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Air leak?
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The bike has developed a bit of an issue today. It starts ok and idles with the choke off after warming up, without any problems. The trouble is anything more than 1/4 throttle and the revs don't rise and the engine splutters? It was dark and cold when this decided to happen, but luckily it happened just as I was about to start a ride, so I could push the bike back into my garage.

I had a quick look around the engine and the only thing I noticed was the metal pipe that goes between the carb and the petrol pipe was a bit loose. I could turn the metal pipe and even managed to pull it out of the carb. So could this be enough to let the carb suck in air instead of petrol as the throttle opening increases?

The only other cause I could think of was iffy petrol? I did top up the tank from a jerry can last weekend but the bike made it to Princetown and back without a splutter. Maybe that ride used up the good petrol and the crap that was floating on the top is all that's left?

I am on the the right track or is there some other carb issue I should be checking out? 



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Hi Dan

The metal petrol pipe is only a push fit into the carb body so an easy fix. Make sure you get any petrol residue off the pipe and its socket so that it's grease free and then stick it back in with Araldite or similar.

If you want to make sure the petrol is flowing freely then put a large rag under the carb, make sure the petrol tap is off, loosen the float bowl drain valve and then switch on the petrol tap. If fuel flows freely then the filters on the tap and the float valve are probably clear. If it doesn't flow freely then check the filter on the tap first as that is easier then getting at the float valve filter - just hope that's where the restriction is.

If the petrol flows freely then check if the joint between the carb and the head is intact. Over time the rubber that the carb fixes to separates from the aluminium stub that bolts to the head.

Assuming you haven't done anything to the carb since you bought the TTR and that it was running OK it can only be a limited number of things. Get these two checks done first and let us know the results. If no problems found we can start to offer other things to check.

Brian



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I had a play this afternoon but haven't found the problem yet. I emptied the tank and took off the fuel tap. There was a bit of fluff around the bottom of the reserve filter but not enough to cause a problem. I put 5 litres of fresh petrol back in the tank and checked the flow out of the carb drain. That looked ok.

I took the bike for a quick spin to see if the fresh petrol had made a difference but it hadn't. The engine starts and idles ok. I ran the bike along a 1/2 mile flat straight and it ran up to 56 kph in third gear on a partially open throttle. As soon as I open the throttle to accelerate though if misfires and tries to stall. It's almost like the choke if being pulled on and the engine is starting to flood?

I haven't touched the carb since getting the bike. I've fitted an alarm and changed the ignition switch but not done anything on the fuel system. I guess its time to get the carb off?



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Dan-in-a-Van wrote:

I haven't touched the carb since getting the bike. I've fitted an alarm and changed the ignition switch but not done anything on the fuel system. I guess its time to get the carb off?


Not necessarily.

Were you able to check the inlet stub? If the rubber has come away from the metal then that could be the problem.

Also, another possible cause of fluffing when pulling at higher revs is that the timing chain may have jumped a tooth on the camshaft(s). Unlikely I know but the TTR is new to you so it is possible that the timing chain is worn or the tensioner is faulty - hopefully not! 

It's a quick check except it requires the tank off. Put the engine at TDC, take off the camshaft cover and check that the timing lines are parallel to the head casting. Photos in this "how to".

If they are then all good then it's probably carb off time - unless anyone else can think of anything?

Brian



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The inlet rubber looked ok, but I'll check it with a torch and a mirror next time. It's going to be too dark and cold after work to carry out any checks this week, but I'll try again next weekend.

 



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Maybe a partially blocked main jet. If starting is ok pilot jet is ok. Part throttle is getting enough fuel through to run ok but full throttle is, by your description, where the issue lies - running far too lean due to blocked jet, or as has been suggested running too lean because of the inlet stub rubber letting air in.
Good luck,
Simon.

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Managed to get the carb off earlier. Only had time for a quick poke around, and couldn't find anything obvious. The "air filter" looked a bit odd. It appears to be a metal mesh but with a "sock" draped over it? I can imagine it wasn't doing much of a job filtering the incoming air. Luckily I've got a new twin-air element from Totally TTR ready to fit.

I'll blow through all the jets tomorrow and see if I've managed to fix it by just taking it apart and putting it back together.

air filter.jpg

 

 



-- Edited by Dan-in-a-Van on Saturday 2nd of December 2017 06:00:04 PM

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EEk, that's not too clever! Keep the wire mesh - that's what holds the filter in place/shape. Oil the TwinAir with filter oil and stretch it over the cage. Make sure the orange foam seats properly round the lip in the housing and it should be held in place by the sprung wire locating on the nipple.
Good luck.

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Doh! Doh! Doh! Doh!

I was looking at one of Brian's excellent "how to" guides earlier today. I noticed in one of the photos that there is a snorkel under the seat. My bike hasn't got this and the space left behind was just the right size for the alarm I fitted. Yep ! I fitted the alarm right over the slots into the air-box.

I re-positioned the alarm and the engine's performance is back to normal. On the bright side the sock air filter has been replaced by a nice new TwinAir and the carb is clean inside.



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That would do it I supposebiggrin

The lesson here boys and girls is when the bike starts playing up just after you've worked on it, go back through what you've just done to see if that's the cause.

Well done for owning up Dansmile Glad you're sorted, AND the engine's got some nice clean air to breathe.

Ride safe,

Simon.



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Glad that was an easy fix, thanks to Bri for his fantastic FAQ on all things TTR smile Must have got lots of people out of trouble.



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