TM33 Tuning woes

I switched to a Mikuni TM33 carb from White Bros. a few weeks ago.Today was one of the first nice days to ride so it was my testing day. I've ridden it a few times down the alley behind my house, but haven't been on the trails.

It's been fairly had to start since I changed the carb, but I wasn't concerned. Today before I put my riding gear on I ran it for about five minutes up and down a gravel road. I thought that it was running good so I shut it off to put my gear on. When I tried to start it again about 15 minutes later it wouldn't start. I tried for an hour and finally loaded it up and headed home. A couple of times it would sputter for a few seconds with the choke on, but would die quick. I've messed with the pilot screw (?) on the bottom side of the carb a little, but no luck.

I know very little about carbs. Before I take it apart tonight and see if there's anything plugged or the float is stuck, anybody have any advice?

The valves have the right clearance and the bike has the free mods with a White Bros. e series exhaust and a UNI filter. It had those mods with the CVK and ran fine.

Thanks for any and all advice.

Riders that haven't experienced pumper carbs often twist the throttle when trying to start their bikes. That's a no-no. It will flood the bike.

Make sure there is a good seal between the carb and the intake manifold.

Enough gas in the tank? Fuel line kinked? If you have to remove the carb, take the bottom off of it and remove the pilot jet and inspect for something clogging it.

Start with the pilot screw out around 2 - 2 1/2 turns.

Good luck


Thanks for the info. I've checked some of the dumb things - e.g. gas flowing out of the petcock, but it could be my starting method.

I'm pulling the carb now and will check the pilot. Thanks for the advice on the pilot screw.

I'm concerned about the intake seal, I had a problem with that when I first installed the carb. I guess I'll check it out.

Thanks a ton!

Uggh. My right (kickstart) leg feels like I ran a one-legged marathon.

I checked more things out last night. First thing I did was pull the plug out. I wasn't able to do that at my riding area, but I was very surprised. It was soaked, opposite of what I expected. I cleaned it up, but still could get the bike fired up. I got a little fire out of it, maybe a second or two, but then nothing.

I thought I might as well pull the carb out and take a look at that. The intake had fuel puddled in it, not a good sign.

Everything seemed fine inside, no grime. I removed the pilot and main and sprayed the passages with carb cleaner. Initially the circuit under the pilot didn't allow much fluid through. After I sprayed a little it was fine.

I reassembled everything, but still couldn't get the bike started. I started trying with the pilot screw 1 1/2 turns out since it seemed to be flooding.

My jet sizes are Pilot=37.5 and main is 145. Elevation here is about 1,700 ft. and temperature is mid 50's. Any ideas? Is my jetting off?

I'm very close to taking it to a local dealer and seeing what they have to say. I try to buy parts through the dealer, but take a lot of pride in doing the work myself so it's a hard decision.

Thanks for any help that anyone can offer.

This is from:

Initial settings...

Main jet - 142.5

Pilot jet - 45

Needle - 3rd clip

Fuel screw - 1 turn out

Are those the jets that come with the carb from White Bros?

Yes - the jets that are in it are what came from White Brothers.

They also seent a 35 and 40 pilot and 150 and 140 mains.

The recommended pilot from that story is larger than what I'm using now and the main is slightly smaller. Any thoughts?

Just to make sure, is the proper starting procedure full choke and no throttle?

Is there a good way to double check my intake seal? It seems like it wouldn't be drawing fuel in very well if it wasn't sealed correctly.

Thanks everyone!

Do you have a "Hot Start" on the bike yet? I read somewhere that's an absolute must with a pumper carb. I've got one even with the CVK carb and I can't tell you how much easier it is to start. Here's the best price I've seen: It looks like a universal kit which is what I've got on mine.

I have the TM 33 for mine but I bought it used with the disclamer that it required a rebuild so I haven't installed it yet. I ordered the jets that are recommended as the starting point mentioned before and ordered one size up and down from there.

I'm not a carb expert either, that's why I'm going with the sizes recommended earlier.

Don't have a hot start, but that's a great idea. I'm going to talk with the local KTM dealer I bought the carb through tomorrow - I know he's a KTM dealer, but he's a great guy and very helpful. I'll fun that idea past him.

When I get it figured out - whether it's jetting, tuning or something else I'll post what the trick was to save you the same headaches Dave.

Thanks for all of the help.

The intake had fuel puddled in it
Sounds like debris in the needle valve or possible float problem/height adjust. Remember that this carb has a slight tilt to it... try blowing some air back through the fuel line to pop-off or clear the needle valve in the carb. Use a clear fuel line to judge where the fuel level in the bowl is by opening the drain and holding the line beside the bowl with the fuel petcock off. This will give you some idea on where the fuel level is...after you shut it down, turn the fuel off and try restarting it later and see if it is still flooded. :naughty: hope this helps?

Thanks for the advice. Let me tell everybody where I stand (barely) right now. I feel a bit like a pirate - only one leg is usable. My right leg feels like it's made of rubber, really sore rubber from kicking my bike over.

Late this afternoon after getting a little more frustrated I attempted to popstart it by rolling it down a hill behind my house. It would turn over several times, but never lit. Seems really strange since it ran good yesterday after unloading it, although hard to start and hasn't run since.

ForDRTnST - Those are some great tips and seem pretty logical too. I'm going to check them out. The float level trick is really cool.

When I had the bowl off of the carb I was surprised at how stiff the spring was on the float.

Thanks for the links Dave - you must have the entire world of dirt biking on the internet indexed. I really appreciate them, I printed the pages and will be reading them tonight. Hopefully my what I figure out will make your install go better.

Thanks for the advice everyone.

My bike started 3rd kick after the white bros tm33 installation. Not tuned perfect yet though.

That's great GreenKLX! When my bike was running it fealt a lot punchier than with the CVK. Now for the update:

I just finished pedalling the one sided exercise bike for a bit. Sorry, I'm trying to maintain my sense of humor.

I didn't even get a sputter out of it. I attached a clear hose to the drain on the bowl and it looks like fuel comes up to where the bowl connects to the carb body. Is this where it should be?

I also blew into the fuel line (yummy) but didn't feel any restriction.

The local KTM dealer recommended swapping carbs back to make sure that I don't have some strange mechanical problem. He also reminded me not to get frustrated, although I already am. It fired almost right after swapping carbs and died after a little bit of sputtering. I got the same thing out of it immediately after that but didn't go any farther because it's a little loud for 11 p.m. and retired neighbors on both sides.

Does anyone know a good way to check the intake seal? I'm wondering if I'm not getting a good seal for some reason.

Regardless, I'm going to pick up the new jets in the size recommended on a couple of sites. tomorrow. The KTM dealer I ordered from isn't sure he has them, but assures me that a guy in town who sells aftermarket stuff for Harley's has them. Go figure.

I guess I'm learning a lot about carbs. Thanks for all of the advice.

Caution about the jets for the Harley....The carb that goes on that is an HSR and the jets are different. I ordered all of the parts I needed to rebuild my TM 33 from Sudco (

Here's what I ordered:

004.197 N100.604 #142.5 Main Jet

004.037 VM28/486 #45 PJ Pilot Jet

004.196 N100.604 #140 Main Jet

004.198 N100.604 #145 Main Jet

004.051 VM28/486 #42.5 Pilot Jet

004.052 VM28/486 #47.5 Pilot Jet

All jets were $3.00 each. The first two are the ones recommended from the earlier post and the remaining are one size up and down from that.

I'm wondering if you disturbed anything electrical when you had the tank off that could be causing an intermittent condition. It sounds like you've tried the obvious things. You might want to pull the fuel line from the petcock and drain into a clear container and time it. You might have something in the fuel tank that restricts the amount of fuel. If it's floating around, you could be fine one minute and starving it the next minute.

Hope you nail it down soon. I know how frustrating this can be :naughty:

The petcock idea is a good one. I've also been worried about spark. I've checked a number of times and seem to be getting good spark. Thanks for the HD jet advice too. My lunch time will be spent chasing parts. I'll keep everyone posted. Thanks again for the advice.

I order jets today - the same thing Dave did. They should be in Friday. I ordered from the guy the local dealer that's been offering the most advice.

Thanks for all of the help, I'll let everyone know what happens when I install the new jets.

My new jets finally came in, I'll hopefully get to install them after getting the kid to bed tonight and post if I have any success.

The dealer I ordered the jets through has a couple more each of 142.5 mains and 45 and 50 pilots. He ordered them for me and is stuck with the extras now. He gave me four jets for $10, I thought that was pretty good. Send me a PM if you want his toll free number.

I installed the new jets tonight and fired up the bike with the seat off and without bolting on the tank. It started on the third kick. It didn't run to bad with the choke on, but died when I turned the choke off after about 15 seconds.

After that good luck I bolted everything back together. I couldn't seem to get it started again and actually had the best luck using a little throttle to start it.

I finally relented to pop starting it on a hill behind my house. It's pitch black out there - no moon tonight. It fired up pretty easily and I rode about three blocks down the alley. It ran pretty good. At the end of the third block I pulled in the clutch to turn around and it died on me. I watched a cop drive by and for some reason he didn't even bat an eye at me. I thought I was going to have to push it three blocks uphill, but it fired up again on the second kick.

I'm thinking the starting issue is finding the right combination between the idle screw and the fuel screw. Am I right? Any tricks to this?

Dave - did you get your jets yet and get your carb installed?

Thanks for everyone's advice.

I've got the parts to rebuild the carb, but I'm waiting on a new air boot I ordered from Bike Bandit (It was back-orderd for a few weeks) and I'm still waiting on the throttle and cable I ordered from Terry Cable.

I'm trying to be patient enough to get everything and do it all at the same time.

Oops! I already asked if you have a "Hot Start" on your bike? If not, I'd highly recommend getting one. The best price I've seen is at The Hot Start will introduce fresh air into the system and help lean it out enough to start. I used to get stuck on a trail because either I stalled or crashed and my bike would not start until I either let it sit for 10-20 minutes or I'd kick like crazy until it would finally fire. After that exercise, I'd be too wore out to ride hard any more. The Hot Start cured all of that. Take a look at "My Garage" to see pictures of the Hot Start I posted for somebody else. Money well spent in IMO! :D

Have you looked at the spark plug yet to see if it's running rich or lean?

I'd say to run the idle up to where it will run and then adjust the air screw to bring the idle down. Run it hard after it warms up and check your plug to see how it looks.

Sounds like you're getting closer! :)

BTW, did it feel any different from the previous jetting? :)

I do think, based on your advice, I'll get a hot start fairly soon.

Glad to hear that you're more patient than I am about getting your carb in order.

Thanks for the carb tuning advice. I'd like to sneak out of work a couple hours early this afternoon and hit a very small (but close) riding spot to try to tune it up a little. I don't think it's going to happen though. I have to remember - patience.

I checked the plug out before I reinstalled the carb, made sure it was clean, but haven't check since. I pretty much parked the bike and went to bed last night.

As far as how it feels - it was certainly different. The throttle response was ten times quicker. That's the only thing that has annoyed me about the KLX (I've had a couple KX's, and a YZ years ago and my wife has a CRF150) compared to other bikes I've ridden - you have to anticipate when the power will come on. This carb seems to solve that problem. Also, the front fealt a little lighter. I didn't get on it too hard because everyone in a three-block radius had their lights off and were probably asleep.

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