Topic: Soooo, new carb boots?

[ev0lve]

Have had an issue with the idle rising as the bike gets warm since I got it back together but this season it's getting a little ridiculous - between 2 and 3 thousand RPM. If I grab the choke full on it will idle just under 1000.

A little pooty (sorry for the technical speak  ) giving it throttle in that condition but it doesn't die outright like I'd expect. Take the choke off and it comes right back to 2 - 3000.

That's gotta be an air leak on the engine side of the carbs, right?

75 CB750K in reasonable tune - it's due though.

[Brian G]

Inasmuch as there's been no other response to your post, I'd guess that you've answered your own question 

Nonetheless; I had a similar situation on another make of bike which turned out to be a sticking spark advance mechanism. If, when she's 'idling' at 2-3000 rpm, try engaging first gear and gently let out the clutch against the brake. The revs (obviously  ) will drop but if they return to the high speed idle when you pull the clutch back in it would tend to indicate a carburation problem. If the engine speed stays at the lower speed, it may indicate a sticking spark advance. Something to look at, anyways...

Hth,
Brian

[ev0lve]

Inasmuch as there's been no other response to your post, I'd guess that you've answered your own question 

Nonetheless; I had a similar situation on another make of bike which turned out to be a sticking spark advance mechanism. If, when she's 'idling' at 2-3000 rpm, try engaging first gear and gently let out the clutch against the brake. The revs (obviously  ) will drop but if they return to the high speed idle when you pull the clutch back in it would tend to indicate a carburation problem. If the engine speed stays at the lower speed, it may indicate a sticking spark advance. Something to look at, anyways...

Hth,
Brian

Sprayed WD40 on the carb boots carb and engine side. No change so maybe the boots are good.

Clutch engaged but returns to 2-3000rpm.

Spose I'll lube the advance when I do the tune up and see unless someone knows something else.

[ev0lve]

Hmmm, just screwed the idle out while I was out for a ride. Idles at 1000 no problem.

All I can think is I did the tune in March and set idle in 40 degree weather with what I thought was a fully warmed up engine but in 90 degree weather it's different? Sound like a reasonable explanation?

Still a noob with my 35 year old machine 

[BigBoi]

Could be. I play with the idle on my bike everytime I ride it. I increase it while it's cool...ride it for a while, come to a stop and she'll idle around 2-2.5K. I reach down, bring her back down. I'll have to do that a couple of times when I ride to ensure it's at around 1K when hot.

[ev0lve]

Could be. I play with the idle on my bike everytime I ride it. I increase it while it's cool...ride it for a while, come to a stop and she'll idle around 2-2.5K. I reach down, bring her back down. I'll have to do that a couple of times when I ride to ensure it's at around 1K when hot.

Is your bike a 750K? My idle knob is behind the petcock between the 1st and second carbs. Not an easy reach - in fact I can only get at it using the tips of both index fingers to turn it.

Now that I think about it I wonder if that's not the reason the petcock was on the right K0 - K4?

[BigBoi]

Mine is a K2. It's behind my petcock as well. I can reach it with my index by wrapping my hand around my number 4 carb.