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Heading down a stromberg rabbit hole

Acollin

Platinum Level Sponsor
Jet centering complete, but still Dieseling. I went through the entire carb set doing the best I could. When I use the lifting pin both carbs work the same ( tap/clunk) , however, when I raise the piston further than the lift pin would allow with my finger, the resistance is not the same. Dashpots have oil.
Again, m
 

Acollin

Platinum Level Sponsor
As I was about to say before my finger accidentally hit send, my car runs very well— with good acceleration/ throttle response.
Based on my reading, I suppose I could have some carboning up in my cylinders. Some say “Seafoam” could help.
most importantly— please advise on the different resistance with lift the carb piston beyond the lift pin distance.
thanks all
Andrew
 

rixter

Gold Level Sponsor
When I rebuilt my carbs, I noticed a previous owner had installed two different piston springs. Also you want to be sure there isn't binding of the pistons in the carb body.
Rick
 

Acollin

Platinum Level Sponsor
Husky drvr: have you ever used a product like ”seafoam” to clean away carbon?

rixter: were the different springs obvious? Different lengths? I have a few I can try that have not been messed with. That said, the different pressure when I pushed up the carb pistons beyond the pin lift feels like suction or as if that one rubber diaphragms has more behind it than the other. Could different weight oils create the situation? We have had cold and snowy weather for the last few days so I haven’t been out in my car, but that is what I felt the day I did the recentering of the jets. Again, what ever this is does not seem effect the cars running/ drivability.

Thanks for the advice and support
Andrew
 

hartmandm

Moderator
Diamond Level Sponsor
I believe the springs will have different colors. For the Alpine they should be silver. When my carbs were returned to me after rebuild, one spring was silver and one was blue. I swapped out the blue spring for a silver spring from a spare carb set I had.

Mike
 

RootesRooter

Donation Time
Different-rated springs don't make a huge difference in the amount of effort to raise the piston by hand. It's more likely the 'stiffer' one isn't fully centralized. It can take several tries to get it right. When you lift each piston as high as it'll go and release it, does it drop and land with at least a slight thud?
 

husky drvr

Platinum Level Sponsor
Husky drvr: have you ever used a product like ”seafoam” to clean away carbon?

Thanks for the advice and support
Andrew

Andrew,

The only thing I've used SeaFoam for is to add to the fuel tank. I've never used it for removal of combustion chamber carbon per the instructions.

If cleaning combustion chamber deposits was in order, I would try a different method before moving up to the level of a SeaFoam cleaning.

I meant to state "carb pistons" meaning the front side of the piston where oil, combustion blowby, and dust build up over time from PCV and air cleaner.

Here are a couple of videos that might be of interest for your question. It's been a while since I've seen the first and not sure I've ever watched the second.

Hope this helps,


 

Acollin

Platinum Level Sponsor
rootesracer: they move slowly and land with a tap more than a thud. When lifting with the lift pin— slides easily and lands to with a tap more than a thud. At one point today, I thought things changed with tightening the cover screws— not sure about that though.

Husky drvr—Those videos speak very highly of Seafoam. Based only on viewing the two it was quite a pitch— very convincing. i wonder how it would effect my dieseling. Still on the fence but seems like an option. I am not aware of a downside.

Mike / rixterI worked on the carbs again today and could not figure out the difference in pressure when raising the carb piston with my finger. I did notice this time, there was also a difference in resistance when pushing in the black capped “air valve hydraulic damper”. I changed the carb oil— tried other dampers— different return springs- chamber covers- carb pistons and needles— no change. I am please I got it all back together and running as before.There is unquestionably a difference still.

is there a vent somewhere that could be blocked?
Thanks for the follow through— stumped here.
Be well all
Andrew
 

rixter

Gold Level Sponsor
I've had diaphragms of varying pliability as well. VB ones were stiff (left) and the ones I got from Joe Curto (right) nice and soft. Back then I took these nice photos that drew some interesting non-automotive comments. Ha ha.

Rick
P1090126r.jpgP1090127r.jpg
 

Acollin

Platinum Level Sponsor
I cannot get out to my car just now or I would check it out, but as I was studying the wsm, i read about a “locater” tab on the diaphragms. I have definitly been playing in that area but I cannot recall if I fit the locater tab in its proper place.

Question: what would be the effect on operating carbs if the locater tabs on the diaphragms were not in the proper orientation?

Update:
Still running really good and my last test— I need to test more— my dieseling was gone after repeatedly adjusting slow running and jets. Carb pistons still showing different resistance when lifted with my finger.
 

Acollin

Platinum Level Sponsor
I ,also, now see what appears to be vent holes in the “depression chamber cover” and in the black cap of the “air valve hydraulic damper”. If these were clogged, could that impede or slow / cause more resistance in the carb piston movement When raised by a finger?

The wsm also calls for replacing the “hydraulic damper” if it is not functioning correctly. How do I know if mine are not functioning correctly? This does not appear to be a mechanism for there to be a lot wrong. Could this be the cause of the difference in resistance of my carb pistons?

I knew this was a rabbit hole. Hope you are all still with me. Heading back to the shop now to run a few experiments.
be well all
Andrew
 

hartmandm

Moderator
Diamond Level Sponsor
Try removing the dampers and test the piston movement. Maybe remove the damper oil and then test with dampers still off. You can also try swapping dampers front & rear.
 

Acollin

Platinum Level Sponsor
I tried 3 different dampers with no change. ****Went without a damper and it moved smoothly and very easily. I also tried clearing the vent in the black cap on the damper— no change, not blocked.

I did not try removing the oil and inserting the damper yet. Not a lot of time today. Is that much different than removing the damper?

Question: If I remove the piston/needle ( to dump the oil) will the jet need to be recentered?

Maybe tomorrow I will have a little more time to try — no oil with damper- see if the vent in the chamber cover is blocked— and see if the locator tab in the diaphragm is where it is supposed to be— not sure why this matters.

Thanks for the suggestions/ help—
Andrew
 

husky drvr

Platinum Level Sponsor
I ,also, now see what appears to be vent holes in the “depression chamber cover” and in the black cap of the “air valve hydraulic damper”. If these were clogged, could that impede or slow / cause more resistance in the carb piston movement When raised by a finger?

Andrew,

Welcome to your master mechanics course. Today's topic is "Is the Other End of the Rabbit Hole a Reality?" Poor humour - I know.

Now that you've decided to inspect the dash-pots, you need to determine if none, one, or two of your carbs have/haven't been modified to meet the Factory Service Bulletin trying to reduce excessive oil loss from the dash pots. Don't know if this might be related to your issue, but it's related to your question.

The damper is mostly a zero volume change device, however the air passages that vent the chamber above the diaphragm might be problematic. From your descriptions, that doesn't seem to be the issue.

Just a thought - The damper with the most resistance in the piston UP direction is probably the one in the most correct condition (unless the needle is contacting the jet - have you tried removing the jet holder completely and the checking piston movement?).

Have a good day,

Here is a copy of the FSB - thanks to TE/AE web site (no illustrations):

SUBJECT: Loss Of Oil From Dash Pots — Zenith C.D. Carbs

MODELS: All Models Equipped With Zenith C.D. Carbs


Where complaints are received of persistent loss of oil from carburetor dash pot pistons resulting in loss of piston damping, it is recommended that the following action be taken:
1. Remove damper(s) and chamber cover(s).
NOTE: Always be sure that the chamber cover is refitted in its original position, otherwise re-centralization of the jet will have to be carried out.
2. Mark and drill a l/16″ (1.5 mm) hole in position shown. Make sure that the hole is drilled so that when cover is replaced, the hole is facing away from the engine, (i.e. the highest point on angled carburetors). The hole must break through into recess above top thread. (fig. 1)
3. Plug the existing hole, with Solex Plug, Part No. 51550. Be sure it is adequately secured and that it does not obstruct the top thread.
4. Refit cover to carburetor. Fill damper with correct grade of engine oil as per Service Manual. Re-fit damper.
J.J. Rivers
Service Manager
Info Category: Factory Service Bulletin | Entry Tags: Carburetor, dash pot, Oil Leak
 
Last edited:

rixter

Gold Level Sponsor
Did you do Mike's suggestion of swapping front with rear dampers to see if there is any difference? The point of the oil and the dampers is to get some resistance to the piston rising too rapidly on the snap of the throttle. So some resistance going up, not much coming down. I am not sure if the piston resistance you may be thinking is an issue is the one that is OK and the one going up too easy is the issue. I think you've not tried taking the oil out yet either. If the oil is different between the two dash pot chambers, that isn't going to produce similar results between the two carbs. You can search on the forum to find 100 different opinions on fluids to put in there, but everyone would agree that they both should have the same fluid and same quantity in each.

As far as the diaphragm locating tab on the perimeter, if not lined up with the groove made for it, it may distort the diaphragm or make the cap not seat properly. Not sure if it would shift the angle of the piston to be creating your issue. There will be a locating tab on the inner side of the diaphragm as well that needs to line up with the corresponding spot on the piston. The attached photo shows this well.

Rick

stromberg diaphragm.jpg
 

Acollin

Platinum Level Sponsor
I did as Mike suggested and siphoned the oil from the air valve piston shaft. The piston slid up and down smoothly with damper in or out- the resistance of oil coated metal. I did not take anything apart beyond unthreading the damper. no change- still hard to raise the piston with just a finger With fresh oil.

I refilled the shaft with oil and took it out for a short spin — about 6 miles or so. The car ran great — the best part was there was no dieseling on shut down- so my blind tinkering did something. Will check plugs for too lean when I have more miles on them.

****A thought: could I be using too heavy an oil? I use 20/50 weight—( cooler outside temps 40s / low 30s overnight) — the same as the crank case. I actually use 10/30 in the motor on the Sunbeam, but had a partial jug of 20/50 from my MGBGT.

Now that the car does not seem to be dieseling, am I looking for a problem that does not exist?

Thanks for all the input
Andrew
 

hartmandm

Moderator
Diamond Level Sponsor
20/50 for Stromberg damper oil? Go with thinner oil. Here is a recommendation my carb rebuilder provided to me:

"Use Automatic Transmission Fluid "Type F" (equiv to SAE 15 oil), or original Zenith-Stromberg Damper Oil (equiv to SAE 20 oil). The lighter oil provides quicker throttle response."

I have been using Automatic Transmission Fluid "Type F" in my Strombergs. The fluid is red, so if it leaks, you can tell where it came from based on the color :)

Mike
 
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