Where to start tuning a pair of 81s

[SoCalCoupe]

I bought an Eddie Meyer hi-rise with 2 Stromberg 81s. The story, which I have good reason to believe, is that it’s an original setup that was rebuilt and installed on an engine by a high quality west coast shop over 15 years ago but never run. The shop has been out of business for more than a decade. The owner of the engine passed away and his family couldn’t bear to part with a lot of his prized possessions. They finally sold the rebuilt flathead that had never run. The new owner put a blower on it and sold me the setup. The point isn’t the truth of the story, but rather that these carbs do appear to have been rebuilt over 15 years ago and never used.

To get to the point, the setup is now on my stock ’41 Ford. I looked at the jets see what I’m starting with. They’re stamped 2. I have no idea what that means. I have some new jets I bought separately that are stamped 041 which makes sense because it says 0.041” on the package.


What are number 2 jets? Does it seem like a bad idea to attempt to start up and tune the car with the number 2 jets or should I start with something else? I’m at sea level. What range of jetting should I expect to settle with?

[flatjack9]

Stock 81's had 35 main jets and 61 power valves. Good place to start. Where's the blower?

[SoCalCoupe]

Originally Posted by flatjack9

Where's the blower?

The blower's on that treasured engine from 15 years ago between a pair of frame rails connected to a T5 being built into an AMBR contender in Los Angeles. The owner built another AMBR contender with the same shop not too long ago.

[Terry,OH]

Contact Max Musgrove, who is the Stromberg tech. and ask him where to start. I see no reason why you could not start the engine and see how it runs. You got a good deal on the intake Carbs and air cleaner! Many of the early replacement Carb parts are not marked or marked improperly, using a set of number drills and you can approximately figure out what size you have by measurement. It is my personal opinion Stromberg replacement parts are the best and Max can set you up. Your going to have to Sync the two Carbs and you only need one choke to function the other can be left open all the time. Do report back to give us your results.

[JM 35 Sedan]

Another suggestion to talk to Uncle Max to get his opinion. I haven't seen him here on Fordbarn lately, but have seen some of his recent posts on Facebook.

[Ol' Ron]

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Yes, start with the stock jets, however you might run what you have, and use anAF meter to adjust the jets for a good tune. The 81s should run a stock engine OK
Gramps

[SoCalCoupe]

Guess it's up to me to ask the dumb questions. When bolting on an aftermarket aluminum intake on a flathead, do you typically use washers? Lots of folks say you need hardened washers with aluminum heads, but I haven't found anything one way or another about intakes. Believe it or not, I can't find very many good pictures to show this detail on the internet.


From the pictures I've seen, I'd be doing the same as most folks if I just removed the paint from the stock bolts and torqued it down without washers.

[34fivewindow]

on an aluminum manifold i use AN washers, on cast iron manifold lock washers.

[SoCalCoupe]

This is going better than expected. Got the stock manifold off and the new one on last weekend. Got the throttle and fuel connections complete this weekend. Didn't get the choke connected because the choke cable has a pressed on fitting I can't get off to shorten it.


Took a lot of cranking to get the car started but it turned that because I'd opened the fuel system, it took a lot to get it primed. I do have an electric pump which I used for that. Car started fine. I'd set the idle mixture screws at 3/4 out. Adjusted them another 1/4 out for one full turn because the car seemed to like it. Used a unisyn to synchronize the throttles.


Oddly, I couldn't use the "Summer" setting on accelerator pumps. The pump rod binds with the throttle and prevents the throttle from closing enough.


Still don't know what jets are in it. I wrote to Stromberg and asked what a jet with a "2" stamped on it means. Clive wrote back in less than 24 hours and said Stromberg never marked their jets that way and suggested I use number 35 jets.


Drove around block a couple of times then a mile out and back and checked the plugs. It's running WAAAYYY rich. Guess I'll be changing out those number 2 jets, whatever they are.


Much to my surprise, the car runs REALLY well. My experience has usually been that any significant modifications make the car run worse until you get it all sorted out. Hard to say if I have more power but I've certainly got more throttle response. That makes sense since the same throttle travel is now operating two carbs instead of one.


The one thing I don't like though is that it idles too fast. Don't have a tach but I"d say about 1000 rpm even with both of the throttles completely closed.

[Terry,OH]

Make sure the accelerator rods are the proper length, about 3.83" for a 97. The 81 may be the same? There should be NO binding in either the S or W position. The pump lever may be bent down too much??? The bending of the lever is an adjustment for when the power valve opens.

If you order from Max you get -10% off. Your going to need the Stromberg jet wrench which Stromberg sells, to change the main jets. Plus get new seals (gaskets) for the jet plugs. Max also has additional springs which help to get the throttle closed.

Make sure nothing is preventing the throttles from closing and adjust idle RPM lower with the Carb idle RPM adjustment. If the sync ball is below the adjustment indication on the gauge just adjust the second carb to the same low point. You can screw the top of the sync guage down to raise the reading ball but do not go too far so it restricts the air flow and idle RPM when the gauge us placed on top of the Carb .

[Tim Ayers]

Looking at the length of your throttle rod, I’m assuming you are running the throttle off the front. If so, that’s why it’s rubbing. Need to run off rear carb and it will clear the rods.

[deuce_roadster]

I have an old EM intake on my 32 5w with 2 stock 2 81s, (stock 59 series engine, crab distrib). Runs great. Like Ol' Ron said see how it runs before you change anything else.

[SoCalCoupe]

I love the Fordbarn! Seriously, I don’t know how got the inside knowledge they needed on obsolete technology for their hobby cars before internet forums like this.

Originally Posted by Tim Ayers

Looking at the length of your throttle rod, I’m assuming you are running the throttle off the front. If so, that’s why it’s rubbing. Need to run off rear carb and it will clear the rods.

Thanks Tim, great eye but I shortened it after I took the picture above. I connected the Ford throttle rod to the rear Stromberg carb. The throttle rod is definitely not binding with the accelerator pump rod. I probably didn’t describe it very well, but the Stromberg accelerator pump rod is binding with the vertical Stromberg throttle lever attached to the carb.

Today:

-o- The richness I saw on the plugs yesterday, a thick coat of soot, after a 1 mile drive disappeared after taking it for a ten mile drive this morning. The plugs now look like new, on the lean side. Kept an eagle eye on the temperature gauge. Never got abnormally hot.

-o- It still idles too fast even with the idle screws all the way out.
I think this points to a vacuum leak. Thoughts?

-o- Noticed when I was using the uni-syn that I would shut down the engine when cutting off air flow to the front carb but not the back. A vacuum leak in the rear?

-o- Pulled off the weird banjo vacuum fitting at the rear of the manifold and it was full of gas. That doesn’t seem right. When moving connections from the old manifold to the new, I tightened it as hard as I thought I should, but it definitely wasn’t too tight. When I looked tonight, I saw that I had installed it with two copper washers, one on each side of the banjo. When I looked at my old manifold though, I found another copper washer. There were two on the manifold side.




-o- I’m 90% sure I have vacuum leak from the distributor retard/wiper vacuum fitting but not sure why. I’ll work on it some more next weekend.

[Terry,OH]

There is something holding the throttle plates open if the idle it too high. A vacuum leak will cause the engine to run very lean. If you put a vacuum gauge on it you should have about 15# which is about 5# lower than one Carb.

[SoCalCoupe]

Three steps forward, two steps back. Had all week to think about this. The plugs were nearly white after about a ten mile ride. Seemed a little lean. Even though I didn't want to take the carbs off and get gas everywhere, I did and pulled the jets. Three 34's and one 32. The 2 in previous post was a 32; used my magnifying glass in better light. That kind of ended the project for this weekend. Ordered four new stock size 35 jets.

With carbs off, it was easier to check the idle mixture. They're hard to get at. They weren't set where I thought they were so I reset them to one turn out.

Perhaps I had a sticky throttle shaft that was giving me idle speed problems. It seems different now.

When the new jets arrive I'll start over with all jets the same size and all idle mixture screws in the same position.

[Brian]

A little trick that may help you getting access to the mixture screws; fit a short length of rubber hose over the knurled ends long enough to be able to easily reach....

[aussie merc]

also put a dab if white on each the idle screws[fuel] 12/3/6/or9 o'clock doesn't matter whatever is easy this gives you a reference point so its easier to tell how far you've moved them [after 1 hour at looking at 4 similar items its not hard to loose track] as for jetting im with ron start with stock and work from there but remember todays fuel is nothing like it was in the 40s so expect some changes

[38 coupe]

Is there anyone in the area with a portable wide band O2 sensor?
I bought one years ago and have it set up to clamp onto an exhaust pipe. Really helps with jetting a carburetor with today's gasoline.

[SoCalCoupe]

Started over and got myself sorted out with the idle mixture screws and settled on 7/8 of turn open on each. Got the throttles re-synched with the Uni-Syn.


Don't think I have a vacuum leak; closing off either carb kills the engine. Still idling a little fast though even with the idle speed screws backed all the way out. When I apply pressure to the throttle lever it slows down the engine speed a bit and one of the accelerator pump rods still binds with the throttle lever. I'm thinking that whoever rebuilt the carbs didn't set the throttle plates all the way closed when they stamped the throttle lever onto the throttle shaft.


Engine is stock and runs really strong and responsive. Even with the stock 0.35 main jets though, judging by the plugs, it's still running lean. Would not have expected to go to a BIGGER jet over stock.


I'll order some new jets and when I pull the carbs off to change them, I'll take a close look at the gaps between the bores and throttle plates when the levers are all the way against the stops. Binding with the accelerator pump rod isn't right and neither is backing the speed screws all the way out. Might have to replace the throttle shaft/throttle lever assemblies.


I actually have a pair of brand new, in the box, made in UK, Stromberg 97s but I'd rather sell them and make the 81's work right.

[Tim Ayers]

Originally Posted by SoCalCoupe

Started over and got myself sorted out with the idle mixture screws and settled on 7/8 of turn open on each. Got the throttles re-synched with the Uni-Syn.


Don't think I have a vacuum leak; closing off either carb kills the engine. Still idling a little fast though even with the idle speed screws backed all the way out. When I apply pressure to the throttle lever it slows down the engine speed a bit and one of the accelerator pump rods still binds with the throttle lever. I'm thinking that whoever rebuilt the carbs didn't set the throttle plates all the way closed when they stamped the throttle lever onto the throttle shaft.


Engine is stock and runs really strong and responsive. Even with the stock 0.35 main jets though, judging by the plugs, it's still running lean. Would not have expected to go to a BIGGER jet over stock.


I'll order some new jets and when I pull the carbs off to change them, I'll take a close look at the gaps between the bores and throttle plates when the levers are all the way against the stops. Binding with the accelerator pump rod isn't right and neither is backing the speed screws all the way out. Might have to replace the throttle shaft/throttle lever assemblies.


I actually have a pair of brand new, in the box, made in UK, Stromberg 97s but I'd rather sell them and make the 81's work right.

If I'm reading this right, you started with .034's and went to .035's and plugs still show a little lean?

From what I've been told, it take two sizes up or down to see impact on richness or leanness. Maybe just go .036 since you said it is running really well as is.