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| ZS Choke/Cable | Rate Topic |
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| Posted: 10-01-2019 09:12 pm |
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1st Post |
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pokeyjoe Member
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I just picked up 19839 and am trying to sort it out. The Strombergs need to be rebuilt (leaking oil and I imagine other issues). I've gotten a bit confused about the choke arrangement. Does only the front carb have a choke with cable? My back carb has the same setup (suppose to use a split choke cable to operate both). Sorting out what the previous owners have done is a bit of a challenge (wrong master cylinder, for instance). I wouldn't be surprised if the carbs need more than the usual attention.
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| Posted: 10-01-2019 09:32 pm |
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2nd Post |
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redracer Member
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The J-Hs had the choke only on the front carb, with a 3/16" fuel hose(**NOT A VACUUM HOSE AS I HAVE SEEN**) going from the the choke tube to a tube on the rear carb.--about 6" long. If you have a choke on the rear carb, sounds like someone put one from TR6/whatever on. I have rebuilt well over 150 pairs but that was mostly before the "internet videos" which I have not seen and can't comment on how good they are. There ARE quite a few tricks to prevent gas from leaking, which I imagine the videos won't show. email me if you want more info. bruce/ RedRacerbm@gmail.com
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| Posted: 10-01-2019 10:52 pm |
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3rd Post |
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pokeyjoe Member
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Thanks for the reply. I do not have an additional hose going between the carbs. They are 175 CDs, but probably not the originals. Last edited on 10-01-2019 11:09 pm by pokeyjoe |
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| Posted: 10-01-2019 11:11 pm |
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4th Post |
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pokeyjoe Member
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I grabbed an image off eBay: I do not have the black hose in the picture, nor do I have that cylindrical device on the back of the rear carb. Here's a picture from JHPS.  I don't have that black hose, either. Not sure what I'm supposed to have now. Last edited on 10-01-2019 11:33 pm by pokeyjoe |
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| Posted: 10-02-2019 12:10 am |
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5th Post |
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redracer Member
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The "cylindrical device" on the rear carb is the vacuum actuator for the by-pass valves, one located on the right side of each carb. This item is "negated/ blocked-off" by either removing it or putting a steel ball in the 90 degree hose coming off the back center of the intake manifold. When doing that, both the bypass valves will have a solid gasket put on to "block" any vacuum leak there. Again, the "black hose" between the 2 carbs is the 3/16" FUEL(****NOT VACUUM HOSE***) line allowing fuel to go from the front carb choke to the rear carb. Hope this helps, bruce
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| Posted: 10-02-2019 02:34 pm |
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6th Post |
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pokeyjoe Member
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It sounds like people are purposely deactivating the bypass valves. Why?
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| Posted: 10-02-2019 02:53 pm |
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7th Post |
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redracer Member
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most of the "extra" items placed on carbs, especially later ones, were for pollution control. If you're that interested in these "extra" pieces, I suggest you read some books on carbs which should explain the added-on items for pollution. You may even wish to try and fuel inject yours would would make for interesting discussions.
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| Posted: 10-02-2019 03:47 pm |
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8th Post |
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pokeyjoe Member
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Thanks, Bruce. I ordered a book. I just didn't know what the bypass valves were for.
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| Posted: 10-03-2019 08:12 pm |
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9th Post |
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Esprit2 Member
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During closed throttle over-run (engine braking, or coasting), a very high manifold vacuum condition is created that leads to a spike in oxides of nitrogen emissions. There are a number of ways to mitigate that, but most involve some manner of catching the throttle before it fully closes, and slowly (several seconds) closing it the rest of the way. A dashpot damper is typical. The Zenith-Strombergs take a different approach. They let the throttle slam shut, then use the Throttle Bypass Valves to shunt a metered flow of air around the closed butterflies. The net effect is the same. The engine is allowed to breathe a little bit, at a diminishing rate, for a few seconds after you let off on the throttle pedal. The small metal cylinder (tin can) mounted toward the rear of the manifold is a control valve. A hose connects it to a spigot on the intake manifold. It gets full vacuum from the manifold, but only passes a metered amount on to the Bypass Valves, diminishing to zero over a few seconds. In 'Constant Depression' carbs (Z-S, SU, etc), opening the throttle starts a chain of events that eventually feeds the engine more fuel. It doesn't take very long, but it's a detectable lag in throttle response. Venturi carbs (Dellortos, Webers, most carbs) have a much more immediate response... very crisp compared to the Z-S carbs. The Throttle Bypass Valves introduce another layer of delay on top of the Z-S carbs' already slow throttle response. Some sportscar folk expect quicker throttle response from an engine, and one of the motives for converting a 907 to Dellortos (besides power potential) is to have a more responsive throttle. Deleting the Throttle Bypass Valves doesn't improve the basic Z-S carb's throttle response (it is what it is), but doing so does remove that extra layer of delay that the TBVs add to the already slow throttle response. It's not a fix as much as it removes an add-on layer of something that makes the matter worse. The 'fix' would be converting to Dellortos or Webers... with a heavy personal preference for Dellortos. *~*~*~*~* While I'm on a roll... The 907s Zenith-Stromberg carbs are tuned emissions lean. They could just as well be tuned sporty-rich, but they're not. They were chosen because they have the resolution that allows them to be tuned that way, and the Dellortos/ Webers don't. They're not bad carbs because they're tuned emissions lean... they're that way because someone (gov't emissions standards) tuned them that way. They can also be tuned 'sporty'... forgetting that throttle response issue. An engine can run acceptably well (least worst) on an emissions-lean mixture in warmer weather; but during a frigid Winter, a slightly richer mixture is helpful. One option would be to tune the carbs rich enough for Winter operation, and it will still run well during the summer. But the emissions standards didn't allow for that. So the Temperature Compensators are an alternative. A bi-metallic strip opens & closes a port in response to ambient temperatures. The result is an emissions-friendly mixture for warmer seasons, and an automatically adjusted cold-friendly mixture during the frigid Winter months. Since most J-H don't get driven in the Winter (no Florida... a 'real' Winter), the Temperature Compensator isn't really required, and it's just something else that can fail and cause problems. An alternative is to remove the Temp Compensator's cover, and turn the adjuster screw in tight enough to ensure that the port will be forever closed, regardless of ambient temperature. Then tune the carbs for 'best running' during the warm part of the year. Don't worry about Winter when the car is tucked away, not being driven, awaiting Spring. Regards, Tim Engel Last edited on 01-11-2024 05:06 am by Esprit2 |
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| Posted: 10-03-2019 10:24 pm |
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10th Post |
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pokeyjoe Member
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Thanks, Tim. Dellortos would be nice, but they do not appear to be readily available. Well, inexpensive ones anyway. Last edited on 10-03-2019 10:40 pm by pokeyjoe |
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| Posted: 10-10-2019 05:47 pm |
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11th Post |
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pokeyjoe Member
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I've been trying to figure out why someone would trade out the Strombergs on my car. Maybe they were doing it just to eliminate the emissions modifications. They are still 175CDs, but have different choke arrangements (as noted above). I could buy a TR6 choke cable (it splits for the two carbs) and just run with them. They do need to be rebuilt, however. The dashpots are leaking oil and there may be other issues.
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| Posted: 10-11-2019 06:38 am |
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12th Post |
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Tim Murphy Member 
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I check on ebay for JH Strombergs, they don't often come up for sale. Triumph carbs are more common. Maybe they were available and not too expensive for the previous owner. I have never heard of TR6 carbs giving better performance on a JH but maybe they do. Many JH owners just bypass or disconnect the smog bits on the stock carbs. In any case, if you can rebuild them yourself, and the kits not too expensive, try that. I don't know if they are worth paying someone else to rebuild, that can get expensive. Keep us posted on how things go.
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| Posted: 10-11-2019 06:47 am |
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13th Post |
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Tim Murphy Member
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Replacing dashpot O ring: There is a small O ring on the needle adjusting screw inside the air valve (piston). The O ring is what prevents the dash pot oil from leaking. Reference the diagram. First use your allen wrench tool turning counter clockwise to completely unscrew the needle from the adjusting screw. 2) Loosen the retaining screw on the side so it completely backs out into the piston body. 3) The metering needle assembly should be fairly easy to pull out. 4) Now the retaining clip on top of the adjusting screw is a star washer that is just a friction fit. Insert some type of rod or long bolt into the bottom and gently tap it with a small hammer. It will push out. Be careful to have those small parts come out onto a place you can easily find them. The small O ring is in rebuild kits and that size is probably available at a good car parts or hardware store. Take care and good luck. I will try to post a picture but not sure how Attachment: ZS O ring repair 40pc.jpg (Downloaded 130 times) Last edited on 10-11-2019 06:57 am by Tim Murphy |
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| Posted: 10-11-2019 06:05 pm |
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14th Post |
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pokeyjoe Member
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I picked up a set of proper JH carbs. I didn't feel like rebuilding the ones on the car.
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| Posted: 10-13-2019 05:23 pm |
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15th Post |
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Esprit2 Member
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pokeyjoe wrote:I picked up a set of proper JH carbs. I didn't feel like rebuilding the ones on the car.I'm not certain I'm interpreting that statement correctly. If you were just referring to not wishing to deal with twin-choke ('enrichment device') Triumph Z-S carbs in a single-choke J-H application... okay. But focusing on the last part of your statement... pokeyjoe wrote: I didn't feel like rebuilding the ones on the car.If the seller hasn't already rebuilt the Z-S carbs you bought such that they're ready to go, then they still have to be rebuilt! The last of the Z-S equipped Jensen-Healeys rolled out of the factory 43 years ago. The carbs are all old. If they were recently on a running engine, then they should have been rebuilt several times by now, and 'recent old' MIGHT be acceptable as is. But, if they're just old, used carbs out of a salvage yard or somebody's parts stashs, then they DO need to be rebuilt before being used... Triumph or Jensen-Healey. There's no dodging that bullet. If you're really trying to avoid rebuilding old carbs, buy a Miata. Regards, Tim Engel Last edited on 10-13-2019 05:36 pm by Esprit2 |
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| Posted: 10-13-2019 07:20 pm |
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16th Post |
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pokeyjoe Member
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I will rebuild the JH carbs. I didn't want to rebuild the ones that came off a TR6 or something. I wanted the right carbs before I rebuilt them.
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| Posted: 10-14-2019 05:26 am |
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17th Post |
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Frank Schwartz Member
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That "O" ring is a #10...available at most car parts stores very inexpensive. Frank
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| Posted: 10-15-2019 04:38 pm |
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18th Post |
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noomg Member
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Joe, My J-H engine is mostly stock, no mods except for K&N air cleaners. My carbs look like the ones in the top picture, one vacuum actuator on the rear carb, single choke on the front carb. As I also live in Long Beach you're welcome to come by and take a look if you think that would be helpful. As far as your brake M/C goes if it's broad and flat it may be from a TR6. It's a common swap because it fits, it's new, and readily available. I think Greg even sells them at his parts store.
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| Posted: 10-15-2019 05:09 pm |
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19th Post |
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pokeyjoe Member
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Thanks for the offer. Once I mount up the carbs, I may take you up on it to check out the vacuum connections and stuff. The M/C has become a bigger project. The check valve was bad and the booster was full of fluid.
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| Posted: 12-18-2023 08:08 pm |
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20th Post |
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vnavaret Member 
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Esprit2 wrote: So the Temperature Compensators are an alternative. A bi-metallic strip opens & closes a port in response to ambient temperatures. The result is an emissions-friendly mixture for warmer seasons, and an automatically adjusted cold-friendly mixture during the frigid Winter months. Since most J-H don't get driven in the Winter (no Florida... a 'real' Winter), the Temperature Compensator isn't really required, and it's just something else that can fail and cause problems. Regards, Tim Enge I wanted to offer an alternative explanation for the temperature compensator, despite the fact that this is a very old thread. If you permanently close the temp compensator, as Tim suggests, you are very likely to run into hot start difficulties, especially 20-30 minutes after shutting off the engine. The carburetors heat soak during that time. When attempting to start the car, air being drawn through the carburetor is heated appreciably, and is therefor much less dense, so the mixture goes super rich - carbs add fuel based on air volume, not air density. If you manage to get the car started, it will run poorly for a minute or two until the incoming air cools the carb sufficiently. This is especially true if the carbs have been tweaked to run with a rich mixture in the first place, as many owners seem to prefer. The compensator solves this by leaning the mixture when the carb is hot, thus the car starts normally. When the carb cools after a minute or two, the compensator closes, returning the mixture to normal. I urge JH owners to NOT defeat the temperature compensator lest they induce hot start issues. This may defy the conventional wisdom, but I assure you this is correct. If you are having the hot start problem, get your mixture correct by using a color tune or plug cuts. Still having problems? Your compensators need to be adjusted back to their factory settings. Vance Last edited on 05-15-2024 04:33 pm by vnavaret |
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