TOPIC:

There is something I failed to mention with regards to leaking fuel and its important. When this occurs there is the possibility that gas is getting into the cylinders. My bike was parked on an incline but I stuck my nose into the oil fill hole anyway because the consequences of fuel in the oil may well result in engine damage.

You'll want to check yours.

Togoster wrote: The other question I had was how does the bike run off idle, like at 30 mph with the throttle open. The carb sync affects mostly the idle and the just off idle responsiveness of the engine. When those slides are open it matters not that much. I'm thinking it best to start with a good bench sync because I just went through this not long ago with my LTD. The manual will tell you how to do a bench sync.

The bike runs okay at like 30mph. It is a little sluggish with acceleration - not very torquey in any gear - but I was attributing that to the carburetors and poor cam timing, but maybe it's something else? I don't notice a lick of difference in torque at half-throttle vs. WOT; the only thing that changes is the noise coming from the exhaust.

There wasn't any crud in the float bowls when I checked them last night, but I purchased an inline filter anyways. I guess I will do a bench sync and make sure the floats are at the right level. I will also check for fuel in the oil.

TexasKZ wrote: One inch from what????
I am not familiar with the 750 specs, but I'd bet the fuel level should be +/- 3mm from where the float bowl and the carb body meet.

26mm from the gasket to the top of the float. Measuring the fuel level doesn't really help since you have to put the carbs on, fill em with fuel, take the carbs off, adjust, put the carbs back on, fill with fuel, check, and readjust. Sounds like a pain in the ass if you ask me.

It is a pain, but it is the most accurate way to measure. The dry measurement will get you in the neighborhood, but not as close as the clear tube method. It can also identify a failing float valve.

I get the sense that we are not looking at one specific problem here but rather a list of things that are either wrong or at least not quite right.

Even the bench sync won't affect running at 30 mph with the throttle open and if you feel that the motor lacks the torque then I would suggest establishing a basic engine health baseline. Check compression would be the first. Timing, check for a strong spark...etc, etc.

Rather than trying to pinpoint the problem by assumption, start eliminating the possibilities for a poor running engine.

That's my best advice.

Oh, and pull the plug and see what they look like. Make sure they are the correct plug gapped properly.

It's time to put this thing to bed

Woo, more work! haha! By the way, I was able to download the 300+ page Clymer Manual and I can't seem to find any information on the Keihin float height. It mentions the Mikuni height should be 18mm, but doesn't go into detail on the Keihins which I have.

I'll get the carbs bench synced, just to start since they are already removed from the bike. Then I will check compression, spark plugs, timing, valve clearance etc...

I really appreciate your help with trying to figure this out! I will keep you updated on my progress.

Have you checked under the Articles tab near the top of this page to see if the factory service manual for your specific year and model is available to download?

Hmmm, thanks for that TKZ, I'll have to try that for my650.

Let's face it these aren't the torqueist bikes in the barn anyway.

I'm happy to "help" but all I've done is make more work for you but I stand behind what I'm saying. You've shown a great patience with this and that coupled with the fact that i love troubleshooting things in general makes for a good combo. It's not easy to figure out what it's wrong and so it should be relegated to procedure when you can't rely on experience. It's even harder when the motorcycle is not right in front of you.

I posted that YouTube video of Lee because to fully understand basic concepts it helps to clear your mind get back to square one and start again. Basically you need 3 things for combustion, compression , fuel and air. Basically. But we not only want combustion, we want performance so we need to fine tune things.

We need to be the fuel, we need to be the vacuum.

And yes, I'm as much of a unit as Bruce was.

Quick UPDATE:
So I borrowed a compression gage from Autozone, but it didn't have the right size adapter. No worries, I ordered a gage online earlier in the day anyway.

Since I couldn't check the compression, I checked the carbs once more, measuring the floats to see if they were in line with each other. I know from yesterday, that 2 of the carbs were low while the other two were spot on. Well as it turns out all of the floats measure within +/- 1mm of each other so unless the springs in the needles are wildly different in spring rate... they are just fine at the height they're at.

I can also say that because the two carbs that were low had significant amounts of rust in the float valve seat. I cleared that out and put on a new inline fuel filter and will double check the fuel levels after I check the cylinder compression.

Proper fuel and air ratios are what you are looking for. An example that i sometimes think about since I work with wood is sawdust. If you have a pile of saw dust and you put a match to it it may burn a little and then it's likely to smolder, but if you toss a shovel full into an ignition source -- stand back because you'll get singed. Grain silos same thing, they can under certain conditions, explode.

The proper ratio is determined by the physical makeup of any given particulate. Gas happens to be extremely volatile but at the same time if you have a bucket of gas and you throw a cigar into it it will likely extinguish the cigar.

The internal combustion engine to this day, I still marvel over whether it's some old one cylinder relic in the Smithsonian or the newest high horsepower fuel efficient engines of the day.

Knowing what size jets you have currently and what the compression ratio is in each of the cylinders will aid in diagnosing the trouble. When you sync the carbs you are basically measuring engine vacuum which is the inverse of the compression ratio in actuality. That is why a difference in compression of more than 10 percent between any cylinder is not desirable and so the reason for the difference needs to be found. There are a few possibilities that I won't yet go into but I just want to follow through on this and explain why I recommend a compression test.

Togoster wrote: Basically you need 3 things for combustion, compression , fuel and air. Basically. But we not only want combustion, we want performance so we need to fine tune things.

Actually, there is a fourth requirement, spark. Unless we are discussing a compression ignition engine, which hopefully his KZ is not.

Doh! Of course you are right, what a marooon I am, haha. I won’t even edit that out I could use a good public humiliation about now.