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Discussion Starter · #1 ·
Hello all!

Bought my first motorcycle ('73 CB350) last month from a guy who likes to 'save' old Hondas. He did a great job fixing it up, and it has been running better than expected from a 46 year old bike, but I ran into 2 issues that I would appreciate some guidance on. I have experience in doing routine maintenance on my car, but I'm new to motorcycle engine work. That said, learning how to do engine work was part of the reason I bought this bike, so I'm eager to get my hands dirty and learn something new.

1. There is a occasionally noticeable power dip when starting from a stop, especially when the bike is still warming up. I'll rev the engine after engaging first gear, but the bike will just make more noise and not really give more power for a few seconds, then the engine sort of reengages and starts operating normally. This does not happen often, but it did happen twice on my last ride. Could this be an issue with the points or carb?
2. I recently filled up the gas tank (for the third time since I bought the bike), there was a very small gas leak that developed after letting the bike sit overnight. I turned the gas tank valve to "off" and that stopped the leak. I've read that this might be due to the carb overflow not being fully sealed, but could it also be due to the fact that the gas tank is completely full and it's just slightly too much pressure on the carb float? Should this be something I'm concerned about, and is it safe to still ride the bike?

Thank you and warm regards,
mntmn
 

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As far as your gas leak is concerned, you should always be switching your petcock to the off position when the bike isn't running. If you don't you'll likely see fuel coming out of the overflow of one or more of the carbs, or worse, seeping into your engine and getting into the oil. As long as there isn't fuel coming out of the overflow while running the float valves are operating as expected.
 

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Also, after knowing you left gas on, pull dip stick and check for gas smell. Just wipe dipstick with clean paper towel. Then smell the towel to check for gas in oil. If gas smell is strong, you need to change oil. Its cheap insurance to change the oil. Better than trying to find parts to fix topend of engine.
 

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Forget "strong", IF gas smell AT ALL, change oil before restarting engine......
 
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Discussion Starter · #5 ·
Thank you very much for the responses on the gas leak! I'll check my oil tonight and see if it's in need of an immediate change.

Any word on what might be causing my power loss while accelerating?
 

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Your clutch could be slipping, if gas has made it's way into the oil it will thin it which will cause all sorts of issues.

If I were you I'd just go ahead and change the oil with the proper 10w-40 JASO MA rated oil.

Let it warm up with the new oil and see if you're still experiencing the same issue with power loss.

--
Mike
 

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Discussion Starter · #7 ·
Hey all, thank you very much for the advice! I greatly appreciate it.

Status report:
I replaced the oil, but did not clean the oil filter, as one of the screws on the housing was completely stripped, and I did not want to go to Home Depot again that day.
After the oil change, the bike ran like a dream again. I rode it for about 20 minutes with absolutely no issues. Problem solved!

However... when I got back home from that ride, I forgot to turn the petcock back to off, and then my wife and I left for the weekend. When we got back home, there was a small amount of gasoline beneath the bike. Quite upset at myself for forgetting about the petcock immediately after changing the oil.

What I should have done was change the oil again. It only takes 15 minutes and I had the oil in my garage. I'm kicking myself for not just changing the oil.

What I did instead was do a smell test and check the dipstick to see if gas got into the oil tank. I didn't notice any gas in the oil, so I took the bike out again for a quick ride and there were no issues whatsoever. Maybe the bike was fine? 2 weeks later, I ride the bike to work, no issues whatsoever. Riding home, when I accelerate onto the first road, the clutch starts slipping. I think "perhaps I can limp my way home", but no dice. I stop at a shopping center less than a mile from work, and the engine won't even idle. I get a Lyft home, drive back with stuff to change the oil, do an oil change, the bike starts up and idles well enough. I take it on a quick ride, it handles the first mile just fine, but the first time I try to accelerate up a hill from a stop, the clutch starts slipping again, and I limp my way back to the parking lot. The bike will idle, but not well, and dies after the clutch starts slipping on first gear. If I can get it into 2nd or 3rd at higher revs, it seems to work again, but starting from a stop is very troublesome. Since I live in Pittsburgh, and there are a lot of hills between work and my house, I decide to leave the bike there with the store owners permission, and go retrieve it with the aid of my friend's pickup, which we're doing after work today.

Obviously, I eff'd up my bike and need to do some more significant maintenance to get it working reliably. What would you all recommend looking into and doing? Here's what I plan to do:
- Drain and clean the carbs
- Clean the oil filter
- Inspect the clutch to see if it needs to be replaced
- Inspect the transmission

Once again, thank you for your time and advice!
 

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Couple things...

Get an impact driver. Those oil cup screws strip way too easily. I bought the cheapest one on amazon and it works a treat.

Do what I do. I turn off the key and close the petcock at the same time. That way it becomes automatic and you won't forget. Learned that the hard way on my valkyrie. Had a float valve stick open and hydrolock the #6 cylinder.
https://imgur.com/6ZeYlre

Now it never gets left on :p

It was mentioned previously, but make sure you are running appropriate motorcycle oil. I personally use Rotella, but that is just me. Make sure it is JASO MA rated and your good. If there was ever automotive oil put in by accident or whatever, your clutch is probably done. Those friction modifiers stick like sh*t on a white blanket.

Start with the easy stuff first. Most of your steps are reasonable.

- Fix your fuel problem. Maybe its float height, maybe needle/seat.
- Change oil and clean the filter. You will likely need to extract that stripped screw. A bit of penetrating oil, heat, and that aforementioned impact driver will hopefully get it off.
- Readjust you clutch cable. https://www.hondatwins.net/forums/48-engine-discussion/8701-350-360-clutch-adjustment-procedure.html


Try it again. If it still slips after that, you can try cleaning the clutch disks. Or just buy a new clutch pack and be done with it. I wouldn't think this necessitates a bottom end tear down to inspect the trans. If you aren't having shifting issues (besides the slipping), then the trans is likely fine.
 

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Discussion Starter · #9 ·
Hey all, just wanted to give you an update on where things stand and ask for a little more advice!

Work I performed:
-- Replaced the clutch discs and springs (purchased from Common Motor)
-- Changed the oil with motorcycle specific oil
-- Cleaned the petcock
-- Cleaned the fuel lines
-- Inspected the air filters (still in reasonable condition)
-- Tested the cylinder compression (both were good)
-- Disassembled and cleaned the carbs (which were in surprisingly good condition)
-- Synced the carbs and throttle cable
-- Checked to make sure fuel was flowing to both carbs
-- Set the points timing

After all this, I turned it on with minimal issues, fiddled with the idle set screws to get it to idle around 1200 rpm, and then realized that only the left cylinder was firing. I took out the spark plugs, and the left looked good, but the right was a tad wet. Both spark plugs are sparking. I then decided to try switching the spark plugs just to see what would happen, and the right cylinder started firing better, but not great still. It would only work when the revs were above 2000. I set the bike to idle at 2000 and took it on a short ride to see if it would give me full power. Here was my ride experience as best I can summarize:

-- At speed, it ran relatively fine.
-- When starting from a stop on an incline (which we have many in Pittsburgh), the engine would be pretty bogged down and sluggish as it was trying to get up to speed. I'd have to give it a lot of throttle before letting out the clutch to make sure the engine didn't die.
-- After it would get up in revs, it would backfire a few times out the right exhaust, and then the right cylinder would kick in and I'd have full power again.
-- This would repeat every time I had to start from a stop, but it seemed like it would take longer for the right cylinder to kick on if I was going up a hill.

I've learned a lot and had a lot of fun taking the bike apart, but I didn't get to ride it for most of the summer, which I'm pretty bummed about. I feel like this issue is in the realm of something that a knowledgeable person could diagnose and fix with ease.

Any idea on what to do?

Also, thanks a ton for the advice and responses thus far and any advice to come! It's very appreciated!

Below should be a pick of the bike during it's most recent tear down.

IMG_20190828_195618.jpg
 

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What's up with the plug wires?....Are they spliced?......That alone could be your problem.....

In general, the Yellow coil wire and spark plug wire are used on the left cylinder (front/left set of points), Blue for the right cylinder (rear/intake side points)


(Can't quite blow-up the picture enough to see accurately)
 

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Discussion Starter · #11 ·
What's up with the plug wires?....Are they spliced?......That alone could be your problem.....

In general, the Yellow coil wire and spark plug wire are used on the left cylinder (front/left set of points), Blue for the right cylinder (rear/intake side points)


(Can't quite blow-up the picture enough to see accurately)
That's the best picture I have of the wiring unfortunately (I'll take better pictures next time I take things apart). I haven't done anything with the wiring yet on this bike, but it worked when I initially got it. That said, it did sit outside during a rainstorm in the spring before any issues started happening, so perhaps there could be some sort of issue with the wiring? Do you think that's something worth pursuing?
 

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Can't advise until I can better see what you are dealing with.....I can see something is apparently not correct......
Those are not the original plug wires... Are they original coils?..... Are they wired correctly?

A picture is worth 1000 words......Several pix would be better (coils, plug wires, points, etc.....)
 

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^^^pictures always help, the more the better... and a proper introduction wouldn't hurt either, I've asked him privately multiple times already
 
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