Valve setting 81 cb750k dohc

X7eater

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Good work.....we learn so much from these old bikes. Just need time and patience! #3 at .003" looks a bit tight, and if you had a smaller shim to bring it up to .005"-.008" then just change that one....but if not, I'd ride it as-is for another 1-2000 miles and them check them again.
 

fg1972

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Just checked my notes from when I did mine. Target was 0.127mm (0.005") with min/max range of 0.102 - 0.152 (0.004" - 0.006"). So yes, definitely worth proceeding with getting the gaps within tolerance. The fun part, you can try playing musical chairs by rearranging what you have to get as many as possible in spec, then just replace the ones you need. There was a guru on here "AMC49" who was a wealth of knowledge on these bikes, sadly I think he stopped contributing due to some kind of issue with another member(s) however many of the useful posts are still here.
 

Rampton

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Just checked my notes from when I did mine. Target was 0.127mm (0.005") with min/max range of 0.102 - 0.152 (0.004" - 0.006"). So yes, definitely worth proceeding with getting the gaps within tolerance. The fun part, you can try playing musical chairs by rearranging what you have to get as many as possible in spec, then just replace the ones you need. There was a guru on here "AMC49" who was a wealth of knowledge on these bikes, sadly I think he stopped contributing due to some kind of issue with another member(s) however many of the useful posts are still here.
Thanks 👍☺️ for the advice have been reading threads and noticed this guy from America, he knows some stuff and would be a hero to this site it's a shame he isn't contributing anymore. Thanks again for the advice will finish valves and put covers back on. Then start on the dreaded carb problem haha 😃. What doesn't kill you makes you stronger. See you around me old pal. 🇬🇧🇭🇲🇺🇲
 

Rampton

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Good work.....we learn so much from these old bikes. Just need time and patience! #3 at .003" looks a bit tight, and if you had a smaller shim to bring it up to .005"-.008" then just change that one....but if not, I'd ride it as-is for another 1-2000 miles and them check them again.
Yep going to order them, the clearances will be bigger than I wanted but if I can get the carbs sorted and get her out on the road for a good blast then check the valves on a regular basis change them out if they alter ( more wear). Thanks for the great advice keep up the good work. It's nice that bikers help each other to keep these old birds on the road. Stay safe🇬🇧🇭🇲
 

Rampton

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Just checked my notes from when I did mine. Target was 0.127mm (0.005") with min/max range of 0.102 - 0.152 (0.004" - 0.006"). So yes, definitely worth proceeding with getting the gaps within tolerance. The fun part, you can try playing musical chairs by rearranging what you have to get as many as possible in spec, then just replace the ones you need. There was a guru on here "AMC49" who was a wealth of knowledge on these bikes, sadly I think he stopped contributing due to some kind of issue with another member(s) however many of the useful posts are still here.
IMG-20210919-WA0003.jpg
 

Rampton

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Good work.....we learn so much from these old bikes. Just need time and patience! #3 at .003" looks a bit tight, and if you had a smaller shim to bring it up to .005"-.008" then just change that one....but if not, I'd ride it as-is for another 1-2000 miles and them check them again.
IMG-20210919-WA0003.jpg
IMG-20210919-WA0003.jpg
 

Rampton

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Good work.....we learn so much from these old bikes. Just need time and patience! #3 at .003" looks a bit tight, and if you had a smaller shim to bring it up to .005"-.008" then just change that one....but if not, I'd ride it as-is for another 1-2000 miles and them check them again.
Hi x7eater hope all's well. Just letting you and fg1972 know that tappets all done started bike and still got same problem. So I am going to start a thread in the carb section asking how to strip and clean the carbs. As always your advice would be greatly appreciated 😊👍 stay safe🇬🇧🇭🇲
 
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Rampton

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Putting carbs back on can be a pain as you know. A trick that makes it a lot easier is to heat the rubbers with a heat gun. The jet under the rubber plug is the troublesome low speed or idle jet. They are either pressed in or have a slot in the top which can be unscrewed. Putting the guitar string in there and also in a tiny hole just in front of the throttle flap with lots of carb cleaner. Not sure if have this carb manual that is really useful. http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
Hi fg I've tried opening the carb manual you sent me but it won't open!!!?
 

Rampton

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Putting carbs back on can be a pain as you know. A trick that makes it a lot easier is to heat the rubbers with a heat gun. The jet under the rubber plug is the troublesome low speed or idle jet. They are either pressed in or have a slot in the top which can be unscrewed. Putting the guitar string in there and also in a tiny hole just in front of the throttle flap with lots of carb cleaner. Not sure if have this carb manual that is really useful. http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
Input the link manually, everything I need to know is there thanks fg! 42 pages just finished reading them there's a lot to take in but there's a lot more than I did when I changed jets and other. A lot more cleaning to do especially on idle circuit. Thanks again brilliant 👍😊.🇬🇧🇭🇲
 

JB hogg

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Morning fg ready for the world now haha,Getting the carb bank off is a bad enough job but did before when I had it cleaned. Had a nightmare refitting them with new rubber boots it took me hours, is there an easy way??? I did slide the air box back. I changed mixture screws and two jets marked #100 second main jet and the other marked #68 primary main jet. Plus the needles and rubber tipped float valves. Set the floats with a micrometer to 15.5 mm. Carbs are vb52s and under the rubber plug on each carb is a pressed in jet which im thinking that these are the slow jets???? Didn't know how to remove them. I did put the guitar string in but couldn't see where it came out or even if it did. Thanks for the great advice keep it comming I will get her running if it kills me. I have a CBR 1997 fireblade that needs some time on the road and a 1996 triumph adventurer Hinckley 900 but the best is the cb750. Thanks again me old mate (Yorkshire saying) look forward to hearing from you soon.🇬🇧🇭🇲
You can not sumpley put the air mixture screws at 1.5 turns out you have to adjust each one to get the highest idle on each cylinderbwhen you adjust the airscrew you should have your bike idleing low so you can tell when your adjusting the airscrew by how fast or slow it's idleing when adj turn the air screwvon eachvcylinder to get the highest idle for that cylinder then when done on all 4cylinders then use the big idle adjustingbscrew that changes all 4 carbs set to manufactures specs for idle then you shouldn't have any of the cylinders running to o lean or too rich at idlebthis should correct any cylinder differences on heat if it's lean it will really n hot so you right chen up the hot cylinders but t you should have to adjust air screws again after the 1st time adjusting them each for highest idle
 
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