Topic: 750 drivability issue

[DH]

Hard to explain symptom, but here goes..Engine acts lean, but I cant confirm this. Riding around my neighborhood
at low speeds, 1/8-1/4 throttle everything is fine. Accelerating past 1/4 throttle, the engine starts to lose power.
Giving more throttle will accelerate the bike faster, but engine exhibits a combination surge/bog behaviour.
It reminds me of how a modern sportbike acts when it is revved to its revlimiter, except not as rapid or cyclical
There's no regularity to it, and its not a dead miss.
There is intake noise, but the engine acts like its run the carbs nearly dry. I tried applying the choke in varying degrees, but it doesnt affect the symptom. Tried stock air filter, k/n "stock air box" style filter, replaced float valves,
set float heights, dwell, timing, different condensers, cracking the fuel tank lid open for venting, different ignition
coils, synched carbs, checked for crud and cleaned petcock. Carbs are clean inside. Plug caps checked a while back
and all were good. Cold starts are textbook Honda, hot starts are 1-2 turns of the crankshaft and it is idling...
Have not done a proper plug chop or clear tube yet. Wanted to run it by the forum. Bike is stock 750k5, except
for factory style K/N air filter and K1 carbs. I'm missin somethin, but I don't know what. Any specific areas to look in that I didn't mention or haven't found yet? This may hae been coming on slowly, and now just severe enough to be noticeable. I've beat this to death. Hopefully it makes sense. Thanks

[Stev-o]

What type of intake noise?  Have you checked your carb boots for leaks??

[Spanner 1]

It may be ignition rather than carbs.I would replace the 4 plug caps. I try to do that every 2nd. riding season. Increased coil energy as you increase rpms can short-out the caps IMO. One bad cap will kill it's sister cyl. too.

[madmtnmotors]

What type of intake noise?  Have you checked your carb boots for leaks??

+1

It may be ignition rather than carbs.I would replace the 4 plug caps. I try to do that every 2nd. riding season. Increased coil energy as you increase rpms can short-out the caps IMO. One bad cap will kill it's sister cyl. too.

+1

I had one cap that tested good, but after it got hot the resistance would spike. Started shorting against the head making an audible "ticking" noise. Start it up in the dark (pull the headlight fuse if you can't turn the headlight off) and check for arcing around the plug boots.

[DH]

What type of intake noise?  Have you checked your carb boots for leaks??

It may be ignition rather than carbs.I would replace the 4 plug caps. I try to do that every 2nd. riding season. Increased coil energy as you increase rpms can short-out the caps IMO. One bad cap will kill it's sister cyl. too.

What type of intake noise?  Have you checked your carb boots for leaks??

+1

It may be ignition rather than carbs.I would replace the 4 plug caps. I try to do that every 2nd. riding season. Increased coil energy as you increase rpms can short-out the caps IMO. One bad cap will kill it's sister cyl. too.

+1

I had one cap that tested good, but after it got hot the resistance would spike. Started shorting against the head making an audible "ticking" noise. Start it up in the dark (pull the headlight fuse if you can't turn the headlight off) and check for arcing around the plug boots.

 carb boots were replaced also, I forgot to add. They are the ones from kenosha kid on ebay. No change. I willl verify they aren't leaking, they don't fit as well as O.E. as far as lining up with ports. They seem to seal once  mounted,
but I'll re check. The intake noise is, other than louder than usual, normal sounding. Will need to check the plug caps,
good idea to check in the dark.

[DH]

Spent this afternoon rechecking some things. Checked intake boots for leaks, none found.
Changed all 4 plug wire caps, same result. Had it on the highway for a bit. Difficult to maintain cruise speed or keep up with traffic. Still not accelerating cleanly from cruise speed. I suspect battery may be weak. Still turns starter, but will drop below 12v if ign or lights are left on for short period.. Been on charge overnight and trickle charge not complete. battery was
never allowed to become totally dead ever. Don't know if this will affect things or not. volt meter reads up to 14.1
(at highest) hooked to batttery terminals and motor revved. Clear tube method halfway done, #1 and #4 check good, little difference between those two, 1/8-3/16" from bowl gasket surface. Had to quit before doing 2 and 3
carb, will finish tomorrow. This thing is killing me.  

[Don R]

 After it gets up to temp, pull over shut it off for a minute or two to let the bowls re-fill, then give it a test, if it's a lack of fuel flow the bike will run OK for a quarter mile or so then run low again. did you say you tested the flow out of the fuel hose already? Could the screen in the tank could be plugged? I had an inline filter that wouldn't flow, I could blow air into the tank through it but fuel would not pass back out. It appeared clean, I guessed some sort of gel was in it.

[Don R]

Low float levels will strangle an engine too, do the clear tube if you can.

[rotortiller]

Have a look at fuel flow out the petcock.

[DH]

Here's what I did. First was the clear tube method on carbs 2 and 3. Seemed ok, So I did it with the engine running and the tubes secured in a safe location. Levels right on, and self correcting when engine running.
Checked flow from tank earlier, ok, so decided to trim fuel hoses from tank to carbs, so that fuel was always headed in a down hill direction, made adjustments, ok......Adjusted air screws
to 3/4 turns out from seated, and got smoother idle as well, ok.....LASTLY, and what I think may have been the cause of symptoms.....Each carb throat on the intake side has an air bleed passage with a drilled and calibrated brass insert. the passage leads to the emulsion tube/needle jet area. I forced air thru this passage on carb 1,
and after a few attempts, fuel was somehow forced OUT of the same passage for carb 2. Seemed maybe like
airbleed was gummed up. did the same for carbs 3-4 and got the same results, but took less effort.
Only other thing I did was reroute the carb overflow hoses from the wishbone area of the centerstand to
an area between the c stand pivot pipe and the frame. Took the test cruise, ready to pull over/shut down/wait/restart and................. all was normal. So for now, I'm good. Thanks to all who read and or responded to this.
A long strange trip it's been