Topic: CB350Fruns but stalls in first gear/power loss/all cylinders might not be firing

[zcb350fb]

I have a 1973 cb350f that fires up fine, idles fine but stalls when I give it gas to go into first gear.

The bike has done this before and at that time I changed the inline fuel filter to a new one. that solved the issue.

I let the bike sit a month and it is doing it again. when I first fired it up after sitting for a month, it started but was leaking gas out of the two inner carb drain screws. I tightened the screws and stopped the leak. after that I found that the bike was dying in first gear. I was taking off on a slight up hill so I turned the bike around. I started it up. it idled fine and I put it into first gear rolling down hill and it did not stall. there are big hills in my neighborhood and after starting it out going downhill it kept running up and down all of the hills. It did feel like it did not have full power and might only be running on 3 cylinders. if I would come to a stop though, the bike would idle and again once I tried going into first gear it would die.

It only sat for a month and was running great prior to sitting. I would go on long rides on it twice a week, prior to letting it sit. It has done this before and again putting a new fuel filter on the bike solved the issues. I put a new fuel filter on and this did not solve it. Next thing I am going to do is drain the float bowls and see if that helps. I also put new spark plugs in it in march.

Is there anything else I should look for? I always put 93 octane non ethanol gas in the bike. I pour a little marvelous mystery oil in the tank twice a month. the carbs were taken a part, rebuilt and cleaned in February

Thank you all in advance!

[zcb350fb]

also, when this happened before, I put the new filter on, rode around my neighborhood and the bike would gain power then backfire. I riding for a few minutes, the backfiring stopped and the bike had full power again.

now I can get the bike to backfire but full power is not regained

[TwoTired]

post pictures of the spark plug tips.

Cheers,

[carnivorous chicken]

Could be a fuel delivery issue -- check to make sure your cap vent isn't cloged.
If you suspect it's not firing on all 4 cylinders, look into that. Is one pipe not as warm as the others?
If it's not firing on two, check points, then coils. If it's not firing on one, check spark plug and check the spark plug cable and cap. Then dig into the carbs.

Have you done a tune-up? Valves, points gap, timing, charge battery, check advance, oil change, carb sync?

These are great bikes and run like tops when they are dialed in.

[zcb350fb]

Thanks for the info everyone. I am on my way out of town and wont be able to dig back into the bike until Monday. Ill post pics of the spark plug tips then.

I have not touched the timing or valves yet i will look into that and check muffler temps to see if cylinders are not firing. Battery was fully charged last night when i dug into the issues.

[zcb350fb]

I am having trouble posting pictures of the spark plugs. If i am able to, ill get the pictures posted on here. I will say that all of the spark plugs looked the same to me. They were all black on the spark end and along the threads.

I did not get a chance yet to run the bike no check to see if all four cylinders were firing due to exhaust pipe warmth. Once i am able to do that, i will let you know as well.

I did take a look at the points last night when i checked the spark plugs. The points are worn and have severe pitting. I did clean the points a little. Also, the felt in the points cluster that rubs against the center lobe was not touching the lobe at all. There was a 1mm gap between the felt and lobe. I did grease the felt and pull it to where it was touching the lobe.

I do have some new points and condensers i bought from 4into1. I will replace those within the next few days. I have never replaced points on this bike before. The only thing I’ve ever replaced points on was an MG Midget i used to have and it was pretty easy. So i am able to do a points change but i wanted to ask do you all have any advice/tips/tricks to setting the points gap and timing on these bikes? I do have a climber manual. Also, does the points gap get the widest just after the “F” mark?

Once i get points gap and timing squared away on the bike, i am going to check and adjust valve clearances.

I changed the oil on the bike 2 months ago so i think it should still be good

[Bodi]

Well, you need three things: fuel/air mix that will burn, compression, and spark.
Changing points is a decent idea. gap is set with the points cam at full lift, that's easy to see by eye I think. Adjustment can be tricky but using a static light you want the points to open at the F mark. Adjust the fixed set first by rotating the plate then move the sub plate for the other set. If the main plate is sloppy in the mounting bosses you will have trouble setting the timing, and the sub plate set may not be able to hit F. You can adjust the gap a bit off spec to get timimg right, there's a fair bit of tolerance in the dwell angle. have a look at the points once it's running, there should be almost no sparking: if there is a lot of sparks then the condensors are probably no good.
You should do a final adjustment with a strobe timing light. Best to adjust it to the advance mark at a high enough RPM that the mark is stable, leaving the low RPM F setting wherever that leaves it.
Once you're confident that you have good spark at the right time - new plugs are worthwhile just in case yours are carboned up enough to misfire - confirm the valve tappet clearances are correct. Too loose will be noisy and can reduce compression as the valve timing is changed, too tight can stop the valves from fully closing and you lose compression.
Then do a few plug chops to check if the carbs are working properly and the jetting is correct.
If the engine is burning oil - leaky rings or valve guides - the plugs will turn black rather quickly.

[zcb350fb]

Bike runs like a top now. I adjusted valve clearances, replaced plugs, replaced fuel lines and filter and replaced points and condensers.

Thanks for the help everyone

[carnivorous chicken]

Good to hear! Those things run great when they are dialed in.