Cranks and Backfires but won't start

[dinger]

I'm at my wit's end right now so I'm hoping you folks can help me out!

I bought a CB-1 this spring and it ran perfectly all spring and most of the summer.
Then one day, it decided it didn't want to start.

It has spark on all four cylinders, and fuel at the carbs.  It will backfire with the choke on and no throttle, but that's about it.

So far, i've checked:

-Replaced CDI box
-Checked coils for proper resistance (primary and secondary sides)
-Checked plug wires
-Checked pulse generator for proper resistance and peak voltage while cranking
-Checked all signals at CDI connector to make sure there was no bad connections in the harness
-Checked timing with timing light while cranking
-Checked for spark by pulling plugs one at a time and grounding them to the frame
-Checked battery voltage and boosted with a lawn tractor battery
-Replaced spark plugs (twice)
-Drained carb bowls and tank, filled with fresh fuel
-Checked for fuel at line to carbs
-Checked to make sure fuel pump was operating
-Checked to make sure Petcock on tank was letting fuel through
-Checked for proper tank venting
-Replaced fuel filter
-Replaced old cracked fuel lines


Any further ideas?

[psubrock]

WOW, I've got to give you credit man that's a lot of trouble shooting.
Sometimes my 1 just doesn't want to start. I went as far as to replace the wiring harness (bad connection with the pulse) which helped but every now and again she just cranks and cranks and cranks until I give up and bump her. One time she didn't start, so I didn't do anything and came back the next day and she fired right up.
Reg rectifier? It's one of the few things you left off the list.

[clarkdw]

It sounds like you have a pretty thorough troubleshooting skill. My suggestion is on the rather simple side but it has tricked me on vehicles other than the CB-1. Make a triple check that your plug wires are routed to the correct cylinders. I'm in a hurry to go to work so more questions in the morning when I get back.

[dinger]

I've also tried bump starting it, and unfortunately that did not help.

I'll triple check my plug wires to make sure they are correct, but it exhibited all of these same symptoms before I tore her down to troubleshoot.

As far as the Reg/Rec I haven't checked it since it shouldn't affect the bike starting.  However, I did unplug it and try to start the bike just in case it was pulling the electrical system down.  No dice.

[REgina CB-1]

Did u follow the manual when reconnecting the sparkplug wires to the ignition? If u did that's your problem. Tge manual's wrong. I think the 1 and 3 wires are reversed in the cb1 shop manual (not the general service manual, the manual spec. for the cb1). I've got a thread about somewhere on he're.
Happened to me.

[a_morti]

Normally I too would have guessed at plug leads the wrong way round. I did that once and got as far as getting a set of spare carbs on there to check it before realising my mistake. But not if the fault just developed over time.

HT leads are (too) long and can break down. Try turning it over in pitch-black, and see if there is any arcing.
pulse sender can fail and still give reasonable readings. Greg / CB1-Rocket the admin at the old site had this and had a nightmare trying to track it down.
Can you get a hold of a spare pair of carbs? If the vacuum diaphragm has given out, you won't get any go. Try opening up the carbs for a quick clean around the bottom, and a really close look for splits and pin-holes in the top.

[clarkdw]

Little more information if you can, please.

When you pulled the plugs were they wet with fuel?

Have to ask: Are you very clear on the difference between backfiring and random firing of single cylinders? Difference is important in that random firing of single cylinders is usually a sign of over-fueling and backfiring does not necessarily go with over-fueling.

I quite often have some difficulty getting my bike started after long periods of sitting. My simple and dirty solution is to open up the airbox and give a small shot of ether quick start to get her going. If it starts on ether and you still have the same problem after having run it for a bit to clear out the cylinders, you have a carb problem.

It seems that the CB-1, as wonderful a bike as it is, has more fussy starting quirks than most vehicles. There are many, many threads similar to this where the bike just seems to randomly decide not to start one day and then magically cure itself several days later with no definite culprit identified. I suspect that some of the problem is the lean jetting from the factory. I know that in the early 90's when Honda began universally shipping the California pollution controlled version of their small industrial engines we used in Kart racing there were horrible problems getting them started in cooler weather due to the lean jetting. There was a mad scramble to locate the pre-pollution carbs.

[dinger]

When I put it all back together, I did follow the factory service manual in reconnecting the plug wires.  Is it really wrong?
If so, that would sure explain the backfires.

I don't have a spare set of carbs to test with.  I can do a quick and dirty clean and check the diaphragms though.

When I pull the plugs, you can see they are getting fuel.  They come out a tad wet, but don't look like they are flooding.  I've tried a bit of ether in the carbs, and that has not changed any symptoms.

It's definitely backfiring though. It will randomly make a boom like a gunshot, and shoot a 6" blue flame out of the tailpipe.  

Thanks everyone for the suggestions.

[clarkdw]

My edition of the CB-1 service manual appears to have the correct plug wire schematic. 1 and 4 from one coil and 2 and 3 from the second. I didn't pull the tank to check the color coding of the low side of the coils. I never had any probs with replacing the wires as mine are numbered on the plug wires.

Because the problem appeared suddenly I expect you do not have a bad plug wire or carb diaphragm problem. Neither of these would occur on ALL cylinders at once and prevent running just out of the blue. One carb diaphragm bad would cause you to lose one cylinder. The wires would certainly have shown some misfiring at high rpm and power loss before causing total failure unless they were drowned in water.

Try adjusting your idle speed screw up and cranking it with no choke. I assume by now you are either charging the battery or boosting it every attempt. If you have a full tank of fuel, try bypassing the fuel pump with a hose. The pump only works when the bike is turning over or running.

The common Service Manual also suggested that you MAY have to put your timing light on #4 plug wire to get a accurate reading. Not all require this but can't hurt.

The fact that ether in the carbs doesn't get it running makes me suspect an electrical gremlin.

Just a bunch of random thoughts. Hope you can find the problem. Let us know how it goes.

[ptlcb1]

Because my CB-1 is a race only bike, it sits for long periods of time, especially over the last two years, since I have not been racing much.  I do start it up from time to time, to let "lil fella" know that I have not forgotten about him.  It may take a few jabs on the starter button, but he always fires up!  There is one thing I do, once I put the key in...












I give him a big ole hug!  Have you tried that???     

[dinger]

Carbs look good.  Slides work good, not too stiff and not too loose.

I had it torn all apart tonight to re-check that the plug wires were right (they were, damn) and noticed that when i gave it a shot of starting fluid that it was backfiring out of the carbs, all four of them.

Is it possible that it could be the pulse generator?  Anyone know where I can find one to try?  BikeBandit shows they are no longer available.

[clarkdw]

There are several folks on here parting out bikes. Hope you get a reply from one of them. The pulse generator does affect all four cylinders. It actually sounds like a reasonable candidate for this problem. The failure occurred suddenly and it is likely related to spark timing.

[91cb-1]

There are several folks on here parting out bikes. Hope you get a reply from one of them. The pulse generator does affect all four cylinders. It actually sounds like a reasonable candidate for this problem. The failure occurred suddenly and it is likely related to spark timing.

Hi, just to rule myself out here i'd like to help but i already sold mine

[a_morti]

Any help?

http://cgi.ebay.co.uk/HONDA-CB1-400-NC27-IGNITION-PICK-UP-/170517976654?cmd=ViewItem&pt=UK_Motorcycle_Parts&hash=item27b3a9d64e

I think you can only use the CB-1 pick up, but you might want to try an early CBR600 part as it will be easier available and "might" fit and work.

[Drewski]

I would have said the plug caps were positioned the wrong way too, only because I've done it on my bike by mistake and the symptoms were exactly the same. They're easy to check as the caps on 1&2, (and 3&4), have different sized plug hole covers to correspond to the different sized plug holes. There are a few jokers around that find amusement in swapping them over, maybe even swapping the caps and leads It sounds like the timing is definately screwed up for some reason.