miss at 3.8K

[billy192]

Strange but good day to day. went to do my test run and went about 12 miles to tescos with her in doors on the back and sur enough it starts spluttering at 4K. i was miffed to say the least.

when pulling away from lights i took it to 7K in each gear and boom no miss, the min i roll the throttle back comes the miss.
when she was getting a few things i took off the overflow pipes to each float bowl, not sure why but I am at the point of tiring anything.

on the way home a went on a little de tour. i went through maisemore to the  M50 and down to a place called Newent which was 15 miles on the M50 and drove at a steady 60 -85 all the way down the M50.

brill. great runs sweet.
now i am going to go out with the tubes back on to see if it comes back.
Billy
not sure what difference these over flow pipes off make but hey its running goooooood

[Green1]

Sounds a bit strange was one pipe pinched?

Mick

[K2-K6]

I was wondering before you posted if you'd checked those overflow pipes, and as mick says they could be pinched at the bottom end of them.
As a point of interest they are named "overflow" pipes and we all now that with a sticking float/valve then the fuel of course comes out of them and helpfully drips onto the floor without covering the bike itself with petrol.
What they are not described as is a more critical function, they leave the float bowl at atmosheric pressure if they are clear. The difference between the vacuum in the carb throat and the status in the float bowl causes the fuel to be pulled into the engine at the rate dictated by the jet sizes, but if you artificially alter the the float bowl pressure then the change in difference between the two areas causes an unwanted change to the jetting calibration so the engine no longer runs as intended......happens if you change altitude as well, which is why carbs struggle to adapt.
Hopefully billy, you'll have got to the bottom of it.....tenacity rewarded i think, well done if it's definitely ok.

[billy192]

i can blow through them but not freely as there are several zip ties. fingers crossed
Billy

[Johnwebley]

Strange but good day to day. went to do my test run and went about 12 miles to tescos with her in doors on the back and sur enough it starts spluttering at 4K. i was miffed to say the least.

when pulling away from lights i took it to 7K in each gear and boom no miss, the min i roll the throttle back comes the miss.
when she was getting a few things i took off the overflow pipes to each float bowl, not sure why but I am at the point of tiring anything.

on the way home a went on a little de tour. i went through maisemore to the  M50 and down to a place called Newent which was 15 miles on the M50 and drove at a steady 60 -85 all the way down the M50.

brill. great runs sweet.
now i am going to go out with the tubes back on to see if it comes back.
Billy
not sure what difference these over flow pipes off make but hey its running goooooood

hope you have sorted it,I live close,and use those roads between Hereford,Newent,Glos,and Ledbury,
these are perfect for sohc s

[Bryanj]

They are until I come round the corner with an artic full of 96,000 glass bottles going to UBL at ledbury!!!

[Bitsa (Ralph Wright - RIP)]

Have my doubts on that but I do hope its cured Billy's bike.I hope Mick gives it a go you never know.I still think its down to modern shit fuels bring back good old leaded.If its not raining tommorrow I will take mine off and see if there is any difference.
Cheers
Bitsa

[K2-K6]

If yours are clear Bitsa, it should make no difference to the running I guess. Billy's seemed to have the problem and then with just the tubes removed but exactly the same fuel supply it appears to be ok, guess we'll have to wait for his final verdict on that to see what he gets.

I know what you mean about the fuel though Bitsa, I've got quite a few small motors and the fuel left in the carbs deteriorates quite quikly and seems to go "crusty" in small jets if left. Doesn't seem to happen on motors using pre-mixed two stroke fuel though, somehow it seems more stable with oil in it.

[billy192]

Well did a bit of trouble shooting.  connected up #3 and #4 overflows and after about 6 miles started to miss. put my hand down an disconnected #4 (only one i could reach) went smooth all through 4-5-6 K connected it back in a lay buy  miss at around 4K. so now i have all but #4 overflows connected with no missing. i did a plug chop at just over 4K and this was the result.



number 1 looking in my humble opinion as OK




number 4 looking rich again in my opinion a bit rich but not much.

this coupled with the fact that i am unable to connect the overflow on #4 suggests something is not right with this carb.

Billy

 

[Bryanj]

Billy there is a vent to atmosphere at the top have you checked this/these?

[billy192]

Bryanj do you know where the vent is?

Billy

[Bitsa (Ralph Wright - RIP)]

Billy
I think Bryan means the vents between carbs 2 and 3 they should have short pipes attached which hang over the airbox.Have you checked the overflow tube is not blocked on the carb you think has problems?If the carb is over filling and this tube is blocked the extra fuel has got to go somewhere.It can flood into the airbox or get sucked in by the engine and probably cause miss fire and rich.Maybe worth a look.
Cheers
Bitsa

[billy192]

when i had-my carbs back from the guy that cleaned and rebuilt them there was a tube joining #3 and #2 sealing them should these vet out to the air box?
Billy

[RGP750]

http://www.cmsnl.com/honda-cb750k6-four-general-export-dkdm_model14382/partslist/E19.html#results
Hi Billy the two pipes, see link numbered 31 should be over the top of the air box ,not joined together.
 Rich

[billy192]

fantastic news, well to me it is. fond the vents and as i described there was a clear pipe joining them (making it air tight)
removed the pipe and connected up the 4 over flows and bingo great acceleration all the way to 90ish
just went to Swindon and back its like a different bike it idles smoothly also.
billy, happy chappy