I have a real fondness for the CB750. In the late 80's, I was about 6 to 7 years old, and every single morning my father, to warm up his bike, would give me a ride around the block before he went to work. I thought his motorcycle was the coolest thing on earth!
Hi Peter, easy way to determine if fuel or electrical is to swap 1 & 4 plug leads around. If the problem follows to No 1, then you know it’s electrical. If problem stays at No 4 you know it’s fuel.
Too much fuel in number 4, do you see the rich smoke when you rev it the other ones are clear. To much fuel keeps it cool in that cylinder so check the float height again and check to see that the jets are the right ones. Very nice bike you have there and it brings me back to the days when I I had a few of these.
that was what I was thinking the entire video, it's prolly the idle jet he showed at the end like he suspects. I was surprised though the spark plug wasn't black but maybe the fuel is washing it clean.
I concur with Darwin, lots of smoke from no.4 stack indicating excess fuel that's why it's running cooler than 12&3. I had similar issues with my carbureted Honda VTR250 & it was the idle jet.
I think you're right about that idle jet being the cause if number 4 comes to life when the revs rise. If it was over-fueling due to a too high float level it would be over-fueling across the rev range, not just at idle...
Hi Pete. I´ve just gone through this process with a boredout 500 K1 and I´m using Your vids along with hackaweek to compare what I did sorta right contra screwed up :) Great build amigo!! My carbs where a chapter for the memoryalbums but I got them sorted after alot of headache. I thing 4th is flooding and if I were You I would change the intakeboots just because every other vital thing is touched. Looking for a twin for a new project.
Hey Peter, don't forget there is a local company that does kits and jets etc for the old bikes. If you need the company name again let me know but well worth a call. Great website too.
When I rebuilt my gsx 1100 and first started it it sounded like that, and after a test run it didn't feel right, checked the cam chain and it was out by a bit, once sussed it just rolled over on idle real smooth.
When you go to fit the hand grips to the bars i'm told that the easiest and best way to fit them is to spray the bars and inside the grips with women's hair spray Hope this helps you. Regards Neville
Is the problem not linked to the smoke on number four? Leaky valve stem seal? Hope you solve it soon and looking forward to the 350 videos. These Honda fours are very addictive!!
I did not see you adjust the idle mixture screws; the ones that point straight down at the engine side of the carbs. Hard to access with carbs on bike, you need a really short screwdriver. It sounds like #4 is turned too far out. Turn it in by 1/2 turns. Also, do you have a set of vacuum gauges to synchronize? I have the mercury carb stix. Works dandy.
I am trying to get the same bike running and I have a question. What do you do with the tubes coming out of the bottom of the carbs? I cannot get them to stop leaking fuel and I am confused as to what to do next. Thanks!
Just wondering about the effects of using the gear change lever as your jumper cable earth point, is there a risk you could burn a bearing race in the selector/gearbox area with the high currents? Ray
smells like fuel issue,not electric, because if first cylinder is working correctly, the fourth should be ok too, only difference is in wiring from coil to spark. Maybe try to switch condenser in ignition circuit, but is easiest to switch whole circuit from points to spark plug.
I have a real fondness for the CB750.
In the late 80's, I was about 6 to 7 years old, and every single morning my father, to warm up his bike, would give me a ride around the block before he went to work. I thought his motorcycle was the coolest thing on earth!
Hi Peter, easy way to determine if fuel or electrical is to swap 1 & 4 plug leads around. If the problem follows to No 1, then you know it’s electrical. If problem stays at No 4 you know it’s fuel.
Honda fours have a sound all of their own and that is a sound I have not heard for 30 years!
Too much fuel in number 4, do you see the rich smoke when you rev it the other ones are clear. To much fuel keeps it cool in that cylinder so check the float height again and check to see that the jets are the right ones. Very nice bike you have there and it brings me back to the days when I I had a few of these.
Darwin Dwelle I agree,
that was what I was thinking the entire video, it's prolly the idle jet he showed at the end like he suspects. I was surprised though the spark plug wasn't black but maybe the fuel is washing it clean.
LOVE the sound when you started it...reminds me of a V12 Merlin sound!
The engine is healthy, the rest is fine tuning. Great job.
Great series of videos. Always lovely to see knackered old bikes brought back to life again. Nice one.
love the straight pipes. Cheers
very good. 95-100% takes lotsa times. comments look helpful. i noticed rich on 4 also.
AAAAW yes , had a long day , so this will help , thank you as usual peter
I concur with Darwin, lots of smoke from no.4 stack indicating excess fuel that's why it's running cooler than 12&3.
I had similar issues with my carbureted Honda VTR250 & it was the idle jet.
I think you hit on it, I bet it is the Idle jet. GL I am sure you will sort it out alright!
So good to hear it run Peter, and a god send here, save me from the blessed football, 350 looks tantalising ..
Love your videos.Got a 77 P in restauration.Good luck solving the fuel problem.
Well done!
So close but you know what you're doing you'll get it sussed 👍👍
No worries Peter. You'll figure it out. Did look awfully rich when you raised the RPM's. Fantastic fun!
I think you're right about that idle jet being the cause if number 4 comes to life when the revs rise. If it was over-fueling due to a too high float level it would be over-fueling across the rev range, not just at idle...
A nice dinner, time to relax! Oh look CB750 Restoration Part 22 time!
oh my that engine sounds incredibly quiet - nice job
damn it sounds good with those short pipes
Still a good result.
peter hi you are a legend 10/10 bob in uk
Hi Pete. I´ve just gone through this process with a boredout 500 K1 and I´m using Your vids along with hackaweek to compare what I did sorta right contra screwed up :) Great build amigo!!
My carbs where a chapter for the memoryalbums but I got them sorted after alot of headache.
I thing 4th is flooding and if I were You I would change the intakeboots just because every other vital thing is touched. Looking for a twin for a new project.
Hey Peter, don't forget there is a local company that does kits and jets etc for the old bikes. If you need the company name again let me know but well worth a call. Great website too.
When I rebuilt my gsx 1100 and first started it it sounded like that, and after a test run it didn't feel right, checked the cam chain and it was out by a bit, once sussed it just rolled over on idle real smooth.
sounds fine on rev up so would be checking for vacuum leak ,check vacuum with gauge on all carb manifolds.
yep definitely a fuel issue my first thought was a stuck open exhaust valve but then I there would have been fire coming out of it.
When you go to fit the hand grips to the bars i'm told that the easiest and best way to fit them is to spray the bars and inside the grips with women's hair spray Hope this helps you. Regards Neville
The thing that got me is the output shaft (front Sprocket) appeared to be turning clockwise . At 12:00
Any part 23? To see it sound?
At the moment, it sounds a bit like a Spitfire Merlin, :o)
Is there no such thing as an electronic points replacement for this ?
Sync the carbs with vacuum gauge
Is the problem not linked to the smoke on number four? Leaky valve stem seal? Hope you solve it soon and looking forward to the 350 videos. These Honda fours are very addictive!!
That's Awesome
I did not see you adjust the idle mixture screws; the ones that point straight down at the engine side of the carbs. Hard to access with carbs on bike, you need a really short screwdriver. It sounds like #4 is turned too far out. Turn it in by 1/2 turns. Also, do you have a set of vacuum gauges to synchronize? I have the mercury carb stix. Works dandy.
Also of course way easier if you disable 2&3 first. Tune #4 while it's running. Have to turn the idle up to get it to run on one to two cylinders tho.
lol- oh great thought I would have to wait a week to see it run
Yeah the cylinder on the right has a problem...
Hi Peter. Can you swap the idle jets between 1 & 4, or is that so much work you may as well be replacing them all at the same time? All the best mate.
I am trying to get the same bike running and I have a question. What do you do with the tubes coming out of the bottom of the carbs? I cannot get them to stop leaking fuel and I am confused as to what to do next. Thanks!
Just wondering about the effects of using the gear change lever as your jumper cable earth point, is there a risk you could burn a bearing race in the selector/gearbox area with the high currents?
Ray
i think its flooding number 4 because the float level is too high
Yep my thoughts too do you see the smoke out of 4?
smells like fuel issue,not electric, because if first cylinder is working correctly, the fourth should be ok too, only difference is in wiring from coil to spark. Maybe try to switch condenser in ignition circuit, but is easiest to switch whole circuit from points to spark plug.
you have smellavison? how does that work ?
kinda.. next time ill use "i think its a" ;)
If compression and spark are good, it can only be fuel.
0490231352 I would love to chat at some point
Hello mate any reason for fitting the "stubby pipes" as opposed to letting the exhaust vent through ports?
Yes warped valves don't ever do it!!!
Darwin Dwelle what?
Oh the poor neighbours....
:)
check valve clearance again
MUSIC !!!!!
Some swearing and foul language should sort that little problem.
Without pipes you can't tune it, I wouldn't even run it