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Continuing on, Pic #4 shows the inside of the housing. There are two ports in the housing, an upper one that at the top, and a lower balance port at the bottom (Pic #5) that keeps the piston from pressurizing the carb bowl on the downstroke. The vacuum port passage crosses over the upper carb body (black arrows in Pic #6). (to be continued....)
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Moving on, the vacuum passage connects with the middle carb body at a hole next to the step-up jet (Pic #7). It continues down the mid/lower carb body (black arrows in Pic #8), and picks up manifold vacuum via a slot in the carb base gasket (Pic #9). For the vacuum system to work properly, the piston/housing have to hold vaccum, the vacuum passage has to be clear, and the right base gasket has to be used. If the vaccum passage is restricted, slow vacuum bleedoff can retard the piston, causing a slow dribble intead of a quick shot. If the piston can't hold vacuum, you're likely in the market for a new carb, as the housing has probably worn out.Comment
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The third item to check is the spring. Square Top carbs originally came with a 50 oz spring (copper color), which was apparently too stiff. A 40 oz spring (silver color) was subtituted in 1948, and a 30 oz spring (black oxide color) was used for altitudes over 5000 ft. Since my carb had been "rebuilt" with the wrong spring, I had to try to find the right spring. The tension appears to be rated at 1/2" compression. 40 oz= 2.5 lbs, so I used a mini-square set at 1/2" less than spring length (Pic #10) to compress it on a scale for tension readings. I found a spring from an E7T2 round top carb that measured 40 oz on the balance beam scale at work- and then it suddenly slipped sideways and- ZING!!!!- it disappeared into NeverNever Land- Never to be seen again! Tie a string around your spring BEFORE repeating my example.Comment
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For a quick & dirty spring test, I marked the plunger from a Carter rebuild kit (Standard Motor Parts # 101A, NAPA # 25066A- no springs!) at 1/2" less than spring height (Pic #11). I then assembled the spring and cap on the plunger and held it in place with a small Vicegrip (Pic# 12). Next, I held the plunger in the the pump well at the correct height(Pic# 13), and carefull released the Vicegrip. This allows you see the accel shot ,and together with the manual plunger test lets you judge its quality.
Finally, the plunger needs to move straight up & down- if it cocks to one side, drag is noticeably increased. When my 1/4" too short spring was used in the Vicegrip test, it did give an accel shot, but only if it was aligned right. I think the correct spring for thes pumps will be long enough to hold the plunger and piston in alignment- like the M37 and E7T2 spring- 1 7/8" long. I didn't notice any significant difference in straight up/down drag between my carb's plunger, the M37 plunger, the E7T2 plunger, or the rebuild kit plunger when the pump well was empty- most of the resistance comes from unseating the pump outlet valve. Hope that helped- now, does any one have a good E7T2 spring they can part with.....Comment
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Perpetual Spring Slavery...
Well, the lost is found again- I let people in the scale area know about a $10 reward for the missing spring, and 5 minutes later a lady came up with it. It's days of freedom are now over- it's back on the plunger (pic #1), and doomed to a life of Perpetual Spring Servitude- HaHaHa!!! You KNOW I'm going to enjoy cracking the whip over this little @#*!- people will think Mario Andretti is behind the wheel, when they hear me shifting.Comment
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Great photos and explanation.
This would make a good PWA article, have you thought of doing that?Comment
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One pic is definitely worth 1000 words- I'm afraid my article would use up ALL the space in Gordon's typical issue in photos alone! Also, my digtal camera is a Sony Mavica that uses floppy discs- don't know if it has enough resolution for Gordon's requirements. Hopefully we got the squaretop hesitation problem scienced out!Comment
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Ta Da,
You may hav saved my day. In one of the above photos in POST # 15, it shows the throat area and the pump plunger being set in place. The photo also shows the accelerator jet and cap screw. If you look at the jet area you can see there is a drill hole at the rear of the jet near the cap screw.
On the carb I have that drill hole is open. When the plunger is pressed in the gas squirts out of the drill hole and not into the throat
via the jet.
My question is " should that drill hole be plugged?"
If I put my finger over the hole the gas will squirt out the jet .
I took some good close ups of my carb but the micky mouse IP I am with is giving me a hard time loading them online. I can send them by email if anyone wants to see exactly what I am talking about.Comment
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I'll have to look at my carb again- been awhile since I took those pics. I assume you have the same B&B- The Round Top may be different. If gas is squirting outside the carb, you have a BIG fire hazard- need to plug that leak ASAP.Comment
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Ha Ha Ha , little misunderstanding. the gas is not squriting out of the carb. I have the lid off it and when the pump is pressed gas squirts out of the drill hole behind the accelerator jet. In your pic. I can see that the drill hole in your pic. is blocked with what looks like a small ball about the size of #6 shot. My carb there is no plug in that hole. But there will be soon.Originally posted by maineSS View PostComment
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Hello MainsSS.
I have been haveing problems with my carter BB ETWI.
I saw in one of your posts a very good photo of the open top of the carb . It is in a post from 3/9/09 post #15 Photo # MVC009F.
In your photo it shows a semi clear view of the accelerator jet area. In the picture you are holding the accelerator plunger between your thumb and forefinger.
Your forefinger is pointing at the accelerator jet assy.
My question is about the body where the jet is held.
There is a screw cap that comes off and you can withdraw the actual jet. The body of the carb where the jet is housed has a hole drilled in it at the rear of the jet that runs verticaly up to nothing but the bowl vent.
Should that port be that exits up away from the jet be pluged? Or is it a vacuum breaker so gas wont be constantly sucked into the venturi tube.Comment
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Kaiser-
In your first question about the top of the accel pump jet having an open port, mine is blocked off with a ball. Did you try blocking yours? Regarding the second question, I'll have to look, as I didn't touch that area during my disassembly.Comment
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I did some experimenting with it. I blocked off the port so that there was no openings in the accelerator line other than the jet itself. It developed a strong stream out the jet when pumped by hand.
The problem came when running. The truck ran like an ill-natured Camel. Surging at idle and at about 1/4 throtle stumbling . At higher speed it seemed better but very rich, IE black smoke and charcoal spark plugs.
I read on one of the many M37 sites that "some ETW1 carbs need a vent at the accelerator jet to break the vacuum created by the venturi tube or gas can be sucked out of the pump circuit and cause a over rich mix. That makes sense. But letting the port open creates a very weak flow at the jet because the flow is bled off at the open port.
I went back and removed the plug and it now runs much better but still has a bit of a gasp if I give it too much gas to suddenly.
I am now thinking the accelerator pump vacuum chamber is worn and I may just have to break down and spend some money on a new carb.
In the back of my head I am still wondering if not pluging the port is shifting some other carb problem that I am not seeing.Comment
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Kaiser-
Have you been running E10 gas- that was a nightmare early this year for me. I ran way too lean for awhile until I spent big bucks on a Carb Shop rebuild kit to get the correct main and stepup jets. After carefully drilling these out, I got about right- and then the gas stations suddenly went back to E5, and I was pig rich! Previous problems I had to sort out was the wrong tension accel pump spring, and a way too high float level from some previous carb "rebuild". I'd suggest you get an Ethanol gas test tube, knowing what your fuel is will make life easier. I still have hesitation on the stepup circuit, even though I'm back on the original jetting, and have adusted the idle speed. Where did you see the M37 data?Comment
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I took the truck out today for another test run. It is still very cold up here so I have to shade my results a bit.
I did a bit of looking at the govorner and it seems OK.
I got a good lesson from Charles on what could be my problem.
Anyway It ran well, no stumbling , no flat spots. It still gasps a bit if I give it too much gas but it gets over it instantly. I feel I can live with the quirky gasp after all the thing is 57 years old, I gasp now and then so I guess the truck can also.
As to the sites here they are I hope they show up for ya.
http://www.carburetor.ca/carbs/tech/...an0016_jpg.htm
www.ibiblio.org/hyperwar/USA/ref/TM/PDFs/TM_9_808.PDF
Alan in Pa.Comment
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