I’m desperately seeking some sort of assistance to help get my 74 CB350F1 back on the road. I’ll give you a bit of the history of why the bike isn’t on the road: you can skip the next paragraph or two if you want to get to the technical details.
I bought the bike two years ago after I saw it collecting dust out in someone’s back yard. It had 63000 miles on it and didn’t run at all. I took her home, fixed her up and got her on the road. It took four months, but she ran alright- except for the burning lots of oil. Anyways, I was out riding her this year around March when my chain ceased and sheered all the teeth off the rear sprocket, the bolts holding the sprocket on and seriously damaged the rear tyre rim. I don’t know why I didn’t crash horribly, as it happened when I was making a left hand turn at 40km/hr. Anyhow, I decided I would walk it 15 blocks uphill to my friends house, come back the next day and fix the chain, sprocket and anything else that was damaged.
The next day I got a phone call from my friend urging me to come over as quickly as possible. I go to get the bike but discover, upon arriving, that his next door neighbour had ran it over with her van. After a week of negotiation a settlement was arranged and the bike was brought back home. I checked the frame, shocks, etc… and everything seemed to be alright. The bike still ran, but the chain was busted. I also happened to get a hold of a friend who had another old CB350F1 that had been close to a burning barn. blinkers were a bit melted and the some parts of the bike were covered in tar. I decided I could see if the motor worked and try to do a motor swap, since I hate burning oil. The bike fired up a few hours after it was delivered (after cleaning it up) and ran quite nicely. So I decided to swap the motor over since it had 8000 miles, only.
Now the motor is sitting in my bike, and I did a test fireup with the exhausts removed. She fired up with a little backfiring, but after a while became very smooth. The next day I went and connected up the exhausts, rear brake system, and replaced the chain, sprocket, bearings, and rim. I also replaced the oil pan gasket and the clutch housing gasket.
Now the bike doesn’t want to fire up at all. The electronic starter turns the motor over fine as does the kickstart, but it doesn’t start.
There is horrible backfiring out of one of the two left cylinders (4-2 exhaust). It is extremely loud and followed by white smoke puffing out of left exhaust. Sometimes it flings little pieces of carbon well across the garage. Sometimes I see purple flames shooting back out of the intake manifold, with note that I have seen flames come out the two middle carburetor intakes at the same time (I don’t think they are suppose to have that firing order).
Here are a list of things I’ve done and checked, in order to make it easier for someone to help me:
I have checked the points/capacitor in the timing housing. The ignition timing is set in the middle for each fine adjustment, to be conservative. I am quite sure the backfiring is not due to any miss fine adjustment to the ignition timing. I have checked with a screw driver with the coils powered up to see if they spark when the points are closed. They do spark quite brightly and intensely showing that the points are doing their job. They are also giving me >12V reading between the point contacts and the ground. I have changed the points and the capacitors(?) to ones known to work but it doesn’t seem to make a difference. I might have installed the points incorrectly so if someone can tell me if there’s some special alignment the crank has to have when installing the points?
I have changed both ignition coils to two different, known to work coils. It doesn’t seem to make a difference. I have also checked the coil to points wire for continuity. The wire was not giving continuity and I replaced it with one that does. It didn’t fix the problem.
The spark plugs are visibly in good shape and they are fairly new (<3000 miles). There seems to be a strong inconsistency with the spark intensity. I have checked just the wires for spark, and all the wires do spark, but they do not always spark. If I test one, it sometimes doesn’t spark, but a few minutes later it will be sparking. I don’t know what this means.
I’ve also checked the carbs but I don’t feel that they are the problem. If I fiddle with the choke while the bike is starting up, sometimes it will backfire, but only on the one side. The engine was running before.
Can anyone suggest anything? This bike has been two years of work
Anything is appreciated.
