Author Topic: #1 CYLINDER NOT FIRING ???? (Read 7181 times)

bluesmoke69 · « **on:** August 13, 2011, 04:36:32 PM »

Bike infrmation( 1976 CB750F with pod filters). First I have read a lot of post on this topic please help!! I have done full carb cleaning with wire and compressed air soaked in SG. I have set valves on cab side and exhaust sides. Replace all fuel line. Soak rubber boot to soften them, and checked for leaks while bike was running. Set points according to service manual. Set carbs to specs. Checked for spark with it had, ohm the cap it was 5.1 I replaced it with new NKG cap anyway. Spark plug was which with a cylinder that was working, and new one was tried too. Plug is wet so it is getting fuel. Try swapping #1 and #4 wires with no luck. >:(ANY HELP OR THOUGHT WOULD BE GREAT!!!!

KingCustomCycles.com · « **Reply #1 on:** August 13, 2011, 05:50:10 PM »

Sounds like you covered your bases. That means you either misinterpreted something or the problem is intermittent. A wet plug is a grounded plug. Also, some plugs will fire in free air, but not under compression, reinstalling the lead may place it back into proximity of a ground if it is cracked or chafing. If it is a coil issue, 1 and 4 may be dead. Thata all I got for now. :-)

Terry in Australia · « **Reply #2 on:** August 13, 2011, 06:04:23 PM »

Do a compression test mate. You've got fuel, you've got spark, but I'm betting that you've got no compression. 2 out of 3 ain't good enough. Cheers, Terry.

KingCustomCycles.com · « **Reply #3 on:** August 13, 2011, 06:12:33 PM »

A compression test would not hurt but I have seen cylinders fire and run with extremely low compression.

Terry in Australia · « **Reply #4 on:** August 13, 2011, 06:15:39 PM »

Agreed, if it's worn rings it'll still run, but if it's a burned valve, it won't.

raymond10078 · « **Reply #5 on:** August 13, 2011, 06:32:48 PM »

If #4 is firing, then #1 is getting to ground somewhere. It has to.

I'd be looking for a spark plug lead that is sparking to ground, or you have a bad coil (the #1 end of the winding is sparking to ground).

You could run the bike without the tank - in the dark would be best - looking for sparks where it should not be. Another quick test - use some wire insulation - or other sleeving material, and sleeve it over the spark plug wire for its entire length. Just thoughts - I'm sure there's other ways to either test, or fix/block the short.

Terry in Australia · « **Reply #6 on:** August 13, 2011, 06:40:24 PM »

Re-read the original post mate, he's got spark in that cylinder, and he's swapped plug leads with #1 and #4 and they both work. So if it's not electrical, and it's not fuel, it's likely a bad exhaust valve. Cheers, Terry.

raymond10078 · « **Reply #7 on:** August 13, 2011, 07:02:11 PM »

Yes - I see now that he swapped wires - I had thought he only swapped plugs.

bluesmoke69 · « **Reply #8 on:** August 13, 2011, 07:30:03 PM »

Did compression test today cylinder #1 148psi #2 150psi #3 150psi #4 150psi

Tews19 · « **Reply #9 on:** August 13, 2011, 09:10:56 PM »

I really to jump in here but your thread got me thinking.. How do you know your cylinder is not firing? Does it mean the header from that particular cylinder is cold to the touch???

bluesmoke69 · « **Reply #10 on:** August 14, 2011, 07:31:52 AM »

Yes the exhaust pipe is cold and plug is wet.

KingCustomCycles.com · « **Reply #11 on:** August 14, 2011, 08:33:05 AM »

You are with the bike, you seem to know all the possibilities, you figure it out and report back your findings. You have been promoted from asking to telling.

Spanner 1 · « **Reply #12 on:** August 14, 2011, 08:38:35 AM »

Pull the #1 pod off and start the bike. Any fuel 'welling' in #1 carb throat ?? Sounds like #1 cyl. is getting excessive fuel PDQ which could be very high fuel level in the bowl, if so ,'prolly a 'sunk float'

RustyJC · « **Reply #13 on:** August 14, 2011, 08:41:34 AM »

If you have adequate compression, correct valve actuation, fuel (in the right amount) and ignition taking place at the correct time, it has to run. Given the results you've provided on the compression and ignition, I have to question the carburetor on that cylinder. It sounds like the carb may be drowning #1 in fuel - if it's far too rich, maybe it can't fire. Are you sure you don't have a stuck float or leaking needle/seat, although I'd expect fuel to dribble out the carb inlet into the air cleaner if you let it sit with the engine dead and the petcock open if that's the case.

Are you sure someone hasn't stuffed a potato up the tailpipe on #1? (Didn't leave a red rag stuffed in the exhaust port or header pipe, did you?)

Rusty

Tews19 · « **Reply #14 on:** August 14, 2011, 08:42:51 AM »

To check the floats, do you have to remove the carbs???

Spanner 1 · « **Reply #15 on:** August 14, 2011, 08:47:28 AM »

If your asking me ........ no, the float in #1 or #4 carb are removable on the old style carbs ( '76 F ) without taking the carbs off the bike..

...... fiddily to do , but doable.

Duanob · « **Reply #16 on:** August 14, 2011, 09:01:34 AM »

I'm betting it's a carb issue. 80% of problems from cylinders not firing usually are. Get yourself one of these:
http://www.harborfreight.com/8-piece-right-angle-screwdriver-92630.html

They are cheap and worth their weight in gold for checking floats while the carbs are still on the bike. Also you might take the pilot jets off and reclean them.

To say all you need is fuel, spark, and compression on these bikes is pretty simplistic. If you don't have the right amount of fuel running through the proper system in the carb, you won't be running smooth.

BTW, I wish my compression numbers were that close!

RustyJC · « **Reply #17 on:** August 14, 2011, 09:10:14 AM »

Quote from: Duanob on August 14, 2011, 09:01:34 AM

To say all you need is fuel, spark, and compression on these bikes is pretty simplistic. If you don't have the right amount of fuel running through the proper system in the carb, you won't be running smooth.

Ummm....I thought I said that. See below:

Quote

If you have adequate compression, correct valve actuation, fuel (in the right amount) and ignition taking place at the correct time, it has to run.

Rusty

Spanner 1 · « **Reply #18 on:** August 14, 2011, 09:11:22 AM »

The old style carbs have a wire 'clip' that holds the bowls on, so no screwdriver required btw.

bluesmoke69 · « **Reply #19 on:** August 14, 2011, 09:20:17 AM »

I made a jig for setting the float bowls double checked each one and was operating smoothly. Uses digital calipers to make jig out of thick cardboard. Will pull pdo and check fuel. I have had this issue for as long as I have had bike when I bought it it ran so smooth that I thought it was running on all four cylinders. Thanks for all the input. If the valve is burn or if their is a carbon deposit on the valve would it not fire???

bluesmoke69 · « **Reply #20 on:** August 14, 2011, 10:04:16 AM »

Spanner 1 took pod off started bike gave it some gas. What I saw was small amounts of gas coming out under slide. It was spitting out in very small amounts. I did check float movement like Hondaman stated in his book.

KingCustomCycles.com · « **Reply #21 on:** August 14, 2011, 10:17:36 AM »

We have already covered loss of compression and fuel fouled plug early in the postings..............which is it?

spot45 · « **Reply #22 on:** August 14, 2011, 02:07:59 PM »

If spark and compression are covered, that leaves two other things to check out. The head to see if it has a bad valve and the carbs. But if fuel is coming out from the slides then it is not #1 carb which is bad. One carb question I am going to ask what are your carb's history?

bluesmoke69 · « **Reply #23 on:** August 14, 2011, 04:20:48 PM »

Carb history is unknown. I bought it with #1 cylinder not firing. Again cleaned carbs according to Hondaman book. When bike is running and slide goes up, as I turn the throttle you can see small amount of gas spiting out from under the side.

bluesmoke69 · « **Reply #24 on:** August 14, 2011, 05:38:09 PM »

I did the switch already with no success. Thanks for the information anyways.

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Author Topic: #1 CYLINDER NOT FIRING ???? (Read 7181 times)

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