Topic: Float height issue on '78 750K

[jdpas29]

i guess i've kinda done things in a wrong order here with this 78 750K.  i just got new exhaust on which i thought would fix my problem.  --  my bike bogs when i goose the throttle.  it runs great at idle and at 1/4 - 1/2 throttle.  after doing a search and reading a few posts, i'm starting to think that one or more of my carbs has more fuel in the bowl than the others. 

my question is...  is there a way (even if not perfect) of setting the float bowl height without taking the carbs off of the bike? 

is turning off the petcock and draining each carb separately into a graduated cylinder worth doing?  then maybe i could take the highest common denominator and set all the bowls to that height... 

i have noticed that when i have the bowls off, i can look across the bottom of the floats and easily see that they are hanging at different levels.  dis this any kind of reference point of use?

[bistromath]

Well, one old trick you can do is to get a nylon threaded fitting that is the same size as the carb drain screw and attach some clear tubing to it (Tygon works well). Leave the end open and hold it above the level of the carb body and you'll see the fuel level in the bowl will be the same as the level in the tube. That will let you measure the fuel level, at least relative to the carb bowl, and you can compare across all four carbs.

Probably the easiest thing to do, though, and the one that would let you sleep best at night, would be to do a carb rebuild and bench sync, including resetting the float heights properly and carefully.

Before any of that, though, do a plug chop. Run it wide open for a 1/4 mile and then hit the kill switch and cut throttle. Pull all four plugs and read them for mixture info. Do a search on the archives for more info on plug chops and carb tuning. Then you will have a much more educated guess as to what your problem really is.

[eurban]

Bistromath's suggestion about the clear tubing is a good one except that you can simply attach the clear tubing to the brass overflow tubes and then, while holding the tubing in a loop ending up higher the the top of the float bowls, open up the drain screw.  No need to replace the drain screw with an adapter.  This method should give you an accurate reading of the actual fuel levels in each bowl.  Probably best to have the bike on the centerstand for this test.  Overall, I think that adjusting your float levels acurately would really require pulling the carbs as it is a bit tricky even when you can see everthing just right.  Your bogging problem could be many things including float level but it would probably be wise to go over the carbs completely.

[Bob Wessner]

Bistromath's suggestion about the clear tubing is a good one except that you can simply attach the clear tubing to the brass overflow tubes and then, while holding the tubing in a loop ending up higher the the top of the float bowls, open up the drain screw.

I'm trying to envision how this would work as described.

[Teach]

It seems like that would only work if there was too much gas in the bowls and then it would only be even with the top of the overflow tube.

[Bob Wessner]

I guess I was suggesting that ff one is lucky enough to have a spare bowl (or four  ) you could cut down or remove the overflow tube and this would work, but then there would be no need to unscrew the drain screw.

[eldar]

You could check float height while carbs are on. Just take the bowls off. You will have to hold the floats closed while NOT compressing the pin in the float. You can then measure. This would probably be huge pain in the ass though if you have to make adjustments or do anything else. Even measuring would be a pain.

I guess I do not think it is a float issue. Could be but not very likely.
Make sure your valves and cam chain are adjusted then do a sync.
Then adjust low speed with a tach.

Start here, then at least you have a good base.

[jdpas29]

the thing is, Eldar, it runs sooo smoothly in low throttle and up to 1/2 throttle, i tend to think that timing is ok and i can't really fool with the valves.  (i'm a noobie and getting that stupid metal slip in between the valve gap thingy is a bit too much for me).

two of the cylinders idle perfectly and two of them idle kinda rough together so im going to set all the floats to the height that the two better idling floats are at and try that. 

thanks for the help guys.  some of your suggestions i would love to be able to do, but i don't have the expertise or equipment to synch carbs/check cam chain, and there is absolutely no one here who will work on these bikes.  ARGH! 

[eurban]

Sorry to dissagree ya'll but the method I described earlier works perfectly well on the 77/78 style carbs (which is what I would imagine mister jdpas29 has on his 78K)!  I have done it many, many times. Perhaps it is different on the earlier carbs?? The drain screw on these carbs is actually a "valve" that blocks (when tightened all the way in) a second port to the overflow tube at the bottom of the bowl.  When you open the drain screw fuel flows thru this hole at the bottom of the bowl and out of the brass overflow nipples.  I have clear lines on my overflow fittings that runs down in between the frame and swing arm to "safely" dump any overflow of fuel.  When I want to drain the bowls I simply put a container underneath the tubes and open up the oringed drain valves and fuel flows out of the bowls and into the container.  If I take these same tubes and hold them high up against the carb bodies and then open up the drain valve, I get to see exactly what height the fuel is in the bowls since it is entering the brass tube from the opening at the bottom of the bowl.  Where does the fuel come out on the earlier carbs when you drain the bowls?  Anyways perhaps it one of the few things that is actually easier with the later style carbs?  Enjoy

[dusterdude]

yep,they is different

[bistromath]

Well jdpas, there's only one way to learn & that's by doing. You'd do well to learn to check your valve clearances since you'll want to do that every couple thousand miles of riding anyway. And the cam chain adjustment is not difficult to do at all. A Haynes manual or Clymer if that's your thing is a solid investment and will save your ass in the future.

I have trouble believing your float heights are the most likely problem with your bogging, but it is possible.

Eurban, I learn something new every day -- on the older carbs the drain screw is really just a screw in the bottom of the float bowl that drains gas all over the engine when you open it up. The overflow tube is just a brass tube set to a predetermined height in the float bowl that lets excess gas drain out. Neat idea with the later carbs to eliminate the mess by draining out the overflow.

[Bob Wessner]

I stand corrected if yours are of a different design.  

Where does the fuel come out on the earlier carbs when you drain the bowls?

Drain screw in the bow also, but there is no connection between the screws and the overflow standpipe, so it just runs out revealing nothing about the fuel height.