Rough idle + pinging

[bubba22349]

You could try your Hollry 1940 out on it, they work fairly good and see if it' not so rich, too bad you don't have a 68 point distrib to try too.

 

[thesameguy]

Yeah, the distributor is the road block there. Also, that 1940 has been sitting for a year or more - it's probably all dried out inside. I am tempted to try it though, even if only to see what it does at idle.

 

[bubba22349]

The rumbly idle is the only upsetting thing - and I am positive it's just running way too rich at idle. I don't think it's an ignition problem.

If it's too rich at idle than you headed in the right direct lowering the fuel pressure. Only a few things that can cause it being too rich at idle first is the fuel level and or fuel pressure, and also the choke if it was not set to full open. Those old Holley's don't like too much fuel pressure I had them work good on as little as 1.5 psi for a stock street car. Any chance your can get them to look over the carb again were they rebuilt it? There is a 1904 core in the for sale section too that would work with your LOD.

I would try that 1940 I ran one on my old 300 six for several years worked good even with the old LOD distrib. soon after swapped in a DSII and was so much better mainly because of the centrifugal advance and hotter spark with less maintenance

 

[thesameguy]

On the way home today I dropped the fuel pressure to 3psi and it was still insanely rich - but still driving 100% okay. I see that you were serious on these carbs requiring very little fuel pressure! Unfortunately 3psi is the lowest my regulator will go. I am probably going to finally dump this fuel pump and get something less, um, potent. It's a GREAT pump, but it's noisy and happily pumps way more than its specified 6psi - maybe a function of running 5/16' fuel line instead of 3/8". I dunno, but I think I am going to go ahead with a diaphragm type pump and save some pressure and some decibels.

Seeing as 3psi did nothing to help my cause, I started installing the 1940 this evening. I ran into two roadblocks:

1. I have NO idea what the fuel inlet thread size is. It's not the same as my 1909 - it's quite a bit larger.

2. After seeing all the pieces, I realized the 1940 has a thermostatic choke & hot air tube, which of course means there is a matching hole in the exhaust manifold I hadn't previously noticed. The hole has a crack at the top, towards the head. Does it seem reasonable I can use some copper RTV to patch that hole, and seal the tube into the manifold? I need to make a new tube - the one on the carb is too short and electrical taped to some vacuum hose. Not sure how that was intended to work.


Edit: I need this brass fitting - any idea what it is?

http://www.carburetor-parts.com/v/vspfi ... 1940_3.jpg

Edit 2: Looks like it's not just a brass fitting, but it's available with the rebuild kit....

http://www.carburetor-parts.com/Holley_ ... p/1138.htm

http://www.carburetor-parts.com/v/vspfi ... 5B1%5D.jpg

 

[bubba22349]

1. I have NO idea what the fuel inlet thread size is. It's not the same as my 1909 - it's quite a bit larger.

2. After seeing all the pieces, I realized the 1940 has a thermostatic choke & hot air tube, which of course means there is a matching hole in the exhaust manifold I hadn't previously noticed. The hole has a crack at the top, towards the head. Does it seem reasonable I can use some copper RTV to patch that hole, and seal the tube into the manifold? I need to make a new tube - the one on the carb is too short and electrical taped to some vacuum hose. Not sure how that was intended to work.

1. I think that it's a 1/4 pipe thread. I used a long fuel filter on mine has hose on one end and is threaded to fit that fitting on the other end (or is also a short one that also works) with a wrap or two of Teflon tape. You could also use an adapter fitting for rubber hose or to fit fuel line fitting if yours is a steel line.

2. I don't know the temp range of the copper RTV usually I would use the orange high temp type on an exhaust manifold. You would not need to worry about sealing it to the manifold. The way it works is pulls air trough the tube inside the manifold IE it's open anyway under the bottom so that air is drawn into and heated by the exhaust this hot air gets pulled up into the choke housing heating the spring which causes it to contract and open the choke blade. you can use a copper, aluminum, or a steel tube (brake line) with a insulating sleeve over it to make one. In the Dormen line also called "HELP" at most auto parts stores they have a couple types of repair kits too.

That fitting is actually the needle and seat that the float pushes against to control the fuel level is yours missing? You just leave it in the carb and screw a filter or adapter fitting into it as needed to fit your existing fuel line. Usually you don't change that unless your rebuilding the carb.

 

[thesameguy]

Copper RTV is good til like 700 degrees. I've used it to seal manifolds to heads before with good results. I didn't realize the tube sucked in fresh air, though, so I guess it's not necessary. I'll just make a new tube and stick it in there.

Now knowing what that fitting is/looks like I had a revelation. The 200ci came with a small box of random stuff, which I totally discounted. Just dug it out, in the box is a mangled fuel line but it has The Fitting still attached. I'm guessing when the previous owner pulled the motor from the car it came out that way.

All my mysteries solved - thanks for the assist. I should be able to finish assembling tomorrow and see a) if the carb is still any good, and b) if it addresses my issue.

 

[bubba22349]

Good luck hope it works great

 

[thesameguy]

Got the 1940 fitted and the car started pretty much instantly. Initial result is a stunning 19" vacuum, which is 2" more than the car has ever seen, and 4" more than I've seen with the new motor. Got the idle set to 725rpm (in park), and dialed the idle mixture back a fair amount. For the first time ever I saw a real result on the A:F gauge - I was actually able to lean out the motor to the point it stalled. I was NEVER able to do that with the 1909. It's now sitting at the high end of stoich, with big swings from lean to rich like an O2 sensor should - before I would see a couple bars of swing, but now I've got a swing over pretty much the entire gauge. Timing is hanging out at about 14 degrees with the vacuum plugged in - I didn't bother to unplug it since it should still be at 12 degrees unplugged. That is also something I have never observed - the vacuum signal having an actual affect on timing - presumably something *else* wrong with the 1909.

Only bad thing is that after opening the throttle the car is very hesitant to return to idle. It may be some of the linkages (choke, etc.) binding in their travel, or the throttle plate may be gummed up. I hosed down all the external moving parts with some Seaform, and sprayed a liberal amount on the throttle plate. I think it actually needs to come back off for some underside cleaning, but that's okay - I need to get new carb & spacer gaskets anyway.

I think it's running *slightly* lean at idle now, but I'm not sure. It needs some more running time, and probably to actually get warmed up. I am going to let that Seafoam soak for a while and replace those two gaskets and the air filter and hopefully give it some more road time this weekend.

I did not bother to mess with the hot air tube. It's summer in Sacramento and the choke is going to be pointless for the next many months. I just capped off the stub of the old/wrecked air tube. Is that the correct approach, or should I leave it venting to the atmosphere? Does the carb use the air coming in that tube for anything and/or will the resultant vacuum in the tube hurt anything?

 

[bubba22349]

That's great news at least on some of it. Did that 1909 have any grantee for it for sure there is something wrong with it? Trying it on two different motors with the same poor results sure seam to verify that. I would send it back and get them to see if they could give you a 1904 or an Autolite 1100 in it's place than you could at least use it on your 200.

Only bad thing is that after opening the throttle the car is very hesitant to return to idle

You can add an extra throttle (universal type would work good) return spring to help that until it loosens up some.

I did not bother to mess with the hot air tube. It's summer in Sacramento and the choke is going to be pointless for the next many months. I just capped off the stub of the old/wrecked air tube. Is that the correct approach, or should I leave it venting to the atmosphere? Does the carb use the air coming in that tube for anything and/or will the resultant vacuum in the tube hurt anything?

Yeah leaving the hot air tube open or capping it off won't hurt a thing. Capped off it's little less vacuum leaked, loosen the choke cover screws and turn the cover so it's holding the choke blades wide open with a little bit of spring pressure (engine cold)

 

[thesameguy]

Thanks! I had a local place rebuild the 1909 - I am going to run it up to them next week with my sob story and see what they offer. I gotta believe whatever is wrong is the result of an innocent mistake or oversight and not incompetence. They are too well-renowned to simply be bad at this stuff.

I've got a big spring returning the throttle now. I'll lock out the choke and play with the Seafoam a little more and see if it loosens up. I'm hoping (betting?) it's just a little rusty and/or gooey from sitting.

 

[bubba22349]

I think your right it should loosen up with some use. If you have some spray carb cleaner might take care of that gumed up varnish too. anyway your close to having a good driver now

 

[78merKri6]

69.5Mav has a good idea. Sounds like cracks in flex plate! Or even spline wear/slipping of internal converter. It can happen.Forgive me if wrong. Gary.

 

[thesameguy]

Whoa, that's a post from the past! The issue was the old motor - not sure what, but maybe a side effect of a seriously worn #6 cylinder. I don't know. New motor cured that issue entirely.

I ended up rebuilding the #1940 the other night. I wasn't quite satisfied with its performance, and a lot of the gaskets looked like they'd had better days. I also read somewhere that the floats can become saturated with fuel and heavy, and thought it might explain a hot-restart flooding issue I was having (pull fuel pump fuse, crank for a bit, car starts right up, plug fuel pump back in), but I also wasn't entirely confident that the needle & seat fitting was in very good shape. Anyway, first time I've ever taken a carb apart with the intention of putting it back together, but everything went smoothly. I also went ahead and made a hot air tube out of brake line and got that fitted. Probably should have used 1/4" line, but I used 3/16" so we'll see how that does. I made a small bubble at the intake side of the tube for a tight fit in the exhaust manifold, and that seems to be working fine.

I need to tweak the mixture & idle settings a bit, but it started right up with good vacuum and good air:fuel anyway. Hopefully this weekend I can get it fully sorted. With all this goofing around lately I feel like I'm getting a pretty good grasp of carburetors which is nice. This is the first time I've ever been compelling to learn something about them. Maybe when it's done, I'll have the courage to attack the q-jet on my Cadillac 429.

 

[69.5Mav]

Maybe when it's done, I'll have the courage to attack the q-jet on my Cadillac 429.

Muscle Car on spike had an episode on rebilding a Q-jet.

 

[thesameguy]

Awesome - I will have to dig that up!

 

[thesameguy]

There is still something not right with the car post 1940 rebuild. It starts great, idles great, and does most things great, but has a *gnarly* stumble just off-idle. I don't have a tach so I don't know what RPM I'm talking about, but it's definitely something related to throttle plate position. Doesn't seem to matter whether the car is idling at 800rpm or 600rpm (where it is now), but as soon as I touch the pedal there is some violent stumbling. It clears up almost instantly as I get into the throttle so it doesn't prevent me driving the car, but a smooth take off isn't possible. Engine temp does not affect the problem - it's bad cold and hot.

I've messed with fuel pressure (3 psi now), float setting (it's slightly lower than spec now), idle A:F (about 1.75 turns out), and idle speed (now 600rpm in Drive) but nothing seems to affect it. I'm thinking it may be a side effect of running an LoM dizzy with no SCV, possibly in combination with a weak vacuum advance. I think when the throttle cracks vacuum fluctuates and timing goes nuts. Maybe. Sounds plausible, anyway. I think I am going to disconnect the vacuum to the distributor and see if the behavior changing. Static 12 degree timing should be not great for anything, but should at least let me know if the issue is vacuum+timing related.

Gonna hit the junkyard this weekend and see if I can find a bracket for the EDIS-6 coil pack. It'll have to be modified, but it will give me a starting point, anyway.

 

[Frankenstang]

.

I'm thinking it may be a side effect of running an LoM dizzy with no SCV, possibly in combination with a weak vacuum advance.

Yeah once the LOM dizzy and SCV carb are 'divorced' all bets are off on what your inevitable ignition curve may resemble...beyond incompatible. There are others here much more versed in ignition options [hopefully they'll chime in], but the main two I know of are 1)'68+ points dizzy and 2)Duraspark both intended for use with ported vac sources.

One 'odd' engineering of the 1940 is the 'around the horn' accel pump...rather than operating off the throttle shaft it wraps around the back of the carb (as opposed to underneath) and operates off the throttle linkage IIRC. You might check that setup/adjustment...the basic first check being a look down the carb throat [with the engine off] to see if there is a 'pump shot' being delivered when you rap the throttle. Good luck

 

[thesameguy]

The accelerator pump is working, and working pretty well. The rebuild instructions came with specs for all those adjustments, and they're dialed in. On the road, the car is great although it seems pretty apparent what a lack of SCV + lack of centrifugal advance does for ignition timing... nothing good! I am betting that's why the car is running a little warmer than it used to - it must be requiring a lot of throttle get the same amount of power at speed.

It *seems* the issue might be idle mixture coupled with the timing dumping at tip-in. I've been bumping up the mixture in 1/4 turn increments, and am probably right about 2.5 turns out right now. The stumble is much, much better. Now it's driving like my old Trans Am - just a slight lack power at tip-in followed by good response. I think one more 1/4 turn will probably dial that out. I think I am using fuel to cover up for a dead spot in ignition timing - ie making it worse but it feels much better.

I went by the junkyard on Saturday and grabbed a pile of coil pack brackets from various Ford vehicles. I think I have the whole collection now - 3.8l V6 (Fox body), 3.0 V6 (Taurus), and 4.0 V6 (Explorer). I guess the early DOHC V6s had the coil pack mounted to the rear valve cover, so I feel deprived. Anyway, I'm hoping one of these can be reasonably modified to mount on the I6 somewhere. Then all I will need is a Megajolt controller and I can kiss the entire distributor goodbye!