Triumph Rat Motorcycle Forums banner
  • Hey everyone! Enter your ride HERE to be a part of this month's Bike of the Month Challenge!

1 - 7 of 7 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter · #1 ·
I have a 2005 Bonnie Black, it is stock with the exception of NARK, AI, and D&D exhaust. I bought the bike used with everything but the NARK. When I got it, the bike ran great, at least I put a little over 1000 miles on it and I never notice any issues. I’m not usually one to tinker with things, and I guess I should have left well enough alone. But I didn’t, I had the NARK done and the carbs rejetted by my dealer when it was in for new tires and the 6,000 mile maintenance. I had read quite a few posts indicating that open exhaust with a stock airbox was counterproductive, so I broke down and went for for the NARK to complete the package.

I didn’t notice anything wrong right away because most of my riding is two up and just cruising two lane country roads. In that mode the bike makes plenty of power without flogging it and runs smooth as can be. But I ran it from 0-60 aggressively the other day and realized that the bike only works great until you try to use more than half throttle.

When I try to open the throttle beyond about half way and wind it out through the gears hard the bike acts like it isn't getting enough fuel. Does that make since? Should I just take it back to the dealer or is there something simple I could try first?

Thanks for your help!

JB
 

·
Registered
Joined
·
20 Posts
Discussion Starter · #3 ·
To me it seems more like a stutter. It doesn't feel like it is under too much load, and I can recreate it by doing 75-80 in top gear and then trying to poen the throttle the rest of the way. It seems to start at about 4500 RPM regardless of what gear I'm in. Sorry if I'm not providing the right info, I don't have any experience with tunning.

JB
 

·
Registered
Joined
·
151 Posts
Sounds to me like you need to have the dealer redo their jetting work, (I'm guessing it's lean on the main jets yet) if it's jetted properly you should be able to ride in 4th gear at 2 to 3 thousand rpms and roll the throttle wide open. It should pull strongly all the way to redline. (there's several good threads in the twins tech archives)
 

·
Registered
Joined
·
212 Posts
The same thing happened to me. Since you are losing power when you give open it up, the likely cause is clogged main jets, which kick in at 3/4 throttle. This problem can arise at any time with the crappy gas we have today. The longer the bike sits with bad fuel in the carbs, the more gunk will start sticking in the tiny jet openings. THe problem went away for me after I took my carbs apart and cleaned both the main jets and the pilots.

Taking the carbs off and removing the jets is not really hard -- if I can do it, anyone can. This site explains the procedure very clearly;

http://www.dinqua.com/Triumph/carbs1.html

I suggest you try it first before letting the dealer do exploratory surgery on your wallet.
 

·
Registered
Joined
·
3,588 Posts
The carbs can easily be rejetted without removing the carbs. Just remember to hold a wrench on the "needle jet holder" (the thing the main jet screws into.

It has been my experience that the dealers mechanics know VERY little about jetting a 790 with open pipes and no airbox. They like to make the needles way too rich and the mains WAY TOO lean. I would not even think about running smaller than 150 main jets on a 790 with your setup. Look below and see the size my 790 runs and it was set up on the dyno.
 

·
Vendor
Joined
·
2,431 Posts
+1 on the dealers ability to re-jet modified twins.

You need to find out from your dealer what main jets he put in, if he shimmed the needles and if he touched the pilots. With this info the knowledgeable guys on here can say if your running rich or lean and also suggest new jetting.
 
1 - 7 of 7 Posts
Top