-
Hi Guest!
You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
There are some perks with a member upgrade!**Upgrade Now**
(PS: Subscribers don't see this gawd-aweful banner
Hey - did you know if you click on the title of a thread it will take you to the first unread post since you last visited that thread?
but were afraid to ask: 
STOP!! Never post your email address in open forums. Bots can "harvest" your email! If you must share your email use a Private Message or use the 
smilie in place of the real @
Pretty Please - add it to our Events forum(s) and add to the calendar! >> 
Fuel Level In Jet -Question-
- Thread starter BDavis
- Start date
Share this page
SilentUnicorn
Yoda
Offline
Thanks, Mark, for the link and the suggestion for shimming. That business on the link you included about backfiring destroying the spring tension of the poppet valve is very interesting. I like the idea of removing/sealing up the hole in the butterfly! That I will do.
However, I think that the fuel level in the back bowl is too low. I seem to remember reading somewhere (years ago) a measurement that the fuel level should be below the shoulder of the jet. With piston and needle removed it should be visible in the jet. And shimming out that valve would only shut off the fuel at a lower level... wouldn't it?? (Solution for a flooding bowl)
I may have to resort to new floats... or find some used ones with the metal arms I can adjust. But for sure the fuel level is noticeably higher on the front carb. Hmm. could it be too high?? ..I don't think so, because the plugs up front aren't sooted up. In fact the only one looking 'leaner' than the others is #4.
Thanks again!
.......Bill
However, I think that the fuel level in the back bowl is too low. I seem to remember reading somewhere (years ago) a measurement that the fuel level should be below the shoulder of the jet. With piston and needle removed it should be visible in the jet. And shimming out that valve would only shut off the fuel at a lower level... wouldn't it?? (Solution for a flooding bowl)
I may have to resort to new floats... or find some used ones with the metal arms I can adjust. But for sure the fuel level is noticeably higher on the front carb. Hmm. could it be too high?? ..I don't think so, because the plugs up front aren't sooted up. In fact the only one looking 'leaner' than the others is #4.
Thanks again!
.......Bill
Offline
Hi Bill,
The generally accepted level is 3/8" to 7/16" to below the jet bridge. It isn't terribly critical as long as the mixture adjustment is within a range that works. It is also pretty hard to measure. The jet would have to be pulled all of the way down to see fuel.
D
The generally accepted level is 3/8" to 7/16" to below the jet bridge. It isn't terribly critical as long as the mixture adjustment is within a range that works. It is also pretty hard to measure. The jet would have to be pulled all of the way down to see fuel.
D
Hello Bill,
have you checked if someone has already shimmed or even used two washers under the float needle valve assembly. When inverted, an HS float should have about 1\8" gap or slightly more (0.187" max as per manual) with the steel needle(early). The later spring loaded needle should have the same gap without the needle being compressed.
I have to disagree with Dave, I would expect to see fuel in the jet, and not really much lower than an 1\8" to a 1\4" below.
You could check that there is no blockage between the float chamber and the jet (rare) and that the float chamber vent is clear.
Alec
have you checked if someone has already shimmed or even used two washers under the float needle valve assembly. When inverted, an HS float should have about 1\8" gap or slightly more (0.187" max as per manual) with the steel needle(early). The later spring loaded needle should have the same gap without the needle being compressed.
I have to disagree with Dave, I would expect to see fuel in the jet, and not really much lower than an 1\8" to a 1\4" below.
You could check that there is no blockage between the float chamber and the jet (rare) and that the float chamber vent is clear.
Alec
Dave and Alec..
Thanks for your replies.
Well, I don't really know where the level of the fuel is *supposed* to be but always thought it should be somewhere just below the top of the jet. And roughly equal in both carbs, of course, and easily visible.
Unlike the front carb which 'looks' normal at just below the top of the jet... When I drop the jet (choke on the back carb) the fuel is waaay down.
Maybe you've hit on the problem Alec. Looking just now in the manual (Complete Official MGB -Bentley- early copy) I see that it shows the "needle" type valve fitted to the bowl cover. The valve in my cover is a ball type!
I will check to see if both valves AND floats are of the same type. I believe they are... but if not that could surely cause a problem!
Which only begs another question.... If I have non adjustable floats were/are they the proper mates for the ball type valves??
Many thanks for both your comments!!
Regards........Bill
Thanks for your replies.
Well, I don't really know where the level of the fuel is *supposed* to be but always thought it should be somewhere just below the top of the jet. And roughly equal in both carbs, of course, and easily visible.
Unlike the front carb which 'looks' normal at just below the top of the jet... When I drop the jet (choke on the back carb) the fuel is waaay down.
Maybe you've hit on the problem Alec. Looking just now in the manual (Complete Official MGB -Bentley- early copy) I see that it shows the "needle" type valve fitted to the bowl cover. The valve in my cover is a ball type!
I will check to see if both valves AND floats are of the same type. I believe they are... but if not that could surely cause a problem!
Which only begs another question.... If I have non adjustable floats were/are they the proper mates for the ball type valves??
Many thanks for both your comments!!
Regards........Bill
Offline
Hi Bill,
The ball valve is an aftermarket accessory sold by Grosse. Some people think they are wonderful, others don't think so. You can get an overview of the valve here.
https://www.jcna.com/library/tech/tech0026.html
Also see this thread
https://www.britishcarforum.com/ubbthreads/showflat.php?Cat=0&Number=89172&an=0&page=0
D
The ball valve is an aftermarket accessory sold by Grosse. Some people think they are wonderful, others don't think so. You can get an overview of the valve here.
https://www.jcna.com/library/tech/tech0026.html
Also see this thread
https://www.britishcarforum.com/ubbthreads/showflat.php?Cat=0&Number=89172&an=0&page=0
D
Hello Bill,
I think it is a common modification in America (Grosse jet?)
But the same principal exists to adjust the jet by shimming or removing shims\washers. If you have no washers left and still the float is too high, when inverted, a replacement needle jet will be required.
Alec
I think it is a common modification in America (Grosse jet?)
But the same principal exists to adjust the jet by shimming or removing shims\washers. If you have no washers left and still the float is too high, when inverted, a replacement needle jet will be required.
Alec
Good info fellows!
As we've determined, shimming out the valve reduces the amount of fuel in the bowl... the opposite of my problem. And with these non-adjustable floats I'm snookered.
Solution here looks like a different set of floats.. adjustable ones with the metal fork. I think I may have some of the earlier needles. Weren't they used forever on SU carbs??? I'll have a look.
Thanks for your help, Dave and Alec.
Since we're on the subject of carbies here's a jpg of a painting I finished last year. (if I can find where to attach it) I've had this box of old SUs in my basement for years just waiting for me to get off my keester and use them for subject matter. Measures 36" x 38" - Oil on Canvas - titled (what else) "Box of Carbs".
Regards......b
As we've determined, shimming out the valve reduces the amount of fuel in the bowl... the opposite of my problem. And with these non-adjustable floats I'm snookered.
Solution here looks like a different set of floats.. adjustable ones with the metal fork. I think I may have some of the earlier needles. Weren't they used forever on SU carbs??? I'll have a look.
Thanks for your help, Dave and Alec.
Since we're on the subject of carbies here's a jpg of a painting I finished last year. (if I can find where to attach it) I've had this box of old SUs in my basement for years just waiting for me to get off my keester and use them for subject matter. Measures 36" x 38" - Oil on Canvas - titled (what else) "Box of Carbs".
Regards......b
Attachments
SilentUnicorn
Yoda
Offline
what about getting the needle seating face spot faced by a machine shop? then you could shim as needed.
mark
mark
Mark..
That's an interesting fix. I'd considered it. I think it would definitely work! Maybe even as simple as using a drill press.. taking it down a few thou and testing. But I think I'll stick to needle valve / float changes and try going that route first.
Regards, .....Bill.
That's an interesting fix. I'd considered it. I think it would definitely work! Maybe even as simple as using a drill press.. taking it down a few thou and testing. But I think I'll stick to needle valve / float changes and try going that route first.
Regards, .....Bill.
Offline
Bill,
Great art work. You have real talent.
In looking back thru the posts, I see no mention of what caused your float level concern in the first place. Is the engine not running correctly?
I would start with standard, for the carb, inlet needles, seats, & floats. If you have the right parts & they are correctly installed, there should be no need to machine or bend anything.
D
Great art work. You have real talent.
In looking back thru the posts, I see no mention of what caused your float level concern in the first place. Is the engine not running correctly?
I would start with standard, for the carb, inlet needles, seats, & floats. If you have the right parts & they are correctly installed, there should be no need to machine or bend anything.
D
Thanks Dave...
For the advise ...and the nice comments on the work. As to the cause for concern... The ole beater just wasn't running 'right'. (it's been on loan to 'relatives' for the last 10 years and seen hard times!) In fact it wasn't running when it returned. So, like a fellow with Alzheimer's, every day is a new experience! And I agree with ya... the correct parts will make worlds of difference. And now to correct the level of fuel in the jet.
Regards.......b
For the advise ...and the nice comments on the work. As to the cause for concern... The ole beater just wasn't running 'right'. (it's been on loan to 'relatives' for the last 10 years and seen hard times!) In fact it wasn't running when it returned. So, like a fellow with Alzheimer's, every day is a new experience! And I agree with ya... the correct parts will make worlds of difference. And now to correct the level of fuel in the jet.
Regards.......b