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dlg Member 
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I've read all the existing posts regarding fuel leaks from the vent hole on the face of the Stromberg carbs but mine is still a mystery. I can start the car and run it for some time at idle, but after reving up to about 3k rpm and allowing to quickly return to idle the front carb occasionally gushes fuel from the vent hole at 10 o-clock on the face of the carb (and then the car sputters and dies, while I'm leaping for the ignition to shut it off). I've taken the carbs off the car twice now to check the float height (fine) and the Grosse valves (TR6 from Moss, clean and apparently working). I would assume that the increased flow of fuel at the higher rpm has something to do with it and maybe the ball valve is not fully closing as the fuel is rushing in to keep the bowl filled. I immediately shut the engine off to avoid a bad situation getting worse, clean it up and then once again turn on the ignition to start the fuel pump and no leak and after waiting a bit I can start the car again and it will idle fine with no leaks. Just FYI -- I have the standard ticking SU fuel pump (purchased thru the club store years ago) and a recently Renu'd fuel tank and fresh fuel filters. Any ideas? |
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vnavaret Member 
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dlg wrote: I've taken the carbs off the car twice now to check the float height (fine) and the Grosse valves (TR6 from Moss, clean and apparently working). Any ideas? The problem is the Grosse valves. They are very prone to sticking, and in my opinion are unacceptable. I used them on my TR6, which led to leaking, dripping, and stained paint. I replaced them with the (more expensive) OEM needle valves, and the problem was solved. An interesting design that is much too sensitive to contaminents that cause sticking. You could try changing out your fuel filter, but the odds of success are low. The Grosse valves do not have the wiping action of a needle valve that clears contaminents from the valve seat, and lack the fine mesh filters of the OEM valves that keeps the larger filth away from the valve entirely. Vance Last edited on 05-12-2024 03:34 am by vnavaret |
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noomg Member
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dig, Grosse jets are a controversial subject like the Strombergs themselves some people love them some absolutely hate them. I've had Grosse jets in two Stromberg cars and one SU car for decades and I've yet to have a problem with any of them but the gas tanks are clean and I have an aftermarket fuel filter them between the pump and the carbs on all of them. Based on that performance I would not hesitate to use them again. You'll have to decide for yourself whether to stay with the Grosse or go OEM. |
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dlg Member
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Thanks for the replies folks. Given that I had no problems with the original style needle valves I think I will try replacing the grosse valves and see if that helps. One last question before I do that (or most likely while waiting for the new valves to be shipped), is it possible that I may have made the grosse valves faulty by using BOTH the fiber and aluminum washers when I installed them? Odd thing is they don’t leak until the fuel flow rate is increased by raising the rpm’s and returning to idle so they aren’t leaking generally. Anyway, thx again and I’ll post the results when this has been resolved in case it helps anyone else. |
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noomg Member
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dig, It's been a long time since I installed one so I'm a bit foggy and since Ive never had a problem with one it's hard for me to say. So let's talk about yours. Did you install them or did you get the car that way? If you installed them did the old valves have two washers? Is two washers what the Grosse directions called for? And has the car always had this problem since the Grosse jets were installed? |
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dlg Member
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noomg - It may be coincidental but this problem has existed since I installed the Grosse valves (I've had the car since 1980 and the Grosse valves are a recent change from the last carb overhaul). I've read other posts that indicate that maybe only the fiber washer is to be used, but given that they don't normally leak (i.e., when starting/idling) and both carbs had both fiber and metal washers installed it's likely not the problem (rear carb does not have any issues). The old needle valves (oem type) had only the metal washers. I'm going to switch back as soon as I can get the old-style valves -- have to take the carbs off again anyway so that seems the best next step. IF I have the same vent leak after installing the oem style needle valves then I'm going to need a new theory! |
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Jh092 Member
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dig, You said you were running a standard ticking SU fuel pump. Have you checked that you are delivering fuel at 2.5psi? Any more than that and you can overdrive the jets. |
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noomg Member
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dig, Sounds like you've pinpointed the problem which started when you installed the Grosse jets. The next logical step would seem to be replacing them with OEM units. You won't be losing anything there's no performance between the two and probably most guys with Zeniths are still running with the OEM units. While I like Grosse jets I wouldn't hesitate to replace them if that solved a problem. |
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vnavaret Member
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I believe that whether or not you are a fan of the Grosse Jet valves, depends on the state of your fuel system in general, your experiences with them, and perhaps your luck with fuel purchases. Having experienced a sticking Grosse Jet valve personally, I can say that they can and do stick. Whether or not your particular installation has issues depends on the cleanliness of your fuel system, your fuel filter, and perhaps the manufacturing tolerances of your particular valves. Contaminated fuel may have something to do with it, depending on the specs on your fuel filter too. Finer filtration may be key in keeping them working well. If you have not experienced sticking, then the Grosse Jets are a screaming deal, and of course you will have positive feelings about them. If you had issues, then they are from the devil himself. The old joke "What is the definition of a conservative? A liberal who has been mugged." has some bearing here. You love Grosse Jets until they take a dump, then you hate them. That describes my experience precisely. Vance |
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dlg Member
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jh092 - Checked the fuel pump pressure after the final fuel filter just before the carb T fitting and it measures just under 3 psi (with my el cheapo dual purpose fuel pressure / vacuum tester). This doesn't seem too excessive if 2.5 is the target, but comments welcomed. Still waiting for the new needle valves and will let y'all know what happens when I get them installed. Thanks again for all the input! |
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Tom Bradley Member
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I'm a bit late to this thread, but I also tried Grosse jets and had problems. They sounded like a superior design, but did not work well for me. Switching back to the standard inlets worked better. Whichever you use, do not mix the two types of washers, they have different strengths, so the pressure to get a good seal with the metal washers will tend to crush the other ones. Do you have the nitril floats? The original ones are not rated for gasohol. Also check that the air valve drops smoothly and bottoms out with a click when lifted all the way up and released. If it hangs up somewhere that could be the cause of what you are seeing. |
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Tom Bradley Member
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Last edited on 05-17-2024 05:21 am by Tom Bradley |
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dlg Member
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All - Got the new OEM style needle valves put in and the carbs installed (again) and as of this writing no more leaks. Still have some work to do to balance the carbs (my uni-syn no longer works for some reason) but it seems to be running pretty well. I guess in my case either I had a bad set of Grosse jets or maybe at my SU fuel pump pressure (high normal at about 3 psi) they just stuck open occasionally. Regardless, on to the next project! Thanks to everyone for the help! |
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noomg Member
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I'm just wondering now if something's changed at Grosse Jets. Of late (talking last 10 years) I've heard fairly regular complaints about them and not just this site also TR7, MGB, Spitfire among others. Makes me wonder if production has been farmed out, suspect at the top of the list would be China. I've always recommended them because I've never had a problem with them. I had a sticky OEM jet in my Austin-Healey and installed Grosse Jets in about 1988 and never had a problem. Installed them in my TR7 around 1992 ditto. My Jensen-Healey around 1995. Since my last problem free install was thirty years ago I've had no problem recommending them. However now I may have to put a caveat on that, at least until more is known. |
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Tom Bradley Member
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Uni-Syns don't work all that well, anyhow. They put too much load on the carb being measured so you have to be quick. These guys work better: https://www.amazon.com/Carburettor-Carb-Balancer-Dellorto-Weber/dp/B0C33ZSXFS You can also do a decent balance by listening to the intake of the carbs with a tube. I did this for years. It is somewhat cumbersome and takes some practice, but works pretty well. Last edited on 05-26-2024 08:23 pm by Tom Bradley |
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noomg Member
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Tom, The Uni-Syn has always worked well for me and my carbs have to be balanced to the gnats ass since I live in CA and if they're not precisely balanced it won't pass the smog test. If you're not getting enough air flow during the balancing process you simply screw the Uni-Syn open to allow more air flow. |
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JAF6025 Member
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So bare with me, when you are talking about replacing the Grosse valve to stop fuel leakage, is that the inlet valve where the gas comes into the float bowl, or are you referring to the main metering needling valve? Thanks. John |
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JAF6025 Member
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Ok, so I just checked Moss Motors web site and it seems I have a series 3 valve that I put on my just rebuilt Stromberg. Still having a fuel leak coming out of the vent hole at the 10 0-clock position just like member dig had. I am stumped? |
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dlg Member
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JAF6025 - It is the valve that is controlled by the floats in the fuel bowl. Ive had no issues since replacing the Grosse jets with the original style needle valves, so at least for me I think that was the culprit. Another thing to consider is whether you are getting rust in the fuel and particles lodging in the valve which can keep it from closing. I suspect it's just the valve though as long as you have good fuel filters in place (i have one in the trunk and one in the engine compartment). Good luck! |
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redracer Member
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Super late to this thread, but noomg might be correct in Grose Jets made lately. I used to order 400 at a time and NEVER had a problem with them(UNLESS one lets their gas sit for a long time which builds "varnish" on them). I have not ordered anymore since the '90s, so if many vehicles are "having problems with them" , then noomg may be correct. Mr. "dig"; the GROSE jets are to be installed with the fiber washer ONLY, until you can just see the edge starting to deform. An aluminum washer on that fiber one will NOT have enough pressure and will likely leak. As for a bit of history, the original needle valves were brass-on-brass; eventually, the brass needle would get a "dent" in it and not seal. The replacement for them years later were/are the ones with a ??neoprene?? tip on the end of the needle. I have hundreds of them, but have no idea how long they will last since I don't use them(however, I carry a few spare im my travel tool kit just in case!) happy T-Day to you, bruce/RedRacer |
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vnavaret Member
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JAF6025 wrote:Ok, so I just checked Moss Motors web site and it seems I have a series 3 valve that I put on my just rebuilt Stromberg. Still having a fuel leak coming out of the vent hole at the 10 0-clock position just like member dig had. I am stumped? Did the leak start when you rebuilt your carbs, or was the rebuild an attempt to fix the leak? If the latter, I would suspect that your float has filled with gas. After 50 years the fuel migrates through the plastic so the float doesn’t close the valve. Holding the float up to a light will show if you have this problem. In that case you will want to replace the floats. Vance |
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JAF6025 Member
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The leak started before the rebuild. It still slowly leaks after the engine is shut down, then stops after I assume the fuel pressure is released. I've replaced the float. After the rebuild I've replaced the gasket under the float valve a couple times ,and added a fuel flow restricter. Going to try a different float valve, ordered all three types from Moss. |
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vnavaret Member
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Hmm. Any chance the float bowl vent is clogged or capped off? The float bowl vent must be open to air. If the emissions gear has been altered the float bowl can get pressurized. Oh snap, you said that is where it is leaking, so it isn’t clogged. Another hmmm. You might pull the plugs for the front two cylinders and inspect them. If they are black it would be a clue that something is amiss with the carb other than simple leakage, and correcting that may alleviate the leakage. Restoring any missing emissions gear might help as well. Make certain the gasket between the carb and air box is correctly aligned and has the cutout for the float bowl vent. I occasionally come across carbs that are using SU gaskets, which do not have provisions for the vent opening or the temperature compensation, although why covering the air intake for the compensation would cause a leak is not at all obvious to me. Rereading your post, makes me think that the gasket is not the problem, but I am leaving that thought in my post in an attempt to be thorough. You might consider posting a photo of your carb plumbing as well, sometimes another set of eyes is all it takes. Just spitballing here. =:-o Vance Last edited on 11-29-2025 04:02 pm by vnavaret |
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noomg Member
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Regarding the jets if you've got debris in your fuel due to rust or dirt or whatever either jet (Grosse or OEM) can stick. A quick fix would be an in line fuel filter and if it clogs you know where the problem is. Vance raised an interesting point about gas migration. I experienced this but not with the carb floats. When my gas gauge wasn't reading I pulled the tank sending unit and found the plastic float was filled with gas. I checked it throughly for holes or cracks and found none after decades the gas had just gotten in there. Something to consider if your gas gauge is sluggish or reads low. |
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JAF6025 Member
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Thanks everyone. I'll send some pictures when I work on it today. |
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JAF6025 Member
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I THINK I'VE GOT IT FIXED. I replaced the float valve with another one exactly like it and placed the thick aluminum gasket under the valve so that the tab on the float itself didn't need to be bent to obtain the correct float level. Maybe because I was adjusting the float level by bending the tab on the float, I was causing the float valve to bind in it's holder. So far so good. Thanks to everyone for the help. LOVE this forum! |
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