EMPI 32/36 DFEV - mixture screw

[phaetn]

Hi, gang. Thanks everyone for your patience as I ask lots of neophyte questions!

I have looked through Brad's pdf carb guides, and have the DFEV schematic, but it only identifies screws as screws, not their particular function. I think I have this right, but just want to check before I start fiddling with the carb:



I would assume that what I have identified as #1 is the idle speed screw (since it connects to the throttle body mechanism) and I would hazard a guess that #2 is the idle mixture screw since there's also a spring behind it. It seems quite difficult to access beneath the air filter, which is why I ask before I start mucking about.

I'm quite familiar with working on carbs on air-cooled motorcycles, but this is definitely the most complicated one I'll have dealt with.

My plugs seem quite fouled (black and sooty) which could be oil from bad rings (though compression is 130 psi for cylinders 2 through 4), or also just from running very rich. I've tried the "Italian service" of changing fuel, changing plugs, and then driving it like I stole it to "clean it out". Now I think I'm going to look at the carb.

There's a definite pronounced hesitation (sounds like a misfire) when I open up the throttle more than about half-way. It's often around 3,500 rpm, but it can happen in other ranges, too. Sometimes it clears up and pulls through, other times it doesn't and just stays running rough so I have to let off. The car otherwise purrs pretty nicely at idle and pulls happily enough if I slowly accelerate with less than half throttle, but if I mash it it's definitely stumbling a lot. I'm wondering if something is going on as the second barrel opens with the mechanical linkage given the throttle position.

Any thoughts?

Thanks again. And just for fun, here's a shot of my younger daughter and some of her friends enjoying a birthday party ride around the parking lot.



Cheers,
phaetn

[bradartigue]

In your diagram #2 is the mixture screw. #1 is the idle stop screw.

Don't let a parts diagram overwhelm you, Webers are not that complex. They are highly adjustable but 99% of what is in that diagram you'll never need to mess with.

Start the car and drive it up to temperature, then pop the hood and turn the mixture screw in (clockwise) until the engine just starts to hesitate or miss, then turn it back out until it is smooth. Adjust the idle speed screw to 850 RPM, then adjust the mixture slightly again, and the idle speed screw again slightly if necessary.

If you can't get the mixture right within about 1 turn of fully seated then go down to the next jet size - e.g. I think DFEVs come with 50's, so get a 47. 45 is usually too small. Conversely if the mixture cannot be made rich enough you would go up to the next size (52 or 55). If you have your old Weber carb the idle jets will likely fit. In your diagram the main jet is #14. The secondary jet (14A) you shouldn't have to mess with.

[phaetn]

Thanks so much for the reply and advice, Brad.

Unfortunately I don't have the original carb from the car, but only have the aftermarket Empi that has been put on sometime in the last five years (PO bought the car in 2008). I'll have to look around for a jetting kit.

I'll try the mix screw first and then down-jet if required. I suppose the other thing I might have to verify is the float height.

Looks like I have some work to do.

Thanks again and cheers,
phaetn

[majicwrench]

Odds are excellent that you will not have to rejet. If you cannot get the idle mix correct, my experience is that usually something else is causing issues. The carbs come pretty dang close.

[phaetn]

Thank you both for your replies, it is much appreciated!

Definitely turning in the mix screw increased revs. It was a very humid day here yesterday (approaching thunderstorms) and I know ambient temp will affect the mixture in a carb -- warmer temps mean richer running. Increasing revs was a good sign to getting the right mix, but then it still hesitated under certain conditions when out on the road. I'll keep fiddling and try to really get the setting correct.

Turns out the screw was dialed out about 3 full rotations from fully seated. Now I've put it to about one out and I'll adjust from 1/8 to 1/4 turns and go from there. With lights on and when the rad fan was running, idle would drop to around 500. I adjusted when fan wasn't on, getting it to settle around 800-900.

Majicwrench - to speak to your point about other possible issues: I'm noticing a bit of coolant loss in the expansion tank. I can't identify where it's going, so I'm concerned it's getting past the head gasket into the oil, which I know is very bad as it can seize bearings if they're not properly and fully lubricated. Plus with the oil its burning, I figure either rings or valves seals are very tired. I seen an engine rebuild in my future, but I was really hoping it would be down the road...

Thanks again and cheers,
phaetn

[majicwrench]

A bit of coolant loss, depending how much, is not neccessally head gasket. So many things can leak coolant. And while your bearing could have issues because of coolant in oil, you would (hopefully) catch issue first, foamy, milkshake looking oil. My 72 smokes a bit, uses a tad bit of coolant, couple times a year I find a spot of two of oil floating in my radiator when I pull cap. Runs great. I'll fix it someday, but I like driving it more than fixing it.
Temp, for what you are doing, really doesn't affect mixture.

[phaetn]

post deleted. similar symptoms to others, so adding onto another post to keep it all in one place.

[phaetn]

I ended spending about $150 on various jets, air correctors, etc. to try and finally sort out the carb and a flat spot/hesitation.

It turns out the 165 indicated air corrector that was installed for the primary looked *way* bigger than the 170, 175 etc. that I just newly ordered. I don't know if it was previously drilled out or what, but it definitely wasn't 165. I'm trying to set everything to stock to baseline performance and then go from there.

So, in that vein, two more questions re. the Empi DFEV:

As I put the electric choke thermostat and assembly back on (it's a p.i.t.a. as I have to take it off every time to get at main jets and air correctors) and then started the engine, I heard a slight sucking sound. As I slightly wiggled the choke assembly, the sucking changed and I could see if came from the area I have circled as "choke air intake". Spraying carb cleaner around there made the engine bog and then recover. It's clearly an area where the assembly meets the carb body, yet there's no gasket or anything to form a seal. Oddly, there's also no screw down there to hold things tight (schematics only show two screws at top, indicated) so it can be quite a bad mating. Turns out the bottom hole in the body is threaded so I used the shorter of the top screws to hold things tight. No air leak now (or at least not as obvious). Is that a good thing? Normally I would think yes, but I'm doing something unorthodox here... Clearly the carb draws some air through the choke assembly, and it's more complicated than just the metal strip opening and closing the butterfly valves up top.



Secondly, I also ordered a new pump jet, size .055. I can see that the new one has holes to both channels for primary and secondary barrels. The current one installed has the double jet shape, but there's no hole in the body for it to draw fuel to the secondary barrel -- it only squirts into the first. The following pic shows the hole for the primary barrel -- there isn't one on the other side.



Is this a know issue with EMPIs? I'm wondering about trying the new one with both holes just to throw more gas in the mix when accelerating and seeing if the engine likes it as the secondary barrel opens up...

Thanks in advance for any replies. I'm learning lots and know I'll give back one day, too.

Cheers,
phaetn

[So Cal Mark]

There isn't any reason to remove the choke assembly to remove the top. Merely disconnect the link from the choke plate. There is vacuum into the choke pull off diaphragm so there has to be an o-ring on that passage otherwise you have a vacuum leak. You have a progressive carb, so there isn't any need to have the accelerator pump fuel into the secondary.
You must have bought quite a few jets to spend $150

[phaetn]

You must have bought quite a few jets to spend $150

My primary idle jet fell out on the road the other day (so car couldn't even hold idle) and I had an "emergency order" from a couple of places in order to make it to a local Italian car club meet this Sunday. Still, it was at least $115 in bits from Carbs Unlimited. $20 for two jet holders alone... I'm in Canada, so it's better to get a bunch of stuff at once rather than a couple here, a couple there, otherwise the shipping is a killer. I want to really try and dial it in so I have a big mix of a couple steps up, a couple of steps down for main jets, idle jets, and air correctors for each barrel.

There isn't any reason to remove the choke assembly to remove the top. Merely disconnect the link from the choke plate.

Thanks. I'll check that out so it will save a lot of time in future.

There is vacuum into the choke pull off diaphragm so there has to be an o-ring on that passage otherwise you have a vacuum leak.

ugh. It's just bare metal to bare metal now so I'll have to undo it and fit something there. The PO didn't have a screw at the bottom so there's no way an O-ring could have stayed in there. Oddly, the DFEV schematic doesn't show a screw, but there clearly is a place for it since the carb body is threaded to accept one.

You have a progressive carb, so there isn't any need to have the accelerator pump fuel into the secondary.

Excellent info!

Thank you so much for your reply and help, Mark. It will really aid me to get this engine sorted!

Cheers,
phaetn

[majicwrench]

You have the right idea. Return EVERYTHING to stock. The stock carb would work well in 99% of the engines it was put on.

And yes, has to be some sort of gasket/O-ring tween that choke housing and carb body. Surprised it isn't shown.

I'm not entirely sure what problem you are chasing, there are lots of things that can cause hesitation other than carb.