Idling rough, missing a beat?

Ok, I have a 95 triumph thunderbird 900 that's kicking my butt and I'm getting tired of not finding a solution...
I did valve clearances, new ignition coils, carbs cleaned, fuel level set. Fuel filter is clear, fresh gas. I run it with tank hooked up and/or aux tank. Pilot screws are set to spec, 1.5 turns out.
Compression is the same in all three cylinders, at around 140.

It runs and rides.
I just can't get it to idle right. It's rough and not steady.
When I have my carb sync tool hooked up, I can see that one cylinder seems to be missing a beat once in a while. The vacuum reading just drops to 0 for a second or two, then goes back to normal until the same thing happens again a minute later.
Not sure if that's a thing but that's what I observe.

Not sure if it is carbs related or not.
I'm happy to take them off again, break them into all individual parts if needed.

Any ideas/help is appreciated

 

have you looked at the carb mounting boots to see if they are cracked? That one cylinder might have a vacuum leak

 

Have you switched your balance tool around to see if the dropped reading follows the cylinder and is not an issue with the tool?

If it does drop then you have a massive loss of vacuum when it does. Either some type of intermittent intake leak or carb problem or stuck valve or broken/weak spring comes to mind.

I’m working on obtaining a 2003 speed master as we speak

 

Have you shipped it to me?
That usually fixes those sorts of problems.

 

jayrodoh, Good call on the valve issue.

That should be easy to check once you pull the valve cover. No burning oil? So that would mean the guide is good, but there could be a spring broken (might make interesting noise when running) or other issue going on. Could even be a damaged cam lobe??? That is a stretch, but if you are loosing all vacuum and or compression on that cylinder has to be either valve issue or the ring gaps are somehow lining up? That would not cause a total vacuum leak though. This one will be interesting to solve.

 

No strange engine sound, revs ok and picks up nicely while riding.
I just synced carbs on my kawasaki a few weeks ago and carb sync tool was fine. There is a bit of smoke but I am currently thinking it's still left overs from when there was way too much oil in the engine. I'll keep an eye on it.
The manifold boots are a bit cracked but don't seem to go all the way through. I will replace them though.

The intermittent issue is what causes my headaches.

I will pull the valve cover again and have another look. Nothing seemed out of the ordinary when doing valve clearances. I want to put a new gasket on anyway and will check again.
Maybe I just pull the engine to make it easier to work on. There is that massive backbone in the way to allow easy access.

Oh another thing is that the bike needs a few cranks to start up. It got much better after doing valve clearances and carb clean, but it's still taking too long.

@k-moe, can't send it to you, it's not my bike. A friend of a friend just asked me to help him get it back running. Funny thing is that I spoke to an old mechanic whose shop specialises in triumph etc. He told me to just junk the bike as there are too many issues with those. But that's when I pretty much accepted the challenge...
I'm sure I'll get it running nicely again but am at a point where I do need some input (hence this thread)

 

Would it be worth trying a colourtune on each cylinder at idle? Surely that would highlight a problem with the mixture.

 

In the case of any hi-volume production machine over 15 years old, "too many problems with them" is mechanic speak for, "I have to charge more than most owners are willing to pay."

 

That is how I just picked up three bikes on a deal....the mechanic showed the bill to the customer and they just left two bikes sit. 1974 Honda CB350 twin and a 1980 Yam SR250. I got the 25o all cleaned up and running today, that will be a quick flip....I hope.

 

Most people forget that even if they find a cheap used bike, there is always something to fix or replace if they really want to make it safe and sound.
And it's not just parts, it's also fluids that just add up, or even a cleaning materials, manual etc.

 

Nice things for the wife so she won't complain.

 

And of course they'll also tell ya that you can't get parts for them either.

Problem is by the time you tally up all that's needed on most older bikes, adding labor to the bill makes it a losing prospect.
Having the time and learning to take on reviving an old machine yourself is also a challenge.
Proper tools, and ample workspace come to mind.

If you plan on keeping it, and enjoying what you put into it, that does help justify your decision.
But you have to have lots of luck on your side on a "For Profit" flip.

I scour the local CL ads an always look at potential deals. Gotta look at initial cost, and what you can get for it "Fixed Up".
Then ask yourself, if I can't really make anything on it, would I keep it and ride it?

Tony

 

And that is a large part (but only part) of why there are so few pre-1930 motorcycles still in one piece. Between "obscelesence" and wartime scrap drives, something like 90% were scrapped and turned into something else. It really wasn't until the late 60's/ to mid-70's that motorcycles became viewed as collectibles and worth reviving/restoring (and then collecting wasn't seen as a for-profit enterprise or some sort of alternative investment vehicle).

From my perspective it's almost always better to fix an old thing and use it than to buy a new thing. The savings has bought me several nice vacations in foreign lands, and that's where the profit lies.