Author Topic: 1973 honda cb350f backfire and weird issues  (Read 2107 times)

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Offline lolzfail

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1973 honda cb350f backfire and weird issues
« on: May 23, 2015, 12:50:01 PM »
Ok so, first post, been creeping though. ok. I bought this bike a month ago. test drove it up to like 30 ran great started wonderfully and all that jazz. got it home got it to about 40 hit the power band in 3rd gear immediate stall. pulled plugs, number 1 cylinder plug was not firing due to bad plug. bought 4 new plugs, put 4 new plugs in, started up immediately, ran stronger than ever, for 20 seconds. then LOUD LOUD LOUD backfire out of the right side, either 3 or 4 cylinder backfired through exhaust. pulled points cover, was horribly timed and everything. but brand new points and that. so. set point gap. set timing. all that is in order, now when I start it, barely wants to start, will idle, if throttle is applied backfire through carb and exhaust and stalls. so im about to get into valve lash, im thinking that it would be a valve clearance issues seeing as previous owner was a twat. would improper valve lash cause this issue? 

Offline harisuluv

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Re: 1973 honda cb350f backfire and weird issues
« Reply #1 on: May 23, 2015, 07:25:18 PM »
Welcome to the forum!

Now, first off you're kind of all over the place.  Take a step back and try to be methodical about your troubleshooting.

First thing I think of is:  we know nothing about your setup, stock airbox, stock exhaust?  year, mileage, general stuff.

You replaced all four plugs, what did they look like?  This will give you some real data about how you are running.

Next, you put in four brand new plugs, look at those too!  This will give you more data.

Backfire on accel would indicate rich, backfire on decel lean.

What brand new points did you get?  Many brands or ebay specials are just garbage.

Lastly, post pictures.  You will be 10x more successful and won't have to explain everything.

- James

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #2 on: May 27, 2015, 06:04:30 AM »
Apologies for being all over the place. When the plugs were pulled they were all black and covered in carbon. It is a stock 4 into 2 exhaust. It has pod filters, individual one for every carb. The new plugs, I have pulled all of them and looked, the plugs in 1 and 4 were black with carbon, not wet in anyway. 2-3 plugs were brand new looking still. The new points were already on the bike, I have no idea what brand they are but the points and condensers I believe they're called? Capacitors? Also are brand new.

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #3 on: May 27, 2015, 07:26:00 AM »
also, 1973 Honda cb350f with about 20k miles on it. bought it from someone that got it from someone that got it from someone and doesn't know any of the issues. it had the new points when I got it from the previous owner, he put them on and could not get it to run right. im not a motorcycle tech by any means, but I am an auto tech, and I know the basic diag and things, im just honestly at a loss right now, and its because this is one of those weird frustrating problems because due to the previous owners lack of knowledge, I think he just blindly went through things, and I feel that im just working in circles. I personally have also set point gap, and set timing, multiple times using the static method for both, properly, setting gap for points and the points cover and all of those timing adjustments and checking multiple times until the points fire exactly at the timing marks. so I know timing is not an issue. I will look into the spark plug wires as soon as I go home, about 2-3 hours from now, and change those around. does it matter which wire, from the left coil goes to which plug? or just left coil to 1-4 and right coil to 2-3, the wire from the coil doesn't matter?

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #4 on: May 27, 2015, 08:11:32 AM »
im going to check just about everything I can before I get into any carb work haha, attempting to avoid that. but I have seen the clear tube method, I believe its even in my Clymer manual

Offline knowsnothing

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Re: 1973 honda cb350f backfire and weird issues
« Reply #5 on: May 27, 2015, 10:14:08 AM »
http://manuals.sohc4.net/cb350/

Print it, read it, memorize it   ;D

Your issues sound carb based.  I know on my 350f, the idles were plugged.  Needed a good cleaning before the bike would idle well
1978 CB750k Green - 811 engine
1978 CB750k Blue - for sale
1974 CB375F Faded Black - had to have that 6th gear
1976 CB400F Red - in many pieces
1973 CB350F TBD - in many pieces

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #6 on: May 27, 2015, 03:31:17 PM »
Ok. So went home and played with it, now just annoyed. Plug wires. The 2 wires from the left coil, go to the farthest left cylinder, and the one immedietly to it's right. Cylinders 1 and 2? And the right coil, goes to the right 2 cylinders. 3-4 I believe? However, if I change this configuration anyway, like putting the left coil on cyl 1-4 and right on 2-3 it will not start, just backfire out the carbs and exhaust upon cranking.

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #7 on: May 27, 2015, 03:37:26 PM »
Really. Going outside right now

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #8 on: May 27, 2015, 03:47:34 PM »
Fixed.......

Offline lolzfail

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Re: 1973 honda cb350f backfire and weird issues
« Reply #9 on: May 27, 2015, 04:04:14 PM »
That was ridiculous. It sounds so happy now <3 thank you