Won't start - but backfires

[gaillarry]

Bringing my 83 back to life. Ready to start up. So fair I've done:

- valve adjustment
- set the timing
- cleaned carbs, all new jets, set float levels, 3 turns out on the mixture screw.
- new battery
- new spark plugs.

Got good spark, fresh fuel, the engine will backfire a bit but won't run. What am I missing?

 

[Kingwj]

Switch the plug wires.

 

[Sgt Hollywood]

Ditto to that. ^

Seems like every time I run into that symptom. some monkey had gone and missed connected the Orange/Grey coil wires.....

 

[gggGary]

Dry the plugs, I like a torch to do it.
Put air filters on.
If you have the TCI sides won't matter on plug wires.
Unplug the voltage regulator see if it makes a difference.
Try the kicker and or a battery charger hooked up.

 

[gaillarry]

Filters in place, has a TCI.

I'll dry the plugs and unplug the v/r.

 

[Paulrxs650]

Double check your timing - Similar issue where i was certain it was right, then after checking a host of other things - realised I was way out D'oh, after embarrasment and adjustment it fired on the second kick

 

[gaillarry]

With help on this forum ( http://www.xs650.com/forum/showthread.php?t=22420) my son and I set the timing. We even pulled the engine again and double checked the timing.

I did mark the end of the cam so I can check without removing the engine. I'll check again this morning. I'll post back later this morning on our results.

 

[littlebill31]

Sorry, noticed you were talking about cam timing, not TCI.

Just a thought, but the carb boots are securely mounted? Vacuum barbs are pluged?

 

[gaillarry]

Boots secure, vacuum barbs sealed.

Kicked it for about 5 mins, spark plugs are dry, but did get one backfire. Re-checked the cam timing. My cam doesn't have the mark inside the end indicating the TDC mark, but I filed a notch and the timing is dead on. I suspect the carbs are the problem as no fuel or very little, going to pull the carbs.

As a side note my son just cross threaded one of the spark plugs. Can't get the plug in now!!! Going to have to get a thread chaser

 

[Paulrxs650]

What about the punch dot mark on the camshaft cog inside inside the engine? was that present? was it lined up ie is the cam installed in the right way (assuming you have had the top off of course)
With a backfire I am still leaning towards a timing issue thats all??
Compression test to check?

 

[gggGary]

Does it feel like it has compression, or have you tested? I tend to try a shot of ether if I am not sure it's getting fuel.

 

[Paulrxs650]

I usually do a rough check with the plugs out, exhausts and carbs off then watch the piston in relation to the operation of the valves - might be worth a look

 

[gggGary]

We have been dancing around it, but are you sure the cam isn't in backwards?
A very quick check, if you hold your hand over the end of an exhaust does it push off when you kick it?

 

[DogBunny]

Uh, well, don't mean to sound insulting, but is your throttle plate (as controlled by the idle stop screw open) open enough for fuel to get to the cylinder? Normally, you make a preliminary set of the throttle stop screw thusly: Make the stop screw just contact the throttle shaft lever, then screw it in a full turn to open the throttle plate enough to start the bike. However, when I start an engine for the first time, I turn the screw in 3 full turns. This makes it really easy for the fuel to get to the cylinder. If you do this, be prepared for high reving, and to immediately back the throttle stop screw back out.

 

[gaillarry]

Thanks for all the replies, it's really appreciated.

Compression is 140 & 135, not great but should be good enough to start the engine.

Cam and timing marks are lined up exactly as shown in: http://www.650motorcycles.com/CamTiming.html Since I have a TCI ignition there's no pin in the end of the cam and the red dot inside the cam is worn out, so I filed a notch. The lobes and dot on the cam end are dead on. The cam dot is on the right side of the engine.

Throttle stop screw set at 2 turns.

Pulled the carbs, kicking the engine over, I feel suction on each intake hole. To me this means the engine is creating vacuum to suck gas from the carbs.

I'm going to concentrate on the carbs for now. I just rebuild them but may have screwed something up. I'll post back my findings.

 

[DogBunny]

Another thing to try is to remove the plugs and squirt about a half teaspoon of gas directly into each cylinder. If bike starts, the problem is probably carbs. If bike still doesn't start, problem could be timing.

 

[gaillarry]

Another thing to try is to remove the plugs and squirt about a half teaspoon of gas directly into each cylinder. If bike starts, the problem is probably carbs. If bike still doesn't start, problem could be timing.

I'll try that when I put the carbs back on, thanks.

 

[littlebill31]

Make sure you are getting a good flow out of the fuel line too. You can back out the float bowl screw a little to make sure the bowls are filling with fuel. Sometimes a tiny bit of debris in a jet, float set incorrectly or a bad flow/vacuum can cause a bunch of trouble.

 

[Splexin]

I had this exact issue and turned out the wire going from my TCI pickup to my harness was being smashed by the engine cover, interrupting the signal. So possibly something with your TCI?? My backfire was a very loud boom though

 

[gaillarry]

Make sure you are getting a good flow out of the fuel line too. You can back out the float bowl screw a little to make sure the bowls are filling with fuel. Sometimes a tiny bit of debris in a jet, float set incorrectly or a bad flow/vacuum can cause a bunch of trouble.

I'm using a portable fuel supply and the bowls are filling (used clear line to check the float level)