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Discussion Starter · #1 ·
My motorcycle will start and idle with ease, but as soon as I give it a little throttle, the engine bogs down (stumbles/misses, not sure of the correct terminology). Most of the time, I can ease it through the bog until I get to higher RPMs (2000+) and it seems to run fine. However, sometimes, the engine will stall during that initial throttle. What is this indicative of? Mechanical wise, everything is stock (air filters, exhaust, etc.) I'm a newbie and not sure where to start looking. Is this an air leak around the carb intake boots? Is this due to dirty carbs? Please point me in the right direction. Thanks!!!!
 

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Sensei
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I'd suspect the carbs first, but the timing advance mechanism could be "sticking" at lower revs.....or the springs could be allowing full advance too soon, and it doesn't perform until the engine speed "catches-up"....
 

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Discussion Starter · #3 ·
I attempted to work on the bike today, but the screws on the hose clamps are stripped. My only transportation right now is my bicycle, so I made the trip to the hardware store to get new hose clamps so I can remove the carbs and actually be able to reinstall them tomorrow. I did however ride the motorcycle a little and a new symptom appeared. It backfired on me a couple of times, and it appears that I have gasoline coming out of the intake on the carbs. The air filters had a little on them and it's also emitting white smoke from the right carb intake. I'm going to inspect the carbs tomorrow morning. Anything in particular I should be looking for?? Thank you in advance!!
 

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Sensei
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" I have gasoline coming out of the intake on the carbs. "

Do you mean the air intake, or the hose barb where the carb intakes the fuel ?

Sounds like you're flooding, which could also explain the initial "bogging"....Clean carbs and reset float heights....
 

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Discussion Starter · #5 ·
yes, the gasoline is coming out of the air intake (the large opening on the the rear of the carbs that is attached to the rubber hose that goes to the air filters). I will remove carbs, check the float level and clean the carbs again. Thank you so much for your information and patience!!!
 

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Sensei
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No Problem....But if I'm ever in Houston, I expect to be able to take it for a spin.....LOL.... :lol: :lol: :lol:
 

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Discussion Starter · #7 ·
If you're ever in Houston, and I can get the bike to run properly, you, sir, are more than welcome to ride it. That being said, today I removed the carbs to inspect them. They appeared to be pretty clean and they passed the straw test. After reinstalling them along with the new hose clamps, I ran into a bit of a problem with the throttle cable that took me about an hour to figure out what was going on and to get it fixed. After a few hours of messing around with the carbs and adjusting the float bowl heights, I was able to the bike started again. Now, it'll start and idle, but as soon as I give it some throttle, the rpms zip right up, but only drop to about 3K rpms. If I let it sit for a few minutes, it will return to around 1300 rpms and I'm not sure if the engine bogging I was experiencing is gone.

I also tried to inspect the spark advancer, but ran into some more stripped screw heads. I'll have to head to the hardware store on monday to get some new screws before I can properly inspect the spark advancer. I did however have some engine degreaser that I sprayed into the area where the spark advancer resides and a bunch of brown liquid crud came out. I was able to ride it up and down the street for a while and it's running pretty smooth, just idling at 3K rpms and it's also blowing out white smoke from the air filters and also backfiring a little. I ran out of time and also got tired of being in the Texas heat, so I called it a day. I did ride the bike to work, which is about 5 blocks away. Monday, I'll have some time to mess around with it again. Obviously I don't have the carbs set up properly so I'll dive into them again. Also, the bike has been sitting for quite sometime (to my knowledge at least 3 years, but came with a license plate that was last registered in 82) and has yet to have a full tank of gas run through it. I'm hoping the white smoke is just years of crap that needs to be burnt off.
 

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Sensei
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It may get somewhat better once you synchronise the carbs, but I suspect low compression is also a contributing factor...Did you run a compression check?...What were the readings?....
 

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Discussion Starter · #9 ·
Well, long story short, the 450 is my only transportation right now and I'm not 100% legal (bike is insured, registered, inspected, I just don't have my mc endorsement) so I'm trying to not ride the bike that much. I have put about 90 miles on it in the past week and the idling issue (slow return to idle) seems to be intermittent, and the bogging issue I was first experiencing seems to be gone. There is a slight backfire at random times. I haven't messed with the carbs at all since resetting the float heights. I did, however, put some Seafoam into the gas tank. I do not own a compression tester and the two autoparts stores I went to didn't have any in stock. As soon as I get the chance I'll get a compression reading. Until then, I'll be riding it. And boy it sure is fun!!!
 

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I had similar problem with my '68 CB450. After adjusting the valve clearance, replacing points and plugs, adjusting timing, checking compression, buying new battery, checking stator and charged, cleaned the carbs and adjusted the float level... I finally figured it out.

The float needle valves were worn which allows too much gas when the bike is vibrating (running) so it ran rich. Black plugs and backfiring. You can see the wear rings in the pic below.

Bought carb rebuild kits for $22 each side and put new float needle valves in. Readjusted floats and now she runs like a top.
 

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Sensei
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The 450's carbs have two jets "stacked" on top of each other, plus the main jet..... I suspect you cleaned the visable jetting, but did not get the "internal" one cleaned well enough ......That's the one that governs the fuel amount during the idle to main transition....
 

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Discussion Starter · #12 ·
I unfortunately have not had any time to work on the bike but after riding it for about 140 miles, she's running pretty good. She's idling a bit higher than what I had previously set it at (now about 1800 rpms vs. 1300 rpms) and she's also returning to idle about 98% of the time when I come to a stop. The white smoke stopped long ago and the minor backfiring is also almost gone. I'm guessing the seafoam treatment cleaned out the carbs better than I did. I've got a few minor issues that need attention such as the brake fluid leaking from the master cylinder cap. It's missing the diaphragm (a new one is on its way). I still need to do a compression test, but I'm assuming it's ok as the bike runs pretty good with plenty of power (though I've yet to try to go over 40 mph on it). I think a carb adjustment will make her purr like a kitten.

Thanks for all your input!!!
 

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Discussion Starter · #13 ·
Well, I spent the past two days messing around with the carbs and installing inline fuel filters. Monday night, the right cylinder started bogging down on me on throttle so I figured it was dirty. It was a pain in the rear to get the bike home.

After cleaning both carbs thoroughly and installing the fuel filters yesterday, the problem was still there. So today, I took the right carb off to inspect, it passed the straw test and everything appeared to be in order. I went back to the spark advance. I sprayed some cleaner on it and voila, bogging issue is gone, but my slow return to idle has returned. I did have it running pretty smooth until this past monday night. I had enough of the texas heat for the day, and after a trip to the hardware store to score some new screws for the points plate and the points plate cover, I was beat. But the bike is running good during throttle, starting and idling is a bit rough. The bike won't seem to start via the electric starter. I did have the points plate off while I was at the hardware store so the timing may be a bit off. I'll have to check that tomorrow.

I still have yet to find a compression tester. You'd think it wouldn't be hard to do here in Houston. I guess I'm not looking in the right stores. I'll get this bike running smooth sooner or later.
 

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I'm jsut reading your posts and I've been recently dealing with the bogging myself on my 72 cb450. I'm confident that my left carb is not getting proper fuel delivery, which would also explain why the contacts on the left spark plug are charred black (too much air/not enough fuel mixture... at any rpm, i give it throttle, and it barely moves, then goes, then boggs down again. I can hear that its only running on 1 cylinder when it does that ( an audible difference via my exhaust).

As for the compression test, go to any AutoZone. They rent the tools there for free essentially. you pay a small fee ($44 for compression tester) and keep the tool for however long you want. when you return it, every dollar is refunded to you.

Definitely set the timing. and adjust your cables..

I'm eager to know if your situation has been fixed though.
 

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Discussion Starter · #15 ·
I've been riding the bike everyday (it's my only source of transportation) and it still has a few issues. I've found that a quick spray of wd40 on the spark advance every few days has kept the bogging issue at bay (but that's a PITA). I am still having some idling issues as the bike will start, idle at around 1500 rpm, but when I come to a stop light, the idle stays around 3000 rpm. If I let the clutch out a little, the idle will drop to 1500 rpm. I was reading a post somewhere on here that said I should lubricate the slides in the carb. I never did that during the 2,584 times I've taken the carbs apart to clean/inspect. I work all this weekend and haven't had any time to mess around with the motorcycle because I just moved. I'm hoping to do some work on the bike on Tuesday. I need to replace the fork oil seals, install new gaitors, replace the rubber on the handlebar mounts and try to clean and properly lube the spark advance.

ps....The compression tester....The nearest Autozone, Advance Autoparts nor O'Reilly's had a compression tester. Not one for sale, and not one as a loaner. At least when I last checked. I ordered one off ebay a few days ago.
 

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Discussion Starter · #16 ·
I finally managed to get my hands on a compression tester today. Both sides measured at about 165 psi. I also picked up some graphite lube today. I'm hoping to tear into the spark advance later today and give it a thorough cleaning and lube job. I have to get my hands on some oil so I can re-time it when I do so (my backpack is how I transport things and I didn't have enough room for the oil earlier today). I'm hoping this will solve my idling issue.
 

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Discussion Starter · #17 ·
Finally got the time to work on the ole girl today. I cleaned up the spark advance and used some graphite dry lube on it. When I opened up the alternator cover, the oil gushing out smelled like gasoline!! Being a novice, I'm clueless as to the reasons gasoline could be in the oil. Where do I need to look and/or check? Advice please.

Thanks!
 

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Sensei
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Change that oil!......Other members here will attest that only a few minutes of running with fuel fouled oil are enough to trash a camshaft and journals....
You HAVE to turn the fuel off EVERY time you park....even if it's just for a few minutes.... Unsynched carbs can cause the high idle, but I suspect since you are close to MINIMUM compression specs the problem lies there....163 is re-ring/rebuild time.....
 

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Discussion Starter · #19 ·
Steve,

The high/slow return to idle problem has been corrected. I will drain the oil and replace ASAP. Is leaving the petcock on the only way fuel can get into the oil? There have been a couple of times when I forgot to turn the petcock off when I parked. I will definitely remember to turn it off from now on.
 

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When parked on the side stand, the carbs tend to allow fuel to seep into the cylinders if they are too full (float height adjustment).....A bad shut-off needle and seat could also contribute .....
 
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