Triumph Adventurer 900 Backfire Issue

[InstructorAl]

Hello to the hive mind that is triumphtalk!

I'm hoping that you wonderful lot can help me get to the bottom of an issue with this adventurer that is literally making me pull my hair out!!

I've recently picked up a 1996 triumph adventurer 900 that was in a rather sorry state. It ran like absolute garbage and maintenance was pretty much non existent. It now runs and it's a totally different bike....but.... I can't get past the last mile to get her back on the road in all her glory!

To start with what I've done so far:
New genuine airbox and secondary
New spark plugs
New ignition coil
K and n air filter
100 main jets (gone back to 95's because it was running way too rich)
Set the air screws to 1 1/2 turns as per Haynes
Fresh fuel lines and filter (currently running off an aux tank)
Coolant change and flush
Valve clearance check
Carb refurb (float heights checked) - main needle currently set to second notch from the top to try and lean out a little but now I'm back on 95's it may be a little lean.
Carb synchronisation
(Plus your standard brake rebuilds, chain and sprockets etc)

Now, unlike when I purchased it, it now holds an idle and it's keen to pick up when throttle is applied instead of cacking it's pants. However, on idle I'm getting an Intermittent backfire from the right hand exhaust (cyl 2/3). I suspect this is worse when hot, but I haven't let it cool down enough to be 100% sure. It also backfires a treat when you hold the rpm in the main jet region too (1/3 to 2/3 throttle).

Ignition coil resistance is in spec, no change when I swap the coils around, HT leads are good, likewise plug caps.

I'm absolutely hung up on this being a carb issue but I'm literally banging my head against a wall and nothing seems to make any difference at all.

I'm really hoping someone has some idea on where I can go next from here before I end up pulling my beard out along with my hair :'-D

 

[Qship]

I'm no expert on these and sounds like you've done mostly all that should be needed. Is the charging system working 100% and is there a crank/cam position sensor that could be bad. Have heard some act up once warmed up.
Hope someone with better knowledge on these older triples chimes in soon with some insight for you.
Also have you checked the Hinckley triples section for a possible situation like yours?

 

[Wire-Wheels]

I have 2 of these old machines. I don't think you said which carbs you have, but it being a 96', I would assume it has Mikuni 36BST's. Those carbs have an adjustment for main jet needle height. Easy to check. Pull the vacuum top off and carefully slide the assembly out. Check which notch your needle is on. Make sure all the carbs are set the same. You may have to raise them up a bit. Also you do not be to rigorous about adhering to that 1 1/2 turn setting on the pilot jets. Set it where it likes to run. My 900 Legend bogged ever so slightly if I lugged it a bit going around slow corners until I got it up to 2 1/4 turns. Happy tinkering. ...J.D.