SOLEX 4A1 to Holley TBI

[Takernz_30]

hello everyone!


I'm thinking of converting the SOLEX 4A1 to Holley 4-barrel TBI (see pic), what do you think fellas?

[Mike D]

Sure is a pricey way to go and quite a bit of overkill. I'd go with the 2BBL GM TBI. It's the same amount of work for probably a couple of hundred less, at least. Heck of a lot easier to find replacement parts for also.

[Hit Man X]

I agree, using the factory 4.3L TBI head will provide plenty of airflow for most motors equipped with the 4A1 (all I have seen are I6). 2.8L is too small due to the low rev nature of them. I have almost figured out all of it for a swap on my M110.

You can pick up a good used setup for probably $50 from a local parts yard. Probably use Tuner Cat to tune it in conjunction with a wideband O2 to really dial it in for max power, then use a simple three wire O2 for stoich cruise.

My only hang up is trying to figure out the hall sensor/magnetic pick up from the distributor.

The TBI system uses the very simple HEI module as the ignition module, most of the pins are simple... 12v, ground, in/out to the TBI main brain, etc. Again, my hang up is if the stock Bosch distributor is able to send out the signal that will be read by the TBI computer. It outputs signal but how the OE module reads it is beyond me.

Maybe I could intercept the signal off the OE Bosch box then go into the HEI module. :shrug:

Anyway, here are the links I have found:



http://www.slantsix.org/articles/dibiase_efi/gm-ign-module-schm.jpg

http://www.tunercat.com/tnr_desc/do_tc.html

http://www.wedgeparts.com/t8tbi-5.html

http://www.clubprotege.com/wil/howto/hei/index.htm

http://www.zcar.com/forums/read/1/2004408/2005760#msg-2005760

http://holdenpaedia.oldholden.com/Bosch_HEI

http://www.zcar.com/forums/read/1/2051380

http://slantsix.org/forum/viewtopic.php?t=15779

[JeffreyNMemphis]

Why are you converting? I am working through issues with my Solex 4A1 carburetor right now...

We fixed the warp on the top by heating and cooling the carb a few times. Now I am having a problem with the idle circuit.

What problem are you having?

[mbbuff]

The only problems I've ever had (in 24 years) with the 4A1 on my 280C are the float, and when warm have to crank it more to start. Minor problems common to many older carburators, IMO. If I were to ever change though, I would go with the Rochester Quadrajet, which is almost a direct bolt on. Elongate the rear mount holes, and modify the linkage appear to be the biggest hurdles.

Jeffrey, what kind of problems are you having with your 4A1 idle circuit?

[Hit Man X]

Why am I converting?

EFI is superior to carburetion.

[Takernz_30]

Originally Posted by JeffreyNMemphis

Why are you converting? I am working through issues with my Solex 4A1 carburetor right now...

We fixed the warp on the top by heating and cooling the carb a few times. Now I am having a problem with the idle circuit.

What problem are you having?

same, idle circuit, it idles crap and keeps stalling at the lights. Maybe I'll adjust the float because the engine starves at high loads or speeds. But converting TBI is fuzzy and challenging but it gives you great drivabilty and less maintainance than carbs

[Hit Man X]

Same, my car will not idle. EFI is simple for me.

[wolf_walker]

Originally Posted by Hit Man X

Why am I converting?

EFI is superior to carburetion.

ding ding

[mbbuff]

Another option...get a stock M110 fuel injection system off a little later model. Should be cheaper than aftermarket injection, and also basically stock parts. I'll stick with something I am familiar with (carbs.) and can easily fix/buy parts for almost anywhere. I once had a brass float on one of my 250S Zenith carbs. take on fuel and sink. This was in the middle of nowhere. Car would keep flooding. I pulled the lid, punched a couple small holes in the top of the float, drained the fuel, put it back together and finished my trip. Later got a new used float (same as a VW bug) and put it in. It's worked ever since. MB wanted $45 (years ago) for the float, I got two used ones for $5. Can't beat that. Don't think you could fix aftermarket injection like that in the middle of nowhere?

[JeffreyNMemphis]

There is a tiny jet that needs to be cleaned on your carburetor. I was having the same problem. If you clean out that jet, problem solved...

[JeffreyNMemphis]

Here is a picture... I made two lines pointing to the jets. You can see how rusty they look.

[wolf_walker]

Try finding a float for a 4A1, quickly, or cheaply, or both.
Hell look at the price of the gasket kits, what little there is of it.
(edit) For the sake of the poor person that one day finds this, I have known antique car
folks, which we aren't far from I guess, using POR-15 to coat old floats and have them last.
YMMV

Jeff in Memphis, the right arrow is pointing to the transfer port for the accelerator pump, the left arrow I can't tell. That is a good spot for clogging, takes a wire brush bristle to gently clean from both directions often to get them clean. If all else is well, the car will idle fine and depending still accelerate reasonably well. The later modified primary venturi's with the atomization slit cut in them seem to help with part throttle transition from the idle/primary circuit also.

mbbuff, I've had the k-jet swap thought also. Trouble is, as much as I like k-jet, buying one off a car that's been sitting for any length of time is a recipie to need a new fuel distributor, warm up regulator, fuel pump, maybe accumulator, and a few other things right off the bat. I sell parts for old Euro stuff and get desperate calls daily from people trying to bring cars that have been sitting back to life. It's not pretty.
Now if one found a rusted out, wrecked, beat up, donor that still ran..
Maybe. Still just as much physical work, swapping everything over, to have what is still an inferior injection system. There is a reason nobody uses carbs unless they have to, can't do otherwise, or are really, really into period correctness.

[mbbuff]

Yes, Wolf, there are alot of options for induction systems for the M110. My point was to keep it as simple as possible and stick with something I am familiar with. As these things get older I am sure all the parts will become harder to come by. If one of these (or any vehicle for that matter) sits for a long time and the corrosion sets in, there will be big problems. Jeffrey's 4A1 looks pretty corroded. I can see why there were problems. I just rebuilt mine last year and put a new float in it. The fiber float lasting 36 years isn't too bad, IMO. My 4A1 still looked like new inside when I took it apart, but it has never sat for any length of time. I knew the float was going out beforehand because it would load up and I had to keep lowering the float level to keep it running. Since the rebuild and float, it works fine. The biggest adjustment problem I had on mine was getting rid of the flat spot going into Stage 2 (secondaries). I had to wind the spring on the Stage 2 air valves to about 2 1/2 turns to get a smooth transition. The other adjustment problem was the vacuum governor. It had never worked properly, but now that it's set correctly, I have found that it is a pretty ingenius device. Keeps the idle RPM stable at all times, with A/C on/off, in gear/out of gear, lights on/off, etc. I couldn't have properly adjusted it though without the shop manual. Just wish I could get it to start easier when it's warm, after shutting it off and letting it sit for about 20-30 minutes. Just have to crank it a little longer.

[wolf_walker]

Originally Posted by mbbuff

Just wish I could get it to start easier when it's warm, after shutting it off and letting it sit for about 20-30 minutes. Just have to crank it a little longer.

That is the only problem I haven't been able to get rid of. My next shot is an electric fuel pump and playing with fuel pressure. I have been told by more than a few people it is a recurrent problem with modern fuel in old carbs, across many makes and models.

On the secondary flatspot, they changed the depth of the transfer passages between the first and second stage, seems like they drilled them a bit lower, or higher, can't remember. It's in the book, and you can effect the change on earlier models. They say it helps, I can't remember if my current franken-carb has them or not. The FSM on w116.org has it in the year to year difference section.


But for the sake of the topic, a nice TBI would fix all this silliness.
I very much vote for the 2.8 or more likely 4.3L unit, as I recall the bores are the same size, just different injectors. I really think the 4 barrel unit is flat out too large, but there are worlds more ability to lower pulse width and still have the thing run, and air velocity through the throttle body isn't nearly as important as with a carb. Apparently one can pretty cheaply tune TBI as well as anything else anymore, though I'm not real up on it off the top of my head. What I'd like to do, is chop out the ignition portion, and if possible while still having closed loop cruise, get rid of the TBI's desire for a speed sensor as well, that'd lesson the stuff-to-do factor installing it quite a bit.
That being said I bet most anything a stock mapped 2.8 setup would fire up and run a M110 pretty decently, it ought to be in the adaptability range.