Bog off idle and up?

[BlueBomber]

Hello,

This is my first post. I have a 1991 RM 125 that I just had rebuilt by Forward motion (pleasure doing business with Eric!)
I used Maxima 927(?) "castor" oil for my premix, mixed at about 28:1(manual says 20:1 but I thought that was a bit much) with 93 octane gas.
I broke it in carefully with several 15 min. low throttle/load rides and then cool downs.
I went to the track this past week and it ran awesome. It always smoked alittle since I fired up the engine but I figured it would be o.k.. It ran great for about an hour then on some up-hills I noticed it started "cutting out" and bogging. If I would let off the throttle it would come back. It got worse and worse, I got it back to the truck, figuring the plug went bad.
It'll start and idle fine but as soon as you give it gas it doesn't rev, it makes a deep, hollow " wah, wah" sound everytime you give it gas. I replaced the plug( which was black and oily) but it does the same thing with the new plug.

Now my gut tells me the exhaust valves are stuck closed, thus restricting the exhaust at higher rpm. Could during the short time the engine has been running the exhaust valves gotten that gummed up that they don't open?
I took the head pipe off for a moment and there was no change. There is black spooge all over the silencer etc. In retrospect I think I mixed too much oil.
I checked the reeds (fine), air filter(new), carb slide operation(fine) and the plug is new and gapped.
I just need ideas for what else to check or if you think cleaning the exhaust valves should do it. It didn't run bad instantly like a light switch, but got worse over time.
If you need any more info let me know. I might take the cover over the e.v. off and see if the e.v. rod is actuating the e.v. mechanism. Thanks in advance, :cool:
George

 

[pro2k]

Sounds lean...and as it gets hotter and hotter it will be worse until your engine seizes! (of course I may not know what I am talking about...

 

[BlueBomber]

I don't know if it's lean, it smoked since i've been running it, there is black spooge dripping from the pipe/silencer junction and when I took the head pipe off to look inside the cyl. it was very oily... not carbon-like baked on, but black and oily like there was too much oil in the pre-mix. I'm wondering how much or how little oily spooge it would take to gum up the exhaust valves to the point that they don't open? and whats the best way to check if they're opening?- because the exhaust port was very oily. It sounds like somehing mechanical and not so much a lean/rich issue because the bike won't rev once you give it gas, but it stays running and idles like nothings wrong. Thanks for the response, anyone else have any ideas or suggestions to look for? :cool:
Thanks, George

 

[petecr250]

suzuki125

ttt

 

[rob129]

If it bogs...your lean, if it hesitates or blubbers your rich.Try to manipulate the choke. If it runs better your lean. But in your case with the spooge coming out of the pipe it sounds like your rich. If the motor is running to cool the oil cannot burn off, hence running the repespective leaner jet's to increase the exhaust port temp. If it is rich on all circuits your motor will have a harder time revving out quickly. It has nothing to do with what mixture your running. You can run 20:1 or even 32:1...but you have to be jetted for it.

 

[cr250can]

just becuase you have spooge in the exhaust it does not necassarily mean you are rich. here are two scenario's i can think of off the top of my head.

1. The fuel mixtue is 28:1 that means there are 28 molecules of fuel to 1 of oil, so this is a "rich" oil to fuel mixture compare to say a 32:1 or 40:1. However no matter what fuel oil mixture you have it all has to go though the primary and secondary jets. so if you you have a "rich" oil mixture that means for the same fuel charge you only get 28 molecules of gas (28:1 fuel/oil mixture) compared to say 40 molecules of gas (40:1 fuel/oil mixture) hence a "richer" fuel/oil mixture will result in a leaner engine. the spooge can be explained in this scenario becuase there is so much oil in the fuel charge.

2. Your losing spark

 

[RM_guy]

First make sure everything is working properly. If you suspect the PV isn't opening then pull off the access cover on the right side of the cylinder and move the PV lever by hand. It should easily move and then spring back quickly. If not then it is gummed up, so clean it up so it moves easily.

After you are sure everythnig is OK mechanically then look at the jetting. A BAWHH when first twisting the throttle indicates a lean condition. Turn in the air screw until it goes away. If you have to turn it in so it is turned out (:think: :)) less than .75 turns then you need to increase the pilot jet size.

With that said you could still be rich at the needle or main jet. I typically like to start with the main jet and work down to the air screw when jetting. There are several good threads on jetting properly.

The Maxima 927 oil that yu are using is an excellent oil but it contains castol oil that can gum up the PV quicker than other oils. I ran it for years until I got tired of having to clesn everythig up frequently. You may want to try something without castor oil. In any case, pick an oil and ratio (32:1 is plenty) and stick with it.

 

[BlueBomber]

Thanks for the replies. I believe I fixed the problem. I took the cover off to inspect the rod that actuates the P.V. and sure enough, when I would rev the throttle the rod wouldn't move. I manually pushed the rod up-thus opening up the P.V.'s and it revved normally like nothing was ever wrong. I disconnected the engine and turned it out so I could access the P.V. cover to get them out(found this method easier than taking the top end off) Man were they spooged up! I cleaned everything up with some parts cleaner( the kind where you soak parts in the metal can), put it all back together, fired it up and everything runs great-no more bog. I will definately be switching to an at least 32:1 ratio, too- much oil residue everywhere with the ratio I used. Looking into the cylinder everything looked great, so at least I didn't blow anything up :yeehaw: I'll also try to keep the rpm's up when I ride, In retrospect I was probably loading her up with the initial low rpm rides which contributed to the excess oil buildup. Once again, thanks for all the suggestions and advice. George :cool:

 

[bikepilot]

I'd reccomend something other than that 927 too, its famous for dirtying up exhaust valves. I'd recomend Mobil 1 MX2T or Yamalube 2R at 32:1.

good luck

 

[BlueBomber]

I will not use the current oil I was using. I was thinking about using Golden Spectro but the bottle calls for 50:1. Would it cause any problems mixing it at 32:1 or so? Also assuming that the lower end is all spooged from the original mixture, will it "re-spooge" the P.V.'s once I ride it again despite the new mix ratio? or will it clear itself out the more I ride?
Any ideas?

Thanks, George :cool:

 

[john3_16]

Hey George, I'll second what bikepilot said...Mobile MX2T...It's a true synthetic, burns clean, and it's much cheaper than what you find at the bike shops...I paid $3.49 per bottle at the local autozone.

I'd stay away from oils that recommend really lean ratios like 50:1...32:1 and a good synthetic oil will work just fine and keep all the high stressed engine components properly oiled.