Hey thanks for the info. I am just a little paranoid about running too lean, that's why I haven't gone below the 87 that's in their now. I also wasn't sure if the exhaust has anything to do with main jet size? I have the fmf factory 4.1, and its a pretty dam big pipe. The back half portion is just as big as a 450 pipe! So I wasn't sure if that has anything to do with whether I go with a smaller main or not

right now the stock heads are at .002, I'll adjust to what you say is correct. Thanks

 

For your jetting issues.

Put needle 2nd from bottom clip
90 main
35 pilot
Turn air screw the whole way in!!! Back out 1/2 turn.
Crank the idle in until it can maintain idle for at least 30 sec.


Now blip your throttle and be jaw dropped how responsive your motor just got! Braap! Braap! Braap!

What I just told you to do goes against EVERY jetting hand book on the planet. The above set up is extremely rich off the bottom, and... Not really richer on top. The bog that happens is from your carb delivering a huge gulp of air.... With not enough fuel... Kinda like blowing out a candle. Blow out a candle with a mouth full of fuel, and see what happens...


Hope that helps

 

Same jet setup even for a stock 50 head?

 

Your brothers clutch is slipping. That's why your faster.

 

I adjusted his clutch, loosen nut, 1 turn clockwise, then counter clockwise until resistance, then clockwise 1/8 to 1/4 turn?

 

Man I have had 4 or 5 88 kits with STOCk heads, takegawa cam and 20mm carb. In ALL my bikes the biggest mains I ever ran where 78 and 82.. Your main is way to big with a stock head... Yes a 92 main is what the 20mm carb comes with but you have to drop it down is size for the stock head. Get a 78 or 82 main it will run great.. Also stock heads dont like large pipes like FMF4.1. They make way more power with a stock pipe or a small bore pipe made for the stock head. Like the small bore BBR or BigGun exhaust. Stock pipe with the screeen removed and endcap installed makes great power on a stock head. FMF4.1 and up is for aftermarket head.

 

Ok, this just answered my last question! I'll go down to an 85 main and that air screw won't be turned out as far. Thanks for the help

One thing I never understood though is that it seems like a lot of guys are running the 38 and 92 jets, maybe I just didn't realize they had aftermarket heads

 

Ok first of all Im surprised no one yet has mentioned to go ahead and check your valve clearances.
Next I would remove the carb and disassemble/clean out all jets then reassemble.
Next check for air leaks around intake.
Are both of these motors stock heads? I personally believe you will never find a way to get rid of bog on a stock head with 20mm carb.
If problem carb checks out clean and still has problems after tuning, just try switching carb with tuned one and figure if its better to downsize.
If all else fails try new pipe.

 

The carb is definitely clean. New gaskets and new jets etc. it ran fine until I thought I could tune it better with the different pipe and altitude adjustment. That's when I messed it up and couldn't get it right. I have it with an 87 main right now, but the air screw is turned out a little far. Maybe 3 turns? Should I adjust that with the needle or should I go to a 85 main?

and as far as valve clearances, should a stock head be at .002? Even with 88 kit and 20mm carb and pipe?

thanks

 

Ok so we tune pretty much the same way

and I was also thinking earlier, pretty much the only difference between the two bikes is this one has a 20mm carb, I'm running a stock carb with only a 62 main, his has an 87 main with the 20mm carb. That's a pretty big difference in jet sizes for basically the same motor. I got it running a lot better with the 87 main, but I didn't have a chance to mess with fine tuning too much. But I'm thinking that trying an 85 main might be worth a shot, or maybe I'm just comparing apples to oranges here with the two bikes.

Ill fine tune tomorrow and see what I can get out of it. Like I said before, I just want to make sure I have it on the rich side, if anything.

And I am thinking this pipe is too big for a stock head. Are there any direct replacement heads that I can bolt right onto this 88 kit? Maybe like a crf70? Or a crf100? Or what else out their can I find for a fair price that I can bolt right up to this thing? And I'm talking more along the lines of a stock honda head, I don't need a high performance race head or anything. I'm just looking for something a little beefier and heavier duty that's bolt on reliable

 

Hey, we'll before I read these last three posts, I put a 87 main, kept the 38 pilot and its running much better! I don't have it quite perfect, but its definitely rideable right now. I was afraid to go to such a low main because I don't want to be lean, I'd rather be on the rich side. So I'll get a new plug and check it after a ride and see what it looks like.

Gaskets are good still and there are no leaks.

As far as the fmf 4.1, just a FYI, the last half of the pipe is just as big, or bigger, than a 450 pipe. I think it's a little too big for this setup with the stock head.

And just another question, here's how I tune a carb once I have chosen a set of jets and clip position, maybe I'm doing something wrong here??

i set the idle low, and move that out until the bike starts and idles. Once the bike starts, I start with the air screw one turn out and then just bring it out in 1/4" turns until it runs and pulls like it should.

Does that sound like something you guys do?

I go out one and a half turns on the air screw and tune from there. The idle low as you mentioned but may turn it up in order to get the bike to run. I am gonna be running an 88cc kit with race head and 20mm carb so the 4.1 should suit me ok. The power from it is just more noticeable on the 88cc and up bikes. Glad you got it running. Great news to hear. Good luck with it man and enjoy.

 

Hey, we'll before I read these last three posts, I put a 87 main, kept the 38 pilot and its running much better! I don't have it quite perfect, but its definitely rideable right now. I was afraid to go to such a low main because I don't want to be lean, I'd rather be on the rich side. So I'll get a new plug and check it after a ride and see what it looks like.

Gaskets are good still and there are no leaks.

As far as the fmf 4.1, just a FYI, the last half of the pipe is just as big, or bigger, than a 450 pipe. I think it's a little too big for this setup with the stock head.

And just another question, here's how I tune a carb once I have chosen a set of jets and clip position, maybe I'm doing something wrong here??

i set the idle low, and move that out until the bike starts and idles. Once the bike starts, I start with the air screw one turn out and then just bring it out in 1/4" turns until it runs and pulls like it should.

Does that sound like something you guys do?

 

I'm running a 92 main and 38 pilot on my 20mm at sea level if this helps at all. I have a takegawa 88cc kit, race cam, tb cdi and big gun pipe but about to install a race head and factory 4.1 pipe so interested to see how much if any tuning I'm gonna have to do after that.

 

Do you happen to have a stock 50 carb around .i picked one up off eBay real cheap and saw another one listed with manifold cheap ..
I'd suggest to throw a stock carb on just to see if the bike runs right,maybe the carb has a problem not seen..
Also make sure to put on a new plug if it's really fouled as spark may be sporadic..

 

I think you're too rich on your main jet for sure. I have this same combo - tb 88cc kit with stock head and tb 20 mm carb and mine runs great. Unfortunately I don't remember what jets I'm using in mine. I would go down to a 87 main or something like that and put the needle back to the middle clip. The 90, 92, 95 jets are for guys with the race head or bigger than 88cc engines. Make sure you have no air leaks! Your intake gaskets should be clean and in good shape. Make sure when you tighten the intake into the head it's sitting flat and not getting hung up something. Also make sure the carb is clean inside and you're using fresh gas. Make sure all your jets can see seen through.

 

I'm about to throw some of my pride out the window and tell my brother to pay for someone to tune it. But for the cost of a mechanic it might be a better idea to just spend a 100 bucks on a mikuni, wouldn't it?? I mean I can't see a mechanic doing it any cheaper than 60 bucks? Then again I have no idea what mechanics charge these days for something like this.

There are so many different combos to try, and unless he gets it right on the first couple try's, it's gonna take a couple hours.

What do you guys think? Pay a mechanic or buy a mikuni?

 

Tried 95 main with clip at very top, and sputtered. I'm going to put the clip at very bottom now and see what happens

 

I read another post where a guy was trying to help him tune his carb at 2000 elevation, and he was saying to go to a 95 main and drop the needle clip to the 4th position from the top.

But do you think I'm running lean or rich? I know it's hard to tell with crappy gas and not having a new spark plug. But it does seem to be pretty black, even after I clean it and check after I try tuning some more

 

And I'm about to throw this thing off a cliff. I've tried every single clip setting on the needle with a 92 main and the thing sputters in first gear as soon as I give it gas. I've tried adjusting air screw from all the way in, to 4 turns out, and nothing. And I know 4 turns out is way too much, just trying to figure out if I'm too rich or too lean.

The spark plug is always jet black every time I check it, I'll clean it off in between checkings. This makes me think that I'm running too lean? So I went down to a 90 main, adjusted the clip and messed around with the air screw, and the same thing. So f@$&ing frustrating!

the thing keeps sputtering in first. With all my adjustments, all I want to do is get on the bike, put it in first and be able to rev it out without it sputtering and bogging.

Keep in mind that this carb did run well, even with the fmf 4.1

once again, here's my setup and maybe someone can recommend a setup for me.

San Diego, 70 degrees at 1900 elevation. 88cc kit with sheng way 20mm carb, original head, with fmf factory 4.1 pipe. I have a main jet kit, all I have is a 38 pilot jet, but I don't feel the pilot jet is an issue since it ran fine with it before

 

You shouldn't be trying to tune your carb with your bike in neutral. There's no load on the engine! Why would the engine run great in neutral on a bike stand and then stumble with your 180 lb ass on it? Think about it. Of course its gonna take a slightly different mixture, the engine has more load. If the bike starts and idles ok then your pilot is close, probably not perfect but its close. At that point I would start riding the bike and trying to tune the main jet. Get up to second gear gear and go WOT. If it just bogs out and the engine wont rev you're too rich, if it surges ie if it picks up and then cuts out then you're too lean. Once you get your main sorted go to the needle. Moving the clip towards the pointy end of the needle will give it more fuel, move it towards the top and its less fuel. If you end up with teh best results with your clip all the way at the end your main should be adjusted.

One last thing I would say is the FMF 4.1 is probably NOT the best choice for a stock head 88cc engine. I'm no engine guru but I think that exhaust is too big to work properly on a stock head bike.

 

What I meant by adjusting it in neutral is that I'm doing the adjustments with the bike sitting still. I'm not riding the thing down the road and making adjustments at the same time.

 

ensure ther are no intake leaks....if your sucking air before carb the engine will bog under load and will idle sparaticaly...........

 

Question for.. the original posters 88..


Would and air leak,or small air leak in the manifold O ring cause a problem like this..

 

Haha, honestly that'd be the easiest thing here. What setup are you running though?

 

It's just to cold here in NJ to mess with it..plus I can't get much testing via driveway here...I can run,rev,and ride the bikes as far as the driways goes ..

.if I hit the sidewalk,street here comes 6 cop cars..

..Test riding has to be done at the track only and it stinks when things don't run right..

I'm hoping my 88 is set up right,I've yet to wind it out in 3rd here..



The bike is the lil blue bike..
Same Principle .jet,air mixture screw,needle..has the same darn problem the original poster has..
dellorto phbg 18
delorto 18 - Bing Images
Sometimes however ..it will get up to speed but break up so bad,with a Blah BLAH BLAH break up sound..something is nit right..
My wife says at the track,man that bike sounds so bad you really have to fix it...I have a bunch of bikes none run like this..

Pictures of the bike apart,carb apart here..
Photos | Photobucket's Top Collections of Pictures & Images

I haven't found anyone with this issue except here..

 

: )

 

My goodness , I'm having the same issue with a bike that ran fine with its factory set settings .raced it a bit and touched nothing.. then it started to do exactly what your bike is doing and it's driving me nuts ..I've been looking at everything reading and reading up on it and still can't figure it out .
What I need a better understanding is:when you raise the clip on the needle what does that make happen ,less fuel?
My dads telling me to put the clip one notch down from the middle but I don't know what the changes.
I hate touching the needle , it's in the middle , the bike idles and screams -revs ..but once I put weight on it it's a bog or severe break up..again it's driving me nuts as the bike ran fine nothing was touched and I can't find a thing wrong with it

 

He raised his up one so you drop yours down one. Process of elimination. Get an answer and share it with each other. I think you guys should swap numbers until you figure your shits out lol.

 

The more I'm reading, it's sounding like the needle is responsible for 1/4 to 3/4 throttle. So maybe I'm going to just have to mess with the different needle clip positions.

Im done for the day screwing with that thing. I've taken that carb off at least 15 times, got a headache from all the fumes, and my hands are swollen from gas getting in all the cuts on my hand.

Ill get back at it in the morning and hopefully I get it rurunning or I might have to invest in a higher end carb

 

I went through the same shit yesterday. I can't jet it until it gets warm anyways so fuck it.

 

Ok we'll I moved the clip up one notch, now it's second down from the top, and I can't get it tuned now. It idles fine, it even revs up fine in neutral, great response and all. But as soon as I put it in gear and start moving, it starts bogging. I started with the air screw turned all the way in, and ended up over 2-1/2 turns out.

Why would it run perfect until there's actually a load on the bike?

 

When you past 2 turn's out you need a bigger pilot jet.

 

Ya they do make stuff for that. But, if it had one, you should be able to see it. Just look for something that yours doesn't have lol. It'd be in plain sight if it were there.

 

Mine is a 2003 and brothers is a 2004. My brothers already had some stuff done to it, most mods actually, and it was ridden by a little kid. So I'm wondering if his bike might have some sort of aftermarket cdi or rev limiter that would give it more bottom end? Don't even know if they make such a thing, just a thought.

Im getting to the carb in 5 minutes