Took another test ride today and after all I've done - changing sparks, air filter, valve adjustment, checking float levels in carb and finally doing a carb sync I still have this pronounced stutter! Searching the forum, it seems like others have had this problem too but the only solution I could find was using Seafoam and I've used something similar to no avail. Any other suggestions?

What do you think about the levels I synced the carbs to in the video? Should I try syncing again?

As soon as I get under 3-4000 RPM's I have to pull the clutch in so the bike doesn't "jump" It's not a nice feeling at all driving around like that lol.

CBR 1000F Carb sync - Balance Readings (After) - YouTube

 

I'm halfway down the same path you've already traveled. A pronounced stutter between 1800-2500 for me. No fun in town. The guys who've done the stick coil conversion say that it goes away after doing the mod. After all of the work you've done, weak spark may be the something to look at

 

coils/wires and I bet number four cylinder exhaust pipe is the last to warm up after
starting ......... that's why I'm doing the stick coil job on my 87 tomorrow

 

Thanks a lot for the suggestion, have to say that if I don't find a cure for this
I'm giving up on this bike. I should point out that the stutter has been there since
I bought it 8 Months ago and nothing has helped yet.

I'm not so into the Electrical system but is there an easy way to determine if
it could be the coils/wires? Such as measuring resistance? I'll check cyl. 4 too.

 

Check the sparks, but when my bike behaved that way it was because the carbs were dirty. I know you've cleaned them, but is it possible you could have missed something?

Also, when refitting the carbs, were the rubber boots seated properly? It took me a few attempts before I got it right. The only reason I new they weren't on properly was because the airbox wouldn't line up with the bolt holes (though it would have been possible to force it). I had to remove them (carbs),again and slacken off the large jubilee clips fully, then they slid on with the help of a short length of 1''x2''.

Apart from that it's, vacuum/air leaks or sparks/coils.

If she's firing on three, I'm sure you'd notice it.

As for the stick coils, it's a nice mod, but these bikes ran perfectly for 20 years without stick coils, just the normal ignition system. Before you go rushing off, buying new stuff, make sure that's the problem first.

Finally, has anyone else looked at the bike? It might be an idea, if you have a friend that can take a fresh look with an open mind

 

Thanks hawkwind for all your suggestions
Will check everything again on your list, I'm pretty sure they were seated properly
because everything went in smoothly there. If nothing else helps maybe I have to clean
the carbs again, just to be sure.

About air leaks they only thing I've noticed was the rubber connector shown in the picture.
It's in pretty bad shape and the connecting hose beneath was cracked but I fixed the
hose, I'm not sure what function it fills, maybe venting the tank?

I did take the bike to a mechanic at a workshop but he told me that's the way they're
supposed to run... Could be he never thinks of keeping RPM's beneath 7000... lol.
One person suggested that it could be the slow jet but since it's all the
way up to 4000 RPM and even over that, I wonder if that can be of influence?

 

my bike didnt run bad but if I was under 4k and got on it there was a stumble/hesitation/delay. I put the stick coils in and its gone. I'm not sure this is your problem but its an easy install and a cheap ebay part mine was 29.99 with the harness.

 

Hojen, the pipe in your picture is just acts as a funnel to collect any excess fuel from the overflow. The funnel then runs down a pipe to the bottom of the bike and dumps it out on the floor, avoiding the engine and hot exhaust

You said you tried something like Seafoam? Maybe it'd be worth trying the real McCoy? Would be the quickest cheapest and easiest thing to do.

If that doesn't help, then it's the slow methodical checking everything on the list

Good luck.

 

The carb sync is spot on, you can't get them any better. Nice job.

I will now preach about the crappy ethanol in the gas. It sucks big time.
I have not done it yet but will soon, take a covered jar of fresh e-gas and put it someplace for three weeks and keep checking on it. It separates. You need to feed the engine more of it and you need a hot spark to light it off.

You may need to turn the air/fuel screw out 2 1/2 turns. I had to, to get rid of some of my stumble. The stick coils with the hotter spark got rid of the rest of the stumble. Coming of a traffic light....errr...ba..ba.ba...errrrrrr between 1500-2500. That's gone now.

The thing is, theses bikes were produced without EGR's or catalytic converters. To pass emissions they were leaned out to the hilt.
Now the introduction of e-gas that requires a richer mixture, guess what happens? I guess it depends on where you live and how much they add. From pump to pump where I live, sometimes the stumble would go away and sometimes the bike ran so poorly it was like a 2-stroke that was highly ported and loading up. At times I had to take it up to 5,000 rpm and slip the clutch to get moving and once it was ba...ba.....ba...ba..ba ..until after 3,500, for the entire tank. Next tank and all is fine again.

re-jetted and turned the screw out 2 1/2 turns from the original 2 turns. Still had slight stumble and the sticks did the trick.

 

Oh so you were the Bad Azz that made that deal disappear

stick coils hojen give 'em a shot