float height

[Stout]

Yeah, I've posted that one from the Airheads list on a few sites in response to queries, just not this one. I owned an airhead a few years ago.

[excess.11]

i actually found a link to the making up of one of these put on  here by melbxs found on another site.http://www.airheads.org/content/view/183/98/ ...........and.................http://brogdensmuse.menofhonorministry.org/Bikes/Carb_Synchronizer.htm

[Stout]

No, I don't. For a keen photographer, I'm lousy at taking photos of things I do in the shed. I've been tinkering with stuff for a long time now (from a very early age) and taking photos as I go has simply never been part of my routine. I'll take a piccy of the manometer and post it up, but there really isn't much to it. It is just four lengths of clear plastic tubing, spaced about an inch apart and linked by two t-pieces and two elbows. About a metre up from this is a small piece of pine with four holes through which the tubes pass. I hang this piece of timber from the throttle grip or mirror using a piece of wire. The bottom of the manometer just about touches the garage floor You could mount the tubes to a backboard of some kind (as was my plan originally) but I didn't bother and now don't think it is necessary. The other ends of the plastic tubes go to the vacuum ports on each of the four inlet manifolds, with a short length of rubber fuel or vacuum line providing a seal between the plastic tube and the vac port. If you used the next size tubing, you could probably just  slide it straight onto the port, but I think the vac line provides a better seal and some insulation from the heat of the engine. Obviously, you need to route the plastic tubing away from the head too.....

[excess.11]

Thanks Stout , there are so many different ways people do this sync of the carbs.I don t suppose you have a pic of yours set up on the bike? iI sure would love to see.

[Stout]

A 4-tube manometer I made using 10m of 6mm acrylic tubing, some irrigation system elbows and t-pieces and filled with ATF.

The four tubes are linked together at the base using the Ts and elbows, so it is a 4-tube 'relative' manometer, rather than four independent or absolute manometers. This means it is very sensitive because any gain on one results in a loss in the others, so you get twice the differential. If you manage to get them to stay level, the carbs are well and truly balanced!

As for 'how', I used the adjustment screws on the throttle linkages. Very fine adjustmenst required towards the end (or maybe I just got to the end because I eventually figured out that only very fine adjustments were required...;-)

Key relationship to keep in mind when balancing the carbs: #3 carb is the 'master', actuated directly by the throttle cable. #2 and #4 are linked to #3 via adjustment screws. #1 is linked to #2 - so adjusting the screw between #3 and #2 also affects #1, but not #4, etc...

[excess.11]

Hi  Stout , may i ask what you used and how you balanced the carbs?

[Stout]

Just to close out my tale....

Because I thought I was on the right track, I only raised the float heights to 24mm, measured from the top of the little step. I then returned the pilot screws to the standard setting and balanced the carbs. I left the needle clip where it was. While I had the carbs on the bench again, I did the 'blow thorugh the inlet hose' trick too. All good, no leaks.

While it was never 'bad' the bike now runs much more smoothly and responds to the throttle better. I also got an extra 20km before reserve out of the last tank of fuel. Hard to be ccertain without a dyno, but I think it may have lost a little power in the upper half of the rev range (though it still feels smoother there), so I may move the needle clips to the middle groove next tune up. For now, I'm very happy with the outcome.

[Stout]

Because I had promised to take a friend's son for a run in the sidecar for his birthday, I took the bike out for a ride on Sunday with the float heights as they were (ie: approaching 25mm when measured correctly). I had assumed I might need to ride around with the choke on a bit, but to my surprise, when I flicked the choke off as I headed down my street, it continued to run very nicely.

Throughout the ride, it was a lot snappier away from low revs and far more responsive to small throttle movements than usual. Most of the popping and crackling on trailing throttle was gone too. In summary, very nice. It had lost a little top end though, which is not surprising - I suspect the mixture was about right in this range before I started. While I still believe it is too lean and the exhaust side of the head got noticeable hotter than usual, there was no pinging (even when I went looking for it) and the plugs did not look like they had been too hot. So I think I'm on the right track, I just went too far....

I pulled the carbs out again last night and they are upside down and open on the bench waiting for me to get home tonight.

[Stout]

Hi Peter,

Thanks. Thought this may have been the case, which is why I asked before going further down the rabbithole...it will be reasonably easy to return to the previous settings from here, but if I keep going..... ;-)

The things that made me think the float levels were too high were occurrences of overfuelling at low speeds (ie: so much fuel the bike starts to run rough and stalls...) bogging down away from lights, and generally seeming rich and smelly. On the open road it has been beautiful though and my fuel consumption has been about what others with XS11 outfits in the past have said they got, so it was probably a bit optimistic of me to think it was that far out. Guess I was mislead by a recent experience with the Mikunl on a trials bike I purchased which was no less than 5mm too high!

[petejw1966]

hi stout,
havent had a chance to welcome u to the forum yet,
so welcome.

regarding ur float heights, u check them upside down without the gasket
at there heighest point, which is at the 'step' that u were talking about
and not at the round part of the float, compared to the earlier brass carbs,
sounds like they were close before u adjusted them,
reset them back at 23mm, making sure there all exactly even,
the way u have them now would make u run extremely lean.

while the bowls are off and the float height is set, keep the carbs upside down
and blow into the fuel inlet with ur mouth, if the needle and seats are  leaking ull be able to hear/feel
the air blowing pass.

id also leave the needles in the 2nd groove from the top.

whats the bike doing that made u take the carbs off in the 1st place?

[Stout]

Where on the float do you measure the float height for the XS1100RH? It doesn't look quite like the sketch in the book (as shown in an earlier post). When the carbs are upside down on the bench, the highest part of the float is on top of a little step up towards the hinge. The top of the round section of float is about 2mm lower and is not the highest part of the float.

The top of the round part on mine were all more or less at 21mm, whereas the top of the step was at 23mm. Because I was convinced my float height is too rich, I set them so the top of the round part is at 23mm. I also adjusted the float travel stops so they don't from down further than 30mm (a guess - I couldn't find a spec for it) Until I did this, it looked like they were coming down way too far and I know from experience with other Mikunis that this can lead to stuck floats and other woes...and I have been having trouble with stuck floats since I got the bike.

Anyway, now it won't run cleanly off the choke. The needles are one clip position lean from standard and always have been since I've had the bike. This is one of the many reasons I believed the floats were rich. The pilot screws were the standard 1 and 1/4 turns. I tried richening them up and winding up the idle and could get the bike to idle with choke off this way, but when I open the throttle it misses. I suspect I need to return the needles to the standard setting, but wanted to check if I had measured the float heights to the right part of the float first....

[petejw1966]

hey miti,
ive had my bike for 5 yrs and had no idea
that the floats effected the acceleration to the extent it does.
i do know tho   if you get your float levels right, the bike will run like a rocket,
get it wrong and itll run like a 250. 
let us know how u go with it.

[Miti]

also ive noticed if the bike bogs down when taking off from a set of lights then your more likely
rich on the floats.

That's me, that is... I thought it was just me fat arse..!!

ive found setting the floats so the mixture screw settings are close to  stock 1 and a quarter turns out then your fairly close, if your mixture screws are set at 1 turn out then your likely rich on the floats, if your more than 1 and half turns out then your more likely lean on the floats.
adjusting the floats by .1mm affected the mixture screw setting by a quarter of a turn. (roughly)

so if you were running at 2 turns out on the mixture screw, you could richen the floats by .3mm
to bring the mixture screw  back to stock settings.

Fek me..!!  You sure it's that critical..? I might just stuff the auld bitch in the garage and get the bus down to the pub...!!


Suppose I'll give it a go... Maybe ramorra...

Miti

[petejw1966]

setting the float heights.

float heights affect acceleration and throttle response.

to see if you need to adjust the float heights,
the engine should accept throttle under load
without hesitation in any gear and at any rpm.

to see if you have the correct float height have the bike in 4th
or 5th gear and the engine running at around 3000rpm,  now
crack the throttle wide open, the engine should accept the throttle without any lag
or hesitation.
to determine if the floats are rich or lean you need to determine what type of hesitation
it is, if the engine bogs down then pick ups the floats are rich if the engine hesitates then  accelerates  flat then the floats are lean.
pretty much if the acceleration is flat when the throttle is firstly cracked open then the floats
are lean.
also ive noticed if the bike bogs down when taking off from a set of lights then your more likely
rich on the floats.

ive found setting the floats so the mixture screw settings are close to  stock 1 and a quarter turns out then your fairly close, if your mixture screws are set at 1 turn out then your likely rich on the floats, if your more than 1 and half turns out then your more likely lean on the floats.
adjusting the floats by .1mm affected the mixture screw setting by a quarter of a turn. (roughly)

so if you were running at 2 turns out on the mixture screw, you could richen the floats by .3mm
to bring the mixture screw  back to stock settings.

also make sure the floats are exact on all 4 otherwise the engine runs like the carbs are  out of sync

i hope this helps and makes sense.   

[petejw1966]

hey miti,
we have the same carbs,
if your running pods i found 115 mains to be the best,
with the stock pilot jets and the floats slighly on the rich side of stock,
the needles were set on the 2nd clip(lean). the bike ran well
with that set up, i tried running bigger main jets 117 gave me a miss
down low 120 gave me a miss down low and around 5500rpm,
im running a dyno jet set up atm wich isnt to bad.