WOT response??

[bikertucker]

1975 CB750 K5, If I suddenly snap the throttle wide open, the engine stalls. Same as if I shut off
the ignition switch. Happens any gear, even at idle. If I back the throttle off a  little, all comes back
to life. Carbs have been sync'ed by me, and had been taken to a shop for cleaning by the PO before
I bought it. I have a fair amount of carb experance, just not with these. I would suspect sudden
flooding but see no sign of flooding out or smoke out of the exhaust when it comes back to life.
Any thoughts would be great.

[Lucky 1]

IT is not WOT that is the issue.

The issue is poor throttle response upon sudden acceleration. Its lean.


But you did not tell us what the intake and exhaust systems are.
You only told us it is a K5.
Also look for some numbers on the carbs.

It probably needs larger idle jets.
A lot of people think all they have to so is increase the main jet.
The main jet mostly controls WOT. That is not that important because very
liittle time is spent at WOT.

[sgtslag]

What about the accelerator pump?

[TOOLS1]

K-5 should have round top carbs which do not have an accelerator pump. I have to agree with Lucky. Try upping the pilot, and moving the clip on the needle down a notch.
TOOLS

[Lucky 1]

Only K7 and K8 had accelerator pumps. Thank god.

[bikertucker]

Bike is total stock, as if just off showroom floor. No accelerator pump is correct. Will remove carbs
and check /adj soon.

[shinyribs]

Roundtops will only take so much. If you do really crank on the throttle hard,they will die. You kinda gotta roll into them. Especially in neutral. Now,once in gear and rolling,if you have some engine speed up (2,000 rpm+)then it should take it just fine

[bikertucker]

These carbs need a 17mm  and 10mm wrench to sync, 10mm for lock nut and 17mm to hold adjustment
nut. Snap throttle open at any gear, any rpm, even in neutral. Engine responce is dead, same as turning
ignition switch off, No stumble, no slow responce, just dead. Roll back on throttle, comes back to life.
Compression is good, but engine responce is not strong. Rebuilt a 1975 Honda CB500T parallel twin
this past spring and right now I think the 500T would take the CB750. 500T pulls strong and
hits 80mph quick, CB750 responce is ( Hold on a sec, I'll get there). Seems running lean is a good call.
When throttle is snapped open and it dies till throttle is rolled back, no smoke or rich mixture smell
is noted as I think would happen if rich condition was the cause. Though I've not owned anything with
these carbs before. Just by removing the float bowl, looks like an after market rebuild kit was installed.
Could you please let me know what recomended jet sizes would be. Kit may be part of my problem.

Thanks All for your info

[bikertucker]

Before taking off carbs. tried leaving the choke on to the point just before it started to
cause the engine to stall. snapped open the throttle and problem was gone. engine ramped
right up like it should. Proves things are lean. After carbs off found clips were on the fourth
notch down already. Hope moving clips down to last notch does the trick. Also found the tip
of each slow jet was plugged. The cleaning of the carbs. must have happened a while ago.

[Lucky 1]

Putting the choke on and checking the throttle response tells you all you need to know.

But wait until the engine is fully warmed up then do a test for throttle response.

[bikertucker]

Engine was warmed up when preformed test with choke. Will move clips down last notch tomorrow.

Thanks Lucky 1

[bikertucker]

Back together and problem about 90% gone. But engine has to be 100% warmed up to respond correctly.
The air box boots need replaced , two of four so hardened and shrunk they have a hard time reaching
the carbs. That may be what I need to correct last 10% of the throttle responce??
Any one know of a  source for  new air box boots?


Tim

[icerigger]

Got mine from Cycle Parts Nation. A tad pricey at $14 each, but when the old ones disintegrate what else ya gonna do?

[bikertucker]

Thanks for the info Icerigger. I'll check them out. It's either $14.00 ea. or trying to find really large
shrink tubing.

[Johnnylevi]

you could probably check ebay, too. I know for my 81 its only about $54. Roughly the same price, but i think shipping is way cheaper.

[bikertucker]

Local Honda  shop still supports the air box boots. $8.75 ea. when ordered on line.

[bikertucker]

Local Honda  shop still supports the air box boots. $8.75 ea. when ordered on line.

[Lucky 1]

Maybe Honda is getting the message.
 Customers feel they (HONDA) are useless as far as getting parts and the owners of the dealerships are greedy. That is why so many aftermarket companies are doing well. And once those companies get going there will be no need for Honda for CB750 parts.

[Lucky 1]

Honda needs to put motorcycle people back in the design dept.

Motorcycles are turning into transformer toys. Throw away items for the wealthy children.
No repairs ....just use and throw away.

[Lucky 1]

IT is amazing that you got a reasonable price from the Honda Dealership!!!
Are you sure you are not just getting the air boot clamp for $8 bucks.