Can valve adjustment make a bike run lean/rich?

stillatwork

Active Member
Curious if adjusting valves too tight / loose could make a bike run lean rich? Just did valves on a 550 and it is running rich. Plugs aren't fouling out, but they're blacker than I'd like, and I can smell gas at times. I was working under the assumption that it's most likely carburetion, but I don't know anymore. Also does timing always have to get done after valves because I didn't check it after. Bike runs rides idles great, slight fapping noise at low acceleration (not a popping), but I think it's because my carb sync might be a tad off. Pressures feel lower on a pipe vs the others is what gives me that assumption
 
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Valve adjustment has no affect on jetting.

if it runs perfectly, your jetting is perfect or very close.

If it stutters/burbles even the tiniest bit when you accelerate, it is rich somewhere . . If it simply hesitates as if it is out of gas, it is lean.

Post a photo of the plug . . The plug on the right is shiny which means it is wet which means its oily . . It is possibly rich too but its hard to tell because of black deposits from the oil . . This engine should be repaired . . The middle plug is perfect . . The left plug is lean.

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eCSbd.jpg


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Plug-2.jpg



This plug is bone dry so the black means it is rich . . If both the threads and the porcelain is black, i would start by reducing the main jet size first . . In the case of a plug that has extremely heavy deposits like this, I would go down 3 sizes on the main because just one will not be nearly enough and two will likely no be enough . . Four would be too much.

spcarbon.jpg
 
The bike ran like shit before the valve adjustment. One of the valve tappet adjuster screws was literally floating around in the top end. So I was riding 7/8. There is no hesitation with acceleration, the bike feels great, it just smells a tad like gas and has rich looking plugs. Even jet with the entire bike stock? Doesn't make sense. I replaced the stock floats with what I thought were OEM ones from 4 into 1, but it wound up not being, you think too much gas could be getting in with new floats? It seemed okay before...just trying to eliminate everything.
 
You neglected to mention changing the floats in the first post of an "Im running rich" thread.

Valve timing, as stated aboove, does not affect the fueling. However, if a bike is out of tune in the valve department, it certainly could lead an inexperienced person to believe that there is a carb issue, causing them to fiddle with the carbs. For example lets say the valve adjustment at some point was causing the exhaust to pop. A person may be tricked into richening one or more carb circuits.

My point here, is that you need to check all maintenance settings when tuning. Check your pilot mixes. Sync your carbs.

Install the correct floats, at the correct height.

Report results.
 
@DOHCBikes old floats were OEM at 12.5MM correctly installed measured from the bowl flange. New floats are that same thing, and pretty damn close to the exact same thing as the OEM floats, I didn't think it would have that big of an effect on it, the thread was about valves. Main jet is the stock 90, and the air screws were at stock spec of 1.5 turns out. Synchronized carbs with a vaccume gauge. The entire bike is stock, so I feel jetting isn't needed. Maybe it just is the floats then, but this post has nothing to do about how to get the bike to run less rich more than just a question about valves.
 
But thanks for imput, will swap over old floats and see what happens..but yeah good point with that what was causing popping on my carbs was a tappet screw being off one of the valves should have check valves first
 
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stillatwork said:
The bike ran like shit before the valve adjustment. One of the valve tappet adjuster screws was literally floating around in the top end.

The excessive play probably beat your cam and valve tip to shit.



stillatwork said:
There is no hesitation with acceleration, the bike feels great...
then you are incredibly fortunate and dont really have a problem other than the gas smell



stillatwork said:
it just smells a tad like gas.

exactly when does it smell like gas...at idle?....on the freeway?

if you have no air box, it can smell like gas . . it can smell like gas from the gas cap vent.



stillatwork said:
and has rich looking plugs.

well you didnt post a photo of the plugs and it runs perfect so go down 1 size on the main jet . . if it starts easily without the choke, go down 1 size on the pilot jet . . if it still runs perfect, lower the needle by raising the clip 1 position.




stillatwork said:
Even jet with the entire bike stock? Doesn't make sense.

it will run and smell differently now then it did in 1970 if you are using corn gas . . that shit smells like...well...shit.



stillatwork said:
I replaced the stock floats with what I thought were OEM ones from 4 into 1

why did you do that if it ran perfectly?



stillatwork said:
but it wound up not being

what did they end up being then?



stillatwork said:
do you think too much gas could be getting in with new floats?

it smelled like gas before you changed the floats and still smells like gas after you changed the floats? . . you could install correct floats and set them properly but since it runs perfect, you could try the jet changes first.



stillatwork said:
It seemed okay before

ok, it did NOT smell like gas before you changed the floats?
 
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stillatwork said:
good point with that what was causing popping on my carbs was a tappet screw being off one of the valves should have check valves first

this normally would have made a very loud ticking sound causing some people to think that they have an exhaust leak or loose valve adjustment.
 
That last question is probably the most pertinent from two perspectives.

If it was like that before, maybe you didn't notice. But all bikes make most power with a slightly rich air:fuel mix and not at 14.7:1 as we hear about. In addition, old carbs are not good at breaking fuel into tiny droplets and as a result there is always some unburned fuel in the exhaust. We have run bikes on th dyno with full gas analysis where teh mixtire looks OK but the unburned HC levels were higher than expected. That was ae case of too much unburned fuel but teh fuel that did burn was in the correct proportions.

What i am getting at is that a slight smell of gas in the exhaust might be normal for your bike now that it is running fine and that brings us back to did it smell before.

If you can find a dyno shop with 5 gas analysis - typically a FACTORY eddy current type comes with that but many sniffers just test A:F ratios.
 
barnett468 said:
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The excessive play probably beat your cam and valve tip to shit.

-valve tip seemed fine I had to the top end off, bike runs very nice even with the tappet off I was able to do 70 on the highway, just with hesitant acceleration with popping, it feels good now.

then you are incredibly fortunate and dont really have a problem other than the gas smell

-very fortunate I thought my bike was fucked.


exactly when does it smell like gas...at idle?....on the freeway?

-idle

if you have no air box, it can smell like gas . . it can smell like gas from the gas cap vent.

-I have the stock air box, the entire bike is stock.

well you didnt post a photo of the plugs and it runs perfect so go down 1 size on the main jet . . if it starts easily without the choke, go down 1 size on the pilot jet . . if it still runs perfect, lower the needle by raising the clip 1 position.

-probably wont touch jets until I switch floats over back to OEM

it will run and smell differently now then it did in 1970 if you are using corn gas . . that shit smells like...well...shit.

-word

why did you do that if it ran perfectly?

-I went through my carbs before I did my valves (stupid) and still was getting popping. Popping is leaner, so I thought maybe the cylinder with the missing tappet was running lean, maybe the floats were just too mangled or something from time, so I got what I thought were OEM replacements.

what did they end up being then?

78 cb550 floats from 4into1.com theyre oem replicates but not oem theyre regular spec height

it smelled like gas before you changed the floats and still smells like gas after you changed the floats? . . you could install correct floats and set them properly but since it runs perfect, you could try the jet changes first.
ok, it did NOT smell like gas before you changed the floats?

I don't really remember not that I can tell. If you'd like I can PM you the entire background of this bike from the time I owned it on.
 
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xlnt job replying to all the questions.

yeah, getting the floats correct would probably be the first step . . then out new plkugs in it so you can see how it is burning.

does it smell like gas from the tail pipe?

as i mentioned, if it starts easily without the choke now and started easily without the choke before you changed the floats, it is too rich on the pilot jet, so i would save myself a step and install 1 size smaller when you redo the floats . . this is a small change so it wont make your bike run like crap.
 
cool will keep you posted. might not be till the end of the weekend. and a tad, its not like reaking just really at stops for a second. it does start without choke most of the time but today for instance i had to use choke. thanks for the help, I'm surprised i have to jet even with everything stock but ill give it a shot they're cheap enough.

really was just curious as to somehow like if maybe adjusting the exhaust screws for valves could like make it smell more like gas, if they were too lose or something, or the adjustment in general. i dont know.
 
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tje gas is not the same as it used to be and like i said, if you are using corn gas, it will be different . . also, the higher your elevation, the richer it will run.
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stillatwork said:
PD46C carbs 78 cb550 four theyre kiihin wheres a good spot to get OEM jets?


Honda will have the jets, but you will need to find a parts person who knows how to look them up.
The 1978 550K runs real lean on all circuits, the F2 was only a little better (but that has different carbs to the K)
 
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