Triumph Rat Motorcycle Forums banner
  • Hey everyone! Enter your ride HERE to be a part of October's Bike of the Month Challenge!
1 - 20 of 23 Posts

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #1 ·
Well it appears I will be doing the Keihin carb upgrade. I am not planning to change the stock air box (it does have a K&N filter). It also has TOR's and will be using the proper carb rubbers for the Keihin's. My question is should I automatically put in 40 pilots in instead of 38's? I also will be setting the fuel screws 2 1/2 turns out and stock 17 1/2mm float setting and stock 98 mains.

The reason I would want the larger pilots as I have heard rumors of poor starting and lean conditions with the stock setup. Does it improve just by adjusting the fuel screws?

Any help and comments would be greatly appreciated!:)
 

·
Registered
Joined
·
444 Posts
I would go with the 38's first, see how it runs, then install the 40's and compare the difference.
 

·
Premium Member
Joined
·
6,462 Posts
The 40s will probably reduce the popping on overun with the TORs. But that's not really about correct ratio mixture in the cylinder, more a question of what's in the exhaust when the 'dead' spark fires.
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #4 ·
Really not worried about the popping what I am concerned about is drivability. I guess what I should have asked everyone is how did your bike run with stock jetting and Keihin carbs and no air box mods?

Thanks:)
 

·
Registered
Joined
·
694 Posts
jets

Brg-Bird: Just my 2 cents........
1. How does it run now with 38 pilots and 98(?) mains?
2. Is it hard to start in colder weather?
3. Is there any stumble or stutter to quick throttle application below 3500 rpm?
4. You have good coils (Nology), and fresh spark plugs.

As a rule, Triumph sets up their carbs to meet emission requirements (lean), and noise requirements (airbox, large). They also build them to a dollar budget so they can make a profit. When we decide to make them run better, we can sometimes make them run worse unintentionally, with the worst case being engine damage from too lean a fuel mixture. So, that said, always go richer than you think when you make a mod, especially if you aren't planning on dyno testing. From what you've said, I would suggest 42 pilots, 100 or 105 mains, and possibly 1, .015 shim on the main needles. Your fuel mixture screw setting in the 2.5-3 turns open depending on exhaust popping when coasting in gear, and your altitude. And, anytime you remove the carbs to make these changes, ALWAYS sync them after re-installation. When I first got my 98 TBS, these were the exact settings I used, with my altitude here in Okie flatland at about 1100 feet. Bike ran perfectly and dyno'ed at 72 hp at the rear wheel. Good luck! Tommyturbo2
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #7 · (Edited)
Carbs are in, stock jetting with 38 pilots and 98 mains with fuel screws set ~3 turns out. I had a shop I trust run it with a "sniffer" and balanced the carbs. Surprisingly the stock jetting was right on with wot actually somewhat rich. It runs very well with no stutter or stumble from below 3500 rpm (or above!) and starts (almost) immediately with full enrichment and it now requires the enrichment to be turned to 1/2 after ~20 seconds and off after about 1 minute.

It has not been *cold* (cold starts in the low 60's), plugs are fresh and have stock PVL coils...

I took it on a test run today (130 miles) in windy weather and testing the power at rpms and different gears and it performs fine with good low end and midrange grunt and a little whoop above 6K! Fuel economy was very acceptable at 45 mpg which reinforces to me the jetting is good...

I would imagine not all bikes will run as well with this setup as no two engines are exactly the same IMO.

Thanks for your input Tommyturbo2!:)
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #8 · (Edited)
I sincerely apologize for digging up this old thread but feel I have given you folks some bad information. After riding the Bird for almost two thousand miles the carburation was not quite what the last post intimated. Most of it is correct except The Stumble. A number of members of this site have stated that the Keihins do not have the throttle response that the Mikunis have. I believe this to be correct although it may have more to do with settings in my case.

The reason for all this is I actually have become disappointed in the performance especially at lower rpm when a quick snap of the throttle would produce a delay/stumble. So after a lot of careful contemplation (studying other posts and carb theory) I decided that the pilot jet may be too small or the slide does not respond soon enough. After working up the gumption today I did install one 1/2 mm shim under each needle and took it for a nice 70 mile ride. It is a nice improvement with most of the delay/stumble at low rpm gone. Throttle response is much better. Also with these Keihins there would a sort of power "surge" around 6000 rpm and now the so-called surge seems to have moved lower to around 5500 rpm. Some of you may call me crazy!:)

My question is what have any of you done to correct this issue? Did you shim your stock needles like I did? Did you put in larger pilots jets from the stock 38's?

Denny, you stated earlier your bike had this issue and am especially interested in your response.:)
 

·
Premium Member
Joined
·
3,797 Posts
Mine has an extra hole in the front airbox, same diameter as the one on the other side. Velocity Stacks on those intakes about 8 inches or so long. I think those probably don't make any performance difference, or very little.

Jetting Summary:
118 mains
40 Pilots
DynoJet needles with clip in second notch from top
Mixture screws 2 1/4 turns out

Farkling Lunacy during my Year of the Wrench - Triumph Forum: Triumph Rat Motorcycle Forums


Judging from the change in fuel mileage, I think mine is running a little rich now.
It is down from 40 - 42 now it is 38 - 40. Although I still get the occasional tank near 50? go figure??

Prior to those mods if i gave it full throttle suddenly at any rpm below about 3-3.5 K it would stumble before taking off. Now it just starts to pull. Even in 6th gear at 2K it will pull smoothly all the way through the rev range.
 

·
Registered
Joined
·
694 Posts
pilots

BRG: Your pilots are too lean, go to 40's or 42's. Throttle response below 2000 rpm is controlled by the pilot jet, mixture screws settings and main needle height as it start to lift out of the main jet. Your Keihins should respond every bit as well as the mikunies do. tommyturbo2
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #11 ·
Mine has an extra hole in the front airbox, same diameter as the one on the other side. Velocity Stacks on those intakes about 8 inches or so long. I think those probably don't make any performance difference, or very little.

Jetting Summary:
118 mains
40 Pilots
DynoJet needles with clip in second notch from top
Mixture screws 2 1/4 turns out

Farkling Lunacy during my Year of the Wrench - Triumph Forum: Triumph Rat Motorcycle Forums


Judging from the change in fuel mileage, I think mine is running a little rich now.
It is down from 40 - 42 now it is 38 - 40. Although I still get the occasional tank near 50? go figure??

Prior to those mods if i gave it full throttle suddenly at any rpm below about 3-3.5 K it would stumble before taking off. Now it just starts to pull. Even in 6th gear at 2K it will pull smoothly all the way through the rev range.
Denny,

I read your post that you thoughtfully shared a link to and remember now reading it before. One question, is that like Al Stewart's song Year of the Cat?!

Where did you get your Dynojet needles? Where they part of a jet kit and are they similar shape (or the same) as the stock needles?

I appreciate the info and am thinking that I may need to go up one pilot jet size and maybe install an adjustable needle...:)
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #12 ·
BRG: Your pilots are too lean, go to 40's or 42's. Throttle response below 2000 rpm is controlled by the pilot jet, mixture screws settings and main needle height as it start to lift out of the main jet. Your Keihins should respond every bit as well as the mikunies do. tommyturbo2
Thank you, sounds like sage advise!:)
 

·
Premium Member
Joined
·
3,797 Posts
Denny,

I read your post that you thoughtfully shared a link to and remember now reading it before. One question, is that like Al Stewart's song Year of the Cat?!

Where did you get your Dynojet needles? Where they part of a jet kit and are they similar shape (or the same) as the stock needles?

I appreciate the info and am thinking that I may need to go up one pilot jet size and maybe install an adjustable needle...:)

A dynojet kit came with the bike when I bought it. Actually those needles were in it when I got it.

2010 was quite a bit of wrenching and fabrication here in my garage, and 2011 was not far behind. I spent lots of time on the Husqvarna and on the sidecar frame. And that reminds me i need to rewrite that thread since all the pics are dead in that one.

900 THUNDERBIRD SPORT 98-04 1 DJT-5116 £118.88 KEIHIN CARBS ONLY
still available ........

DynoJet Jet Kits

I'm sure you could find it somewhere on this side of the pond.

EDIT:
As far as the shape of the needles, They all look pretty similar to me, but I am sure there is some subtle difference.
 

·
Registered
Joined
·
92 Posts
Thanks for bringing this thread back to the top. I'll be installing my Keihins shortly, possibly next week, if the weather holds up and I don't get too focused on the Norton.
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #15 ·
Ok after a good long ride yesterday in much cooler temperatures (mid to upper 50's) I am pretty well convinced to go up one size in pilots to 40's. I do have a question in how this will affect steady state cruise 4-5000 rpm in mixture and economy? I am not riding a motorcycle for economy but have dealt with some poor mixtures in the past (for a variety of reasons, poor setup from a PO and worn Mikunis) and do not want to subject the old girl to any more. My thoughts are that it is a combo factor of pilots and needle/needle position that the bike will be drawing off and larger pilots will not have a detrimental effect. Any thoughts are greatly appreciated!:)
 

·
Registered
Joined
·
92 Posts
brg ...as Tommy and others state...this is on my 98 TBS..40 pilots, 100 mains , kn filter with removed/toolboxed secondary airbox....and small 1/2 hole in the right side of the primary airbox... 1" drilled out stock mufflers, sealevel...6 speeds mind you... 55 mpg at 60 mph... The bike starts ,idles low speeds...,accelerates perfectly....having said that; I am about to put in 110 mains and drill/hole the air box more....
 

·
Registered
Joined
·
694 Posts
fuel mileage

BRG: Your fuel mileage should be pretty good. I've had a set of FCR 39 Keihin flat slide racing carbs on my 98 TBS for about a month, and I've been getting just over 40 mpg even with a heavy right wrist. Getting ready to install speed triple cams, and raise the rev limiter to 9800 rpm! Love this bike! tommyturbo2
 

·
Premium Member
Joined
·
5,170 Posts
After a lot of experimenting I found out that the best throttle response came with Keihin carbs and the restricted Mkuni rubbers, along with #90 main jets. it runs perfectly. I also have TORs and a K&N panel filter.

I also went with #40 pilot jets, but as the pilots are adjustable via the mixture screw there is a certain amount of overlap between adjacent sizes.
 

·
Registered
Joined
·
2,026 Posts
Discussion Starter · #20 ·
1 - 20 of 23 Posts
Top