 GMT -5
Quick question - my air filter setup is not stock. I've aquired some of the components but not all. I have a feeling the non-stock setup is choking it. Can I tune it without the air filter on? Will the air filter throw it off that much?
The reason I ask is if I pull the air cleaner, it will die. I was looking for a new filter to what I have and noticed it's only spec'd for 10 CFM.
Feeling like I'm chasing my tail some.
My accel pump was off a bit - 1/4" - I set it as you mentioned in your youtube video and got a hair over 17/64th (digital calipers) and then reset the metering rod (with a dial indicator). Still gave me some issues, but then started wondering about the filter...
Yes, it should. If you go to my YouTube channel you'll see my videos of the final tests for my clients. No filter attached. You appear to have an early industrial motor with the early distributor and short oil filler/breather tube. I'd like to verify something. Can you send me a shot of the carb side of the motor?
Do you have any reproduction metering rod gauges? I used the dial indicator to set it - throttle plate closed, screw backed out; set the metering rod fully seated. Set the pin height to allow the free travel of the rod at .040" (I'm fairly certain this is correct, but it still wont idle well)
Pump travel is correct as you showed. Then I set the metering rod as above. 3 turns in on the throttle screw, 2 turns out on the idle screw. It was running around 1100 RPM - 23 hg (steady, max). When I back off the timing it would barely give me 100 rpm lower. Turning out the throttle screw barely would lower the vacuum to 19-21 hg (bouncy). Might get 900 RPM. Turning in the idle screw (brass) I could get it down around 750 but it'd often stumble and die and the vacuum would be very bouncy.
Light choke (maybe 10-20%) helps. The above was without an air filter. Was hard to restart at times - pump, light choke - start, backfire or run.
Tried propane around the carb - didn't seem to notice a difference. The shafts didn't feel too bad to me. I used copper spray gasket on the manifold gasket, as well as the gasket on the base of the carb (both sides, torqued to 33ft lbs).
I am noticing some condensation forming on the outside of the throttle body while I've been trying to tune it. Been in the 80's here.
This was the first time I've ever rebuilt a carb, so I've been revisiting some of it to make sure I'd set things correctly. No filter on it yet, but the bowl was clean. Fresh fuel too (and it was running before all of this, but apparently was choked as hell with the air filter and I know I'd set the metering wrong originally).
Still "backfiring" huh? First, you need to determine whether it is backfiring out the exhaust or back up through the carb. We usually refer to an exhaust backfire as a "backfire", and backfiring through the carb as "spitting" or "coughing".
"Backfiring" is usually caused by a spark plug "sparking" when it isn't its turn and the exhaust valve is open. If your air/fuel mixture is too rich and you have unburned fuel in the exhaust system, cross firing from one spark plug wire to another can occur if they are touching each other and when this happens while the exhaust valve is open, it will ignite the rich / unburned mixture in the exhaust manifold and tail pipes and result in a big bang.
Having timing that is too late (retarded) can cause this same thing sometimes if your engine is running too rich. When the exhaust valve opens, the mixture isn't done burning so it ignites the unburned fuel in the exhaust system and causes a loud bang.
Back firing can also be cause by a cracked distributor cap, or one that has carbon tracking inside which causes cross firing between the terminals inside, which in turn, sends spark to a spark plug that isn't ready for it yet. Inspect the cap very carefully.
Backfiring through the carb (spitting or coughing) usually occurs in the morning when a carb's air/fuel mixture is a bit too lean. This usually goes away once the engine warms-up. It is also commonly caused by the accelerator pump inthe carb not squirting enough fuel before the main jets start working. If you spit the instant you blip the throttle it is probably the accelerator pump in the carb not working, plugged up or out of adjustment.
As with backfiring, coughing or spitting can also be caused by a bad ignition system, such as cross firing, which sends a spark to a cylinder that has the intake valve open. When that plug sparks out of turn, it lights the fuel in the cylinder and the pressure has to go somewhere... so if the intake valve is open, it goes right back up through the intake manifold and out the carb with a "spit" and sometimes even a flame. When and how it backfires or spits will give you an indication for where to look.
It's not unusual to find a later head on an older block. It's so common in fact, it is to be expected. But that won't affect the motor's operation as the only difference is the decoration of the top and the ribs on the much later head.
"and the vacuum would be very bouncy." How bouncy? In what range? and at what frequency? Read the article at this link, Second Chance Garage. Then tell me what you've seen.
The inability for the carb to idle any lower than 750 with a "FULL RICH" setting, as you have described, tells me that some air is leaking in somewhere. Whether it's the carb or the manifold, it's hard to tell. Are you sure the copper rivets in the diffuser have been crushed properly?
Post by brianjenkins on Jul 19, 2015 17:38:38 GMT -5
Getting when the RPM is over 1k, the vacuum gauge is steady. At 1200, it's around 24. Again, steady. Retard timing 100 RPM and I hit 21 +/- .5 (fast sweep)
When I back off the steel throttle screw, I get down around 950. It's a little more jumpy here, but around 20 (it'll bounce - very fast, about +/- 1)
Trying to set the brass throttle screw in I can get it down near 850: 18.5 +/- 2 (very fast)
800 RPM is between 15-20, again very fast.
Used an unlit propane torch, and no real changes. Tried starting fluid and got a slight rise in RPM near the PS of the carb. Everywhere else, no change. Retorqued manifold bolts too. PCV is installed. Copper washers on the base of the carb were crushed, and I used 'copper gasket' spray on it as well. (I'd previously had trouble with this and used indian head, but it melted all over the intake. It's not a fair comparison because at that point, I was choked so badly it was way off. Although I was able to get down around 500 RPM, but again the air filter was a choke)
My lesson for today: Bump the starter when you think it will "spit" - because otherwise it'll break the clip on the end of the Bendix drive and it'll fall apart.
It's never "back" fired - it's always been through the carb. The engine is warm, and it spits when I give it quick throttle. If I goose it, it's fine, and will stay there. I know the pump is correct, but I'm still wondering about the metering rod since I don't have a gauge. Based on what it's doing - is that likely it?
If you still believe it's a vacuum leak, I'm tempted to pull everything apart and use "The Right Stuff" (It's rated for 450* continuous, 500* intermittent) over top of the gaskets to see if that helps any. Is the leak at the throttle shaft enough to throw it off?
Post by Scoutpilot on Jul 19, 2015 18:38:09 GMT -5
Your description of the vacuum gauge would tend to lead me away from a serious valve issue. But the spitting through the carb tells me your timing is not what it's supposed to be. Did you inspect the distributor cap for cracks or carbon trail? What is the Dwell reading? It should be 41º- 42º of arc. The throttle shaft and the bores it passes through will wear into an "egg" shape. A gap of .005" will leak. When the shaft is rotated the gap opens and sucks air. The normal reaction of the owner is to make the mixture richer to accommodate the increased airflow. Think choke. This leads to changes in timing and more enrichment of the mixture and...to a high idle with choke applied. Yes. the shaft and bores are that critical. Nominal dimension for a new shaft is .3125" OD and the bores are .3125" ID. Yes. That is a close fit. Most come to me with shafts that measure .308" - .309" and bores have mic'ed out at .313" - .315". They all leaked. Oh and I don't recommend using ANY type of sealer on the diffuser gasket. Properly torqued, it won't leak. As far as the Air Filter goes, were I you, I'd be looking for a complete oil bath air cleaner setup and a correct oil filler tube with the cross tube. The engine will breathe easier and last longer with that proper setup and the PCV installed. Go ahead and get the Metering Rod gauge. You'll thank yourself.
Post by brianjenkins on Jul 19, 2015 20:15:21 GMT -5
Here's a video:
This is a new electronic distributor (The IGW had play in the shaft and springs were loose). So no cracks. The dwell isn't adjustable on the elctronic, but the IGW was 41* with a .020 point gap. But both dizzys acted the same way at idle while trying to time.
I have the pieces for the oil bath, but they need cleaned up. In the mean time I picked up a cone/type filter at Advanced. There was no change in the motor when I put it on, so it's not restricting too much. I agree on the oil bath being better.
I'll pick up a metering rod too, I think that's the only piece I haven't been able to verify.
Post by brianjenkins on Jul 19, 2015 20:47:39 GMT -5
I found this on the 2a page:
"Look in carb?" - you can also just listen (without air filter connected). You should hear a clean "hiss" with no gurgling. If it also sounds like a kitchen sink faucet is on - like water is running - then you'll probably see fuel dripping from the venturi, or you'll see a very wet throttle plate if the metering rod is set too high at idle. (The gurgling sound you hear is the fuel being sucked past the throttle plate.)
I'm definitely getting the gurgling, and fuel drips down the venturi. So hoping the metering rod gauge fixes it!