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I used tiny brass washers to raise the needle on a Harley I had a few years ago. From memory, they were 0.5mm (0.020"") thick.

They are available from any hardware shop...

Cheers,

Roden
 

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One wee update following some full power, max speed runs is that on my bike i found that decelerating from 130+ mph down to 40mph and then rolling the throttle back on caused the engine to buck and feel like it was missing on one or more cylinder.

There`s no need to panic as all you need to do if you do find this happening is to turn the pilot air mixture screw out another half turn so it`s then 3 full turns out and you`ll be all systems go with no hesitation at all. I tried this today and no matter how hard i tried i couldn`t get it to do it again. Oh! The hardship of bike testing :D
 

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Right that's it I'm getting a set....well I'd already made my mind up but that has confirmed the idea :)

Several things will happen :

1. better MPG
2. Rejet the carbs to allow decibel killers to come out of the pipes
3. All the other stuff aje has just mentioned

Anybody want to buy a set of Mikunis this winter ?????
Well I just bagged a set..I'd been outbid on a few sets over the last few months or so..!! These are 15 thou miles old off a Thunderbird Sport. Just in time too because the Sprint is playing up and I think it's carbs again, so the plan is to get the old Mikuni's off the S3 onto the Sprint and get these onto the S3...Tempted to do the Pod set up Matt descibes..?

Ah well got a little time to decide
 

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so the plan is to get the old Mikuni's off the S3 onto the Sprint and get these onto the S3...Tempted to do the Pod set up Matt descibes..?

Ah well got a little time to decide
Time to source a different set of airbox-to-carb rubbers, keihins are smaller, and the mikuni clamps are too large if you're going to use the T3 airbox which is the minimum required to get them running halfway unless you embark on pods. As I learned recently (I'm ntb sometimes) that the airbox plays a significant role in the grand scheme of things. I had them on for a test drive sans airbox and the it was just terrible, would barely run.

Something to be said for keeping the number of new variables small to sort out changes.

Interesting to watch for success stories on these carb and filter swaps as there's always something to learn ;)
 

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Time to source a different set of airbox-toi-carb rubbers, keihins are smaller, and the mikuni clamps are too large if you're going to use the T3 airbox which is the minimum required to get them running halfway unless you embark on pods. As I learned recently (I'm ntb sometimes) that the airbox plays a significant role in the grand scheme of things. I had them on for a test drive sans airbox and the it was just terrible, would barely run.

Something to be said for keeping the number of new variables small to sort out changes.
A lot of people say the same thing about the airbox yet matt.speedtriple has been successful with his pod conversion. I am going to have a crack at it, if it doesn't work, I can always revert to original!

Good score btw Mot ;)

Cheers,

Roden
 

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When you can get the three pods for £24 from most bike shops then it`s got to be worth a go as it saves so much hassle getting the carbs on and off.

As for setting mixture screws then all you have to do is to pop off the centre pod, loosen off the intake rubber clamps, slide the carbs back a bit and then tilt forward and there they all are ready and waiting for you.

No stress, no hassle and you even get to keep the skin on your knuckles :D

Give it a go Mot as i`d be interested to see what you think of my input. :assimilate:

By the way Mot, cheers again for the shock and although still a bit soft then it`s so much better than that other saggy arsed new one i`d got. :bow:
 

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Hey Matt, your posts are great and very informative. Thanks! In my case the timing couldn't be better. I've got a set of Keihins in the mail and I will likely be fiddling with them over the next week or so. I'm running Micron exhausts, 3 into 2, as in the picture on my Trident, with pod filters. Do you think I would need the 152 mains or would 140 be ok? Also, did you use the same for all cylinders, or was the center different? Thanks in advance
Bernie
 

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Well I just bagged a set..I'd been outbid on a few sets over the last few months or so..!! These are 15 thou miles old off a Thunderbird Sport.
Hi Mot,

I have also got hold of some Keihin CVKs from a 'classic' model. Mine are from a Legend, but I believe they are the same as the Thunderbird Sport. I have been thinking about fitting them to my Sprint, and done some "research" prior to fitting them in the future. Without modification, they are not suited to the cams fitted in the 98ps engines, etc....

There are 4 internal parts that are different, as standard. The main jet & pilot jet, as we can guess, and the Vacuum Piston & its' Spring:
- The vacuum port in the piston is different, increased from 2.5mm to 3mm. So by using a 3mm drill bit (eg. Dynojet Mikuni kit style) I hope to avoid buying new vacuum pistons.
- I am guessing that the Spring has a different rating, and so I plan to buy these prior to fitting (part# T1241021).

I am some time off doing this upgrade (other priorities), but hope my "research" helps you.

This is an excellent post by Aje, and especially with the jetting information from Matt.

Lechyd da,
Geoff
 

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Cheers Geoff...

The part numbers will come in very useful ta. Bernie also gave me a heads up on the drilling and spring, makes you wonder how many people are just bunging them straight on ??? Carbs have turned up yesterday and look in good nick...

I would like to go for pods I think and will hopefully kill 2 birds with one stone on the re jet, I've now got the decibel killers out of the Scorpions and would needed to have re jetted anyway.

Matt is the drilling, spring thing part of your set up too ??

With any luck by the time this thread has run it could make a good point of reference for the CVK's
 

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Hi,

A couple of photos that may be of interest?

The first (intake) shows the head to carb connectors:
The Keihin connector is part# T1240086. (Fyi, the Mikuni connector in my photo is actually a restricted connector [identified by the dimple] taken from my '95 Hinkley Thunderbird which internally reduces the normal 36mm down to around 29mm, but the unrestricted connectors [now fitted] are identicle otherwise).

The second shows the carb to airbox connectors:
The Keihin connector is part# T2200001. (Apologies for the state of the Mikuni connector - it came with a spare airbox from Eb*y).

I guess you could retain the Mikuni intake connectors to mount the Keihins, but it looks to me that the spigot retaining depressions are slightly different and the Keihin connectors would provide a more secure hold on the Keihin CVKs.

The Mikuni airbox connectors should not be used with the Keihin CVKs, if retaining the airbox. I think you can see the difference in size on the carb openings shown in the second photo?

Ciao,
Geoff
 

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For info to those that will drill out the vacum hole in the slide here in the US a 3mm drill bit might not be easy to find. (slower cam Keihins had a 2.5mm hole vs the 3mm hole in the longer cam kehin slides found on the sport bikes). What is available are precision bits conforming to what the industry refers to as "wire gauge size" though there are probably dozens of wire gauge sizes depending on where in the world you are. I chose an Irwin bit from the local ACE Hardware store. A #32 drill bit is a little small, a #33 drill bit is a little large. I'm using a #32 and will make the hole a little loose. Normal 64th increment bits are way off.

B
 

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If you don't mind going mail order, McMaster-Carr stocks metric drill bits. I just looked & they have 17 options in 3mm drill bits!

I just ordered a left-handed drill bit & some A4 stainless bolts from them; they're really good for hard-to-find stuff like that.

Cheers,
-Kit
 

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Hi folks,

Just read some of the latest posts and yup the slide lift hole need to be 3mm rather than the 2.5mm the cruisers used.

I note that in some country`s then getting a 3mm drill bit could be a problem so just use this size and you`ll be close enough 3mm = almost 1/8 inch as the speed of lift is also determined by the spring strength as well as induction.

As for the difference between the cruiser and sports slide springs then i really wouldn`t worry about changing them as CV carb slide lift is determined by intake induction pressure and you really wouldn`t notice the difference between them.
 

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Hey Matt, your posts are great and very informative. Thanks! In my case the timing couldn't be better. I've got a set of Keihins in the mail and I will likely be fiddling with them over the next week or so. I'm running Micron exhausts, 3 into 2, as in the picture on my Trident, with pod filters. Do you think I would need the 152 mains or would 140 be ok? Also, did you use the same for all cylinders, or was the center different? Thanks in advance
Bernie
Hi Bernie,

The difference between 140 and 152 main jets is a lot and i feel you`ll be running weak up at the top end of the revs with only 140`s fitted.

I note you say your already running pods but you need to be aware that the air intake side of the keihin carbs are a lot smaller than the mikuni`s so you`ll need to fit a smaller set.

Jets are exactly the same across all carbs as using pods then there`s no problems with restricted airflow.

Cheers, Matt :D
 

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Hi,

I thought this picture may be useful, showing the 3mm hole needed if using the 'classic' model Keihin carbs.



There are several sites with information about this mod (for other motorcycles), many quoting 1/8 inch drill bit - concurring Matt's feedback, if you cannot get hold of a 3mm drill.

Also added is a picture showing the different spigots (is this the right word?) for you to make-up your own mind about the intake (head to carb) connectors.... [Keihin left/Mikuni right].


I think I am going to have to accelerate my plans, and 'phone Allens for some jets next week. I am keen to try these carbs now....

Cheers,
Geoff
 

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A new twist

I just pulled apart a set of Keihins from a 1999 Legend and guess what, they had the 3mm hole! I expected to find the 2.5mm hole in the slide.....The previous owner said they came off a stock bike with the milder cam in place. Guess that some Keihins in later bikes were identical (except for the jetting) to those in the sport bikes.
 

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I just pulled apart a set of Keihins from a 1999 Legend and guess what, they had the 3mm hole! I expected to find the 2.5mm hole in the slide.....The previous owner said they came off a stock bike with the milder cam in place. Guess that some Keihins in later bikes were identical (except for the jetting) to those in the sport bikes.
Well Bernie, now you've made me pull the top off mine....and guess what ???

3mm hole too, again off a stock TBS. So the spring must be right too :)

Shopping list is now filters, jets, breather filter, new fuel lines, already got a fuel filter & a new throttle cable, carb rubbers & a few shiny nuts & bolts...
 

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Hi,

I wonder if the later 'classics' did go to 3mm? Mmmm....I will check mine tomorrow too.

Apologies Bernie & Mot. I had not meant to mislead you, as you can see from my attached Thunderbird Sport fiche copy.

I'll let you know what I find in my carbs.

Geoff


*** Update - Have now checked my carbs, and the vacuum port is 3mm as well. My Keihins came from a Legend. ***
 

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No apologies necessary Geoff, we are all on a bit of a learning curve here and it's a good thing we have discovered this.... anyway it was a good excuse to get on the S3, get down to screwfix and buy stuff !!
 
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