UPDATE: I've now solved this, check my latest update below: In short it was the carb and the timing.


Have just had a bad time of starting our two XT600s after 3 weeks in the garage. We rebuilt the engines of these in the autumn so this wasn't good news! Not something I'd like to deal with once we bust them out of a crate in Kazakhstan.

Bike A: 1991 3TB with older bodywork & frame
Bike B: 1993 3TB with newer 4PT style frame and bodywork

Prior to Christmas both bikes were rebuilt and running fine clocking 200miles each with a first oil change. Cold starts might be ~20 seconds of cranking if the bike was left more than a week but if used the day before would start on the button.

Tonight Bike B started after >3minutes cranking. Bike A ran the battery flat and wouldn't start. After what felt like 10 minutes backfiring happened after a few turns and I quit for the night.

I've been trying to put a plan together - all help most appreciated!



With all this my feeling is these are likely culprits:

1. Spark plug condition
2. Carb - I've not serviced this, any ideas what I could be looking for once I get it apart for a clean?
3. Timing (please no!) on rebuild I lined up the horizontal marks on the top cam wheel and at the bottom the middle of the elongated 'H' symbol which felt at TDC. Took my time over this and if I got it apart would be hard pressed to do this better/different. Do I need a timing light? or is it worth the guess of moving the chain a tooth (and which way?). When it was previously running it seemed fine - maybe a little low on power.

Experience / advice welcome. I'll give it another go tomorrow

Cheers

Tom

For setting the cam timing the mark used on the flywheel should be the " I ", not the " H ".
The " H " is the ignition timing mark.
The " I " is top dead centre which is used for cam timing.
see here http://www.horizonsunlimited.com/hub...-produce-67846
Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

It's also a good idea to close the fuel tap and run the carbs dry(or drain them) if you're not going to use the bike for more than a few days. Makes starting a lot easier.
Just have to remind yourself to open the fuel tap before starting
Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

hi there as mezo says the little filter on the petrol flow valve needs to be checked , i would remove it and fit a in line filter they cause BIG problems on xts . also you seid you reused the inlet rubber o,rings did you use any sealer on these . even with new ones i smere a little sealer on them useualy instant gasket , wipe any eccese off , dont forget the inside before it cures . air been sucked in here is not good . the later xts use a rubber diaframe for the secondary carb , (mine is a 1985 43f with a solid one) undo the 4 screws and remove the top folowed by the spring then remove the rubber diaframe and LIGHTLY stretch the rubber to see if it has a hole in it also if the rubber is hard its on its way out and will not react as it should . use super unleaded petrol as normal unleaded has ETHANOL in it this will cause bad starting if the bike is left for a week or more . as seid run the fuel off if you know the bike is not going to be used for a while also check the timing as stated. if you have the carb off to check/ remove the filter remove all jets also mixture screw under the carb carefully screw it in until it lighty seats noting how many turns to do so before removing it, clean / blow all jets out also all passage ways in carb. also check any electrical conections you disturbed while removing engine . good luck zigzag

I will agree big time with the using only premium fuel, plus for the extened times between starting put fuel stabilizer in the gas and run the carb empty for storage. The bike that won't start I would bet has some varnish(dried up fuel) that has clogged the pilot jet, and probably other holes. Inline fuel filter would be a must, plus throw in a couple extras for the trip along with some clamps and extra hose pieces.

I would go through the carbs on both bikes.

It sounds like a simple carb-clean could/should do the trick.

Thanks everyone, really great responses

So tried again yesterday - checked and reset valve clearances. Just more backfiring! Plug was sparking fine but looked dry - (must be fuel in exhaust for backfire though?).

Have taken the carb out and will give it a good clean out - will probably take me a couple of days to do, see if that gets it, will come back with an update and try and summarise for future searches.

mezo:
Fuel filters are a good idea! I've ordered a couple for the tank lines. As for kick starts, knew it was possible but not sure where I'd find the parts, especially for the 3TB engine? We'll definitely bring a set of jump cables.

Bobmech:
That is a really good link - the workshop manual is not very clear on this! It is possible I'm a tooth out and if I can start it once the carb is cleaned I should take a look at this. Does a timing light mean I can check timing without cracking the top off - takes ages to do on the frame, clean and regunge!

zigzag:
I didn't seal them, although the manifolds look liked they'd been replaced recently. As I've yanked out the carbs I'll take your good suggestion and stick some sealant in there when I refit the carbs. Interesting about the ethanol, wasn't aware we did that in the UK. Cheers for the carb advice - its something i've not done before so that'll help me not miss anything.

jjrider:
Worth a go for the future - I suspect with two in-line filters and piping thats probably a couple of miles of fuel once the taps are off - could be quite fun to guesstimate.

You cannot check the cam timing with a timing light. A timing light will only tell you when the ignition is firing.
Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

Update since last week. A bit longwinded but wanted to record everything I've checked/tried.

Timing. This was a concern before today so I rechecked it. With the crankshaft at TDC marked by the single I notch (not the H this time) prior to adjustment the cam-sprocket timing marks were about ~1mm high on the left and ~1mm low on the right. I therefore moved the chain on a notch 'backward (wrt bike)' the new position looked a little high on the RHS once the cam chain tensioner had been refitted. Personally before and after looked equally 'out' in different directions but as my cam chain is new and short I recon that as it lengthens I will now approach perfect timing rather than move away. Hope this makes sense - if not I'll do some sketching! I'd like to discount timing from my starting woes at this point - unless its ignition timing but I cant see how 3 weeks in the garage could have altered that.

Carbs disassembled and fully cleaned.
* Jets blown out with air and there was some fluff in the intake float needle mesh. big rubber diaphragm didn't have holes so refitted.
* I also dropped down both needles one setting (both now sit 4/5) this was not about the starting issue but something I've wanted to do for fuel economy and high altitude anyway.
* What I did notice was that when holding the carb upside down the clearance between the bottom of floats and the flat of carb bottom was not in spec (something like 22mm not 26-27mm as per manual) and the needle valve button was being depressed (manual says no). Actuating the needle valve it did make a good seal. I did not adjust the float tang as I was approaching limits of my experience and reasoned it had originally worked! Manual also says to conduct a fuel level measurement on the bike - with a special tool and the picture isn't clear - I haven't done this, anyone got tips?
* Notes on fuelling when trying to start. When I take the airbox side off and use a hand to block the primary carb intake while cranking the bike I get a good load of fuel out on my hand. Spark plug is wet. Subsequent cranking may make the faintest of engine kicks or small backfire out of the airbox. When cranking normally with no throttle and choke on the plug seems to be a little dry. Full throttle and choke makes a wet plug.
* Perhaps carb is not totally AOK but today I have had fuel in the cylinder with a spark and presumably some air - why not even a hint of starting?

Sparks:
* Spark plug is new - changed spark and ht from bike B with no real difference. Initially sparks looked pretty unimpressive before lunch (small little red snaps) but this afternoon were blue and bright. Not sure what this was perhaps this was down to cleaning the input low voltage terminals of the HT coil, or maybe battery/jump voltage or current.
* As for the timing of sparks I dont know a way to test this but cant think why this would go wrong just in the garage for 3 weeks.

Fuel:
Got about 15 out of 20litres in a plastic acerbis linked with two in-line filters (so fuel definitely going in). This is the same fuel I purchased mid-early december and was 95-unleaded (not super). I suppose its possible this is the constant that is wrong as others have pointed out but all of it going so bad I cant start? Seems a little unlikely? Varnish not an issue as the carb was cleaned, and I can see in the inline filters fuel has filled the carb. The other think I tried today was easy-start spray into the airbox (caused a minor fire in the airbox and several hilarious moments of panic until my mate swatted it out with his bare hands) and directly into the sparkplug hole. Not a sausage.

Persistance:
Cranked the battery flat and then more cranking this afternoon, a small burble is the best I've had today. On the jump leads this afternoon cranks OK and spark looks ok so assume the jumping isnt the issue.

Would love to have better news but I'm all out of ideas!


TL; DR I've had fuel, a spark and presumably air in my engine but no combustion

Fuel stabilizer is good. I stored a portable Generator with a Honda engine for 3 years with "Stabil" brand. I got worried about it so went to the storage facility, drug it out. It started on the second pull. I went ahead and ran all the gas out and drained the carb.

Another very good way is to use AVGas available at Airports. In the USA, 100 Low Lead is about all that is available. I am not sure what is available in other parts of the world. 100 LL does have a small amount of lead in it so do not use it in anything with a catalytic converter. Just replace all the old fuel with the AVGAS, doesn't take very much, let it fill the carb, then start and run for awhile. AVGAS doe NOT turn to varnish, ever. Condensation in your tank is still a possibility and AVGAS will not prevent this from happening. AVGAS really keeps things clean and ready to run next season. Good for power tools, lawn mower etc. It is expensive, probably twice as much as car gas.

Steve

__________________
'84 XT600 is now bored to 2nd oversize and new OEM pistons and rings installed. No more smoking.

Problem located as Carburetor by fitting known good one from bike B. Bike now starts.

Fixed my carb, refitted and now bike A is good to go:
Messed around with the float tang, first massively overfilling then bending it down some to roughly back where it was (no real changes here!) Getting a level measurement was tough so we just went with it. I think the final fix was to pull out the mixer screw (was 2 turns, now 4).

Starts and runs like a champ, im glad I fixed the timing too. Not the most fun weekend but definitely learned a good deal.

Moral of the story: Your carb can prevent starting completely and no amount of poking fuel into the spark plug or air intake will help you. Give it a good clean as per the workshop manal, try and check the float level and see where your mixer screw is. Also cam timing on a new chain can be the lesser of two evils but match on the I (not the H) and you should be good

Many thanks Mezo (again!), Bobmech, zigzag, jjrider, Jens Eskildsen and steveloomis if you ever wind up near Derby the s are on me.

Glad you got it sorted.
Bob

__________________
Remember that Assumption is the mother of all f**k-ups.

hi really pleased you got it sorted, well done mate . zigzag