Triumph Rat Motorcycle Forums banner

1 - 17 of 17 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
On my 08 Thruxton I installed the British Customs package that included Predator pipes, AI removal and airbox removal. I rejetted with the supplied jets. Everything installed fine but the bike is usually difficult to start, takes a long time to warm up, and idles erradically once it is warm. At stop lights the idle will suddenly creep to 1500-2000 rpm by itself I either release the clutch a little and it drops back down, or I adjust the idle knob, which works temporarily. Quite often there is a popping sound and loss of power, like its backfiring thru the carb, especially when cold. None of this was happening before I put the new pipes and air filters on.

Is it running super lean or what is going on? Should I be adjusting the idle mixture screws or what? Any ideas? Thanks
 

·
Registered
Joined
·
305 Posts
With that package you should have 140 mains 42 pilots and mixture screws 2.5 turns out ( you need the D tool for that ). All so make sure you don't have any air leaks, like the black caps are on your manifold, exhaust has RTV where you put the cans on, your pods are on right, manifold clamps are on right. Sounds like your sucking air some where. I hope you get it worked out, this package is great. If you lived in San Antonio I would lone you the D tool
 

·
Registered
Joined
·
2,741 Posts
Based on what you have written I would suspect a vacuum leak somewhere; it would be a really good idea to check all connections & vacuum caps for loose fastners, cracks, &/or leaks before you do anything else.

What is the current setup for mains, pilots, & pilot screws?
 

·
Registered
Joined
·
305 Posts
Hey dillonhead let us know if your get this problem fixed, want to know what you think about the new mods
 

·
Registered
Joined
·
7 Posts
Discussion Starter #7
I took a look at the bike today. I ran the bike and sprayed a little starter fluid around all the suspect areas including the manifold boots, carbs, etc, and and made sure to inspect and snug up the clamps holding it all together. I did not find any air leaks.
All the vac lines seem to be where they should be. There aren't any plugs missing (except the one on a metal rod piece that connects the carbs which I was told to leave unplugged with AI removal on the '08 model).
I double checked my jets and its running a 140 mains and the stock 40 pilots. I tried setting the mixture screw to 2.5 turns out but the issue still persists.
Think changing the pilot jets to a 42 is gonna do the trick?
 

·
Registered
Joined
·
2,741 Posts
I took a look at the bike today. I ran the bike and sprayed a little starter fluid around all the suspect areas including the manifold boots, carbs, etc, and and made sure to inspect and snug up the clamps holding it all together. I did not find any air leaks.
All the vac lines seem to be where they should be. There aren't any plugs missing (except the one on a metal rod piece that connects the carbs which I was told to leave unplugged with AI removal on the '08 model).
I double checked my jets and its running a 140 mains and the stock 40 pilots. I tried setting the mixture screw to 2.5 turns out but the issue still persists.
Think changing the pilot jets to a 42 is gonna do the trick?
I don't have experience with the 08 "metal rod", so I defer to BC for that.

You used starter fluid?
Did you check the AI bolt plugs?
Check the rubber vacuum port caps (a/k/a squirrel condoms)? Those buggers can crack easily.
Did you have the diaphram caps off, to say change or shim the needles?
Did you put the intake manifold rubbers on properly? (they are directional)
I suggest at the very least least pulling the carb caps & make sure that the diaphram rubbers are properly seated. Then pull the pods & check to see that the slides raise smoothly & evenly.

The problems you are having sound like more than what would be cured by simply upping the pilot jets by 1 size.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #9
The metal rod I speak of is a piece that goes between the carbs, its got a T shaped piece in the middle that had a hose going to some emissions junk under the tank.
There is a vac hose that goes from one carb to the other, a plug on the left manifold, and a hose from the right manifold that goes under the bike into some mysterious emissions canister. Other than that, I don't see much else in the way of vac line on the carbs.
I have not opened the top on the carbs. I didn't remove the carbs from the bike at all and haven't even messed with taking off the boots.
I took off the airfilters and it seems like the popping/backfiring sound may be coming from the right carb. The slides on both vibrate like hell when I rev it up. Is that unusual?
I haven't checked the AI plugs yet but I will do that as well.
I didn't really think upping the pilot jet would solve this but is that a good thing to do anyways?
 

·
Registered
Joined
·
305 Posts
yes you need to put the 42 pilots in and turn the mixture screws out. You have a open system and your taking in to much air
 

·
Registered
Joined
·
1,394 Posts
Find your right jetting . Buy a jet kit and play around . You can't really go with what everyone else is running because most bikes run different . For example I had 138/40s and was good to go with the same set up .
Get the jet kit and find that sweet spot.
 

·
Registered
Joined
·
2,741 Posts
...I took off the airfilters and it seems like the popping/backfiring sound may be coming from the right carb. The slides on both vibrate like hell when I rev it up. Is that unusual?...
Let me explain further...what I intended to communicate was to take off the pods & gently raise each slide by hand (finger) with the motor off. The slides should each raise smoothly, but under constant spring pressure, with no binding. If they don't, somthing is wrong on the top end of the carb. If they are OK, then you've ruled out a potential issue.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #13
with the motor off I verified that the slides do indeed move freely and without getting hung up on anything. I also checked the chain tension while going 60mph on the freeway. heheh. I'm gonna grab some 42 pilot jets tomorrow at the local shop, play around with the mixture screw and see what happens.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #14
I got the 42 pilot jets today at Cascade Moto Classics and swapped them out. Quick and painless job because I already replaced the screws with hex bolts.
I turned the mixture screws out to about 3 turns and it seems to have done the trick. The popping/backfiring is gone and the idle doesn't hang when you rev it anymore.

I absolutely love these mods. If anyone has any question whether or not to ditch the stock airbox and exhaust, let me tell you it is worth every penny! Its rediculous what a difference in performance it makes. And the pipes sound amazing too.
Thanks to everyone who read my thread and helped out!
 

·
Registered
Joined
·
7 Posts
Discussion Starter #16
When I had the stock 40's in there I had them set to 2.5 turns out after installing the pipes and pods. I have no idea what they were at with all the stock parts.
 

·
Registered
Joined
·
964 Posts
2 1/2 turns out on the idle mixture screw is the stock setting for Bonnevilles and Thruxtons, according to the Factory manual. My problem was on the other end of the scale; too rich at idle/low RPM. The tuner/mechanic went back to the #40 pilot jet,and opened the idle mixture screw to 2 3/4 turns out. The idle mixture screw regulates the air in the circuit; the more turns out the leaner the idle mixture becomes. Every motor is different, even with the same mods. To know for sure, find a competent tuner w/ a dyno to set it up. ---James.
 
1 - 17 of 17 Posts
Top