[luckymick]

Guys, I've searched and have found tons of hits on "AP Mods" but have yet to find what exactly the "AP mod" is?

Just purchased an '07 CRF150RB from my son; the carb idles high (140 main(?) 42 pilot(?)) I believe it's the 'hanging idle' issue. Wonder if doing the AP mod might help? Bike sat for a while too, so I need to crack that carb open to ensure it is clogged or varnished.

Any help on the AP mod would be appreciated!

[Asmith]

Hey Lucky, welcome to the site.

A hangin idle would caused by a partially clogged pilot. That will need to be cleaned before you go after a bog.

The AP mod is designed to get rid of an off-idle bog. It consists of using an o-ring to tie the two AP actautor arms together, thus eliminating the lag time between throttle twist and fuel delivery.

[luckymick]

Thank you so much for clearing that up!

... and yes, I figured pilot might be clogged up. I'll go in and clean before the next ride!

Thanks again!

[Collin]

As of right now, there are several people hear facing the same problem. I found a clogged #42 pilot jet and replaced it with a #45. I changed the 130 main back to the 135 stock main. None of these changes made a difference. I notice a lot of people complaining of the same problems. I took my bike to the dealer where it had been tuned in the past by the previous owner and am waiting to hear what they think. Was there a difference in the 2007 and 2008 carb? I see this most frequently with the 07 bikes. Is it possible the slow speed circuit in the carb is getting clogged up. I am sure it is not coincidence that both of our bikes pilot jets were clogged. Should we be adding an inline filter before the carb. If dirt is an issue in mine, I am sure going to try it.

[Collin]

btw, the AP mod didn't fix any of my issues. I am also sure it won't hurt.

[luckymick]

... thanks for your insights. Yeah, this bike I purchased has the 140/42 main/slow jets. Previous owner rejet'd for the FMF Factory 4.1 pipe.

You guys that have cleaned your carbs: I noticed in the owner's manual that one only needs to loosen the carb 'twist' it and take the bowl off while the carb remains attached to the engine/bike? Is this true? If so, I'm impressed, someone finally thought of making maintenance easy!

[Collin]

I highly recommend the 45 pilot jet as alot of folks here have found this beneficial.

My biggest problem turned out to be a sucked valve, so if you have 20-30 hrs. on the bike this could be a sympton of something else. My pilot jet was clogged again when the dealer looked at it. The dealer didn't remove the carb, nor did I when I cleaned the jets. Hmmm, maybe I should have tackled that. Apparently the petcock strainer doesn't filter the fuel good enough. I am going to buy an inline filter. Anyone have any suggestions for one?

[luckymick]

... have a recommendation. Never put an inline filter before.

As far as your valve as a cause for the hanging idle: seems strange. I'm not questioning you or your dealer... just not registering for me. If anything, I'd think it wouldn't start with a sucked-up valve?

[Asmith]

As far as your valve as a cause for the hanging idle: seems strange. I'm not questioning you or your dealer... just not registering for me. If anything, I'd think it wouldn't start with a sucked-up valve?

The zero clearance valve would cause hard starting before it would cause a hanging idle. However, once it was bump started, it might cause a hanging idle due to a lower intake vacuum. This might cause a lean pilot circuit and in turn a hanging idle.

[luckymick]

... exactly. If I have to continually bump-start I would have the bike in the shop to do a valve job. I wouldn't wait. Basically I wouldn't allow the vaccum pressure to suffer based on a valve. (not faulting Collin)

[Asmith]

... exactly. If I have to continually bump-start I would have the bike in the shop to do a valve job. I wouldn't wait. Basically I wouldn't allow the vaccum pressure to suffer based on a valve. (not faulting Collin)

I agree 100%...but you'd be surprised how long some guys let it go before doing the right thing.

[Joe V]

...once it was bump started, it might cause a hanging idle due to a lower intake vacuum. This might cause a lean pilot circuit and in turn a hanging idle.

Would you mind explaining this further for me?

[Asmith]

With the overlap timing of the valves, the intake normally opens from 10 to 20 degrees BTDC. If it is open prior to that it actually begins to pressurize the intake tract. Once the piston passes TDC it begins to build vacuum. If too much pressure is already present, the downward movement of the piston can't build as much vacuum as it should. Less vacuum pulls less fuel thru the pilot and results in a lean condition.

[Joe V]

How does this occur only when bump starting?

[Asmith]

How does this occur only when bump starting?

It does not only occur when bump starting. I used that as an example because, when the valve zeros, bump starting is usually the only way to get it to start.

Starting becomes difficult when the intake zeros because the intake vacuum becomes low and compression is not allowed to build.

The inertia created during a bump start will overcome this enough to get the bike to fire. Once the bike is started and warmed up, the clearances grow and you will be able to start normally while warm/hot.