Won't start, has spark - driving me nuts
 

I've pretty much run out of things to try so I'm hoping for some ideas please. The bike ('89 3AJ) had been getting very reluctant to start so I sent the carbs away to be cleaned and reset to factory settings. When they came back I fitted them and now it won't start.

I checked for spark and after tracking down a bad connection in the key ignition barrel I now have spark. This was tested by taking the plug out and firing it resting it on the engine fins.

I drained the fuel and put fresh fuel in.

Exhaust pipe smells of fuel after cranking it for a bit.

It was working before so it shouldn't be anything major but I've run out of things to try:-( Ideas anyone?

A few possibles
 

I would maybe replace the sparkplug, and check the valve clearances. Always worth doing a compression check too....

You have vapour reaching the exhaust, but that does not mean you have enough to ignite. Have you check to see how good the fuel flow is from the tap to the float bowl?

Then it might be worth checking to see if the main and pilot jets are unblocked. WHo knows.

It could even just be a case of a flooded engine if you were used to starting it up with a bit more gas, perhaps you don't need to anymore.

Testing
 

Alex,

If it's not the plug i'd suspect something has gone wrong with the carb rebuild.

You're welcome to use anything from my bike to test if it helps.

Air filter? Will it run on choke?

I've been trying to get an engine I bought recently to start, checked everything still no joy, I was getting a spark, fuel was getting through but was backfiring, yesterday decided to remove the generator to check the woodruff key which was found to be broken, this causes the ignition timing to go out, i've replaced this and it started first time

:scooter:

keep 'em coming
 

Thanks for the suggestions folks.

Warthog:
I'm getting a good spark from the plug that's in there, I might swap it out to check though. With the drain screw open it lets plenty of fuel through and doesn't stop. I've been using the car to jump it so I've tried lots of combinations of choke, no choke, throttle and no throttle. I wait too to let it clear in case it is flooding.

I could try the clearances and a compression check but I can't see these changing since it was running a few weeks ago.

Roamer: Might take you up on that, it would be hard to prove the carb was poorly set up otherwise.

KTMmartin
It won't run at all now, choke or not, it used to like me using the choke. Air filter looks ok, but I haven't soaked it or anything.

Coils?

Where was the bike when it had the inlet manifold open?

You've got a spark and you've got fuel, are they meeting at the right time ? Check the timing, if you can. As far as the air cleaner is concerned, take it right out and try to start it, if it starts, it's the air cleaner ! It should run ok without the air cleaner, but don't do it for too long.

Texastrike:
I'll give the air cleaner thing a whirl, easy to try. The timing thing I'm dreading, I don't really want to start pulling the rotor out of the alternator. It should be ok since it was running before...

Warthog:
The bike was in its luxury spot under some trees on my street while the carbs were off. I stuffed the head with rags and then taped a plastic bag around them. Are you thinking moisture in the cylinder? The coil works cos it sparks.

Got a spark tester? Little clear plastic types that go on the plug in the cylinder, or a thing like a drawing compass that goes in the HT lead gives a certain answer.

It has been known for plugs that work rested on the head not to work down the plug hole. Usually it's a corrosion issue at the cylinder head or main earth connection, or a weak coil. You get a fat blue spark in one place, weak and yellow down the plug hole.

Trust a Triumph rider to know about engine electrical faults :blushing:

Andy

Possibly water or corrosion. If the bike was fine, but now is not..it could be. I am think that the carb work may have been pants. Carb works, leaves, comes back and doesn't work...

As for the coil: its working when the plug is out, but under compression conditions it might not. My mechanic once said that spark with plug out and spark with plug in were not always the same... My only thought

Get a can of power start or carb cleaner etc...

Spray it into the airbox while turning the engine over...

The mixture mixture should EASILY ingite and the engine should turn over...

If it does run with the power start then its your carbs/fueling...

If it doesnt run, its either electrical or mechanical..

As well as the above advice, you could try the old trick of heating up the plug in a flame, like a camping gas or something; when it's very hot, quickly screw it in the cyl.head and try to start it quick before it cools down.

It's fiddly because you have to do it all without finger contact.

hi there i agree with the spark plug tester idea ,as you cleaned the ignition switch and got a better spark you may have more bad wiring , this may have been your problem all along. did the carb rebuilder find a problem with your carbs. you need a big fat blue spark not a faint yellow dancing all over the place one. a clean air filter and proper tappet clearance are a must , do one thing at a time then try to start it then you know what has improved matters. zigzag

Hehe, I developed asbestos fingers through having to do that nearly every day on an old Jawa two-stroke I used to own. Throwing them in the air like a juggler is good for reducing skin contact :) Or wear gloves ...