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Discussion Starter #1
Well, my spring, er... summer project continues. After tires, chain, fluids, etc. my T120 bobber won't idle. It was running fine, but then I did the following:

1. Drained oil from oil tank
2. Drained ATF from primary.
3. Added new 10W-40 to the oil tank
4. Removed spark plugs
5. Kicked bike several times to prime oil into the system
6. Replaced spark plugs
7. Added new ATF to primary

Usually, the bike starts right up on 1-3 kicks. It took probably more than a dozen. The bike ran for a few seconds, then stalled. Repeat... same result again and again. I can get the bike to run with some continuous throttle application.

Is this somehow related to the oil changes? Should I try to adjust the idle or troubleshoot something else? Is that easy with Amal carbs? Thanks.
 

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That doesn't make sense. Is there ANYTHING else that you did?
How much oil is in the tank? Not that it should matter much for now, but my 1971 Triumph uses 20w50. Why did you use 10w40?

Did you check for a good spark in both plugs?

Don't mess with the carbs at all if it ran good before you changed the oil.

Unhook the fuel lines and let it run into a jar to see if it the gas is flowing good from the gas tank.

What did you put in it for spark plugs? And did you try the old plugs that you took out of it to see if it runs better on them?
 

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Discussion Starter #4
Well, I thought it was nuts too. I did not change the plugs. Same old plugs went is as came out. The were a bit black, but I just put them back in anyway.

I check fuel line flow tomorrow. Seems like it is basically starved for fuel (except when on throttle) so a pinched line or blockage seems fairly likely.
 

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As long as the carbs are tickled enough it should idle for a few minutes even with the gas off. So I don't think it's a pinched fuel line.

How about the spark? I would start there.
 

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It's got nothing to do with changing oil.
If you want to check fuel flow,take both drain plugs out of the float bowls and turn on the fuel.150ml/minute on each carb would be borderline at full throttle/peak power.300ml/minute or more is better and more normal.

You probably have blocked pilot jets.Take note of the setting on the idle mixture screws (like1-1/2 turns from lightly seated),then screw them back out and remove them.A piece of wire,0.016" diameter or less,should push into that hole at least 1-1/2" deep into the carb (usually 1-9/16").
A number #78 drill or a 0.4mm drill is the best thing to clear the jet,but you need to extend the drill to reach that far.
A piece of wire from a plastic bag tie measures 0.014".Melt the plastic and strip it off the wire.With some WD40 or carb cleaner and patient probing/twisting with the wire,you should be able to clear the jet.A guitar string,the right size,would work even better.

When the jets are clear,replace the mixture screws to their original setting.You should check their adjustment when the engine is warm.
Also check the balance tube between the flanges to make sure it's not leaking.
 

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I would check for spark on both plugs first...it's easier and quicker than tearing into the carbs.
 

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Bet I can pull out an idle mixture screw,as quick as anyone pulls out a plug.
5 seconds later,I'd have the wire in the pilot jet.
 

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I agree with Mr. Pete that it does sound like a pilot jet is clogged. But I have a hard time picturing that the pilot jet could have clogged so easily. Unless there isn't any fuel filters in the line?
But if it was my bike I would start with the spark. And yes, in both plugs.
So how about it UtahRAT, is there a good blue spark in both plugs?
 

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Bet I can pull out an idle mixture screw,as quick as anyone pulls out a plug.
5 seconds later,I'd have the wire in the pilot jet.
Absolutely. But, he didn't do anything to the carbs. When he R&R'd the plugs he could have torn a boot, cracked an insulator, pulled the terminal off the wire, grounded it (bent the ground electrode), etc... That's my chain of thought...I go after the things I disturbed.
 

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Discussion Starter #13
FIXED IT!!!

Started by testing spark, as that's the easiest. Looked good.

Then, I tried a suggestion from a friend at work and checked the throttle cable for slack. There was quite a bit. There is an adjuster on my bike to bring slack in or out. By tightening it just enough so there was no play in the twist-grip, it idles again.

Thanks to everyone on this forum. My goal was to ride it more this year, but I wanted new tires and needed a new chain. Since then, it's been tires, chain, battery, tail light, headlamp repair, engine oil, primary oil, thottle cable adjustment, clutch cable lube, and probably a few more things. Nevertheless, I think I can ride it as soon as the rain stops.
 

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I don't see how this changed just by you changing the oil. Anyway, yes, there should be just a touch of free play in the cable, but it still should allow the slide to bottom out on the throttle screw in the carb. You should slacken the cable again, adjust the throttle stop until it idles, then re-adjust the cable. You shouldn't adjust the idle speed with the cable.
 

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Discussion Starter #15
There is a nut that holds the cable adjustment in place. It was loose. The bike has been up and down on the lift several times, front end on and off, etc. So any loose cable had a chance to be tugged and pulled.

I look at the throttle stop adjustment though. Thanks.
 

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definitely adjust the idle on the carbs with a little slack in the cable...also if its a T120 we assume 2 carbs which need to be synced..if it needs the cable slack taken out to idle I can almost guarantee the carbs are a mile out of sync and the bike will not be running anything like its potential...properly synced carbs are night and day difference in running
 

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UtahRat that couldn't be the problem. It seems to me that you are using taking all of the slack out of your throttle cable and pulling the slides upward to make your bike idle?
Which is a very bad idea.

Did you try adjusting your idle screw instead of tightening your cable?

Have you adjusted the throttle stop screws, air screws, and sync. the carbs yet?
 

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Discussion Starter #18
Only 1 carb on my bike... It's a hardtail bobber, so far from stock.

I think the bike most likely was previously relying on the throttle tension to maintain idle. So, I just got it back to where it was.

This weekend I will try to get it right with the throttle stop screw.

The local brit bike/car show is a couple of weeks away, so maybe I can get some more help there if I can't figure it out.
 
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