Thunderbird 900 Carb Refurb

I've posted a few times sorting out various issues with my once reliable and beloved thunderbird 900. Bike was overheating. Fan Switch is fine and I've had the thermostat out, testing it in a saucepan. It might well have been stuck closed as it seemd to stick when i was testing it but seems ok now. Maybe the bike overheating cooked it? Im leaving the thermostat out of the bike for now just to see whether it stops overheating. However I can't test the bike because it's now running like crap, oiling up the right spark plug.

Carbs are a strong possible source of gremlins. Anything else would be worryingly expensive. So I have got em on the bench for a thorough cleaning and a stern talking to.

I've messed about with old 2 stroke outboard carbs many times but this is the first time I have grappled with the Tbirds carbs.

They came out OK. Leaving the throttle cable on the carb and removing it at the grip was a great tip (thanks Carl Rosner Triumph). I had a problem removing the choke cable, seemingly unable to turn the rounded end tube connector out of it's metal mounting point. Embarrassingly i eventually I had to bend the metal surround. Not ideal. If there is a trick to it I'd love to hear about it.

On the bench two of the carbs came apart without issue. The very last screw on the third float bowl is giving me trouble. I'm soaking it with penetrative oil and will have to cut a slot as the cross head has dissolved. I am really hoping not to havr to drill it out. Maybe heat it up with a soldering iron to break the grip?
I assume it is possible to buy new screws, but one thing at a time.

The carbs intakes, where the black plastic vertical gate comes down, looked pretty grubby but the internals look clean. The inside of the float bowls looked clean. I've bought some liquid carb cleaner (as in not a spray can) and will soak everything once disassembled. It was interesting to read that ultrasonic cleaning isn't always the gold standard it seems to be as the liquid does not get into the narrow passages. I'll be using the carb cleaner and forcing liquid into the channels with a syringe.

I was tempted not to touch the idle screw though as I don't want to have to take it to a garage to get it balanced. I know I could count the turns, but perhaps just not touch this part?

I need to take the needle and jet bits apart of course. Are there any issues I should watch out for there?

I need to check the casting tonight to see whether the carbs are mikuni or keihin carb.

What carb kit should I get? I know I should get new gaskets and the little rubber washers. But some kits seem to have needles etc and cost £70 ish.

I guess I'll need to inspect the needles I currently have as I disassemble. Can I eye ball a worn needle and jet?

The carb rubber manifolds that connect from carb to engine block look a bit ropey . Iinternally they seem fine but I guess it makes sense to replace those now.

 

Thanks. Will have a look. I have been watching a few videos e.g. Superbike Surgery. Poor quality gaskets and o rings seem a common issue so Id rather pay a couple of quid more and not have problems in a few months.

 

Ok, I got the last stubborn screw off eventually.
Penetrating oil, a slot cut in the head and a bit of persuasion with an impact driver got it off (yes I was gentle).

I'm documenting my carb clean journey this as I'm new to this. Perhaps if i make a terrible decision someone could alert me. Thank you.

I need to replace the cracked rubber manifolds (carb to engine) and Ill go with Sprint as per advice here. My instinct is to go with the original 30mm diameter rather than the 36mm, which apparently give more top end power at expense of mid range. I'm doing this because as a naked bike she is fast enough for my needs and I do a fair bit of town riding so quite like enough grunt to move the ol girl along. Has anyone got experience of the 36mm?
https://www.triumphparts.co.uk/prod...thunderbird-900-cylinder-head-to-carburettor/

Im also buying an o ring kit from Sprint.
https://www.triumphparts.co.uk/product/mikuni-carburettor-seal-overhaul-kit/

Assuming all goes well, I will no doubt need to balance the carbs on reinstall.
Balancing kits seem to start at £40.
https://motorcyclepartswarehouse.co...xs7p1Yv8AqSYaY8eHetxP9YYPmQChnckfgzdCTNCGcDV3

I did see a YouTube video where they used glass bottles. Seemed wonderfully simple and potentially more accurate than a bottom price carb sync kit. Has anyone tried this?


Cheers lads.

 

Ok. I've had the carbs on the bench for a while. Thoroughly cleaned. Not much evidence of fuel varnish tbh. The slides were caked in black oily dust. Apart from that no issues. I did buy o rings but only used the little one to the left of the plastic membrane as Haynes said this must be done. The others all looked fine.

The mikuni carb needle and float assembly does not come apart so I just gave it a blast of air. Comment above suggested adjustment but I have not done this. No sign of leakage though.

I did buy new carb manifolds. The rubber tubes from carb to engine looked cracked but were actually ok on the inside.

Refitting carb onto engine went ok. But fiddly but pushing and wriggling got it in eventually.

Getting airbox into carbs was a bit more fiddly. But we got there . I think.

Engine runs on all three cylinders but is popping at idle.
Does this mean too rich or too lean?

I did not touch the three pilot jet screws on disassembly but maybe I need to readjust the mix. Note the pilot jets are the small brass tubes inside the carb. The pilot jet screws are mounted onto e body and are accessed from the outside . They adjust the fuel mix. However I don't see why this would now be changed so will leave it for a moment.

I suspect I've either made a mistake rebuilding the carbs or refitting carb to the bike.

I'll check the seals on the carb manifolds but I'm pretty sure they are ok. Maybe the connection between box and carb is not right. Would that cause popping?

I'll check the Haynes manual again. It all seemed to go together right but maybe I missed something.

I started all this because the right plug was oiling up. I put a new one in to test it and she started well yesterday. We shall see today whether she starts up easily again.

My best guess is the box isn't on right.

 

OK so box was not on correctly.

That folded lip was in the blind spot. It's on the bench now with a lolly stick holding it open,which hopefully will remould it slightly.

Getting the airbox on is tricky. I think I will try to fit the front part of the box onto the carbs, so I can see whether they are seated right. Then I'll fit the filter and bolt the back half on.

Incidentally I've bought a K&N filter. The current one looked a bit ropey. I have cleaned the filter before, but not accoeding to the 3000 mile recommended schedule. When I was cleaning the carbs I noted the the slides were covered in oily black dust. Apart from that the carbs acrually looked great, but that gunk cant be good. I read recently that clogged air filter symptoms include oiling up of plugs. I am not certain it is a factor for me though as why would only one plug be oiling up? I'm still concerned that the valved might need attention, but let's work on what we can work on for now.

I'm just waiting for a new idle adjustment screw as the old one was rusted solid. I have been reading up, and if I am to adjust the fuel mix screw I need to be able to set the idle just right.

When I split the airbox to look at the filter I noticed some imulsified gunge in the bottom.

This seems to be coming up through this hose. I'm not quite sure what I'm looking at here and need to check Haynes.
This pipe is hard to remove as it is wedged behind the starter motor. The right angle cap at the bottom end just popped off so maybe water is getting in at this point.

I will clean out this tube and look at fitting an o ring or something.
Ill fit the new idle adjuster, then reassemble everything. Then I'll try tuning the fuel mix. Then I'll balance the carbs. Fingers crossed my rough running, over heating and oily right plug issues are resolved.

 

All back together. Seems to be running MUCH better. I have not messed around with fueling or balancing. I want to see of over heating issue has gone, and the oily plug issue. It seems possible a dirty airbox filter and slightly gunged up carbs caused these symptoms. Time will tell.

 

All back together. Seems to be running MUCH better. I have not messed around with fueling or balancing. I want to see of over heating issue has gone, and the oily plug issue. It seems possible a dirty airbox filter and slightly gunged up carbs caused these symptoms. Time will tell. Should be dry next week so I'll be commuting to work and back which will be a good test.

 

Carbs back in. Nee plugs. Spark checked. New k&n airbox filter. Not trued balancing or messing with fuel mix screws. Running better but a few rides this week.will tell me whether it is still oiling up the that right plug. The over heating issue also needs checking. Time will tell.