Grose Jets

JeffYoung

JeffYoung

New member
Having some fueling issues on my car (ITS TR8, 175 CD Zenith-Stromberg carbutretors). It's rich at idle, VERY lean through the power band (confirmed at a dyno day).

I've got the "rich" needles, but stock jets. Grose jets are now available for this carburetor for the first time in a while. By looking at the design, it appears to replace the entire needle assembly? There is a ball that sits in the needle seat and I assume it is used to regulate fuel flow, as opposed to the needle? Anyone have any experience with these? Are they an acceptable alternative to a finding new, larger diameter standard jets?

Thanks.
 
Having some fueling issues on my car (ITS TR8, 175 CD Zenith-Stromberg carbutretors). It's rich at idle, VERY lean through the power band (confirmed at a dyno day).

I've got the "rich" needles, but stock jets. Grose jets are now available for this carburetor for the first time in a while. By looking at the design, it appears to replace the entire needle assembly? There is a ball that sits in the needle seat and I assume it is used to regulate fuel flow, as opposed to the needle? Anyone have any experience with these? Are they an acceptable alternative to a finding new, larger diameter standard jets?

Thanks.
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Hi Jeff
The gross jets only replace the needle and seat in the float bowls and have very little to do with mixture. It is the profile of the needle and the diameter of the tube (jet) it runs in that set the fuel curve and mixture. PM me and I will give you some useful information.
 
Then only thing good about Grose jets, is that you can throw them really far. Which is what you should do with them if you ever get close to them :happy204

George H.
 
Where did you find Grose Jets? I'm a firm believer in them as are the guys I race with, but they disappeared from the market along with SU's and Strombergs. I heard that someone was selling them again, but haven't been able to locate them. They work perfect in our Weber's. PM me if you'd like and have the info.
 
Paul Yaw installs them, but I ave had issues...like in tech when my fuel pump was on, and a small puddle began to delope. Tap tap and all is good...ecept for the carb filed with a pool of gas.
 
Then only thing good about Grose jets, is that you can throw them really far. Which is what you should do with them if you ever get close to them :happy204

George H.
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George, I have to agree with that use of them.
 
Steve or anyone else who knows,

What is the issue these jets are trying to solve? I could only find a couple of pictures on the web and they seem to resemble a ball in a cage, sort of like a ball valve on a float bowl.

Jeff is after some adjustability, which he can get from larger mains. Are these Grose jets in some way adjustable? If so, I'm not seeing it.

And, if they really are good things then I might wish to use them on my Jensen, which has the same carbs as Jeff. But, the jury seems split on their use - throw them far or put them in!

R
 
I am certainly not a carb expert but it has not been stated here though it has been alluded to.

If I understand right the gross jets are just on the float bowl. I have seen a car lean out at high rpm because the float bowl was emptying. gross jets may help that. but so can higher fuel pressure and larger fuel line. I had to go to 1/2 I.D. steel hydrolic tubing
 
i use them and love them.
the leancondition that these solve are the float bowl running out of fuel at high rpms.
they come in different sizes.eg. 190 to 250 depends on the hp levels. if you go with one that's too big .at idle they would flood the engine as fuel would leak past the seat. if you go too small fuel bowl would run dry at high rpm.
you need to experiment with different sizes to get which is best for you .you can also calculate your fuel consumption and figure out the correct size for your application. i hope this help everyone understand these a little better and give them a 2nd chance.
p.s. they don't use very high fuel press. about 2.5 to 3 psi.
 
Alright,

so these things essentially replace the needle valve the float usually opens and shuts? So they would have no effect on mixture at WOT UNLESS the bowl was running dry, correct?

I think you'll need mains Jeff because I don't think the bowls are running dry, but we can definitely check that.

R
 
Alright,

so these things essentially replace the needle valve the float usually opens and shuts? So they would have no effect on mixture at WOT UNLESS the bowl was running dry, correct?

I think you'll need mains Jeff because I don't think the bowls are running dry, but we can definitely check that.

R
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EXACTLY!

I had to make a jig to set the float level in a carb of mine that was not cooperating (turned out the two floats were not the same), but i watched thru a clear "float chamber" how much these things flow, and it's a LOT! As mentioned you can get them in different sizes. If you have issues with the level getting loo low, they can solve it.

Even if you think you aren't running the float bowls dry, remember that vibrations can really make fluids get pretty aerated and your lower jets could be seeing something less than a solid source of fuel.

Also, of course, make sure that your float settings are correct for the application. (This is where you might be on the leading edge in an orphan because there may be no info about how to tune the setup for the rigors of the track)
 
Anyone know where to find Grose jets for an IT7 Mazda carb?

Looking to buy Grose jets for my 83 RX-7 IT7 carb. Anyone have any for sale or know of someone who does?

Please feel free to contact me directly at [email protected].

Thanks.
 
nate22 said:
Looking to buy Grose jets for my 83 RX-7 IT7 carb. Anyone have any for sale or know of someone who does?

Please feel free to contact me directly at [email protected].

Thanks.
Click to expand...

Having just been through an "ordeal" or two with the stock needles and seats of my 1st gen carb, and believing that it is fairly common knowledge that the Grose jets are the right "setup" and eliminate some potential issues, the question is "Are they available from any source,.... anywhere....?". If someone were to have a supply of them, they could probably sell a fair number. I am actively seeking the acquisition of some. Any suggestions? Also, does anyone have any knowledge regarding any availability or source of RX-3 floats? I am informed by an acknowledged reliable and experienced source that the combination of Grose jets and RX-3 carb floats eliminates the potential of some adverse issues.

Cheers.
 
Jeff, do the needles run through the center of the jets? If so, they can be sanded like we did with the old Mikuni MX carburetors. We changed the taper and final end size to get the fuel curve we wanted. The middle of the taper controls part throttle mixture, and the very end takes care of WOT. Chuck
 
Rich, as noted before the Grose Jest will only help if you are getting fuel starvation filling the bowls due to too small of needle and seat. You can measure the hole of the seat with a numbered drill bit (not the sharp end). The meetering needles are the thing that control your mixture. Occasionally you can open up the hole in jet that the needle goes into but this will change the mixture accross the range not just in certain areas like the needles.
The British 4cyls are pretty well known for what needle ranges to start with. With your V8 combination I would waste no time in contacting Joe Curto in NY or a specialist in England for needle recommendations. For the small cost of these parts you will be far ahead in taking someones starting recommendations. Few people know the TR8 carbs for racing in the US. One good fix is to get an adapter that allows you to use SU needles, for which there is a far better range of needles off the shelf.
Last, and you IT guys will love this, you can tune your carbs by using different oil in the damper. Many people would simply run carbs without oil because it takes a while to figure out. The oil works like an accelerator pump by raising vacuum (by slowing down piston rising). This draws more fuel for that brief high vacuum time. This allows you to run a leaner mixture and still get off the corners well.
FYI, years ago some people complained that the ball bearings in Gross Jets were falling out causing uncontrolled fuel flow. This could have been a sizing error or been from damage. Manty people stopped using them because of the rumered problem. New needle and seats with Viton tips are as good as you can get for SUs and Strombergs.
 
The TR 8 carbs need the float as high as you can get it . The fuel slosh from racing can starve the jet and the engine cuts out. My TVR did this and now has 2 in ,round bowl SU carbs.
RE Grosse jets might still be available from TWM . they were pretty good. Or Mark from British Auto in NY.
Re; high end. You can trim the mid range with a washer( weight) on top of the piston, under the spring. It takes a few tries . The WOT , on a dyno, read the fuel ratio or EGT and look into the carb, if the piston/needle is not opening all the way, reduce the weight, dont stretch the springs!!. Run it again and note the needle exposed, hand polish with 400 paper, over a flat file. a very small area of the needle, that is set in the jet at WOT. Use a flat file so that you can measure how much you have removed and dupe that figure to the other carb.Round or flat has not seemed to make any diff, just easier to measure.
It may take a few needles, go slow and careful.
Dont foreget that these jets can be pressed down into the carb and richen up the whole thing. Measure the jet height under the piston and balance both. Measure the needle up , etc.
If you dont know the basics, look around for the SU/ and stromberg book.

Run trans oil in the shox.
MM
 
I visited Mr. Grose at his basement shop in the late '70s in Mass. We talked about his invention and why he came up with the idea. I had been experiencing fuel starvation in hard cornering with a Porsche and thought baffling was the answer. He explained that sometimes the centrifugal force was keeping the needle stuck closed in the seat and as the bowl emptied the main jets sucked air. The Grose jet has two balls in the cage, one to contact the float and push the smaller ball up to shut off fuel when the float level was correct. The Grose jet is not subject to the centrifugal force; the small ball uncovers the fuel opening in the seat. I found that setting the float level was extremely important (sometimes very thin fiber washers rather than what was supplied in the kits).
He manufactured many different versions of the jet depending on the carb in which it was to be installed. The two differences were the size of the opening for the small ball (flow rate into the bowl was determined by size but fuel pressure was usually low 2-4 lbs), and thickness of the seat/cage that screwed into the carb top.
I've used Grose jets in many different carb applications both in racing and on the street and never had a problem. But initial set up float height is critical.
Regards,
Chuck
 
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