TOPIC:

I'm not really sure how to even word my question. My bike is an '82 GPZ 750. It has pods on the carbs and was jetted correctly, all of this before I bought the bike. Stock exhaust. It has always run well from idle to redline so I've had no reason to fool with the pods until I just wanted to go back to the air box, which I will at some point. No running rich, plugs are good, electrics are good. Bike starts well even on a cold morning, choke works perfectly. The issue I am having is almost like the carbs are loading up. When I am sitting in traffic, the bike will begin to bog down slightly. Not a lot, but I have to clear it out once I get on the move again until I get to another spot where I sit and it does it again. The bike has never stopped on me, but it's been doing this for a few weeks now. Last weekend, I noticed that it has begun to do this while at speed. If I am cruising at any speed for more than a minute or so, it begins to choke a bit until I alter my speed. A slight change is all that's needed, but it's obviously something wrong. Fuel mileage isn't great at 35mpg, but it isn't awful either. No leaks that I have found, fuel or air. Hell, I'm not even sure it's a carb issue, but all signs seem to indicate it is.

Any ideas?

Could be a torn diaphragm in the petcock that is allowing a little fuel to run down the vacuum hose into a carburetor.

You may also want to check fuel levels in the carbs, one may be a little too high.

Have you checked the spark plugs? They may tell you if it is a problem with a single cylinder.

TexasKZ wrote: Could be a torn diaphragm in the petcock that is allowing a little fuel to run down the vacuum hose into a carburetor.

You may also want to check fuel levels in the carbs, one may be a little too high.

Have you checked the spark plugs? They may tell you if it is a problem with a single cylinder.

I'll check that. Plugs are all good and even. Nothing out of line at all. I put "carb sync" in the title because I wonder if that might be part of the issue but I'm unsure any of my symptoms are synonymous with the need for a sync.

Would (1) assure valve clearances are within spec, and (2) perform the clear-tube test on each carb to assure that fuel levels are within spec.

Too tight valve clearance often results in worsening performance as the engine reaches normal operating temperatures.

Too high fuel levels often result in worsening performance as the spark plugs get loaded up and fouled from an excessively rich air/fuel mixture.

Good Fortune!

when you have time, try turning the petcock to PRIME for 15 minutes with the bike off and you watching it. then start it.

if it leaks gas on the ground, a hint. if it wont start becuase it is flooded, turn petcock to ON, wait a couple of hours and it will. then you know somehing is wrong with your floats.

could also be choke sticking on somehow.

A carb sync is usually incident to enhancing smoothness of engine performance at idle rpm and helping enable a strong steady pull-away from idle.

Once underway -- say at cruising speed, for example -- carb sync contributes little if anything to engine performance.

Good Fortune!

Go back to basics
Check or better yet drain fuel system including carbs to remove this as a running variable. Fuel quality can make all other checks skewed and you may chase your tail. Not saying for sure its fuel, dirt , or water , but remove this as a cause.
Dave

Check valves first, then ignition, then move on to the carbs.
Steve

Like Patton said, this doesn't seem to be a sychroniation problem. Out of spec valve clearances can certainly cause what you describe, and far too many previous owners avoid doing it.

Patton wrote: Would (1) assure valve clearances are within spec, and (2) perform the clear-tube test on each carb to assure that fuel levels are within spec.

Too tight valve clearance often results in worsening performance as the engine reaches normal operating temperatures.

Too high fuel levels often result in worsening performance as the spark plugs get loaded up and fouled from an excessively rich air/fuel mixture.

Good Fortune!

This is a wonderful idea. The only thing is that the performance is fine, idle to redline. It only does this when I maintain a certain rpm for more than a minute or two. The plugs are all fine. No fouling and all 4 are the same color.

I'll check the valves today, as per the suggestions and using my manual of course, as the weather is shit again. It's rained for 3 weeks straight here in Richmond with the occasional sun poking out for a quick ride. I feel like I'm in Seattle or possibly England with the crummy weather.

If I am cruising at any speed for more than a minute or so, it begins to choke a bit until I alter my speed. A slight change is all that's needed, but it's obviously something wrong.

. . . performance is fine, idle to redline. It only does this when I maintain a certain rpm for more than a minute or two. The plugs are all fine. No fouling and all 4 are the same color.

The following test might help with diagnosing the cause of the reported symptoms --

When the symptoms appear while riding, if the same throttle position is maintained while manually adding choke, does manual addition of choke have any effect on the reported symptoms?

The above exercise may help indicate whether air/fuel mixture could be an issue when the symptoms are occurring.

Good Fortune!