air cleaners and improving air mixture on 250 six

[Gumby]

Petronix works for some and doesn't for others, I know so many more who hate them with a passion, id never use one.

Your using an old school can coil, should be a no brainer there less its really old. [ newer epoxy filled coils hold in heat, heat kills ign parts ]

[66Submarine]

Glad I can help!

The fuel pressure thing is just related to the fuel pump itself. A lot of new mechanical pumps make too much pressure; you'll just hook a pressure gauge of some sort up to the outlet/carb side of the fuel pump (line to the carb) and see what the pressure is.

A vacuum leak from the booster should make it run leaner than when it's not hooked up, so I don't think that's your issue.

BTW, the damper might have slipped the outer ring if the mark has to be that high for it to run. You might try just turning it over by hand with the plugs out and watching for the #1 piston to come to TDC. Won't be super accurate, but it should tell you if it slipped and moved a bunch.

I like the OE points or a later GM HEI myself, but the Pertronix thing that came in the engine I have in my truck right now seems to work fine most of the time (seems like it might have an intermittent weak spark/hard starting issue when hot/heat soaked, but I can't say for sure right now).

The running rich at idle sounds like a potential overpressure/needle and seat issue. What might be happening is that at road speeds the engine can (more or less) burn the extra fuel, but at idle it "loads up" with extra fuel and starts to run rough. If this is the case, you might notice revving it up some (say, to the speed you normally shift at) for a few seconds will clear the extra built up fuel out and let it idle smoother (in worse cases you might have to do that just to keep it running).

You have a good day, too.

[70STOVEBOLT]

This question might be a little off-topic, but would fuel pressure being too high cause the carb to leak from the power piston linkage just below the float bowl, AFTER shut-off?
When I shut my truck off, after about 10-15 minutes it will leak fuel from that area, then it will be a little harder to start. It always starts when cold with just one pump after pulling the choke out. It also has a slight pop thru the exhaust at idle, but runs fine above idle. I have adjusted the mixture several times and cannot get the slight pop to go away. The plugs all look normal.

[66Submarine]

Originally Posted by 70STOVEBOLT

This question might be a little off-topic, but would fuel pressure being too high cause the carb to leak from the power piston linkage just below the float bowl, AFTER shut-off?
When I shut my truck off, after about 10-15 minutes it will leak fuel from that area, then it will be a little harder to start. It always starts when cold with just one pump after pulling the choke out. It also has a slight pop thru the exhaust at idle, but runs fine above idle. I have adjusted the mixture several times and cannot get the slight pop to go away. The plugs all look normal.

Yeah, it could. When the carb heatsoaks like that, the fuel pressure increases as the fuel heats up and expands--which can obviously push fuel past the needle and seat. If you start out with too much or almost too much, it can't get much better from there! My father's truck had bad hot-start issues, and after regulating the pressure down he says it hasn't done it since. It could also potentially be just a heatsoak thing, or a slightly leaky needle and seat. I'd just check the pressure and go from there.

[70STOVEBOLT]

What is the ideal pressure for a 250? I've read most V8's use around 7 psi.

[66Submarine]

The spec is 3 to 4.5PSI for the inline sixes.

[70STOVEBOLT]

Thanks for the info, I will check it out. FWIW I replaced the needle and seat with a new one when I rebuilt the carb and it still pukes out gas 10-15 mins after shut down. I will post here after I check it out. Nobody has mentioned fuel pressure as a possible cause of this, and I have searched and searched and posted on here before asking about this.

Thanks again,
Mark

[DBD]

if the timing marks are off, why not get them right and then time it right? I bet a lot of this time you're spending on tweaking the carb is just a bad timing curve...

[old cool]

First I'd like to thank 66 Sub for sharing his knowledge on every question I've ever asked. Great resource along with all the others. Great membership.
Since i started the thread, I have tried different things (looked at float for hang up/drop and lots of screw turning). Finally heard about this fuel pressure thing. It makes sense since I always seem to have plenty of fuel in bowl w/o giving any gas. I also have wetness around float bowl but never a drip. I look forward to feedback from DBD. I too will be doing a pressure test. Oh, and some old timers are not very fond of Rochesters for various reasons - fwiw. Maybe they have a personality.
As of today, I set timing and carb with vacuum gauge. It came out different than using a timing light. I think the vac gauge is more honest on older engines due to slipped pulley. Thanks to Sub for that too.
Process:
1. I disconnect vac advance and plugged off
2. Vac gauge was teed in, engine running
3. Turn distributor to max vac (more movement than i anticipated)
4. tweaked distributor to steady vac reading which was actually advancing
5. reconnected vac advance
6. Vac gauge still set to read
7. turned mix screw to lean out until idle became lumpy
8. slowly turned mix scew counterclockwise until max vac
9. made it a tad richer using engine sound
10. reset idle
RESULT: My truck has a little different sound and the carb is set leaner. I think the truck is a tad slower, but smoother. Only drove a couple miles so not sure of full results. time will tell. BUT, the distrib and settings are DIFF when using vac gauge. (Popping sounds like timing/misfire issue as I believe all have said at one time or another)
OTHER: I checked spark at each plug for spark power and engine stumble when disconnected and truck running - obvious one at time.... this tells about coil /ignition. I also concentrated on all vacuum connections, hoses, pcv, and sprayed carb cleaner on intake gasket to see if idle changed. Im not sure of internal probs but externally, I think I covered idle-trouble-makers. Oh, and watch those power boosters if you have one. Prob could be right at check valve. For all vac tests i either pinched hoses to see what the engine would do and I used a piece of hose (stethascope) to hone search for leaky air noises. Thought i heard slight air sound on hose connected to intake manifold (intake to power booster). Tightened clamp seemed to go away).
SO, I'm told, old timers use vac gauges to do their tune ups. Might be worth a try.

Hey SUB, i think the vibration is u-joint related. Heard clunk in rear end today on some take offs. Vibration is now consistent between 10 and 35 mph; whether speeding up, slowing down, or down shifting. Seems to lessen if I put in neutral and coast.

[66Submarine]

Again, I'm glad I can help.

FWIW, I think that setting the timing to max. idle vacuum will probably result in an excessive amount of timing (IME). I would suggest determining TDC, and probably trying to come up with another balancer if that one is in fact loose/slipped; I'd be afraid of it slipping around again and making a break for freedom! Just watching the piston moving in the spark plug hole would probably be good enough to see if it's slipped and moved a bunch.

To truly optimize the timing you'd need to tune it on a dyno to see where the power peaks at under load. Otherwise it's trial and error/guesswork. The benefit with the timing light is that you get a relatable number, which helps that. If you decide you want (for instance) 36º of total mechanical timing, you can rework the advance curve to put idle timing where you like it with total timing @ 36º. With the vacuum gauge method, you are only tuning it for a no-load condition at idle. Might run great there, but have too much timing where you drive. Low compression engines like the 250 also take more to make spark knock/ping, so that's not really a great indicator. The timing light method works great on old/tired stuff if the balancer is good.

BTW, how much richer than peak vacuum did you go? I normally find that peak vacuum (or a little bit leaner) works nicely.

[66Submarine]

Also, to both you and 70Stovebolt:

With the timing set at something like 10ºBTDC (IIRC) on my other 250*, it would pop a bunch at idle if I hooked the vacuum advance up to manifold vacuum instead of ported (because of the extra timing). Didn't run it there (just a "what if I did this" ten second experiment of boredom), but it might be something to check/try on yours. My old 283 liked all the advance at idle with the vacuum advance hooked up to the manifold, but the six didn't seem to care for it.

*Haven't tried it with the one in my truck I'm driving, but I expect the same thing would happen.

[old cool]

I have been using a timing light all along. I heard about the vacuum method of timing and looked it up online. Believe it or not, I actually turned the distributor clockwise to get maximum vacuum. Hence I was retarding it from where I was when using the timing light. I also found that I was able to turn the mixture screw further in two get maximum vacuum. Here again, this was one of the things I wanted to achieve. I turned it very little to the richer side. Using ear only to make this adjustment. could be a coincidence but I think it runs and sounds a little better.
I will drive it for a while as is and let you know. I will also put a timing light back on it to see how it compares. this may also give me an idea about balacer slippage. As always, thank you. i will keep you posted.

[66Submarine]

I thought you said that you set the timing by ear and the light showed the balancer mark as way past the pulley/it didn't want to run when set like it should be? I really think you should go ahead and do some sort of TDC check at this point; not hard to do. A piston stop only costs a few dollars if you want to go that route, and then you'd know for certain if the timing marks are accurate or not.

I do not recommend the vacuum @ idle timing method at all, because it is really only optimizing the timing at a no-load idle, and it lets the timing at the vastly more important operational/driving RPM range just end up wherever it happens to end up.

[Gumby]

Originally Posted by old cool

this may also give me an idea about balacer slippage.

One of those things, if you think its off any, just change it, it can ruin an engine.

['68OrangeSunshine]

Originally Posted by Gumby

Petronix works for some and doesn't for others, I know so many more who hate them with a passion, id never use one.

Your using an old school can coil, should be a no brainer there less its really old. [ newer epoxy filled coils hold in heat, heat kills ign parts ]

I'm not a Pertronix tech rep, but I have been running one for a few years on my 292. The system is designed to be used with their proprietary coil. The Ignitor [1] requires the Flamethrower [1] coil of 40,000 volts [1.5 Ohms]. Ignitor II requires the Flamethrower II coil of 45,000 volts, [0.6 Ohm]. Ignitor IIIs are available for V8s only, but require the Ignitor III coil [45,000 V, .032 Ohm].
If a coil from another manufacturer has the same or higher voltage it probaby should work.
Like the HEI system, one must supply a full 12VDC to the coil (+) Positive terminal. Using the stock Yellow 20 wire gives you 12 volts on startup, but drops to about 9 VDC as the resistance wire [20 Orange/Purple/White] heats up.
From personal experience, I've had GM HEI modules heat-soak on me and lose power, but the Pertronix worked good.
The old Ignitor [1] would sometimes burn out if the igniton key was left in "ON" , but the Ignitor IIs shut themselves off.

[Gumby]

Originally Posted by '68OrangeSunshine

I'm not a Pertronix tech rep, but I have been running one for a few years on my 292. The system is designed to be used with their proprietary coil. The Ignitor [1] requires the Flamethrower [1] coil of 40,000 volts [1.5 Ohms]. Ignitor II requires the Flamethrower II coil of 45,000 volts, [0.6 Ohm]. Ignitor IIIs are available for V8s only, but require the Ignitor III coil [45,000 V, .032 Ohm].
If a coil from another manufacturer has the same or higher voltage it probaby should work.
Like the HEI system, one must supply a full 12VDC to the coil (+) Positive terminal. Using the stock Yellow 20 wire gives you 12 volts on startup, but drops to about 9 VDC as the resistance wire [20 Orange/Purple/White] heats up.
From personal experience, I've had GM HEI modules heat-soak on me and lose power, but the Pertronix worked good.
The old Ignitor [1] would sometimes burn out if the igniton key was left in "ON" , but the Ignitor IIs shut themselves off.

plus your talking trucks, in a performance app to lose points us where folks saw problems, why many now convert old points dizzy to HEI or trigger to skip that step.

[old cool]

great, great wisdom and experience. I probably do have the correct coil. the problem I am experiencing has to do with the previous owners. The truck was nicely restored at some point (not original) and I dont have one single receipt. everything I do requires some level of research. thanks to each of you, I am learning a lot.

[old cool]

To SUB and all others. I did a double check and liked the results. I did use vacuum gauge and tweaked distributor to max (bout 18 + inches). I also checked timing with light and it read about 8-9 degrees btc. I used vac to get mix screw right and it read 18 again with vacuum advance reconnected. I dialed in idle and it seems run well. Still think it gives off too much stench.
The vac gauge is suppose to provide lots of info re guides and valves, etc. Haven't done all checks yet. It would help to have another person to do some of these tests.
Way back when, I did say the helper set timing by ear and the mark read too high. But it was a great improvement from rich/retarded state. Since I have tried and retried with your help it seems to be reading (timing light) appropriately. I'm sure when I get the pinion or drive shaft business out of the way, I'll know more.
FYI, I stumbled into an open air-element and really like it. It's very,very old and about 6-7 inches wide. I've never seen one. Probably off a tractor or something. May have to be fabricated; hope I can get it usable.

[old cool]

UPDATE for this older post.
First to 66SUB. I created a 3" spacer between carburetor and air cleaner. I was able to use my $5 find. Note - I reversed the lid as well and that also allows more air into carb. Haven't yet recorded improved mileage as I've only driven about 50 miles since change.
Also been examining truck for vacuum leaks. I changed out the grommet and check valve on booster and also ran hose type stethescope around all connections and manifolds. The only thing I haven't dealt with is the pcv as it rattles well.
I found I have a faint air sound from power booster when I put the hose up to the brake push rod from inside the truck. It is continuous and unaffected when I depress the pedal. Hope this slight air sound is normal. As I now know, a booster leak will also create running problems at some level. BTW, my pedal is very light to use (read that a firm pedal can be caused by a leaky booster).
Bearing in mind that engine performance is based on AIR, IGNITION, and FUEL, I will update whenever improvements are accomplished. Please continue with feedback folks. It's meant a great deal to me and others I'm sure.