Won't idle when cold.

Hi All,

Finally go the T80 registered and burning up the streets of Sydney, not! Riding to work each day about 20 miles each way, the T80 does it easily.

One problem that I do have that is a annoying is when I start it up in the morning or after it has cooled down, the engine won't idle at all, even with the choke on, it just stalls. The choke cable is operating and moving the choke as per normal.

Once the engine is warm it is fine, it idles like it should and even then sometimes when I come to a sudden and complete stop and it is still in gear, it will sometimes stall. Very frustrating in traffic. Does anyone have any ideas or had this problem and sorted it out. Before I go into the garage to take a closer look, I thought I would ask.

Cheers, Frank.

You say it idles ok when hot so not much wrong, it wont idle with choke on & not when cold. Maybe tickover needs to be increased a bit & the air screw adjusted. Start off with it 1 5/8 turns out and adjust from there to get even idle speed which should be 1700 rpm. If this does not cure it you have a partually blocked pilot jet in which case you will need to strip carb & clean the jets out with an air line.

Thanks John, I will try that and see how that goes. Cheers, Frank.

Hi John,

I have done that, pulled the carby apart, cleaned out all the jets and body with a compressor, adjusted the pilot air screw and idle screw as per the service manual, but it still won't idle when cold even with the choke on. The choke is working as it stalls the engine when opened, when the engine is at normal operating temperature but not too sure what more to try. Not a major drama but it is a pain when taking off to work early in the morning and stopped in traffic when it is still cold and it just stalls. I'll just have to keep tinkering.......

3hundredspartans wrote:Hi John,

I have done that, pulled the carby apart, cleaned out all the jets and body with a compressor, adjusted the pilot air screw and idle screw as per the service manual, but it still won't idle when cold even with the choke on. The choke is working as it stalls the engine when opened, when the engine is at normal operating temperature but not too sure what more to try. Not a major drama but it is a pain when taking off to work early in the morning and stopped in traffic when it is still cold and it just stalls. I'll just have to keep tinkering.......

Depends how cold the ambient temperatue is, obviously the colder it is the longer it takes to warm up. My bike takes only a few mins to warm up enough to idle ok. In very low temperatures you can get carb icing even after the engine has got hot. This will cause the engine to stall until the heat has thawed out the carb.
The pilot jet may still be blocked as its such a small hole the air may not have cleared it, try poking it through with 5 amp fuse wire.
Also another cause of poor idle could be the petrol tap if the diaphram is leaking. Remove the vaccum pipe from the tap, plug end & then try
You will of course have to move tap to Prime position.
Finally are you sure you are using the choke the right way, Closed (choke on) is whan lever is pushed to left, Open (choke off) to the right

Well, I think the issue is that I have a broken o ring on my idle screw and the pilot air screw is missing a spring and o ring.

I have just received a rebuild kit for a Yamaha YFM80 Badger/Raptor Quad that I purchased on ebay which I can use some parts from it but the service manual schematic on the carby is not very clear as to how the throttle stop and pilot screw assemblies go together. If you have the service manual, it is item 4 and 5 on the pull apart schematic of the carby. I can see the screw, then the spring and o rings on both but not too sure what that other part is in part 5 - (Throttle Screw Assy).

Clarification would be appreciated.

Cheers, Frank.

No idea what the other part is on part 5 but as you appear to have solved the idle problem in your other post https://yamahatownmatet80.forumotion.co.uk/t300-chattering-on-idle-what-is-it I assume its now irrelevent

Hasn't really improved to the point of not being a problem. It will still not idle at all when cold, period. I have adjusted the carby as much as I can but just won't idle. When it is warm it is fine, stopped in traffic and it idles normally. The other problem I have noticed also is when I am doing top speed in 4th gear and let off the gas it slows down ok, but when I throttle up again, it bogs down and I have a big flat spot until it gets going again and even when cruising, it jerks and surges so not running smoothly which can be attributed to an air leak. I am running Shell 98 Octane fuel in it, a new spark plug, fresh engine oil. Any one else had similar issues and solved them?

Any suggestions appreciated.

Regards, Frank.

3hundredspartans wrote:Hasn't really improved to the point of not being a problem. It will still not idle at all when cold, period. I have adjusted the carby as much as I can but just won't idle. When it is warm it is fine, stopped in traffic and it idles normally. The other problem I have noticed also is when I am doing top speed in 4th gear and let off the gas it slows down ok, but when I throttle up again, it bogs down and I have a big flat spot until it gets going again and even when cruising, it jerks and surges so not running smoothly which can be attributed to an air leak. I am running Shell 98 Octane fuel in it, a new spark plug, fresh engine oil. Any one else had similar issues and solved them?

Any suggestions appreciated.

Regards, Frank.

Other thing to look at are the O rings where the carb bolts to manifold & manifold to cylinder head, may be an air leak here.
Is the accellerator pump working ok & is it adjusted correctly ? (refer to manual)
Is the vaccum pipe to petrol tap leaking air ? (they perrish with age)
Is the fuel tap diaphram leaking air thus causing fuel starvation? (remove vaccum pipe from tap, block off end & turn tap to PRIME position, if it clears the problem its the fuel tap diaphram. New tap needed as you cant buy replacement diaphrams)
The carb may have a blockage in one of the internal passages, if so there is little you can do about that, having it ultrasonically cleaned may clear debris but failing that it looks like another carb. There is one on eBay at the present time http://www.ebay.co.uk/itm/YAMAHA-T80-TOWNMATE-MIKUNI-CARB-ASSY-/400524315843?pt=UK_Motorcycle_Parts_13&hash=item5d411c0cc3 but here in good old blighty, so dont know if seller would post it to Australia

Thanks John,

I'll have a closer look at those things you mention.

I am watching that carby on eBay. Seller has said UK only.

I can get it shipped to our office in London and get a work colleague to send it to OZ.

Let you know how I go.

Cheers, Frank.

Carb sold for £10.50 which considering it had the rubber connecting tube to air filter was not a bad price.

Hi John, I bought it. I'll see if it is better than the one I've got.

Cheers, Frank

I am sure it will be OK

I have gone through and done the following:

• Replaced the seals of the throttle mechanism.
• Replaced the inlet manifold o rings and carb o ring.
• Cleaned the fuel tank.
• Cleaned the fuel filter.
• Checked all hoses, OK.
• Cleaned fuel tap, had water droplets in it, cleaned and let it dry for a day dismantled.
• Cleaned air filter, washed it and oiled it.

Verdict: Still won't idle when cold but does run alot smoother when cruising and will idle when warmed up.

One thing I have noticed though is that when it is cold, moving the kick starter with my hand is very easy and it has very little compression but when it is warm, it has twice as much compression which might indicate it needs new piston, rings and a hone. This leads me to believe that it does not have enough compression when it is cold to idle but when it is warm it does have enough compression to idle.

Has anyone else had these symptoms and if so, what have you done to rectify the problem?

Cheers, Frank.

Have you checked the tappet clearance?

cdi might be on its way out weak spark when cold and rich mixture the spark might be blown out? but when warm things get easier to ignite or else dodgy plug?

No John, I haven't. Now that you suggest it, I'll have a look and make sure it is within specs. I'll reply back soon.

Thanks, Frank.  

Hi JohnW,

Well, I take my hat off to you my friend.

My exhaust valve was out of spec by very little, reset the clearance to factory spec and it has transformed the bike. Intake is within spec.

It now idles when cold, does not stall when coming to a sudden stop in traffic and there is more compression which I can understand as it would have been leaking through the exhaust valve.

It's easier to ride, smoother and has more on-tap power and the exhaust note is noticeably more punchier.

Thanks again JohnW with your tip. Problem solved!!!

Best Regards, Frank.

Glad you have fixed it Frank, its better to run with the clearances a bit on the high side than have them close up. You are lucky you have not burnt the exhaust valve out. Might be worth checking again after a few hundred miles to see if the clearance has reduced due to valve settling in on its seating. Haynes says check every 4000 miles or 6 months. I would half that.

Thanks John, will do that, I'll be checking it from now on every 2000 miles or so.

Thanks again.....

Cheers, Frank.