Need help - Original handle bar VS throttle with Mikuni 26mm carb

CT70 K0

CT70 K0

Member
Hi everyone,

I am running into some questions.
I am going to install a 108Cc engine with 26mm mikuni carb into my OG CT70 K0, and keep using the original handle bar + throttle.

However I have been told today that the throttle on the OG handle bar will not open enough for the mikuni carb.

Does anyone know how I could solve this problem?

thanks for help.
 
CT70 K0

CT70 K0

Member
futher research I found that throttle might fit my original handle bar:
DSCF1708.jpg

Anyone having any advise on this?

thanks.
 
kirrbby

kirrbby

Well-Known Member
If you try the original cable, you can figure out what needs to change for it to work. Then have a new cable made at your local bike shop. They could add a adjuster into the cable somewhere for finer adjustment. You can get a Mikuni cap with a adjuster on it too I think.

The slide on throttles are a good option too if you don't have qualms about non original look. One thing I've found with those is they stick out past the bar a bit. Making the right bar longer than the left. If you email DRATV and give a good description of what you're doing he may be able to recommend a solution...likely a throttle and cable combo.
Who did you buy the carb from? Maybe they can help.

Btw, having a cable made is pretty reasonable as far as price...don't be scared.
 
6

69ST

Well-Known Member
There's ~23-24mm slide travel inside the groove in the handlebar and that's tight with a VM22. It does work, with everything perfectly adjusted and functioning as it should. For a VM26, I'd be looking to add another 3-4mm of travel; 3 would probably do the job but that's cutting things close and there are variations in production tolerances.

First step, determine how much farther the throttle pipe can be rotated without the internal helix coming out of the slide (the metal piece that actually pulls the inner cable). Having the slide go past the end of the helix is dangerous...the throttle will be stuck at, or near, wide-open and will not return without disassembly. That would be...ummmm...inconvenient while riding :shocked:. If you can get it to safely move the slide another 5-6mm, then start by cutting 3mm from the RH end of the cable slide. If that gives you enough travel, you're done. If not, decision time.

There's ~8mm of metal at the thin side of the slide, you want to leave at least 4mm intact. If you can't get enough travel within these parameters, it might be possible to extend the groove by 1-2mm...just be 100% certain that the helix remains engaged with the slide BEFORE modding the handlebar. A :censored: up slide is cheap, easily replaced. A handlebar, not so much.

The only other place to get a little more travel is at the cable anchor/cable slide interface. However, there's only ~2-3mm additional clearance possible. There's not much metal at this end of the slide; I'd not remove more than 1mm, at most. The cable anchor can be thinned by 1-2mm. Proceed with caution, the threads are just shy of 4mm deep.
 
6

69ST

Well-Known Member
If you prefer an aftermarket external throttle setup, go for it. That gives you far more options (these bikes have garden-variety 7/8" handlebars) and they're basically all plug & play. For some reason, I was under the impression you wanted to keep the OEM, internal twist-grip throttle assembly.
 
CT70 K0

CT70 K0

Member
racerx said:
If you prefer an aftermarket external throttle setup, go for it. That gives you far more options (these bikes have garden-variety 7/8" handlebars) and they're basically all plug & play. For some reason, I was under the impression you wanted to keep the OEM, internal twist-grip throttle assembly.
Click to expand...

I initialy planned to keep the original throttle however when I saw the takegawa throttle setup I though it would add a good period correct style modifiction with the 108cc engine.

this is the build bike I am into:

http://lilhonda.com/webboard/showthread.php?t=19586&page=4

13086824_10154801445902892_953529208107044451_o_zps5muchmby.jpg
 
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loopiemclooperson

loopiemclooperson

Active Member
image.jpg

I may be late to the party but I have a few ct70's with the vm26 mikuni and the ko style throttle.
No issues getting it to open all the way. I used the steel and brass portions of the original carbs adjuster and the mikuni adjuster to make a hybrid that gave me the correct freeplay and pull. Hope the picture helps.

I do love the look of that takegawa piece though.
 
6

69ST

Well-Known Member
If the inner cable stick-out length is too short, which is the most common problem when upsizing a carburetor, the simple solution is removing a couple of coils from the outer cable housing. If it's too long, otoh, you'd need to clip the excess inner cable length and replace one of the end ferrules.
 
CT70 K0

CT70 K0

Member
Hey Guys,
so I made some trial this evening installing the original throttle and original throttle cable with the Mikuni carb.
After measuring my grey cable (inner 876mm, outer 789mm) I found that it was the long version.

And the inner cable was too long so I need to find an additional spacer to get it work.

I have tried what ''loopiemclooperson'' was suggesting in previous responses, see his picture below, but I could not get the top ferrule stay aligned with the bottom ferrule.
So How have you been able to keep them aligned bot together?

If I am able to get this work I think this will solve my problem

attachment.jpg
 
Last edited:
loopiemclooperson

loopiemclooperson

Active Member
CT70 K0 said:
Hey Guys,
so I made some trial this evening installing the original throttle and original throttle cable with the Mikuni carb.
After measuring my grey cable (inner 876mm, outer 789mm) I found that it was the long version.

And the inner cable was too long so I need to find an additional spacer to get it work.

I have tried what ''loopiemclooperson'' was suggesting in previous responses, see his picture below, but I could not get the top ferrule stay aligned with the bottom ferrule.
So How have you been able to keep them aligned bot together?

If I am able to get this work I think this will solve my problem

attachment.jpg
Click to expand...

In the picture I used the original VM 26 adjuster (middle), screwed to the original 70 adjuster (top) Then I cut the threaded portion from the original ct70 carb cap to use as a nipple they both sit into. (The portion with the lock nut) If that makes sense?

I have one of those 90 degree adapters from tbolt also but does not leave enough free cable.

The adjuster on my other bike was made exclusively out of an old ct70 carb cap. I cut the steel tube off flush with the aluminum cap. Removed the brass adjuster and threaded the steel portion into the vm26 cap. I then cut it to the appropriate length and threaded the cut end with a 6x.75mm die. Reinstalled the brass adjuster and went for a ride. I can send you the link to some pics I posted on the other mini forum if needed?
 
CT70 K0

CT70 K0

Member
loopiemclooperson said:
In the picture I used the original VM 26 adjuster (middle), screwed to the original 70 adjuster (top) Then I cut the threaded portion from the original ct70 carb cap to use as a nipple they both sit into. (The portion with the lock nut) If that makes sense?

I have one of those 90 degree adapters from tbolt also but does not leave enough free cable.

The adjuster on my other bike was made exclusively out of an old ct70 carb cap. I cut the steel tube off flush with the aluminum cap. Removed the brass adjuster and threaded the steel portion into the vm26 cap. I then cut it to the appropriate length and threaded the cut end with a 6x.75mm die. Reinstalled the brass adjuster and went for a ride. I can send you the link to some pics I posted on the other mini forum if needed?
Click to expand...

Yeah please post either the link or picture of the 90 degree adapter you fabricated. I think I wil try to go this route.
thanks again for help.
 
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