Carb swap or ?

[brad sweet]

OK, picked up a sweet deal on a Honda CRF100f this weekend for my son.
When we went to look at it, the bike would not really idle and eventually wouldn't even start. The owner was a former motocross racer so has some knowledge about engines (this was a bike for his son). Since he literally had it priced for half what many are listed for, I had to grab it.
It's an '05 but cosmetically is in the best shape of any I've seen. He swapped plug and air filter and it's running but not perfectly. It does two weird things I can't figure out.
1) Intermittently but fairly often the rpms will 'lag' coming down. Meaning if you give it gas while idling or adjust the idle up it frequently (but not always) takes a long time for them to come back down or they may just 'stick'. When you load the engine, they drop back down as normal. Is that a throttle cable sticking (doesn't feel like it all and again it may do it when just sitting idling) or something internal in carb?
2) The owner told me he often ran in it with the choke in the 'half' position as in his view it ran lean. It will, more often than not, have the popping/crackling exhaust especially under harder accerlation followed by deceleration.
And yes, when asked about ethanol, he was clueless (which was really odd). I'm pretty sure this bike has been sitting, too much in recent months.
Carbs are cheap (thankfully) and I "think" a swap would be easy but since I have about zero mechanical inclination, I'd figure I'd ask first if it might be something else.
To be clear, the bike runs OK (hard to tell if it's running hot or not. I did do an immediate oil change (which was clearly overdue). It goes WAY faster than I thought it would/should but it's obviously not perfect.
To make matters worse... now I want a dirt bike.

thats a mainjet stopped up and running on the pilot jet and air mix jet...clean the carb pull the slide and needle and degum the entire carb

 

[Blskypilot]

Leak somewhere is very likely, torn diaphragm's possible, dirty jet circuits won't help. Probably electronic ignition, so shouldn't need adjusting. Whatever you do, it'll need the cabs synched afterwards. I think I've go a neat little electronic balancer somewhere, which makes it simple and is plenty accurate, if you want to use it.

You only sync carbs on multi carb setups. A little crf100 isn't going to need carbs synced as I am pretty sure there is only one.

I'd look for gummed up jets and needles. I usually take the carb completely apart and run wire or torch tip cleaners through all the small passageways and jets.

 

[Allsmiles]

Sounds like jets have varnish/gunk on them somewhere. Have you put any seafoam down the carbs yet. Brad sweet sounds like he has done this before and I would try his suggestion. BTW, if you take out the little phillips screws on the jet cover plates, replaced them with allen heads and you won't have to worry about stripping them later (don't ask how I know this).

 

[StuP]

Thought it said 1000, not 100 ! not up on all the Honda models

 

[brad sweet]

yes got lots of Yamaha carb soak..bring it to me!

 

[woodstock]

yes got lots of Yamaha carb soak..bring it to me!

and buy his bike for sale, you will want to ride with your son.........

 

[Ken Ford]

thats a mainjet stopped up and running on the pilot jet and air mix jet...clean the carb pull the slide and needle and degum the entire carb

Agreed, there is a foam carb cleaner that I have had great success with in small carbs. Pull the jets spray and wait a few. The hen blow out and try that, if not you will have to be more thorough. Or you could just do it all the first time and be done with it.

 

[brad sweet]

Agreed, there is a foam carb cleaner that I have had great success with in small carbs. Pull the jets spray and wait a few. The hen blow out and try that, if not you will have to be more thorough. Or you could just do it all the first time and be done with it.

every bike i get i have to do this..some will start and run but very badly,some will idle with choke only..some just flood out and some dont..35 years of working on them and car carbs too..just got to break down take your time do it right once have the confidence to know that any other drivablity issues are non related and knowing the difference between them

 

[brad sweet]

and buy his bike for sale, you will want to ride with your son.........

i was told im keeping it by my 4 year old baby girl...she loves to ride

 

[brad sweet]

OK, picked up a sweet deal on a Honda CRF100f this weekend for my son.
When we went to look at it, the bike would not really idle and eventually wouldn't even start. The owner was a former motocross racer so has some knowledge about engines (this was a bike for his son). Since he literally had it priced for half what many are listed for, I had to grab it.
It's an '05 but cosmetically is in the best shape of any I've seen. He swapped plug and air filter and it's running but not perfectly. It does two weird things I can't figure out.
1) Intermittently but fairly often the rpms will 'lag' coming down. Meaning if you give it gas while idling or adjust the idle up it frequently (but not always) takes a long time for them to come back down or they may just 'stick'. When you load the engine, they drop back down as normal. Is that a throttle cable sticking (doesn't feel like it all and again it may do it when just sitting idling) or something internal in carb?
2) The owner told me he often ran in it with the choke in the 'half' position as in his view it ran lean. It will, more often than not, have the popping/crackling exhaust especially under harder accerlation followed by deceleration.
And yes, when asked about ethanol, he was clueless (which was really odd). I'm pretty sure this bike has been sitting, too much in recent months.
Carbs are cheap (thankfully) and I "think" a swap would be easy but since I have about zero mechanical inclination, I'd figure I'd ask first if it might be something else.
To be clear, the bike runs OK (hard to tell if it's running hot or not. I did do an immediate oil change (which was clearly overdue). It goes WAY faster than I thought it would/should but it's obviously not perfect.
To make matters worse... now I want a dirt bike.

XL250