Triumphrat

gliderace

(I have been seeing similar threads to this, my problem, all over the Forums and wanted to see if anyone had something related with _all_ of my symptoms in line)

Bike: '97 Thunderbird, 23K, Mods: slightly larger main jet (in '98).
Recent work: replace airbox and filter with standard OEM in October 2007.

Symptoms (started a few months ago):
1) The bike will start just fine when cold (very cold; not ridden for 24hrs), but
2) The bike will be extremely hard to start when warm
3) When engine is under load or revved up, there is a popping (backfire?) from the exhaust
4) When the throttle is relaxed and revs come down, there is a popping
5) When throttle is at 0%, the engine takes 3 seconds to come down below 2KRPM to idle speed (slow to drop)
6) ...and here is the goodie: Bike just plain stops as if all electrical is removed (though all lights work) and as if there is no fuel at all. If the bike stalls out completely, it is nigh on impossible to re-start until a long time (1 hour or more) has passed.
7) If bike is warm (has been ridden), the bike will cut out almost consistently after 3 minutes of riding
8) Bike cannot idle at all, really, without a lot of choke or constant throttle jockeying

To date, I have performed the following:
A) Replaced the airbox and filter, checked all carb junctions
B) Checked carbs for air leaks, vacuum leaks (none that I can find)
C) Removed the tank vent filter/valve
D) Tried opening the tank cap and starting/running to see if there is a venting problem; engine still will die even after 20 seconds of opening tank
E) Checked ignition pickup gap (OK) and coil OHMs (OK), ...but only on COLD bike ...
F) and of course checked fuel level in tank!


I am at a loss. I have been reading about possible coil problems, but would all 3 coils go at the same time? The engine dies as if everything just STOPS at once. When I try the inevitable restart, there is no sound as if there is a spark or any combustion. Wait a long time and then it will start. However, it still hardly idles and will certainly die on me mid-ride.

Once more onto this problem!
Thanks in advance.

Woody1911a1

i'd be thinking clogged idle jets

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gliderace

Thanks!
...yeah...I am thinking something due to lowering the fuel getting into the engine...strange, however, that this thing dies more frequently when it is warm. Maybe a combination carb jets and coils (ugh...)?

Does anyone think that carb cleaning solution in the tank is good to use rather than take the whole dang thing apart? (e.g. something like Marvel M. Oil)

denny

I don't know about Marvel Mystery oil, but Seafoam works as long as the Carbs are not too dirty.

Nothing will do as good as taking the carbs apart for a good cleaning.
And while you are at it clean the tank out real good too.
Do you know about the tiny duckbill filter in the gas line?

The symptoms you've stated sound like electrical problem to me.
I'd get the igniter checked by a dealer, and also the ignition pickup sensor.


I usually try Seafoam first and if that does not do it, then it's time to bite the bullet and give them a good cleaning.

The ignition pickup can get dodgy at high temps when it starts to fail.
Also the igniter can do that, but it usually just dies suddenly.

Coils usually just effect one cylinder.

That what I've gleaned from this forum over the years.

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Cheers,Denny

Tbirdnz

I would try the carbs first, seems fuel related, sounds like if you've had the problem for months you've been storing it or not running it too much. Probably old fuel that's gone to varnish and blocked your jets. Follow denny's steps of a clean-up right thru the system.


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Ride on !

IrlMike

Not sure if this is relevant to your problem, but I discovered a 'quirk' in setting the float height on (Tbird) Mikunis.

The float 'frame' is pushed up tight by the bottom of the float bowl. When the float bowl is off, the float assembly 'springs' up (down) a couple of mm from it's rubber mount o rings.

I noticed this on all 3 carbs where the float bowl stands off the body until it's pressed down or the screws tightened. It had to be the float assembly - there's nothing else & gasket was well clear.

So either hold the float 'frame' down (...up when carb upright) when measuring float height, or compensate for it.

If you don't, the float height could easily be lower (richer) by 2mm or so. As Haynes quotes 14.5 mm, I'm assuming 0.5 mm matters. (I used digital calipers)

Just ridden my Tbird after some mods (K&N, 3-1 pipe & dynojet kit) & she pulls like a train from 2000rpm (or a bit lower) when I wack the throttle wide open (important area for float height). I'd set FHs to 14.0mm - gave it a tad richer as I had 'worked' the inlet rubbers a bit also.

Sounds like you have other carb faults & mbe FHs are not even relevant - but something to mull over anyway - good luck !

jimmyj900

Without hands on the bike and from the symptoms you describe it could be electrical, ignition system or fuel supply.

After the bike warms up and shuts down, connect a spare spark plug to a plug wire, ground the big end of the plug to the engine or chassis (an auto booster/jumper cable works well) and crank the engine.

You should have a fat blue spark if the ignition is working properly and either no spark or a thin yellow spark if there's a problem.

If you've got no spark or a thin spark the problem is either electrical or ignition related.

Check this first and get back to us!



If the spark is fat and blue, the problem is most likely fuel supply related.

It might sound silly, but check that your fuel valve is in the 'on' or 'reserve' position and not someplace in between.

Also check that there is a single hose coming out of the back of the fuel tap. It's possible that a previous owner replaced the manual tap with a vacuum-operated tap and they can either stick closed or develop a leak in the vacuum line that prevents them from opening fully.

Check that the fuel line from the rear of the tap has a smooth curve in it. If it's got a pinched, twisted, crimped or flattened it may be restricting fuel flow.

Turn the fuel tap to 'off', connect a piece of clear tubing to the fuel outlet of the tap and check the fuel flow when you turn on the tap.

If it flows freely and continuously then the fuel tap is working and the inlet filter inside the fuel tank is not clogged. If if flows briefly and quits or dribbles slowly then you probably have a clogged filter inside the tank.

If the flow from the tap is good then it's most probably a clogged 'duckbill' filter in the 'T' where the fuel line connects at the carburetor. You'll have to pull the carbs to get at that.

Check it out and get back to us for the next troubleshooting steps to take.

Jim

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gliderace

Hey y'all, thanks for all of the advice. After a long period off (7 months), I am getting back into diagnosing and repairing.

To date, I have performed the following:
1) removed carbs and cleaned all carbs
2) checked all float heights and replaced carbs
3) on replacing carbs, engine was VERY hard to start, but when it did, it raced on up to an extremely high RPM...frightening, in fact.

After stopping the engine, it would not start. Again. I pulled a plug and tried checking for spark and NO spark. Same on all plugs.

I pulled the ignition pickup and checked the resistance; there was NO resistance/continuity. As the manual says, that indicates a need for a replacement.

So my question to you good sages (and I am serious, y'all are good) is this, in parts:
1) why would it rev up so egregiously high?, and...
2) is there a relation between going up so high and then a catastrophic pickup coil failure (or was that a fault all along)?

I am resigned to get a new pickup for the ignition since that seems to be kaput. Hope that starts me down the road.

Tbirdnz

High RPM in your case could have been sticking throttle cable or the mechanism at the carb since you had removed the carbs. Check that the throttle is working ok.

Sounds like your initial problem was a vacuum to the carbs.

Now you had better check the electrical connections/fuse to the ignitor, may be too much of a co-incidence you suddenly now have an electrical failure which you did not have before.


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Ride on !

p.s. when you stopped the enginge revving high you didn't stop it with the kill-switch did you ?

Bbogie

Check your throttle cable adjustment. After pulling my carbs I had the same thing happen with the high revving. It turned out to be just the cable was not letting the carbs close all the way.