Topic: 1975 cb750f front brake problem, idle problem

[alec868]

i have only just gotten the bike running, the last time it was registered was 1980. i also took it in to the mechanic about a week ago to tune the carbs adjust valves, timing and cam chain, and also to look over the rest of the bike to see if there was anything i missed. they seemed to thing there was no problem with it when i picked it up. the bike seems to run and drive well, however i have had it die while idling at a stop sign once or twice, the bike was plenty hot at the time (maybe too hot?). it also has a very noticable rattling noice, i dont notice it at high RPM. it also will not idle when cold, with the choke full on, i have to hold the throttle at around12000-1500rpm to keep it from stalling. its fine once its warm, except for the once or twice its stalled out.
i have rebuilt the carb, it has fresh gas, new plugs new breaker plate assembly, i can only assume what the mechanics did they did right.
one sideline issue is, i can only start the bike when its in neutral, wont start in gear with the clutch engaged. is that how its supposed to be?
on to the brakes, i rebuilt the caliper, new pads, when i took the bike to get safety inspection (ny state) i had the mechanic put all new brake lines in. when i left here he seemed to think the brakes were all good. i cant remember what they felt like when i left.
now it feels like you have to go pretty far to engage the brake at all and then very far to get any kind of decent stopping power, just seem very soft. mastercylinder? rebleed them? doesnt feel safe, wondering what i should do about that.

thanks
Alec

[BeSeeingYou]

It would have been best to do the master cylinders and rear calipers on a bike that had been sitting that long.  At least try and bleed them again, it sometimes takes a few times to get them right.  Make sure your tank is clean and the petcock filter is in good shape(unlikely).  I don't think that is your current problem but it will save you trouble down the road.  I am thinking that an idle jet/s is plugged. They have a very tiny passage.  You can get at them dropping the carb bowls and unscrewing them.
    These bikes tend to rattle a bit at idle, sometimes it's the cam chain needing adjustment(seems like you should be ok there), carbs needing to be synced, or the normal clutch rattle.  Or a combo of all three.   Does it get better when you pull the clutch in?

[TwoTired]

however i have had it die while idling at a stop sign once or twice, the bike was plenty hot at the time (maybe too hot?).

Any rust in the tank?

it also has a very noticable rattling noice, i dont notice it at high RPM.

Have the carbs been vacuum balanced?

it also will not idle when cold, with the choke full on, i have to hold the throttle at around12000-1500rpm to keep it from stalling. its fine once its warm,

Completely normal.  It has no fast idle cam and no computer/sensors to adjust speed or mixtures when cold. This is, therefore, operator responsibility to hold the throttle in the correct position and modulate the choke lever properly.

except for the once or twice its stalled out.

Rust in tank? Fuel filter issue?  Could also be float or fuel level issue in the carbs.

i can only start the bike when its in neutral, wont start in gear with the clutch engaged. is that how its supposed to be?

Kick start only in neutral with clutch fully engaged - Normal
Electric start needs either trans in neutral OR clutch disengaged. - Normal

on to the brakes, i rebuilt the caliper, new pads, when i took the bike to get safety inspection (ny state) i had the mechanic put all new brake lines in. when i left here he seemed to think the brakes were all good. i cant remember what they felt like when i left.
now it feels like you have to go pretty far to engage the brake at all and then very far to get any kind of decent stopping power, just seem very soft. mastercylinder? rebleed them? doesnt feel safe, wondering what i should do about that.

Pretty nebulous description, other than you'd like to have better brakes.  These were never intended to be one or two finger operated.
Lever travel can be related to excessive caliper stationary pad adjustment (.006 clearance).
A faulty master cylinder.
Or simply low brake fluid in the reservoir.  (this can also make the brakes spongy as low fluid can introduce air into the system.)
Is the master cylinder on stock bars in the level position?
Weak brakes can also be caused by fiction pad contamination form fork oil or brake fluid.

Cheers,

[alec868]

ok. so really rattles and squishy brakes arent to worrysome. i have rebuilt the front caliper, not mastercylinder though. i rebuilt carbs and had them synced
the bike will not start in gear with clutch engaged (squeezed) that isnt normal right?

[Bankerdanny]

ok. so really rattles and squishy brakes arent to worrysome. i have rebuilt the front caliper, not mastercylinder though. i rebuilt carbs and had them synced
the bike will not start in gear with clutch engaged (squeezed) that isnt normal right?

When you say won't start, do you mean won't start or won't turn over? If it's the latter then you probably have a bad clutch lever interlock switch (or at least a bad connection). This allows you to start in gear with the clutch lever pulled in. If the former, well, that's just odd and I'm not sure how to proceed.

[alec868]

yes i mean nothing happens. as if i dint have the clutch in and tried to start it. doesnt turn doest click. nothing.
clutch lever interlock switch sounds like the likely culprit

[TwoTired]

Kick start or electric start?

[alec868]

the bike has both. on electric start it wont start if in gear.

[TwoTired]

the bike has both. on electric start it wont start if in gear.

Oh really?  I never would have guessed.

Good luck!

[Spanner 1]

Note to O.P...... clutch 'engaged' = clutch friction plates together, i.e. in gear you would be riding down the road. Clutch 'disengaged' = no forward movement in gear 
Start safety switch on the clutch lever seems to be the problem, trace the wires and see what'up.........

[Jon]

For your non starting symptoms check the switch in the clutch lever mount as others have said, if you have a multimeter the switch should close the circuit when you squeeze the clutch.

What rpm does it idle at when warm, too low an idle will make any rattles worse and make it more likely to stall.

cheers
jon

[alec868]

it idles at 900. ill check the switch. thanks

[Court750Cafe]

@Alec you ever fix that rattling noise?? My bike has been doing the same thing. Higher RPM's and no noticeable rattle but when idling around 1200 rpm, i hear a louder rattle.. I adjusted the cam chain tensioner twice but nothing happened. I feel like the cam chain is loose and its needing to be tightened. Can you get at the spring for the cam chain tensioner easily?? How can you check if the cam chain is loose or methods to tighten it other than loosening that bolt and retightening?