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Discussion Starter #1
Hey,

Very novice home mechanic here. After cleaning my carbs (for the first time) I began to smell gas in my oil. Sure enough one of the pilot jets were missing a spring and the screw was very loose. Replaced the spring and for the first time set my fuel mix. Turned the screws out to factory spec, idled the bike at 1K, and adjusted the jets. To my untrained ear it sounded best at about 1.5 and 1.7 turns out (respectively). Waiting on a new oil filter before changing out the gassy oil, so I can't ride the bike and smell the oil to determine if this recent adjustment has fixed my problem. I did check the floats (they're not stuck) and I have not ran a compression test.

I have a few questions:

Given the narrative, the chances that the gassy oil was caused by the loose pilot jet is more likely than a lack of compression, right? After all, the bike ran fine until after I cleaned the carbs (stalled once with clutch fully engaged).

This being the first time I've set my mix (by ear), how much room for error do I have? If the bike isn't stumbling and both exhausts are firing about the same, then I should be good, no?

Finally, given this narrative please feel free to make any other comments

Thanks.
 

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First, welcome! Next, what bike are we talking about (year)?

Are you shutting off your fuel petcock each and every time you park it for the night? This is the #1 way to get fuel in the oil.

Regarding the mix, there seems to be plenty of margin. You get your best read of mixture by doing plug chops.
 

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Discussion Starter #3
First, welcome! Next, what bike are we talking about (year)?

Are you shutting off your fuel petcock each and every time you park it for the night? This is the #1 way to get fuel in the oil.

Regarding the mix, there seems to be plenty of margin. You get your best read of mixture by doing plug chops.
Thanks! My bike is an 82 cb450. What's frustrating is that I never smelled the oil before cleaning out the carbs, so I can't pin point exactly what lead to gassy oil. My thinking is that if the screw was loose enough to (presumably) cause the bike to stall with the clutch fully engaged, then riding the bike in that state for a few days would have gassed up my oil. As for the petcock, I forget every now and then to shut it off. Could leaving it on over night a hand full of times since my last change (a year ago) lead to gassy oil?

Also, good call on the plug chop. I never heard of it till now.
 

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You SEEM to have confused the idle mixture screw and the pilot jet....
The mixture screw has a spring to enable it to hold its adjustment....
The pilot jet is a non-adjustable orifice hole combined with several "emulsification holes" in a single brass part that screws or is pressed in, but does not get a spring.....
MOST Hondas "standard" idle speed is closer to 1200 RPM, and without knowing the SPECIFIC year and model you have, we can only guess as to the correctness of your mixture settings...
Since we now are "guessing" that you have a 1982 to 1987 bike, we also are assuming a 447cc SOHC engine, so I am moving your topic to the correct section of the site......

YES, leaving the petcock on and/or improper float adjustment are the likely causes of fuel in the oil...... Running the engine in that condition even a few minutes can, and often does, cause serious damage to the bearing surfaces within the engine including the piston ring to cylinder wall seal.....
Change the oil, inspect the cam bearing surfaces, and run a compression test....
 

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Discussion Starter #5 (Edited)
You SEEM to have confused the idle mixture screw and the pilot jet....
The mixture screw has a spring to enable it to hold its adjustment....
The pilot jet is a non-adjustable orifice hole combined with several "emulsification holes" in a single brass part that screws in, but does not get a spring.....
MOST Hondas "standard" idle speed is closer to 1200 RPM, and without knowing the SPECIFIC year and model you have, we can only guess as to the correctness of your mixture settings...
Since we now are "guessing" that you have a 1982 to 1987 bike, we also are assuming a 447cc SOHC engine, so I am moving your topic to the correct section of the site......

YES, leaving the petcock on and/or improper float adjustment are the likely causes of fuel in the oil...... Running the engine in that condition even a few minutes can, and often does, cause serious damage to the bearing surfaces within the engine including the piston ring to cylinder wall seal.....
Change the oil, inspect the cam bearing surfaces, and run a compression test....
I am not confusing it. The pilot jet screws have springs that hold them in place after they have been set. My bike is a 1982 cb450sc.

Also, you are right. Standard idle is at 1200. I only brought it down to 1K to establish my lean/rich boundaries by bringing the bike to a stumble with the pilot jets.
 

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Sensei
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See the pic below (Thanks LDR)....

IIRC, The RED circle is around the plug over the PILOT JET.....

The YELLOW circle shows the MIXTURE SCREW.....

The mixture screw has a spring...The PILOT JET does NOT......

rebuilding-vbulletin-carbs-photo.jpg
 

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Discussion Starter #7
See the pic below (Thanks LDR)....

IIRC, The RED circle is around the plug over the PILOT JET.....

The YELLOW circle shows the MIXTURE SCREW.....

The mixture screw has a spring...The PILOT JET does NOT......

View attachment 61965
No, that is not correct. The plug in the red circle covers the slow jet. The yellow circle indicates the pilot screw, which is sometimes covered by the wonderful idea that is the limiter cap.

Here are some photos from Clymer:

carb 1.jpeg carb 2.jpeg
 

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Sensei
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Well,........ Your using a Clymer manual explains a lot......

Here is the definition of "Jet" from an automotive dictionary.......


  1. A small precision-made hole. Often in a brass fitting placed inside one of the passages of a carburetor to control the flow of gasoline, air, or air/fuel mixture.
  2. The nozzle containing such a hole.

Please explain or show where the hole is in THIS part: (The Pilot SCREW... Also referred to as the mixture screw or Idle air/fuel screw)

screw-set-a_medium16016KC2970-01_a2b5.jpg
While not absolutely precise, the terms "pilot jet" and "slow jet" are often used interchangeably as sometimes one part provides both functions.....
Some carbs stack the two separate pieces (a pilot jet and a slow jet) to achieve the same overall effect......
 

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I'm having the same issues with an 83 cb450sc. I've ran a compression test and found it to be way too low, 100psi on the left and 90psi on the right. FSM says 185. However, I am not getting any smoke from my exhaust signifying that the rings are allowing oil into the cylinder, nor does the exhaust smell like burning oil. Could something else cause low compression and where else would gas be able to enter the oil? are my valves not set correctly maybe? The bike runs like a champ despite the low compression and gassy oil, but I know that this is a big problem and needs to be fixed before serious damages occur. Thanks!
 

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With that low of compression numbers the engine will not run right if it even starts. So either you have a faulty compression tester or the test was done wrong. With both plugs removed screw the gauge in one cylinder. Choke is OFF, knob pushed in fully, Throttle is held wide OPEN. Crank the engine until the gauge stops rising, usually about 10 revolutions.
I would suggest adjusting the valves first.
If the compression remains low then add 1 teaspoon of oil to each cylinder and retest. If the compression rises then the rings are not sealing, if it doesn't then there's a valve problem. Also try a second gauge. The Harbor Freight units are known to be mostly faulty, sometimes you get a good one.
 

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I totally agree with Jim The valves are very close set if you used teh specified value of .03mm, although most of us use .05mm as its is easier to set and safer.
 

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Or I'm a doofus that forgot to test compression with the throttle wide open :lol: 160psi on both sides cold looks a little better. Haha. My gauge is a bosch gauge from O'rilley. With that being said, that's 1psi lower that factory pressure (185 +/- 14psi). If it is a ring issue, would just one pound outside of tolerance cause that much gas to squeeze itself between the ring and cylinder wall? When you say add one tsp of oil to the cylinder, you mean straight through the hole for the spark plug? I'm going to try that first, if thats what you mean, before I tear the valve cover off and adjust them. Thanks for the help guys!
 

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Did some more research and tried a wet compression test. Compression jumped up to 170psi on left and 180psi on right :( She smoked pretty good when I started it back up afterwards! That definitely doesn't happen under normal operating conditions so I don't think the motor is burning oil, but maybe with borderline low compression there is just enough gas coating the cylinder walls to get caught up with the oil and sucked back down into the crankcase before being combusted? I don't know. Or could a rich mixture introduce gas into oil too?
 

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The only way fuel will get into the oil is if the carbs are flooding, floats/needles sticking, in which you should be seeing fuel coming out of the drain hoses. If there's been a lot of cold starting on choke then the oil will start smelling a bit like fuel but that's not a concern since it'll evaporate quickly once the engine is hot and run.
Your compression isn't that bad, Honda did change the specification in the manual in 1986, that reads as 175 +/-30 psi. Once the engine is set up correctly, tune, carbs, etc, and run for a few days you may find the compression raises some.
 

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Awesome! Thanks for the input. I'll probably check the valves clearances and keep an eye on it. I don't have any flooding because the drain tubes have been clear. The first set of carbs I had on the bike were faulty and would not run right, flooded, etc. so I know there was gas introduced there, but I've changed the oil a couple times after I got a pair that worked so maybe it's just residual gas fumes getting filtered through as the oil moves through the engine. I haven't ridden the bike much because I've still been tinkering here and there so anytime I start it to tinker it is choked and not run for a long time. Makes sense now. Thanks so much!
 

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I'd be a little suspect of the results of your compression test. I would attempt to do another test with a different gauge and also be sure that you're performing it correctly. If you're using a standard automotive gauge, it may be giving you low numbers because of the long attachment hose. Also, be sure that the choke is not on and that the throttle is held open while the engine is cranking.

Gas in the oil is almost always caused by gas seeping past the rings. It may be from worn rings, but could also be caused by excessively rich jetting, float too high, excessive idling with the choke on, short trips not allowing the engine to completely warm up, a leaking petcock that allows fuel to seep by when the engine is not running, and more....

........Paul
 
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