351/TM33 tuning for dummies
#1
04-26-2018, 03:55 AM
351/TM33 tuning for dummies
First things first -- fair warning that I have no idea what I'm doing. I bought a KLX used and it's my first motorcycle, period. But I know how to use a wrench and have an okay understanding of 4 strokes....
I got lucky, had a friend help me find a killer bike: KLX250S with the 351 bore kit, TM33 carb, muzzy header/exhaust. I've put about 200mi on it and I'm thinking it's running pretty rich -- soot in the tailpipe, jerky power, delayed throttle response, worse at altitude... I pulled the spark plug and it was definitely fouled, replaced it and it ran a lot cleaner. Now about 120mi later its acting up again. Seems like its worst on the low end, 4-6k, and better on the top 7-8k rpm. On flat road I'm usually shifting at around 5500.... When its at it worst, I'll get mild popping (not really like backfiring) or gurgling, each time it does that it loses a bit of power. Happens like once a second
Does that sound like its rich? Should I try to retune it? I tried to find info on adjusting that carb but got overwhelmed pretty quick. Theres not a lot of info out there for the perspective of a beginner...
I got lucky, had a friend help me find a killer bike: KLX250S with the 351 bore kit, TM33 carb, muzzy header/exhaust. I've put about 200mi on it and I'm thinking it's running pretty rich -- soot in the tailpipe, jerky power, delayed throttle response, worse at altitude... I pulled the spark plug and it was definitely fouled, replaced it and it ran a lot cleaner. Now about 120mi later its acting up again. Seems like its worst on the low end, 4-6k, and better on the top 7-8k rpm. On flat road I'm usually shifting at around 5500.... When its at it worst, I'll get mild popping (not really like backfiring) or gurgling, each time it does that it loses a bit of power. Happens like once a second
Does that sound like its rich? Should I try to retune it? I tried to find info on adjusting that carb but got overwhelmed pretty quick. Theres not a lot of info out there for the perspective of a beginner...
Last edited by ldkr; 04-26-2018 at 03:57 AM.
#2
04-26-2018, 02:00 PM
Might contact Bill Blue, probably his carb set up and definitely his big bore.
If it gets worse as altitude increases I'd think you were on the right track. Maybe drop the needle a notch (clip in higher groove) to lean it out and see what happens, since that is an easy no cost start. If it helps, continue down that path. Grab a main jet or two leaner.
If it gets worse as altitude increases I'd think you were on the right track. Maybe drop the needle a notch (clip in higher groove) to lean it out and see what happens, since that is an easy no cost start. If it helps, continue down that path. Grab a main jet or two leaner.
#3
04-26-2018, 05:48 PM
There is no way to help without your elevation.
You are going to need to find out what you have now for jetting, and go down from there. We don't know what is in there and you don't either, only one way to find out unless you know who did the upgrade.
Either take it to a shop or figure out how to adj your carb, your call.
There are some manuals online, but you need to find out what carb you have. Oh, and that was a little harse, my bad.
You are going to need to find out what you have now for jetting, and go down from there. We don't know what is in there and you don't either, only one way to find out unless you know who did the upgrade.
Either take it to a shop or figure out how to adj your carb, your call.
There are some manuals online, but you need to find out what carb you have. Oh, and that was a little harse, my bad.
Last edited by durielk; 04-26-2018 at 07:12 PM.
#4
04-26-2018, 07:14 PM
Join Date: Mar 2016
Location: Texada Island, BC
Posts: 157
I'd suggest taking the time to get familiar with tuning carbs.
Learn how to do plug chops (if you dont already know how) so you can determine if your rich or lean.
Make one change at a time and keep a log of the changes and results.
Learn how to do plug chops (if you dont already know how) so you can determine if your rich or lean.
Make one change at a time and keep a log of the changes and results.
#5
04-26-2018, 07:27 PM
durielk - nah all good. im at sea level riding up to 4000ft max, usually around 2k. the previous owner said that it's the straight up kit from Bill Blue, so whatever comes stock from him in the TM33.
but yeah i need to start learning. I'm going to take everything apart, see if i can find out what jets are in there, and try moving the clip on the main jet.
i put a line out to Bill to make sure im in the right direction... i suppose i should also check the airbox
but yeah i need to start learning. I'm going to take everything apart, see if i can find out what jets are in there, and try moving the clip on the main jet.
i put a line out to Bill to make sure im in the right direction... i suppose i should also check the airbox
#6
04-26-2018, 10:23 PM
Raise the clip on the needle. Not the main jet lol.
There’s lots of ppl running that carb that’ll hopefully chime in and post their jetting/needle settings. Your in the right place to get answers. People around here are very helpful.
There’s lots of ppl running that carb that’ll hopefully chime in and post their jetting/needle settings. Your in the right place to get answers. People around here are very helpful.
#8
04-28-2018, 07:03 PM
Here's a pic of the plugs: https://imgur.com/a/OVo9w0J
Left is the one that was on the bike, pulled it ~60mi after i got it. The right was installed brand new no more than 130mi ago.
The last owner said he's never fouled a plug in 10yr and the dude knows bikes. He also said he recently cleaned the carb very thoroughly
I called Bill Blue and he was kind of at a loss, given that I haven't changed anything on the bike since I got it -- except for maybe riding style and gas (i'm filling premium). He said riding style shouldn't affect mixture or how the bike runs, which makes sense. He said ****ing with the tuning is the last thing I want to do -- the problem is probably something else if it was running fine before. In order i should check: airbox/filter, get jet sizes and report back, check timing, check valve clearance
I pulled the airbox and filter, a little dirty but nothing crazy. Some filter oil collected in the airbox but nothing crazy, some oil residue on the tube between the airbox and carb, nothing crazy. Here's a pic: https://imgur.com/a/VCqNBGP
Does that look OK? Any other ideas on why i might be suddenly fouling plugs? Bunch of soot on the mouth of the tailpipe, could the muffler be clogged? I will pull jets next....
Left is the one that was on the bike, pulled it ~60mi after i got it. The right was installed brand new no more than 130mi ago.
The last owner said he's never fouled a plug in 10yr and the dude knows bikes. He also said he recently cleaned the carb very thoroughly
I called Bill Blue and he was kind of at a loss, given that I haven't changed anything on the bike since I got it -- except for maybe riding style and gas (i'm filling premium). He said riding style shouldn't affect mixture or how the bike runs, which makes sense. He said ****ing with the tuning is the last thing I want to do -- the problem is probably something else if it was running fine before. In order i should check: airbox/filter, get jet sizes and report back, check timing, check valve clearance
I pulled the airbox and filter, a little dirty but nothing crazy. Some filter oil collected in the airbox but nothing crazy, some oil residue on the tube between the airbox and carb, nothing crazy. Here's a pic: https://imgur.com/a/VCqNBGP
Does that look OK? Any other ideas on why i might be suddenly fouling plugs? Bunch of soot on the mouth of the tailpipe, could the muffler be clogged? I will pull jets next....
Last edited by ldkr; 04-28-2018 at 07:11 PM.
#9
04-28-2018, 07:14 PM
Your airbox looks totally normal. My husky was stumbling and I replaced the spark plug and it ran fine after. Hopefully just a fresh plug will get you right back to where you were before. Remember 2 strokes & carrying extra plugs?
#10
04-28-2018, 07:15 PM
Are you running lidless? With or without snorkel, original or kdx snorkel? This can make all the difference in the world. Sorry if I missed this info somewhere but mine ran just like that with the original snorkel installed until I remembered I told Bill I was installing the kdx snorkel and he jetted it accordingly. My jetting wouldn't help as I'm running stock exhaust and I don't remember anyway.