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I'm getting 15 from the vacuum gauge, cant really squeeze anything more than that unless I advance the timing past 10
That's the whole point of using a vacuum gauge to set the timing. Vacuum doesn't lie, while the damper indication from a timing light can be suspect for several reasons.
While some allowance needs to be made for higher elevation, in a stock motor 15 is way too low. Retarded timing would be first possibility.
Ping is engine knock due to excessive timing advance. Too much or too little is bad.
Been under the bonnet for the last 3 hours. The vacuum is showing 15 to 16 at idle. At 3000 its near 20. Are we talking about idle or 3000 for circa 18-20?
The best I can get the truck at the moment is 9 degrees. Mechanical advance takes it up to around 29 and with vacuum added I get around 36-38.
I had a play around with the float and needle in the Holley carb. I went for a drive with a screwdriver and stopped and tweaked the needles once I had the floats sorted.
I will have a play around with it tomorrow but most of the hesitation has gone, is really difficult to tell with our lovely bumpy roads in the UK
Idle spec of 500-600 a healthy stock engine will draw 18 to 20 at sea level. Sounds like something else is going on.
Possibly your carburetor is not adjusted properly. Make sure butterflies are completely closed at idle, and engine is drawing on idle circuit only. Set idle mixture screws both 1 and 1/2 turns out from seated. Set idle RPM to spec.
Then adjust idle mixture screws evenly for maximum vacuum and smooth idle, should be around 1/2 turn in. Make the idle circuit work for a living, readjust idle speed back down to spec as necessary. Blip throttle, wait for carb to catch up with new setting. It will be distinct adjustment, just a hair turn - "one potato two potato" idle note is OK.
A misadjusted carb is probably good for at least 1" to 2" of vacuum. Another possibility is the engine is seriously worn, with bad compression. This should be checked carefully.
As for total mechanical advance (vacuum disconnected)
Disconnect and plug vacuum advance. Avoiding the plane of the fan for safety, you'll have run the motor up to at least 4000 to see full advance on the mechanical. If you're not getting 34 or so, something else is going on.
Ok, still getting nowhere. I can dial it in to get 16 out of the vac gauge but nowhere near 20. I have seen on other forums that for older motors 15 is a good setting in vac for idle but not sure. The gauge I have also shows that idle should be a better vac reading.
I have tried tuning the carb, been up and down with timing. Checked the coil input voltage, which threw me for a while If you read with engine off you get 7v with engine on you get 10v, however disconnect the coil/ignitor and you get 12.5v (all good I belive).
I have checked the spark plugs, and set them with a bigger gap (which made the truck run rough), I then set back to stock which was better but still stumbling at either low speed or high (depending on the timing set).
Not sure what to check next. I have quite a bit of gas/exhaust coming from the PCV valve hole when I take the valve off. I understand this is normal but worth mentioning.
Anyone have any ideas? I'm stumped, just keep running round in circles
Here are some more pics, hopefully someone will spot something.
Anything? can't see whats wrong, or work out where i'm going wrong
Hole in top of vac chamber. Did try and block but made no difference.
Well in the picture that looks to be 14", way too low. Not sure where you're reading 15" is OK. Not on a stock motor it isn't. As you can see on the gauge itself, 18" to 20"+ is indication for a healthy V8 at sea level. Subtract 1" for every 1500 feet, etc.
This is what it comes down to, you'll have to eliminate the possibilities until, what remains is the only possible explanation. One possibility is low compression.
Probably a major vacuum leak is another? With such a low reading I'd think you should hear it, maybe not. One technique to find a leak is to investigate with an unlit propane torch around intake manifold, base of carb etc at idle. If idle picks up RPM noticeably, there is the location of the leak.
This needs to be investigated. If the compression is good, no vacuum leaks, then there is very little else that can cause a low vacuum indication. A non-stock racing camshaft, slow or "retarded" engine timing, and poor carburetor tune, From your reports both the timing isn't advancing enough and the engine vacuum is too low.
I checked the torque of the all inlet manifold and carb bolts at the weekend. everything fine. Also tried squirting brake cleaner (only thing I had to hand) around the inlet manifold gasket, and I did notice a change if idle revs on the left hand side of the inlet manifold.
To get to the bottom of this, and get it resolved I have booked it into my local American classic car garage so that they can do a compression test and get to the bottom of vacuum loss. They can also (once the issue is resolved) re-setup the timing and carb for me.
Will update once they give me the heads up to whats wrong
Not an authority, appears your carburetor is similar to the 4160; if so, did it come with the carburetor adjustment sheet; if not, I can post pic's of the 3 page sheet. The adjustment info came with a couple rebuild kits I purchase and found them very helpful. Appears your carb is new, or rebuilt so suggest not getting into internal adjustments at this time.
Your vacuum gauge indicates the engine is running in the 'good range'; whereas, my ancient vac gauge shows in the 15-16 range then possibly the timing is off, or intake air leak, seems tried everything thing else might try lightly spraying carb cleaner around parameter and listen for surging??
With the 4160 In my 65 with the 4160,with the manual choke, there was a slight clearance between the throttle plate and the edge of the air horn, a # 9 drill bit rings a bell but could be mistaken. Anyhow, had another urge to chime in!
Your vacuum gauge indicates the engine is running in the 'good range';!
Actually not, if you look close at the gauge I suspect that is the scale range considered "good" when operating the engine for best fuel economy i.e. driving around.
The diagnostic idle vacuum indicated range is the inside scale and looks to be the 18"- 20"+ range to be in the "green" as it should be. Hope this helps.
I popped into the garage earlier to discuss with them what i did to try and rectify the issue and give them a heads up about the what I thought was wrong. During the discussion I told them that I had measured the coil input voltage, and though it was a little low. With the truck on (but not running) i measured 7volts. With the engine running 10-11volts was measured. They looked confused when I mentioned this, they explained the 12volts would be required for the electronic ignition to work correctly.
It appears that they had already bypassed the regulator so 12volts should be present at the plus terminal of the coil. Under the load of the coil the voltage was dropping, which was caused by cable degradation between the coil and under the dash. They have installed a new wire and 12volts is no measurable at the coil.
It looks like this is the issue! I will not be able to confirm tomorrow when I collect the truck but it does make sense. The engine would have trouble igniting the fuel, which would give the sign of an over-rich running engine.
I am a little disappointed that I had spotted this, and told the garage who installed a new cable (which I could have done). I guess I need to put this down to experience, and knowing what voltage is needed at the coil to make things work correctly. I did second question myself, and feel that this was the issue of the stumble when I measured the voltage originally.
Not sure if the vacuum will increase, will check that out when I get the truck back. Crossing fingers that it now no longer stumble
... I told them that I had measured the coil input voltage, and though it was a little low. With the truck on (but not running) i measured 7volts. With the engine running 10-11volts was measured. They looked confused when I mentioned this, they explained the 12volts would be required for the electronic ignition to work correctly.
It appears that they had already bypassed the regulator so 12volts should be present at the plus terminal of the coil. Under the load of the coil the voltage was dropping, which was caused by cable degradation between the coil and under the dash. They have installed a new wire and 12volts is no measurable at the coil.
So the shop guys installed a new wire between what and where...?
I guess the source of the original wire. Will check it out when the truck gets back. I had an electronic ignition installed in the truck when I brought it. The truck was missing then, but we put it down to electronics being old, and the carb flooding the engine. It could be down to the connector block on the firewall, a broken or corroded wire.
I guess it doesn't hurt upgrading/replacing the electronics and installing a new carb. will run a bit better, use less juice, emissions will be a little better etc etc.
