'Don't fool with stuff if there's nothing wrong with it...'
I wish I'd heeded that advice.
Anyway, I've been mucking about with carbs on my 750 L lately.
I sent a set of grungy, stored-for-years bodies out to be water-blasted and got the steel stuff all zinced up nice and shiny.
Spent a half-day with a can of carb cleaner and got every last gallery/venturi/jet/passage squeaky clean.
Used all my best parts, cleaned to within an inch of their lives.
Put it all back together, the carbs look better than brand-new OEM, but the thing runs like a dog. I mean, really bad.
I've set the carbs back up exactly as they were from factory for an L - 47.5 pilots, screws out 1/4 turn, 110/107.5/110 mains, 120 butterflies, standard Mikuni needles, new needle-jet o-rings, all other bits standard Mikuni etc etc.
The mains and needle seem ok, but on the pilot circuit it's horrendous - depending on what pilots I use (I went back to 45's to see what difference it made) it either hunts and hangs and has no power, or it bogs badly and has no 'snap'.
It's almost like I need a set of jets in between 45 and 47.5 - it feels too lean on the 45's and overly rich on the 47.5's.
Adjusting the pilot screws with either set makes stuff-all difference.
I have two different types of 47.5's - one set is plain, the other has bleed holes drilled in the side.
My question (sorry about the long lead-up) is, what difference does a set of pilots with bleed holes make compared to ones without?
Best I can tell is the one's without essentially 'block' an air gallery - the one that leads from the LH side of the intake.
Thanks
Paul
Pilot jet issues...
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pjmcburney
- To the on ramp
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rngdng
- AMA Superbike
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There are two types of pilot jets that will fit the GT750 carbs. If you have CV (BS40) carbs, you need the fatter ones, that have less holes. If you have the 72-73 VM carbs, you need the skinnier ones with the extra holes. They are not interchangable.
I accidentally got the fatter ones in my 34mm VMs, and it DROWNED the engine with fuel. Perhaps Coyote still has the pics I sent him when he had the same problem, but I can't find them on my drive.
Lane
I accidentally got the fatter ones in my 34mm VMs, and it DROWNED the engine with fuel. Perhaps Coyote still has the pics I sent him when he had the same problem, but I can't find them on my drive.
Lane
If you stroke it more than twice; you're playing with it.
Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........
Too many bikes, too much time, ENOUGH SPACE, FINALLY! Never enough money.........
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tz375
- Moto GP
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- Location: Illinois
Apul, Sounds Like Lane is onto something there. Your pilot jets should have holes to mix air and fuel.
When you had teh bodies off, did you "flow test" all the drillings? a really simple test is to squirt carb cleaner through one passageway and then repeat on the other two carbs. Each should be very similar.
On the BS40 you also have to check the float bowl because it has so many drillings and the starter jest are down there too. The slow screw adjusts the total amount of air/fuel mix coming out, but I think it only covers one of the outlets. There;s two bleed holes that also need to be checked.
When you had teh bodies off, did you "flow test" all the drillings? a really simple test is to squirt carb cleaner through one passageway and then repeat on the other two carbs. Each should be very similar.
On the BS40 you also have to check the float bowl because it has so many drillings and the starter jest are down there too. The slow screw adjusts the total amount of air/fuel mix coming out, but I think it only covers one of the outlets. There;s two bleed holes that also need to be checked.
