Topic: 1980 Honda CB650 - Cylinder 2 & 3 not getting fuel

[lil_buddy00]

Hello everyone.

I haven't been able to find anyone with this relative problem.  I have (obviously) a 1980 Cb650c that I just am finishing up.  I've run into an issue with the carbs?  There doesn't seem to be any fuel getting into cylinders 2 and 3.  The engine runs and idles on cylinders 1 and 4.

All the general run down:

- Compression is good on all cylinders - plugs out, carbs off, all cylinders are 155+ with a warm engine.  Manual says 172 +/- 28 PSI is proper range
- Spark is good on the plugs - I've done all sorts of tests here, rotated coils around, plug wires, even got (1) new coil - everything is good here.  As well, after the bike is running, I pull all of the plugs - 1 and 4 are perfect tan color, 2 and 3 look brand new with a little bit of black on the ceramic where the spark happens.  No signs of fuel on the plugs - not even a smell.
- Timing is set properly on the crank - adjusted air gaps on pulse generator
- Valve clearance have all been set to spec
- Carbs have been cleaned and re-jetted - the bike has had pods on it since the PO and so I put proper jets in - 120 mains and 90 slow jets

That's pretty much all I can think of in terms of info for you - if anyone has any idea of what I should look at that could be causing this, please let me know.  Thanks in advance.

Daniel

[arncruz]

Have you tried putting gas into the cylinder 2+3 to see if they will fire. If the engine fires on all 4 cylinders then you know its the carbs and you'll have to go through them once more.  Make sure that you can blow compress air through all the passages.  Also  Check that the floats in the carbs are to the correct height.  That's all I can think of right now. Good Luck!

[mrbreeze]

I would look closer at the ignition system. 1&4 fire together as do 2&3. Usually on these bikes a problem with either of these pairs turns out to be ignition related.

[lil_buddy00]

Thanks for the replies.

I haven't tried putting gas directly into the cylinders yet - is there a "best practice" for this?

The 2 things I keep going back to are -
1. Valve clearance/timing on the center two cylinders - it really just seems that there is a blockage of some sort getting in the way.  The only thing I could think is that the valves just aren't opening at the correct time
2. Fuel not getting through the slow jets - I've pushed carb cleaner and compressed air through all of the passage - but it wouldn't hurt to do it again

Thanks again for the help - so frustrating.

[arncruz]

The slow jets are very small  and sometimes there is just old gas build up.  If you can take them out and run a small wire through them to make sure the passage is clear.  I would do this with most jets.  As far as putting gas into the cylinder directly, I sometimes shoot carb cleaner into the cylinder I want to test with the carbs off the bike.  That way you can test #2 then test #3 separately.  If you get the specific cylinder to fire, then you know your timing and spark are working. 

[CB650CPastor]

Barring an ignition problem... if those cylinders kick in at WOT, then it's your slow jets that are clogged. If those cylinders never kick in, I would check the fuel crossover pipes and float levels in cylinders corresponding to the the non-firing carbs.

[lil_buddy00]

I just went through today and checked static timing, and changed spark plug wires around - I know that 1 & 4 fire.  I also went through and made sure all the jets and air passages weren't blocked, ran compressed air through all and then did another compression check and still getting 155+ on the two "dead" cylinders. 

I set float levels to spec in all 4 carbs yesterday.  As well as a vacuum sync on the 4 carbs, so I know there is suction.  It has actually helped the two cylinders that are running, run better.  But, the two center plugs are still bone dry.  No evidence of fuel getting through.  When I had the carbs off, I checked to be sure that the intake and valves were opening, which they were.

I'm at a loss here and almost about to pull the cylinders and replace the rings - but that wouldn't make much sense with the compression that I'm getting.  It's almost acting as if there is a physical blockage in the intake.  Like the valve isn't opening a the proper time.  Maybe I pull the top off and make sure the cam timing is art properly to the marks.

[scottly]

I'm at a loss here and almost about to pull the cylinders and replace the rings - but that wouldn't make much sense with the compression that I'm getting.  It's almost acting as if there is a physical blockage in the intake.  Like the valve isn't opening a the proper time.  Maybe I pull the top off and make sure the cam timing is art properly to the marks.

The problem isn't the cam timing, or # 1 and 4 wouldn't be firing.
Check that the 2 & 3 float bowls are actually filling with gas by opening the drain screws first.

[lil_buddy00]

Agreed with the timing comment. That's just where I'm at with what it could be. Lol

I'm 100% the bowls are getting the proper amount of fuel fuel on all 4 carbs.

[lil_buddy00]

If there is something wrong with the pilot screw in these two carbs, would that keep fuel from getting through?

I replaced the screws when I rebuilt the carbs, just a thought.

[mrbreeze]

When my bike had this problem, it turned out to be the coil power wire. It comes from the on/off switch and branches to 2 wires.....each feeding a coil. The problem was intermittent but steadily got worse. I found it by wiggling the wires. I was running it with the gas tank off. One of the wires was loose in the connector and had a bit of corrosion (from arcing). Of course before I found the problem I had been through the fuel system. I even thought my Dyna 2000 unit was acting up.
If you think I wasn't pulling my hair out trying to find the problem you were wrong! Try this......when it's acting up....put a timing light on 2 or 3 and wiggle the wires. It should be obvious if that's the problem.

[lil_buddy00]

I'll check that out. But, it still seems as fuel isn't getting into the cylinders.  The plus don't have a fuel smell to them at all. Only color on them is in the bottom electrode where the spark happens.

But, I have to put a timing light on, just to be 100%. So, I'll put it on 2 or 3.

[Hondawggie]

I'll check that out. But, it still seems as fuel isn't getting into the cylinders.  The plugs don't have a fuel smell to them at all. Only color on them is in the bottom electrode where the spark happens.

But, I have to put a timing light on, just to be 100%. So, I'll put it on 2 or 3.

That got my attention.  I just had a similar issue and solved it. 

1) pulled the carbs off the first time, pulled all jets, etc. and let sit in Berryman's Carb Cleaner over night.  I have 4 cans of this, one for each carb.  Each can has a metal parts basket to hold all the little parts -- you can see that parts basket in this photo:


Some people forget to pull the pilot air screw  (aka idle air screw) on carbs that have them.  And/or forget to set that idle air screw to the factory setting.   You could have clear pilot jets but if the idle/pilot air screw is blocked your pilot circuit is compromised and at low RPMs you will know it.

Some people forget to check if the float needle pin freely moves up and down -- it's spring loaded and must move up and down freely.   Also,  the float needle must not be sticking or binding in its socket.  Deviating from this can lead to poor or no gas flow into the float bowl

I used 110psi air from my compressor, and spray can carb cleaner with red straw on the nozzle of the can, and the high E string of an electric guitar to run through the carb's passageways.   I blow the living crap out of every hole I can find -- and make sure when I spray aerosol carb cleaner in one hole it comes out the other side (or more guitar string probing and 110psi air is called for).

I put the carbs back on -- not getting gas in #4 and #2 cylinder.


2)  pulled the carbs off -- pilot jets were clogged.  "WTF I just cleaned them!"  I cleaned them again.  "How did the pilots get clogged so fast?"

The fuel tank provided a bit of sediment.  That's how.

This can happen if the filter screens on your gas tank's petcock have a hole or are missing.

I put an inline fuel filter in the gas supply line from tank to carbs.  Put the carbs back on.


BAM fixed it.  Firing on all 4 cylinders.


You have to solve the 'gas not getting to cylinder' problem.

[mrbreeze]

This can be the problem but seeing that it occurs on those 2 cylinders is what my diagnosis is based on. Another thing you could try is swapping the 1&4 wires to 2&3 or you could spray carb cleaner directly into 2 or 3 and see if it picks it up. These kinds of problems can be frustrating but if you stick with it, the cure can be found. I'm not familiar with 650's but I would think that they are similar to the older bikes.

[scottly]

  The engine runs and idles on cylinders 1 and 4.

Are you sure it isn't idling on all four cylinders? It wouldn't idle very smoothly if only two cylinders were firing. Do the spit test on the exhaust pipes: start the bike up, and see if spit sizzles off the pipes near the head. The pipe on a non-firing cylinder will only be warm, compared to one that is firing.

[lil_buddy00]

Hondagwwie - I actually cleaned the tank out completely - a few rounds of apple cider vinegar, and then resealed the tank with RedCoat.  I also have an inline filter on the fuel line.

MrBreeze - I've swapped 1&4/2&3 wires around and the opposite coil still fires 1&4 (yes, put appropriate leads from the pulse generator on the coil), so I know it's not the coil.  I'm wondering if it may be the 2/3 side of the pulse generator that has gone bad.  I did a resistance check on it and the readings were in spec per the manual.  But, I'm assuming that reading isn't all-telling.  Could still be bad.

Scottly - The temp of the headers was actually how I initially discovered they weren't firing.  About 10 seconds after start on idle, the headers on 2 and 3 are virtually the same temp as if the bike is off.  And the headers on 1&4 are already almost to the point that I can't touch them. 

I'm going to see if I can find a new ignition pulse generator online and swap that out - hopefully that will do the trick.  I also need to check the oil to be sure that, if 2&3 are in-fact getting fuel and I just can't sense it, the unburnt fuel isn't getting into the oil through the cylinders.

[lil_buddy00]

Something caught my attention as I was reading some other posts - mainly a comment by Kit.  She said, in response to another comment, that these 650's typically run so lean that it's very unlikely that you will see any part of the spark plug being "wet" with fuel. 

My question would be - would it be plausible that, if the timing is off just enough to not fire at the correct time, it's not combusting the fuel and I'm just not seeing it because these machines are typically very lean?

Just some food for thought.  Going to throw my timing light on it this evening and see where it's at.

[lil_buddy00]

Ok - so I there my timing light on. And, timing was off slightly on #1 and 4. However, when I put the receiver on #2 and 3, the light fires - so I know the wires are getting signal. But, if I'm not mistaken, the light on 2 and 3 should be triggering at the 2.3 fire marks, correct? It's no where near the marks when the light triggers.  I'm assuming this may be causing the issue. Any thoughts??

[lil_buddy00]

I wanted to put this here for resolution - I finally figured out what the issue was, after putting the timing light on the bike and realizing that 2 & 3 were firing direct opposite of what they were supposed to be. 

I had rewired 99% of the bike and when I rewired from where the harness connects to the pick-ups and then up to the spark boxes, I had the 2 yellow wires backwards going into the spark control boxes.  Switched those around and immediately knew it was fixed.  Bike sounded completely different.

Now just to make sure everything is burnt out of 2&3, put new plugs in and tune her up.

[lil_buddy00]

Thought I'd add a photo, as well.

[scottly]

I knew you were onto something when you noted the timing was way off on 2&3, but I never would have guessed reversed pickup wires!! Sure enough, one of the blue wires and one of the yellow wires has a white sleeve at the plug end.
Thanks for telling us what the issue was!

[lil_buddy00]

Yea - after I wrote that post out, I went back and looked at the colored wiring diagram online. And there are small white squares that note the white tags.