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Griz

Griz

Jedi Hopeful
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After 5 plus years of rebuild the BJ7 roared to life on Valentine's Day with 60psi oil pressure and no oil leaks, only a couple minor coolant leaks. That's the good news. However, old Griz needs some guidance from the wizards here. The carbs are gulping gas. I've checked the float bowls and they are working correctly and no gas is flowing out the overflows. I ran the jets up flush with the bridge in the throat of the carbs, double checked that the needles and jets are centered, and backed the jets off as directed in the adjustment instructions. Engine fires right up fine, then shortly begins to stumble especially when I work the throttle. When I shut it down gas flows out the inlet manifold drain tubes. I even ran the jets all the way up as far as they would go to lean out the mixture and I still had gas running out the manifold drains on shutdown.

Any advice??

Griz
 
John, not sure what valves are in it...however they are the originals (I believe), so should be whatever came with the car.
 
Check with su as to the correct jets , floats and needles
 
John Turney said:
Are the floats set to 5/16" (I believe)? What float valves are you using SU with Viton tips or Grose or?
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"John, not sure what valves are in it...however they are the originals (I believe), so should be whatever came with the car"

That's where I would look first. Old, unused float valve seals will perish, and leak. I've seen that a lot in cars we've brought back to life from long-term storage. Grose jets used to be a great substitute for the Viton-tipped valves, but I think I've read on this BB that they aren't what they used to be (kind of like me). GL, Jim
 
Looked through my parts bin and found a new set of viton needle float valves that I had purchased but forgotten about. Installed them, and even put a shim washer on the threads in an effort to lower the fuel level in the float bowl. Also double checked that floats have no fuel in them. Fired up the engine and no improvement...still stumbling and fuel leaking from the manifold vent tubes on shutdown. Pulled the plugs and they are wet and black. Is it time for new jets and lean needles?

Griz
 
Griz said:
Looked through my parts bin and found a new set of viton needle float valves that I had purchased but forgotten about. Installed them, and even put a shim washer on the threads in an effort to lower the fuel level in the float bowl. Also double checked that floats have no fuel in them. Fired up the engine and no improvement...still stumbling and fuel leaking from the manifold vent tubes on shutdown. Pulled the plugs and they are wet and black. Is it time for new jets and lean needles?

Griz
Click to expand...

Man, that's unfortunate. Is your fuel pressure too high? That might cause fuel to get past the valve seals. Just a WAG...I really can't think of anything else. If the jets/needles were too rich, it might run poorly, but the bad flooding makes me think there is something else going on. Jim
 
steveg said:
Check nylon floats for leakage and set float level.

BJ7 has HS6 carbs - no diaphragms. Section DDD.9 in the Bentley manual describes setting the float level with a "1/8 inch bar".
Click to expand...

Don't the HS carbs have cork gaskets and/or O-rings around the jets? Old cork and/or rubber could crack and leak.
 
Bob_Spidell said:
Don't the HS carbs have cork gaskets and/or O-rings around the jets? Old cork and/or rubber could crack and leak.
Click to expand...

Yes, or if an O-ring or cork gasket was pinched during assembly, I think gas might just siphon into the carb body. That would certainly cause flooding, as would something making the choke function stick. The last SU's I worked on were on my dad's P1800, about 8 years ago, and the 100/6 is a project that is still in storage, so I can't check right now, so, YMMV, but good luck!
 
Still sounds like the levels are too high in the jet wells, regulated by the float bowl level. What's the condition of the jet-needles? if they were previously mis-aligned, it doesn't take long to ruin the needles taper, or turn the jet-well oval.

If you want it to run smooth and even, there are a lot of factors to perfect, especially if you want maximum available power, crisp response. Yes, even with a device as primitively simple as an SU carb__oh c'mon, THREE (3) moving parts is pretty simple__you want all calibrations to be spot on!
 
Randy, that's just it, I don't know the condition of the jet/needles as I bought this car totally disassembled. Don't know how it was running when last on the road. I'm sure the problem is very basic as the carbs are so simple, but I just have not yet been able to figure it out. My next thought is to completely tear down the carbs, check for damaged parts, and reassemble. Jim mentioned fuel pressure, I plan on checking that too, to eliminate all possibilities, even though I don't believe this is the problem. I'm beginning to think I should change the name of this thread to "It's Alive, but Sick".

Griz
 
If all else is well, that sounds like a minor illness - a mild cold or flu. Congratulations on making it as far as you have!
 
Even the tiniest bits of dirt in the fuel line cause this, so put a filter in the supply close to the carb.

turn float lids upside down and make sure an 1/8" drill slides across the face of the lid and just under the riveted bit on the top of the float.

Needles and jets are usually fine, but set jets 35-38 thou down from jet bridge. This is what the works did when new. That will be spot on and if it isn't, the spindle bushes are worn and leaking.

SUs are a real pain after a rebuild and just tapping the float bowls with a heavy spammer might get the needles sealimg and stop the overflow.
 
Griz said:
Randy, that's just it, I don't know the condition of the jet/needles as I bought this car totally disassembled. Don't know how it was running when last on the road. I'm sure the problem is very basic as the carbs are so simple, but I just have not yet been able to figure it out. My next thought is to completely tear down the carbs, check for damaged parts, and reassemble. Jim mentioned fuel pressure, I plan on checking that too, to eliminate all possibilities, even though I don't believe this is the problem. I'm beginning to think I should change the name of this thread to "It's Alive, but Sick".

Griz
Click to expand...
The current line of Genuine SU rebuild kits are very complete; they have all the correct parts in them (except the needles themselves, they must be ordered separately**). I'd have those on hand when tearing them down, and if you find significant wear on the throttle shafts, in all but the worst cases, replacing the shafts with the stock size__NOT the oversize ones__will resolve that (so no complicated reaming to oversize on the bodies).


** In the Moss listing, turns out there are two (2) rebuild kits listed; the Master Rebuild Kit includes the shafts and bushes, but no needles, and the Rebuild Kit includes the needles (but presumably, not the shafts?). Both kits are complete to cover the pair (2) of carbs fitted to the engine.
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=60525#top

A phone call to Moss might help clarify exactly what is contained in the Master and Rebuild kits.
 
Well, I think we are on the right track. Disassembled the carbs and found nothing amiss, but did lower the fuel level in the float bowls again. The only means for doing this on my carbs is by putting shims on the needle valve threads. (Floats are completely made of plastic and there is nothing to adjust on them to change fuel level.) Started the car up and let it warm up a bit. Revs right up from idle without stumbling but when I shut it down there is still a little fuel dripping from the manifold drain tubes. I've ordered new grose valves, a complete spectrum of needles, and new jets. Should be able to fix it with that lot! I'll keep you posted on the results.

Griz
 
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