Triumphrat

tetsusan · 06-11-2009, 09:21 AM

Greetings,
I'm a new owner of a '98 TB with approx. 6K miles. I had thought that 1998 was the year that TB switched from Mikuni to Keihin, but to my chagrin upon getting my new bike home I noticed the Mikuni name on the carbs.
The bike runs ok, but has abit of a rough idle and occasionally dies. I also noticed more of a gas smell from the exhaust (running rich?) and an ever so slight gas leak from the top of one of the carbs. Otherwise no problems up to redline, but I had thought there would be a little more oomph past 5K rpm.
My question is, do I bite the bullet early and just go straight to a Keihin setup like so many others on this board? Or are the Mikuni's worth the trouble to get working right. I was hoping to add TORs and tweak the jets in the future, but am wondering if Mikuni's are the right place to start.
Thanks in advance for any advice.

Slinky · 06-11-2009, 10:44 AM

The problem with the Mikunis is they are prone to wear, especially on the need jet which is a brass insert- it tends to go oval. The throttle slide is plastic and they they get scuffed up pretty easily. Lastly, the float bowls are only held on by two screws, and they have been known to warp.

I switched to Keihins on my 98, and I sold the Mikunis on ebay for what the Keihins cost, so the net cost was nil.

In theory you would also want to switch the inlet rubbers but I am using the originals, everything fits fine. The Mikuni rubbers are restricted to suit the jetting on the Mikuni carbs. The Keihin carbs have larger main jets so the unrestricted inlet rubbers would be a better match,

R0B · 06-11-2009, 10:45 AM

I would suggest that the carbs could do with a look at...........6k in 11 years isn't a lot........I've just replaced the float bowl seals and fuel hoses on my 98 tbird, as they has perished and were leaking, and my bike has 18k on.

The carb inlet rubbers on my bike were the restricted type, and I certainly noticed a difference when I changed them to the unrestricted type. I have to say that my bike starts and runs beautifully, and I have no intention of changing them unless there is a problem. my bike is totally standard.

Rob

tetsusan · 06-11-2009, 11:11 AM

Thanks for the advice, but that's the rub, the whole intake was gone through by a Triumph mechanic within the last 2 years (~ 1000miles ago).
If I was to go the Keihins route, any sources beside Ebay or Craigslist? There's a dearth of used setups stateside.

MickMaguire · 06-11-2009, 11:58 AM

It sounds like the carbs just need a clean

However if they were "gone through" by somebody who doesnt know what they are doing the jetting could now be wrong. At 6k there shouldnt be anything much wrong with the carbs - they are pretty much new.

CLean the filters, jets and float bowls out, check the air filter (or replace with a K&N) - give her a tune (air screws and carb balance) and you'll be set for many happy miles.

tetsusan · 06-11-2009, 12:42 PM

Thanks, I think some part of me was just looking for an affirmation that this is not a major issue.
I had a Triumph TR3 in my youth that traumatized me with endless mechanical/electrical gremlins. My poor TB may just be the recipient of my PTSD projections, but fortunately there is therapeutic help here on forum.
I'll take another more discerning look/review of the Mikunis, I was wanting to look into less restrictive inlet rubbers(Rob's suggestion) anyway.
Cheers!

MickMaguire · 06-11-2009, 01:26 PM

Just ask the guys on the T3 sport touring forum about Mikunis - they love em. However, they do foten swap to Keihins when they wear out but just for availability of parts

cafetbird · 06-12-2009, 12:38 AM

Heck, I love my Mics - they have been great for over 40k on this bike. I dpon't know about the comment on the float bowls - mine have 4 screws in them. The diaphragm covers only have 2 screws, which is great for quick adjustements while on the bike...

If the bike has only gone 1000 miles in 2 years, they may need a good going through again, that is about it!

cafetbird · 06-12-2009, 12:39 AM

Heck, I love my Mics - they have been great for over 40k on this bike. I don't know about the comment on the float bowls - mine have 4 screws in them. The diaphragm covers only have 2 screws, which is great for quick adjustements while on the bike...

If the bike has only gone 1000 miles in 2 years, they may need a good going through again, that is about it!

tpeever · 06-12-2009, 02:07 AM

I don't have any experience with Keihin carbs but do have a Mikuni single carb conversion on my Commando (VM series carb) and Mikunis on my 96 T-Bird. Mikunis seem like solid, well-made carbs to me and yours should be basically brand new. I think your major problem is that your bike has spent most of its life sitting around and the carbs need a thorough cleaning. I bought a 96 T-Bird with 4500 miles on it last fall. Needless to say, the carbs needed complete disassembly and cleaning. You will also need to balance your carbs to get the bike really running well.