Topic: No gas in the cylinders!

[cbass*gxc]

Well got my engine completely together today and have been trying to start it but it wont start.  So I decided to check the plugs to see if they were flooded but there was nothing on any of them.  I took the carbs off and looked and it seems to be clear.  I tried spraying starter fluid in the carbs and when I do that the exhaust backfires. 

ANyone know what the problem may be?

Jay

[scondon]

Ignition timing?

[johnny_from_bel]

Check basics.

1. Ignition. There is ignition as it backfires.
    You may have switched plug cables.

2. fuel. See if fuel comes to the carbs. Open the drainplug and see it fuel comes out.

3. Cam timing. You may have the cam chain 'one tooth' off.

[cbass*gxc]

Well I just took the carbs off again and felt in the intake and they were not wet at all.  The only side that backfires is the #4 cylinder, the others do nothing. 

I checked the timing and 1&4/2&3 seem to be opening up at the same time but they seem to open past the F marks.  COuld this be the problem?

[cbass*gxc]

Ok so I got the points firing right on the F mark, I took the valve cover off seeing as I had to replace all the bolts anyways and it is lined up exactly like it says in the manual, check the plug wires for position and spark again and they are right, but I still get no fire.  It did start backfiring more from the #4 cylinder and I checked the plugs again and a couple of them seemed to have either gas or starter fluid on them, so at least it looks like I am getting fuel.  But the damn thing still doesnt fire.  I repainted the valve cover because it had a few scratches from putting it back together, so I have to wait for it to dry, then I will put it back together and try it again.


If I hold my hand over the exhaust or over the carb intakes, I can feel air moving in and out of them.   I also checked the valve tappets and they are all moving up and down.

[mattcb350f]

If it's backfiring out the exhaust than the ignition is way too retarded, firing long after TDC or on the exhaust stroke. Could also be valves stuck open by having them adjusted too tight.

Check valve adjustment, check to see that all sparkplugs are firing,

Is there a way that the points wires could be switched to the wrong coils?
...1-4 points running the 2-3 coil?... that would cause the problem too

 Matt.

[johnny_from_bel]

Well I just took the carbs off again and felt in the intake and they were not wet at all.  The only side that backfires is the #4 cylinder, the others do nothing. 

I checked the timing and 1&4/2&3 seem to be opening up at the same time but they seem to open past the F marks.  COuld this be the problem?

What type of engine is this.

I can run my engine (750) on starter spray only.
Let us eliminate ignition.

Check if you have a spark on all 4 plugs.
The check the sequence to make shure no wires are crossed.

*EDIT* Sorry Matt, you beat me to this.

[pampadori]

Well I just took the carbs off again and felt in the intake and they were not wet at all. 

i don't think you are getting fuel.  check idle jets make sure they are clear and make sure the bowls have fuel in them.

[TwoTired]

Did you take the mechanical advance mechanism apart?

Are you using the choke?

Are you sure the choke butterflies are closing completely?

[cbass*gxc]

I think I just figured out the problem.  I read what you guys had posted and went and started checking the sequences and noticed the sparks were firing right after the exhaust stroke so I think the cam shaft needs a 180 degree turn.  That would cause the back fire.


Going to wait to see if this is the problem then I will switch it.


EDIT.  I just looked in the manual again and I do have the shaft backwards so back out I go to take the valve cover off for the 3rd time today.   I lined up the notch to the left instead of the right.  Spent an hour trying to figure out how to get it back on then decided to search and found the way.  Must have just been in a bad mood and didnt realize what I did.

[cbass*gxc]

Well got the cam turned and it tried to start once.  Now it seems to be back firing from both sides. 
I checked the timing of the valves and the spark and it seems as though it sparks right as the inlet valve is starting to open.  I tried adjusting the points plate in both directions and it still sparks at the same time.

The woman went to bed so I guess I am done for the evening.

[mattcb350f]

If the cam is now timed correctly, than it sounds like the ignition is firing 180 degrees too early.

Not sure where the problem is though.

 Matt.

[cbass*gxc]

Is the ignition supposed to fire twice in one up and down stroke of the piston?  I noticed the plugs would spark once when the intake valve would open and once when the exhaust valve would open.

[Gordon]

Is the ignition supposed to fire twice in one up and down stroke of the piston?  I noticed the plugs would spark once when the intake valve would open and once when the exhaust valve would open.

These bikes run on a "wasted spark" ignition system, meaning they spark on both the compression and exhaust strokes.

[Cvillechopper]

Just saw this.  I did the same thing on my first rebuild.  Cam went in 180 out.  Once I figured what I had done, I fixed that, but was not very patient getting it back together.  Ended up adjusting the valves very poorly the first time and had forgotten to adjust teh cam chain tensioner.  Go back through and make sure the tensioner is snugged up and that the valves are adjusted correctly.  Once you verify that, take a look at the electrical timing then see if she'll fire up with a little starter fluid into the carb inlets.

That reminds me of another question.  Have you been trying to start the bike with or without the airbox on?  If it's still off, that would explain the lack of fuel in the cylinders.  You'd need most of the choke to get fuel to pull through. 

[cbass*gxc]

Cville what do you mean adjusting the valves?  Are you talking about the tappets?  I adjusted the cam chain tensioner and sprayed a little starter fluid in it before work and it seemed like it tried to fire the first push but then it would just crank with some rumble coming out of the exhaust.

I have been trying to fire it with out the airbox but I have tried firing with the choke full, half, and off.  The bike seems to back fire when I have the choke on full and try giving it a little gas.

I guess this evening I may check the cam shaft again and see if maybe I was wrong about it being backwards.  I thought it was on F1-4 and the notch was to the left but I could have had it on the F 2-3.

When exactly is the plug supposed to spark?  I noticed last night that it would spark right as the valves are opening?  Isnt it supposed to spark when the valves are closed?

Edit-I got to thinking I took the clutch switch off the bike and took the green/red wire and put it straight to ground.  That is the way it goes right?  What exactly does that switch do?  Would I be getting spark if it was not done right>?

[Cvillechopper]

Cville what do you mean adjusting the valves?  Are you talking about the tappets?  I adjusted the cam chain tensioner and sprayed a little starter fluid in it before work and it seemed like it tried to fire the first push but then it would just crank with some rumble coming out of the exhaust.

Yeh.  Tappets.  Sorry.  I'm just used to saying adjusting the valves but you are correct.  You can only adjust the tappets that move the valves.  You say you adjusted the cam chain tension before work.  Did you do this BEFORE adjusting the tappets?  It has to be done in that order. 

I have been trying to fire it with out the airbox but I have tried firing with the choke full, half, and off.  The bike seems to back fire when I have the choke on full and try giving it a little gas.

I guess this evening I may check the cam shaft again and see if maybe I was wrong about it being backwards.  I thought it was on F1-4 and the notch was to the left but I could have had it on the F 2-3.

When exactly is the plug supposed to spark?  I noticed last night that it would spark right as the valves are opening?  Isnt it supposed to spark when the valves are closed?

With the airbox off, it'll be hard to start but you should be able to get a quick rumble by using some starting fluid (I prefer WD40 cause it's not as harsh on paint).  You'll have to keep spraying it lightly to keep it running.  If you just did a shot into each carb then turned her over you would only get the result you described.   One quick attempt to fire, then nothing.  No matter, it'll run like crap without the air box and filter.

Also, here's a great illustration of the firing sequence for these bikes.
http://oldmanhonda.com/MC/engine.html
It's a 350 twin with the points directly on the cam but the firing order is basically the same.  Only difference is that you'll have a spark on both the compression and exhaust stroke on the 4s.

Main page has tons of good info as well.

[cbass*gxc]

I have not adjusted the tappets at all.  That is something I plan on doing this evening. 

So from what I am seeing from that illustration it should spark when the valves are closed?  If this is the problem what would I do to adjust this?

Sorry for all the questions.  This is my first engine work ever so I am learning as I go.

[Cvillechopper]

I have not adjusted the tappets at all.  That is something I plan on doing this evening. 

So from what I am seeing from that illustration it should spark when the valves are closed?  If this is the problem what would I do to adjust this?

Sorry for all the questions.  This is my first engine work ever so I am learning as I go.

No problem with the questions.  That's how you work though problems.

Not having adjusted the tappets, you should not be trying to get it to run.  You risk bending a valve and causing yourself MUCH trouble.  Adjust the tappets then check back.  Everything else is mute until then.

Here's why.  The tappets control the actual opening and closing of the valves.  If they're not right, you'll not have the valve open to pull gas in, closed to create combustion, or open to release exhaust at the right times.  An open valve when the piston hits TDC will be a BAD thing and can be caused by a tight tappet.  If they're all loose, you'll just not get ANY air/fuel flow through the chamber.

[cbass*gxc]

Will do.  I will check the tappets first thing when I get home then report back.

Actually I may do it at lunch.

But as far as the plug sparking should it be sparking when the valve is open?

[moham]

But as far as the plug sparking should it be sparking when the valve is open?

The intake valve opens to let fuel/air into the cylinder, then closes. A spark causes combustion, pushing the piston down, then the exhaust valve opens and allows the spent fuel/air mixture to escape. This is a simplified explanation, and I am sure will be elaborated on by others...

[cbass*gxc]

Ya got that but it sparks right as the tappet starts to go down, which seems a little early.

[moham]

Ya got that but it sparks right as the tappet starts to go down, which seems a little early.

Sorry, I guess I don't understand the question...

[Cvillechopper]

Don't worry about when it's sparking relative to the tappet until you know that the tappets are set right.  The spark will occur at both the exhaust and combustion strokes.  Sounds like you're talking about the spark that happens just as the intake valve starts to open (exhaust stroke just finished pushing all of the used fuel/air out).  The 180 of that will spark when both valves are closed (assuming you have the cam in correctly) and they remain closed for the downward stroke. 

[cbass*gxc]

If you look at that illustration that cville posted it shows the spark firing when both valves are closed.  Mine spark as the valve is going down.

Thanks cville that answered my question.