Bogging at Full Throttle

I

iSack1L

Been Around the Block
Facts: Replaced points and condensor, reset timing and new plugs. Road probably 45 minutes yesterday and everything was well. Seemed to run better than ever with the new items and stuff. I'm awaiting new Dyna coils and got new spark plug wires.

Symptoms: Today, road out to the grocery and it was fine on the way out. On the way home, however, the bike decided to bog down at open throttle. It would not go over 40 mph and decided to give me trouble going up any kind of incline. Hard to tell while riding, but it seemed like the deepest note was coming out the right side exhaust. Is this strictly a fuel issue (running rich/lean) or may it have to do with timing. If someone could link me to a previous post on this that would be great or offer some input. Thanks. I won't be working on it until the new coils get here on Monday.

Isaac
 
First question (of course): what did the plugs look like? Betcha didnt check!

Im assuming it was at full throttle in all gears, not just 5th. Either your fuel filter is clogged, tank vent isnt venting, or you need to bump the mains up.

I cant remember, have you re-jetted recently?
 
Rich,

I was gonna check the plugs, since I knew that would be a good indicator (since they were brand new). What should I look for with that?

Also, I haven't rejetted. When I torn down and rebuilt the bike last summer, the Carbs were rebuilt by Honda, since I couldn't find the right gaskets and they did it affordably.

The fuel filter was full of fuel. Not sure if that means its not going through the second half or what.

I also changed octane (from 87 to 89). Could that impact it?
 
If they are generally dry and white, its running lean. Probably what they look like if you chop them at WOT.

The fuel filter may look good, but still be clogging. Get a new one (preferably the exact same as what you have now) and remove the current one. Wipe the gas off and blow through it with your mouth - then do the same with the replacement. You'll probably notice a difference in flow.
I tell everybody that it's not the octane that you use, it's the quality of the gas itself. But i would go with the 87 - higher octane is for higher compression (from my understanding)
 
Disconnect the filters from the carbs and point them at a large enough clean container - preferably a fuel can. Open the tap and see how much flows out. Don't need to measure unless the flow is bad. As long as lot of fuel flows out of the filters for a minute or more, you are probably OK there.

If the flow rate is really slow. Remove the filters and repeat. If it's OK now, get new filters

If it's still bad, drain teh tank and remove and clean the fuel tap.
 
deeper exhaust note is generally from over rich mixture, lean mixture leads to 'droning' sound
your going to have to go through carbs again
 
crazypj said:
deeper exhaust note is generally from over rich mixture, lean mixture leads to 'droning' sound
your going to have to go through carbs again
Click to expand...

PJ, by deeper exhaust note, i meant when it bogs down it sounds louder on one side than the other. Its not a consistently deep note. I still have yet to mess with the mixture and stop screws since changing the timing etc.
 
The plugs (brand new two rides ago) are blacked out. I gapped them properly. Do you think this will just be a matter of adjusting the mixture, and do you think this would have caused the bogging down? Changes that will be made next week include the addition of dyna coils and dyna plug wires. New condensor and New points are on now. I'll change the octane back to 87 and replace the filters. I'm not sure what filters I'll use. Recommendations or advice on the problem?
 
Take the carbs off and clean them.
Check shut off valves don't have any dirt making them stick open.
re-set float level to 21mm if your running pods.
Make sure main jets didn't fall out (what size are you using?)
 
crazypj said:
Take the carbs off and clean them.
Check shut off valves don't have any dirt making them stick open.
re-set float level to 21mm if your running pods.
Make sure main jets didn't fall out (what size are you using?)
Click to expand...

Unfortunately, I'm sort of a Carb-virgin. I had them apart two summers ago when I got the bike. I took them to Honda and they put them in a sonic bath and rebuilt them. I was having problems finding the right gaskets for the bowls (not the O-ring, its the one for the twin that sort of shaped like a box with a triangle, if that makes sense), so they rebuilt them. I'm running stock airbox and exhaust, so I didn't change the jets from original. Thoughts?
 
iSack1L said:
Facts: Replaced points and condensor, reset timing and new plugs. Road probably 45 minutes yesterday and everything was well. Seemed to run better than ever with the new items and stuff. I'm awaiting new Dyna coils and got new spark plug wires.

Symptoms: Today, road out to the grocery and it was fine on the way out. On the way home, however, the bike decided to bog down at open throttle. It would not go over 40 mph and decided to give me trouble going up any kind of incline. Hard to tell while riding, but it seemed like the deepest note was coming out the right side exhaust. Is this strictly a fuel issue (running rich/lean) or may it have to do with timing. If someone could link me to a previous post on this that would be great or offer some input. Thanks. I won't be working on it until the new coils get here on Monday.

Isaac
Click to expand...

Sounds like a carb issue; easy way to tell it to get the bike to the RPM that bogs down, then pull on the choke some. If it gets worse, you are too rich. If it gets better, you are lean.

Did you check that your spark advancer moves freely? Sometimes they can dry up and seize.
 
Magnang,

can you explain that a bit more regarding the spark advancer? How is it supposed to move? What is it you mean by "freely?" Sorry for the amateur questions. I'm still pretty new and slow at this point. I'm starting to get frustrated beyond belief though. Sick of the bike teasing me by letting me ride and then breaking the next ride. I'm like this close to trying to find a buyer lol.
 
iSack1L said:
Magnang,

can you explain that a bit more regarding the spark advancer? How is it supposed to move? What is it you mean by "freely?" Sorry for the amateur questions. I'm still pretty new and slow at this point. I'm starting to get frustrated beyond belief though. Sick of the bike teasing me by letting me ride and then breaking the next ride. I'm like this close to trying to find a buyer lol.
Click to expand...

Not sure what exact bike/year you have (CB450??), but usually the points assembly is attached to an advance mechanism. It's a set of springs and weights that allow the points cam to advance 20-30 degrees as the revs climb to make better top end power.
 
magnang said:
Not sure what exact bike/year you have (CB450??), but usually the points assembly is attached to an advance mechanism. It's a set of springs and weights that allow the points cam to advance 20-30 degrees as the revs climb to make better top end power.
Click to expand...

1972 CB 350 twin. So I just look behind the points at the advancer? What do I look at to make sure it "moves freely" as you say?
 
iSack1L said:
1972 CB 350 twin. So I just look behind the points at the advancer? What do I look at to make sure it "moves freely" as you say?
Click to expand...

you should be able to turn it 20-30 degrees freely, the weights should be able to seperate from the assembly with minimal resistance

# 11 on this pic
cylinder-head-side-coverspark-advancerpoints-cb350-super-sport-350-k0-us_bighu0018e6002_d2fa.gif
 
iSack1L said:
Dirty airfilters is more than likely since I'm still running stock, but would it really cause that bogging down?
Click to expand...

You cannot diagnose a problem effectively until you rule out all other causes. A dirty air filter will cause your bike to run rich due to the limited airflow. Adjusting the carbs is of no use until you get a new airfilter.

I replace/clean mine every 10,000km (~6,000 miles). This is a fairly standard interval. Replace them more often if riding in dirt/dust/offroad.

I would highly recommend an aftermarket filter for your stock airbox. Unifilter and K&N are two reputable brands, both of which make reusable high-performance filters.

Cheers - boingk
 
boingk said:
You cannot diagnose a problem effectively until you rule out all other causes. A dirty air filter will cause your bike to run rich due to the limited airflow. Adjusting the carbs is of no use until you get a new airfilter.

I replace/clean mine every 10,000km (~6,000 miles). This is a fairly standard interval. Replace them more often if riding in dirt/dust/offroad.

I would highly recommend an aftermarket filter for your stock airbox. Unifilter and K&N are two reputable brands, both of which make reusable high-performance filters.

Cheers - boingk
Click to expand...

Boingk, I'd like to avoid rejetting if possible. I just purchased carb rebuild kits after opening the carbs up tonight. See here....http://www.dotheton.com/forum/index.php?topic=9005.30.
 
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