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Discussion Starter #1
Hey guys,


So ive done my research needless to say, ive tried a few tricks to no avail....



bike details

426
11.1 wiseco
stage 2 hot cams
stock head
airbox no lid
stock carb
Full shorty FMF exh
Pump fuel 91 oct


Current jetting 42P 2.5 a/f needle middle notch 175M


Alright... so when I got the bike it had 38P 200M needle middle clip, obviously ran like hell. Plug came out carbon fouled.


I then went straight to a 45P and 175M and started to mess around. the bike started but seemed rich no matter the a/f position, and plug came out carbon fouled. The idle was a bit eratic and couldnt hold a consistent RPM (was not hang idle) it didnt start THAT easy.. but it started with a bit of effort with choke at half or so. (doesnt like full choke one bit) I ran it around the yard and it would run fairly clean however it did let off 1 large back fire after about 5 mins of riding.. i was in the higher revs fully let off and it let out 1 large back fire... im assuming thats from fuel build up.. so meaning its rich.

SO then dropped to a 42P the thing barely wants to start ever.. I fight with it for a solid 10 mins before I can get it started constantly cranking it over. but once started it runs very well, clean idle, plug doesn't seem to get carbon fouled ect like it did with the 45P.

The only issue i noticed was, if I give it some gas then let off, the RPMS will drop well below the set idle rpm and then climb back up to the set idle rpm after a couple seconds.


I am at a loss on what to do... im familiar with working on these bikes.. i could throw back in the 45P for easier starting but its going to be overly rich according to the plug.

ive never had a bike idle and run good at set rpm and after hitting throttle having the rpms drop below set idle and climb back up to set rpms...


oh I also tried giving the bike 3 shots of the throttle before starting as some have mentioned doing... didnt help any.

Good spark from what I can see, good compression and its getting fuel

Any ideas, opinions?


Thanks! (Genuin Keihin jets are being used)
 

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I would bet your mixture screw has some build up on the tip. Pull it all the way out and make sure its a clean brass color. If its black or dark at all clean it and the seat it goes in. It will make your mixture setting sporadic. And also i would try adjusting it around alittle bit. 2 1/2 is a base line setting. It will start on that setting but you need to tweak from there to get it just right. Sometimes you get lucky and 2 1/2 is perfect tho.
 

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Discussion Starter #3
ill pull the screw and clean it tonight.


Yea as for the a/f screw... I played around with it mostly with the 45P from 1.5 to 3.5 turns. then dropped to 42 and been messing around with it from around 2 to 3.5 turns, once it was running it was idling its highest at 2.5 turns.

im still reading up on all the posts i come across for hard starting.. some guys say 2-3 pumps before starting works while others are saying 5-6 pumps... so i guess i could try pumping a lil more fuel in there to see if it was "catch" after I inspect the a/f screw
 

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When its tuned properly you wont need to pump at all. The guys that are pumping dont have it tuned right or jetted right. Before i cammed my 416 i had it starting first try in 0 degree weather just fine. The hardest thing is tuning when its already cold. So now with the cam i got it close enough to ride it but cold starts suck. Until it warms up i cant really tune it in very good anyway so i figure why try. Jetting and tuning can be lots of trial and error so be patient. You will get it!
 

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Discussion Starter #5
yea ive been through a lot of jetting ordeals with a good few different bikes... been there done that 1000 times to say the least lol... but easy to overlook stuff while your at it so outside ideas and opinions really can help.

I know that cold weather makes it much harder... but I got to work with what I got... its going to be a littler warmer here the next couple days (floating around 30-32F)

Its just that.. seeing and knowing the 45P is showing too rich on the plug throwing it down to the 42 with adjustments to the a/f of 1/2 turns I would of found the sweet spot to make it easier to start.

If the a/f screw cleaning wont help, Im tempted to throw back in the 45 to see if its any easier with some more tinkering of the a/f.

plug seems to be carbon fouled with the 45 but it definitely wasn't that hard to start when it was in.

Considering this isn't my bike... I got to also relay on them that the valves are to spec and timing was set properly.
 

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tight intake valves will cause odd idle fluctuations sometimes giving you headaches like this.

since your pilot at 42 is where you need to be running wise id leave it in there. 2.5 is kind of the max i would go on the a/f needle, ill go 2.75 sometimes but if i have to go to 3 i go up a pilot size.

something else to consider, with the 42 in there raise the needle one click, this will help richen slightly too and improve response, also making it slightly easier to start.

you should NEVER pump the throttle before starting, this floods the machine making it hard to start and fouls plugs. it will even cause backfire causing premature damage to internals and even set your air filter on fire sometimes. always use the choke to cold start the machine and let it warm up at half choke until it takes throttle with the choke off. usually no more than 2-3 minutes. the "pump to start" method came from guys with full racing carbs that either had the choke deleted or an aftermarket carb with no choke at all on it, those are the only bikes that should be pumped prior to starting.
 

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Discussion Starter #7
25f or so today cleaned fuel needle like mentioned was a lil dirty so took tht out along with the washer n oring used q tip and carb cleaner and got it clean.


went to start and battery full on quit and fried... it used to last 2-3 tries before needing boosting so i lnow it was about to quit sooner then later if i kept boosting it



fuel needle now set to 2.75 i may back it down once i get it started.... if hard atarting still present ill test the 45 again and see if it improves any... i know every bike is a little different if i can get this thing to even almost start il be happy... this thing will just keep cranking over n over n over and just not fire up
 

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get a new battery. boosting it with a car or jump box will eventually fry the wiring harness since the amperage is too high, and can even burn up the starter. if the engine rotation is too slow it wont crank right either. id recheck the valve clearances if i were you first though.
 

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25f or so today cleaned fuel needle like mentioned was a lil dirty so took tht out along with the washer n oring used q tip and carb cleaner and got it clean.


went to start and battery full on quit and fried... it used to last 2-3 tries before needing boosting so i lnow it was about to quit sooner then later if i kept boosting it



fuel needle now set to 2.75 i may back it down once i get it started.... if hard atarting still present ill test the 45 again and see if it improves any... i know every bike is a little different if i can get this thing to even almost start il be happy... this thing will just keep cranking over n over n over and just not fire up
I think you may have solved your own issue. . . . . The battery is not creating enough current for the bike to run properly. . . . . I had this very issue. 42P 2 3/4 clip in the middle and a 175 main. Then read the link in my sig on jetting. . . . .


tight intake valves will cause odd idle
fluctuations sometimes giving you headaches like this.

since your pilot at 42 is where you need to be running wise id leave it in there. 2.5 is kind of the max i would go on the a/f needle, ill go 2.75 sometimes but if i have to go to 3 i go up a pilot size.

something else to consider, with the 42 in there raise the needle one click, this will help richen slightly too and improve response, also making it slightly easier to start.

you should NEVER pump the throttle before starting, this floods the machine making it hard to start and fouls plugs. it will even cause backfire causing premature damage to internals and even set your air filter on fire sometimes. always use the choke to cold start the machine and let it warm up at half choke until it takes throttle with the choke off. usually no more than 2-3 minutes. the "pump to start" method came from guys with full racing carbs that either had the choke deleted or an aftermarket carb with no choke at all on it, those are the only bikes that should be pumped prior to starting.
I agree with most of this . . . however, Try starting my quad with out pumping the gas 2-3 pumps. lol not gonna happen and it's spot on. I have no choke either haha. a few pumps isn't going to load the cylinder. If you sit there and keep pumping and pumping then yes, you might get a little detonation. With it being 30 out the air is more dense thus requiring more fuel. . . . BTW 2.25 is the stock setting. . . . 2.75 is the 1/4 turn needed to compensate. any more than 3.5 turns the pilot is too small. The needle isn't effecting anything at idle, only after about 1/8 throttle pressure.
 

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Discussion Starter #10 (Edited)
using the booster to crank it over was making it crank over plenty fast... using the booster too much def isnt good on the harness and stator so I did try to stay away from boosting or trying to start it too long with it... id use the Boost option for a few tries then let the battery trickle charge for a while.


Yea The needle is at the stock middle clip... I did try pumping the throttle 2-3 times like mentioned and didnt help any previously... but maybe the fuel needle wasn't 100% set when I tried it.. who knows.


Yea ive read plenty of jetting how to's and guides... i originally found the "sweet spot" with the 45P until I checked the plug on idle and it was carbon fouled just on idle... thats when I decided to drop it to a 42P and try again but starting has not been easy since but plug came with a nice color the one time I was able to get it to idle


Keeping in mind I didnt free rev the motor unloaded that would give an off reading for sure...
 

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moose yours not having a choke is why you need to pump it. i was talking about pumping it AND using the choke at the same time will flood it quickly, especially if you pump it and turn it over no start, pump it turn it over no start... ive watched people do this so many times thats why i say dont pump it.

the 2.5 turns max is a habit of mine because on FCRs the air fuel mixture screw likes to vibrate out from lack of spring pressure. the 400EX carb you can go further out i just have my habits.

was recommending a needle clip adjustment in case he was experiencing bog at initial opening with the 42P and see if it cleared it up vs going to a 45P making him think the 45P is better when its actually a hair too rich. were on the same page man lol.
 

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Discussion Starter #12
yea I will admit to trying both the shot of gas and choke.. but have also tried without.. either way it didnt work.. and def didn't continue to shoot gas to keep trying... last thing I need is to contaminate the motor oil with fuel after flooding the crap out of the bike.


there was no hick up from low to mid the last time I rode it.. it felt great other then the 1 large backfire through the pipe after about 10 mins of riding around in the yard and was only after a high rev wot pull in 2nd or 3rd.. so could of been from a rich main and among the pilot or needle....


Yea Ive always worked by 2.5 setting you could go up 1 size on the pilot... wether it be on a 450, 400 or a banshee... but sometimes it does run a lil better when pushing that to 2.75 or even 3 turns...


I got a new battery from the guy today.. so ill be back at it tonight when i get home from work
 

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Discussion Starter #13 (Edited)
So got at it with the new battery in place.

It wanted NOTHING to do with the 42Pilot no matter what fuel screw setting.


I threw back in the 45Pilot and left the fuel screw at 2.75 turns and it started right up without a fight.

Now the ODD part...


As I had adjust the idle high and was setting the fuel screw for highest idle, the more I screwed in the fuel screw the higher and cleaner it idled...


I ended up screwing in the fuel screw all the way in and it still idled fine?! Usually tells me way to rich.... The cleanest idle spot was around 1.25 to 1.5 turns at most

I think come Summer with warmer temps a 42Pilot at 2.5ish will be PERFECT but in the winter the 42 being too lean and 45 seemingly too rich...


I left the bike idle for about 10 mins... tapped the throttle once or twice let idle more... then killed it... plug is coming out carboned up pretty good... Was hoping for the plug to be a little more cleaner then that...


Im thinking maybe the carb needs a rebuild, but I stripped it apart and cleaned the crap out of it a-z and it was all clean and nothing was really worn visually.. carbs not leaking or anything... only thing was the fuel screw had a bit of black on it which got cleaned out good
 

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I agree... this sounds like your idle circuit may be dirty.... try some enzyme fuel treatment

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Discussion Starter #15
Yea what I was debating on... this is where a ultra sonic carb cleaner would come in handy!

even so.. a 45P at 1.5 really isnt FAR off from what most people run... ive been through a few odd ball bikes that where a touch off what most people would run... but the plugs don't lie as far as build up and color go. Ill throw in some K100 I have on hand and leave it go... its running rich so I know its safe.. as long as the plug doesnt foul up which is pretty doubt full if its only a few turns too rich...
 

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Yea what I was debating on... this is where a ultra sonic carb cleaner would come in handy!

even so.. a 45P at 1.5 really isnt FAR off from what most people run... ive been through a few odd ball bikes that where a touch off what most people would run... but the plugs don't lie as far as build up and color go. Ill throw in some K100 I have on hand and leave it go... its running rich so I know its safe.. as long as the plug doesnt foul up which is pretty doubt full if its only a few turns too rich...
45 @1.5 turns means the pilot is too big.... I know what you said with a 42 but the only time I have ran a 45 is with a larger bore engine with port work. I'm pretty sure you have some dirty carb issues.... also don't mistake a little rich for being good..... that means more fuel entering the cylinder which in turn will wash a cylinder out.... too lean will burn a piston too.....

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Discussion Starter #17 (Edited)
Ive always went based on 1.5-2.5 turns on the A/F screws as ideal settings.. any less or more can mean a change in pilot. From sleds dirt bikes atv's ect... well on Keihins anyways...

Ive made few exceptions mainly taking into account temp changes especially in winter when temps can vary largely...

Also thinking about it, the bike ran on a 38P before the owner brought it to me... (in summer time) so ofcourse the warm temps made it even possible to start... but that tells me if there was debris blocking the pilot circuit that 38P would of been an issue as well.

Every time ive had that 45P installed.. ive always started off at around a 2.5-3 turns on the fuel screw... MAYBE would it be possible that in those few mins of warm up / idle at that "rich" setting that the plug formed its carbon from an overly rich setting and by the time I got it set to a alright setting at 1.5 turns the plug already took that carbon build up.. and we all know once a plug has its build up, it doesnt "wash out" or change color back to "normal" that quickly

Usually when your at the point of washing out a cylinder, the plug doesnt come out soot dry black but more of a wet black soot and highly likely to foul cause hard starting ect the pipe will also shoot flames after pro longed stationary idle when you give it a few shots of gas and even on decel will backfire ... a good sign is also not needing the choke in cold temps when the motor is cold showing a rich setting in the pilot circuit. (been through it when I built a kfx 400 to a 470 learned a lot from it to say the least)

With the 45P it needed full choke, then it "almost caught" I backed down to half it started up, then turned choke off and idled on its own a little rough until I fine tuned the fuel screw.

I know every bike is a little different so I dont see running a 45P to the point of washing out the cyls... If it needed a 48 or up... I would of flagged it and did some digging but 1 pilot up at a 1.5 setting is pretty darn close to a 42 3turns to some extent.


Curious.... do you guys get a nice brown burn on your plugs are are they more leaning to a blackish Ive see these accelerator pumps cause some havoc if messed with... I had fun dialing a quick shot on a yfz450 a few years back...
 

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Discussion Starter #18
I forgot to mention..... since I cleaned out the fuel screw area.... the 45Pilot seems to idle cleaner and I dont seem to have that RPM fluctuation like it had before.
 

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My chops I run have the porcelain a light to white with a nice medium tan ring almost towards the bottom.... this is a WOT chop..... with the mid to low circuit chop I get an even medium tan over the whole porcelain. .. though this isn't always the case. But mostly this is where I try to be. I wast a lot of plugs haha

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Discussion Starter #20
thanks... Yea ive burned through COUNTLESS plugs when I was jetting my banshee doing plug chops...

Now I tend to keep jetting rich till it runs worse.. drop 2.. call it a day.. lol still rich.. not a dyno tune but runs good.. usually fair OVERALL color on the plug and allows room for colder temps without the need to re jet.

Chasing weather temps, humidty, ect for that perfect tune is a pain.. so I gave up on that haha. as long as its not lean and not too rich im happy... ideally what im aiming for on this bike as I highly doubt the owner is going to be swapping jets every 10degree change...
 
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