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Stuck Needle Valve - Rough Running

Novamonte

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After I noticed that small amounts of fuel leaked from one of the floats on my Tricarb I replaced all the valve needles in May this year. That cured the leak and the car continued to run well.

About a month ago the car howeve started to run very rough and lost power. The problem was intermittent, it came and went, so I suspected that the ignition was the culprit and replaced disty cap, leads, plugs and condenser, but the problem remained. I tried disconnecting one lead at the time, but that did not yield any conclusive evidence. A compression test showed good compression in all cylinders (10.4 - 10.9 bar, around 150 - 160 psi) on a cold engine, so no valve train issue (I suspected a stuck lifter).

I then opened the float chambers on all three carbs and saw that the fuel level was very low on the middle one. It turned out that one of the new needle valves had a tendency to get stuck and wouldn't open, so the car ran on two carbs. The hole in the brass seat didn't seen to be round all the way down, so depending on how the needle was positioned it would stick.

Just something to remember to check if someone encounters a similar problem. It may have been a bad batch from SU (altough the two other ones I purchased do not have the same problem). I am happy that I found the problem before putting the car away for the winter (we had a second frost night yesterday). :cold:
 

steveg

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The Grose jets reportedly had problems some years ago - mine are evidently from the old days and continue to perform flawlessly. The design with the ball would seem to preclude strange wear as described above.

Are the new ones quality? Maybe that would be the way to go.
 

Kainopong

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My mechanic (who I believe is as old as my Healey) suggests using 90wt gear oil in lieu of the dashpot oil - may want to give that a go and see if it helps as well??
 

steveg

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My mechanic (who I believe is as old as my Healey) suggests using 90wt gear oil in lieu of the dashpot oil - may want to give that a go and see if it helps as well??

If your needle seat was manufactured such that the needle hangs up at an angle, the seat and possibly needle need to be replaced.

The heavy oil will make the "acceleration" phase richer than the normal oil would. Damper oil functions as the "accelerator pump". This from the book: "SU CARBURETTERS TUNING TIPES & TECHNIQUES", p. 4:

CarbDamperActionExplanation.jpg
 
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Joe Schlosser

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It is always the last thing you touched
 
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Needle valves have been a bug-a-boo on pretty much every carburetted car I've worked on (several). Like Steve G, I installed Grosse (sp?) Jets in my BJ8 decades ago, and they have been flawless. Bought a set for the BN2 a few years ago, and the little ball--that actually does the 'valving'--would get stuck in its recess. Dang.
 

steveg

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Needle valves have been a bug-a-boo on pretty much every carburetted car I've worked on (several). Like Steve G, I installed Grosse (sp?) Jets in my BJ8 decades ago, and they have been flawless. Bought a set for the BN2 a few years ago, and the little ball--that actually does the 'valving'--would get stuck in its recess. Dang.

Did you install the viton-tipped ones instead?
 

dklawson

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The Grose jets reportedly had problems some years ago - mine are evidently from the old days and continue to perform flawlessly. The design with the ball would seem to preclude strange wear as described above.

Except the OP reported these were new float valves that stuck so this would be a manufacturing error, not a wear issue. There are numerous stories of the needle of traditional float valves being made slightly "large" which can cause them to stick and not close properly.

General Footnote:
Grose Jets have been around since I first worked on British cars some 40+ years ago. Grose Jets were once made by a family business. The current owner/maker rinses the inside of the valves with a protective coating to keep the steel balls from rusting while in storage. Before using any Grose Jets, use spray carb cleaner, some shaking to rattle the balls, and more carb cleaner to wash out the protective coating. Failure to do so can result in the valves hanging open or closed.

I have installed a half dozen Grose Jets and experienced problems with every one. I no longer use them. I much prefer the Viton tipped valves. To each his own.
 

Joe Schlosser

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I do not know the reason why but when I started racing my FP 1275, 3-4of the front runners told me not to use gross jets in race motors.
I used the Viton tipped float valves for 20 years without an issue. However, note that the float valve is very rairly closed in a race motor so maybe the gross jets did not flow enough fuel.
 

steveg

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