Access to mixture screws

For all your mechanical queries, or for sharing your mechanical know-how. Also used for arguing about which oil to use...

Access to mixture screws

Postby Budgie » 20 May 2019, 13:00

Hi all
First post on the forum for me.
I've just bought a 1995 C5 zephyr 750 and have had the carbs off for cleaning.
The bike stood for several years before my ownership.
It now running fairly well but I want to make some adjustments to the mixture screws while the bike is running.
1 2 and 4 carbs are relatively easy to get at ( I brazed a brass nut onto a small screwdriver bit ) but the number 3 carb above the cam tensioner is proving almost impossible to adjust due to lack off access.
I really dont want to have to remove the carbs just to tweak this last screw.
Any advice
Thanks
Budgie
 
Posts: 4
Joined: 19 May 2019, 04:41

Re: Access to mixture screws

Postby hugojose » 20 May 2019, 22:55

….The cam chain tensioner is just in the way. Either, you would have to remove the tensioner..not so easy, but a lot easier than removing the carbs....or try something like a one hair tweezer leg cut off and bent. Is tricky but possible. I used to do it like that.

......I have since replaced the factory tensioner with a manual one. Not because it ever failed, but because it makes maintenance, and access to the carbs in place, so much easier, once you understand how the the automatic factory tensioner works.
hugojose
 
Posts: 57
Joined: 05 Sep 2017, 01:43

Re: Access to mixture screws

Postby Freddy » 21 May 2019, 02:20

Budgie wrote:It now running fairly well but I want to make some adjustments to the mixture screws while the bike is running.


If you want to have the bike running to help guide you on the correct mixture setting by listening to the engine 'beat' (like a car down draft carby for example) you may be disappointed.

The only noticeable difference from altering the mixture screws with the bike stationary I have ever observed is a change in idle speed. The 'beat' at idle remains identical no matter the mixture screw setting (once you raise or lower the idle speed to reestablish the correct idle speed).

And you can't use idle speed as a guide because the idle speed always increases as the screws are opened, and the opposite as you close them. I believe this rev change is a result of changes to the volume of air/fuel being allowed in, not a change to the AFR itself.

I have found the best setting for the mixture screws to be that which minimizes (and nearly totally eliminates) the engine 'bog' at take of around the 2000 rpm mark. Something that requires a bit of trial and error and testing on the road.
Freddy
 
Posts: 394
Joined: 06 Sep 2017, 12:06
Location: Sydney Australia

Re: Access to mixture screws

Postby Budgie » 21 May 2019, 05:05

Thanks for the info.
I realise now that my main problem was trying to make the adjustment while the engine was running and hot.
Having read several posts regarding the mixture settings I decided to settle on 2 1/12 turns out for 1 and 4 and 2 3/4 for 2 and 3
It was then a whole lot easier to get my hand in with an even more cut down screwdriver bit and make the changes. Did about 15 miles last night and it runs like a dream.
Happy days
Budgie
 
Posts: 4
Joined: 19 May 2019, 04:41

Re: Access to mixture screws

Postby Freddy » 23 May 2019, 04:00

Budgie wrote:Thanks for the info.
I realise now that my main problem was trying to make the adjustment while the engine was running and hot.
Having read several posts regarding the mixture settings I decided to settle on 2 1/12 turns out for 1 and 4 and 2 3/4 for 2 and 3
It was then a whole lot easier to get my hand in with an even more cut down screwdriver bit and make the changes. Did about 15 miles last night and it runs like a dream.
Happy days


Good to see you got it sorted.

As you discovered its near impossible to adjust the screws with the engine hot. I find a short but reasonably broad screw driver 'bit' from a set of hex tools designed for an electric drill to be the best tool for to job. Is about 1 inch long, and the hex drive end gives a reasonably good grip between finger and thumb.
Freddy
 
Posts: 394
Joined: 06 Sep 2017, 12:06
Location: Sydney Australia

Re: Access to mixture screws

Postby Budgie » 30 May 2019, 05:07

Freddy
I drilled out a brass nut and soldered it to the bottom.of the screwdriver bit
Centre punched some marks on the flats of the nut so I knew where I was with the adjustments and it worked a treat.
Thanks all
Budgie
 
Posts: 4
Joined: 19 May 2019, 04:41


Return to Mechanical

Who is online

Users browsing this forum: No registered users and 2 guests

cron