Engine don't start; ideas please!

Still working on my 1983 750L. Petcock now works so I put the fuel tank on the bike but I can't start the engine. Engine turns over (with starter and battery) but no running. Not even a single "fireing" (sorry for my lack of the right word…) from the engine.

There is spark on all plugs but they all seem to be dry (no gas on the tip). Green wire is on #1/4 coil so it is as what the wiring diagram shows. As I wrote, petcock is OK and there is fuel in the four carb bowls. There is vacuum on the pipe that connect to the petcock. I tried starting it up with the petcock on "prime" position but no help.

Thinking that I could have forgot to remove the rags in the head (or carb) intakes, I just took the carbs off (but no rag at all). When looking in the head's (spark plug) holes, I see the valves going up and down when I push the starter button.

I think taking the carbs apart but I don't know what to look for. I did not try new spark plugs but because they seem to remain dry, I don't see what it would change…

I'm kind of clueless by now. This restoration is about done now and I'm really looking forward to finish up this bike. Any idea please on what could be wrong?

Thanks!!

Spray some starter fluid into the airbox / carb mouths. If it fires with starter fluid then you know the issue is carb related. Blocked jets or something like it. 

You need compression, ignition and fuel.  Check compression first.  Then check ignition and timing.  Then check fuel.

Some ideas;

+1 on the starter fluid /Quick Start suggestion
What carbs ? Do they have choke butterflies ? If so then roll back an airbox boot or two and check if operating correctly. You may also be able to hear them click into place when choke lever operated.
You could do a quick and rough check of the fuel level in the carb bowl with some clear tube attached to the drain nipple and opening the screw. To low a level and no fire. Perhaps caused by upside down float(s)?

Warren3200gt wrote:

Spray some starter fluid into the airbox / carb mouths. If it fires with starter fluid then you know the issue is carb related. Blocked jets or something like it. 

Good suggestion! Bought a can yesterday and will try it up as soon as I put the carbs back on the bike. Thanks!

hardrockminer wrote:

You need compression, ignition and fuel.  Check compression first.  Then check ignition and timing.  Then check fuel.

Didn't think about compression; will check it pretty soon!
When you says "timing", are you thinking at electronic timing or valves/cams/crank timing?
Thanks!

JR wrote:

Some ideas;

+1 on the starter fluid /Quick Start suggestion
What carbs ? Do they have choke butterflies ? If so then roll back an airbox boot or two and check if operating correctly. You may also be able to hear them click into place when choke lever operated.
You could do a quick and rough check of the fuel level in the carb bowl with some clear tube attached to the drain nipple and opening the screw. To low a level and no fire. Perhaps caused by upside down float(s)?

Should have mentionned that beside a 4-1 Kerker, the bike is stock. So, carbs are OEM BS34 which do not have choke butterflies put transversal shaft mounted one.
The first thing I did on this bike is carb cleaning. I do have an ultrasonic cleaner and I went through every jets as well as air screw and float height adjustment. I would be surprised the problem lies there. Thanks!

As hardrockminer wrote, engine compression could be the problem. I should add that I don't know much about this bike except that it has been sitting about 20 years in an unheated shelter before I pick it up.

I heard stories of stuck piston rings and that one of the solution was to fill up the engine (and I mean fill it up right to the spark plugs) with diesel fuel and let it soak. However, this solution is messy and stinks a lot and I'm sure there are better way to loose up those rings (without taking the engine apart). Ideas please!

Thanks again!

First thing I would suggest is to measure the compressions to see if there is a problem, if you have the facilities you could rig up a "leakage tester" with an air line which would tell you conclusively where the pressure is going (if it is low) if you have to go the release oil route you only need a small amount (just enough to soak the rings) I have used WD40 in the past as you can direct where you squirt t but I am sure there will be endless suggestions of products. you can then remove the excess with a rag over the plug holes and spin the motor over (don't spin it with the plugs in before this stage as if you over did the oil you could hydraulic the motor and bend a rod) then put the plugs back in, the remains of the release oil will be burnt off as smoke out of the exhaust DON'T FORGET INCORRECT CAM TIMING WILL ALO SHOW AS LOW COMPRESSION

Were you using any type air filter when attempting to start the bike?  If not that could be part of the problem.

gd4now wrote:

Were you using any type air filter when attempting to start the bike?  If not that could be part of the problem.

Yes, stock airbox and filter. This could be a problem?? How?

Wookie58 wrote:

First thing I would suggest is to measure the compressions to see if there is a problem, if you have the facilities you could rig up a "leakage tester" with an air line which would tell you conclusively where the pressure is going (if it is low) if you have to go the release oil route you only need a small amount (just enough to soak the rings) I have used WD40 in the past as you can direct where you squirt t but I am sure there will be endless suggestions of products. you can then remove the excess with a rag over the plug holes and spin the motor over (don't spin it with the plugs in before this stage as if you over did the oil you could hydraulic the motor and bend a rod) then put the plugs back in, the remains of the release oil will be burnt off as smoke out of the exhaust DON'T FORGET INCORRECT CAM TIMING WILL ALO SHOW AS LOW COMPRESSION

I do have an air compressor but no equipment for a leak test (don't know how to set this up anyway...).
WD40? As simple as that? I was expecting a mix of Marvel mysterious oil and some other unobtainium product...
Does the engine need to be turned long to remove it? Does the engine oil need to be replaced too after this?
Thanks!