xs that won't start

[grizly6969]

lol, yes I came straight from the gas station with the can and filled it. That would be a heck of a mess.

with the charger on it it will crank good untill the starter disengages and spins free.

[thewiz]

Does this mean ...

will crank good untill the starter disengages

would you say ... at least 20 seconds?

[thewiz]

Also this ... when you pull a plug, ....

ground it to the side of the cyl head away from the hole then crank the engine, how does the spark actually look? Thick, blue, loud and snappy? Otherwise?

[grizly6969]

The Wiz

I think so and yes

[grizly6969]

OK I have been doing some digging and it is looking like the motor is off of an '81. From what everyone had told me that would make no difference but from reading on here I know find out that it can. I bought an engine off ebay when original engine started burning a lot of oil. From all appearences the engines looked the same, both had vacume advance, bolted right in and everything plugged right in. I thought Yamaha would at least change the plug-ins if they would not interchange, but I've been wrong before. Thanks for all your help and the information on this site.

The vin# on the engine is on top of the transmission, (correct)?

[thewiz]

Can't see how the year of the ...

replacement motor would make any diff ... at least in this exercise.

Ok ... let's review the basics .... take inventory, so to speak ...

SPARK ... you have a good, stong, snappy blue spark in all cyls, right? It also must be sparking at roughly the correct time to run. Wires are on the plugs correctly, right? Cams and crank are in time you have said, right? ... just curious, have you had the cam chain tensioner off the motor?

FUEL .... you have known good gas in there and it is getting to the plugs, right? They do appear wet, yes? If oil fouled, replace 'em or spritz 'em as clean as you can with electrical or carb cleaner. You should also try spritzing a little carb cleaner in the plug holes or into the carb throats and crank it again.

There must also be air getting in there to mix with the fuel ... no plugged snorkel, right? (small animals have been known to take up housekeeping in airboxes) ... if not sure, take off the bottom of the air box and crank it again.

COMPRESSION ... you say there is 130 plus all the way across, right? That's a reasonable number on a cold motor and plenty to start it.

If you are CERTAIN that all the above conditions are met, there is NO WAY it cannot run !! ... assuming, of course, that you're not disconnecting the charger the second it fires once (it will not run on a dead battery) ....

If you're not giving up ... re check these things ... cuz, if it won't start and run at least badly, AT LEAST one of the above conditions are NOT met ... and that would be your stopper.

[thewiz]

I tried to add ...

that you should be using a TCI that matches your year and model ... 2H7, I think is the one for your year.

[DiverRay]

The vin# on the engine is on top of the transmission, (correct)?

That is correct.
The ignition system under the left crank cover is off what bike? That should be switched to match the rest off the ignition parts on the bike. If you have a '78 and put in an 80 engine, you want all 78 ignition parts on the engine. Everything WILL swap over. The '80 and newer engines used a break away bolt to hold down the timing plates. They need to have the heads drilled off, and replace them with standard cap head screws.(or allens) This is also the time to look at the pick up coils. They will be out as a set, with the wires loose so you can verify that there are no bad wires.

[thewiz]

He says he has done that, Diver ...

also the time to look at the pick up coils. They will be out as a set, with the wires loose so you can verify that there are no bad wires.

If he has strong, continuous spark at each plug, the PU coils must be triggering, right? As I understand this situation, this motor doesn't run at all ...it only backfires Go figure??

[grizly6969]

yes I took the chain tensioner off and reset it figuring to have to change cam timing, it was right.
Gas is good, plugs are damp, gave it a shot of starting fluid last night. still nothing
I have taken the airbox completely off the bike to make removal of the carbs that much easier.

yes it is a 2H7

I'm going to take the carbs off, again and clean them. My father bought this bike new so I hate to trash it and start over.

[dbeardslee]

I thought the 81's used the 4R0 TCI and no centrifigal advance, in which case wouldn't the advance mechanism under the pickup coils need to be changed to make it work with the 2H7?

[thewiz]

Dbeard, you're right ... I can't find now ..

why I thought it was a 2H7... but I think it was because he said somewhere he was putting in a newer '81 motor. He woulda' kept the TCI to match the chassis and not the engine, I think. That would mean it could ONLY be a 2H7... that's all I can think of. But as you and the Diver have now BOTH said, he probably needs to put on the 2H7 timing guts for starters, cuz for sure he needs a cent. advance on the crank snout with 2H7 .... that may do it right there.

Say, Griz ... don't take this wrong, .. but also ... did you do your comp. check before or after you R&R'd the cam chain tensioner? If your answer is "before the cam chain tensioner R&R". Take a few minutes and re run it. I thnk we're gettin' pretty close now.

[grizly6969]

I think I forgot to release the tensioner, as far as the comp check, I did that after the initial tensioner check (before removal of the tensioner, after adjusting it once) Thanks guys

[thewiz]

Hate to even think this, Griz ...

think I forgot to release the tensioner,

but if your replacement motor is, in fact, actually the 'late' style timing stuff and swapping back ALL the timing stuff from your original motor, which would need to be done regardless, doesn't get you going, then it's very possible that you have valves that have been bent. Hope not, but it's more common than you might think and it has happened to some of the best XS wrenches on this site .... hope not you .... but a quick compression check might be in order.

[grizly6969]

the compression in #1 is down to 120, but the other three cylinders are up to about 140. Thank yall for everything