Yamaha XT 350 Xt350 jetting and airbox pipe mods

I got this bike running really good this eliminates all of the coughing and hard starting and you will have a lot more power. The main jet is from a 1986 XT 600 it’s a 130 size. the jet on the secondary carburetor is from an 1986 TT 350. I think I still need to increase the pilot size because I need to run it with the choke on for a little while then partially on until it stops coughing. when it’s fully warmed up it runs smooth. I have the pilot screw way out so I know that the pilot jet is still a little too lean  I ended up using a .4 mm drill on the pilot and removing the air box side cover. Runs better!

[@nicholasthomas9587]

I have an 86 that I absolutely beat up every weekend. Love the thing. Only bike I refuse to sell as it needs nothing, always runs and is too much fun leaning into that little motor wide open. Thanks for showing a pristine example.

[@trevore6583]

Sounds awesome thanks for the tips

[@shopken1]

I have an XT350 that I have used as a trailhead access bike for mountaineering and scrambling. I bought it because it was cheap at the time and I knew that there would be a very high theft risk when leaving a motorcycle on a trailhead. I have since that time, put about 15K on a machine that was already past that mileage, well worn and abused. No bike is perfect and all machines have weak points in their designs. As a retired mechanic that has operated the machine over time, here is a summary of the strong and weak points of the XT350 and how I have modified it. (I originally bought the machine with jumped timing and oil leaks) Good points: 1) Couch of a seat. Deluxe in contrast by today's modern duel sport standards 2) True wide ratio, 6 speed transmission. 3) Super quiet stock exhaust and air intake (Yes I still run the stock exhaust) 4) Decent performance. (I can cruise at 70-75 mph on the interstate when I must) It will keep up with bigger bikes and eat a stock Honda 300. 5) Low vibration at highway speeds. (Even better with tall gearing) 6) I have seen low 80 mpg figures on the highway! 7) Fairly large stock fuel tank and long range. 8) Starts very easily with the oem decompression starting system. 9) Very reliable and long lasting engine. 10) The stock snorkel in the airbox works well and makes this bike a deep water crossing submarine. ** Summary; Current duel sport offerings could learn a lot by visiting what Yamaha already innovated in the XT350. I wish I could by a new model with electric start and fuel injection. This machine was well ahead of its time. Problems; 1) Carburetors are too lean. Primary carb. pilot and secondary carb main and needle is too low. These cause long warm up cycles on choke, stalls, surging at speed and overheating. 2) Intake boots separate from flanges. 3) Timing chain tensioner eventually fails, and the valves bend. (kills most XT350s) 4) Stock gearing is far too low for road travel of any distance and revs the crap out of the poor thing. 5) Clutch release rod uses a noise suppression oring that hardens and causes clutch slippage / slow release. 6) Oil leaks- eventually rubber seals and bake and require replacement. a- Only the oem valve cover and valve cover bolt seals will completely seal the cover. Rubber valve cover caps that set on the valve bearing caps will also bake and will not allow correct valve cover gasket tension. b- Decompression seal in the head 7) Threads in the cylinder head for the valve cover and cam are weak and will eventually pull out. There is a little air scoop for the spark plug well that bolts to the valve cover retainers- as far as I can tell- this thing ends up destroying the threads in XT350 heads on every one that I have seen. 8) Stock suspension is way too soft for even spirited speeds on old roads and grows softer with age. 9) Ignition coils and spark plug insulator caps fail- likely due to heat when hot soaking after shut off. 10) Ignition Modules eventually fail. (Aftermarket are available for reasonable cost) 11) Primary ignition coil and pickup coil eventually short out. Entire stator is still available from Yamaha or individual coils from oem or aftermarket. 12) 438 drive chain stock 13) Speedometers trip odo will eventually seize up. 14) 12v charging and lighting system are too weak. 55w headlamp is not enough and no reserve capacity for heated grips. 15) Plastic body parts are getting hard to find on the white plastic models. Mods: 1) Carburetors are too lean in stock configuration. (I ride from sea level to 7000') a- Increase primary carburetors pilot jet one size. b- Increase the secondary vacuum carb main jet one size c- Add one washer to the underside of the secondary carb diaphragm needle (lift needle the equivalent to one clip position) 2) Gear the machine very high. The engine torque is strong enough to pull very tall gearing with ease. I have retained the lightweight 428 chain for lower weight and use a DID oring chain with several different countershaft sprockets for different types to trips. I can tolerate a very tall 1st gear without stalling. 3) Install a manual timing chain tensioner or replace the stock one every 10k. 4) Remove the spark plug air intake off of the cylinder head. It will cause oil leaks from the bolt holes and wear out the threads in the cylinder head. 5) If your engine has over 15k on it- replace the cylinder head 6mm bolt holes with helicoils. This includes the cam tower bolts. Lots of heads get scrapped over this and they are still very serviceable. 6) Replace or repair the stock air intake manifolds. Clean surfaces and apply windshield urethane for a permanent repair to the stock boots. (I have cast boots for obsolete machines in the past with this stuff) 7) Helicoil the oil filter threads. They eventually fail. 8) Add pvc spacers to the forks for additional preload. (the air caps are worthless for preload) To stiffen- cut a coil or 2 off and compensate with a pvc pipe spacer (short spring is stiffer than a long one) Make sure to calculate minimal total compressed spring height so that you do not "coil bind" and ruin your spring. 8) Compress the stock rear spring and move its preload position to the second retaining clip position (Yes, it has one hidden under the spring retainer) You can also cut the spring shorter and add compensation spacers but as I stated on the fork springs- beware of going too short and causing coil bind) 9) Gut the trip odometer from your speedometer when it siezes up to extend the useful life of the instrument. 10) Gusset the rear frame loop if it is used for rack support. The frame will crack otherwise. 11) Replace the stock oring on the clutch rod (inside the transmission shaft) as soon as you notice slower than normal clutch release. I used a smaller than stock oil rated ring with out any detectable chatter and improved clutch action. 12) I use the stock airbox and snorkel and they work great. You would only benefit from increasing the airflow if you run the engine at high rpm- which I dont have any need to do. 13) I run the stock exhaust. The machine is so quiet that I often roll up on wildlife before they even know I am there. The performance is actually decent so I see no need to modify the stock exhaust in any way. 14) Install wide, modern YZ250 footpegs. I spend hours in a standing position, this mod is a must do. Drill the stock undersize pins to install the pegs with a bit of peg grinding required. You will loose the return spring function, but this is not an issue for me. 15) Installed high bend handlebars for an ideal standing position. 16) Install a Slipstreamer, Spitfire windshield for longer highway trips. 17) I have used Mobil 1 10w30 with supreme results. The clutch and shifting action is smooth as butter and the engine is not showing any detectable wear, even after all the added miles as of last valve adjust.

[@ericsacco7406]

INCREDIBLE INFO THANK YOU!!! That is amazing you know these bikes!! I sold ours as we were not using it but they are pretty cool! DRZ400 is much better and DR350S is also wtih a better chasis. Thanks for all the input!

[@shopken1]

@@ericsacco7406 The DRZ400 and 650 are great machines but they are somewhat crippled by the 5 speed box and low stock fuel capacity. The old XTs double their fuel economy and then some. The seats lack enough decent padding for long trips. Both have So much better suspension, handling and brakes than the old XT! I have owned and repaired lots of Dr350s through the years. A much better seat than the Drz's.

[@LOOKOUT2012]

Excellent! Thanks for sharing. Mine goes great but may try the air box mod. I have a full predator exhaust system which is larger diameter pipes than stock so more air should help! That's in amazing condition 👌 Would love to see some more videos of ripping around and top end speed etc. Thanks for sharing 👍

[@ericsacco7406]

She RIPPS! Easy 3rd gear wheelies with no clutch just a tug on the bars... just right I can get them in 4th. Best way to determine power. Thanks yes she is CLEAN.. only 1500 miles was a garage queen. I did end up having to remove the airbox cover also as it needed a little more air. Glad I could help!

[@LOOKOUT2012]

You should do a video of ripping around.... Would love to see that and head her 💪💪

[@simplybeautifullandscaping5895]

Great info

[@erwinvb70]

Very nice, I will try some mods myself and see if I can get mine to run at least somewhat better than stock. You may want install the air scoops under the gas tank again to avoid overheating

[@ericsacco7406]

yep they are on they were off for the Vid

[@kasperbang7295]

Do you mean it pulls power wheelies? :O

[@JAventura680]

Te felicito compañero de máquina xt 350 qué año lanza que me das yo tuve una.18 años. Ahora tendría esa motocicleta mía 47 años. Cómo me gustaría tenerla

[@deathcogunit106]

It's been around 6 months, still running well? Mine is stock except one size bigger on the main jet. Still seems like it runs a bit lean and if this is still working well for you I might as well give it a try. The bigger main jet alone made a noticeable difference in getting the front wheel up.

[@ericsacco7406]

Yes... she runs perfectly. I keep mine with Av gas in it as I do not have to worry about the ethanol fuel and she does not get ridden much. You will notice MUCH easier starting, more power and will run cooler. I start mine this way... choke on full, kick until it fires off and stops... you get about 4 strokes or so of running. Then choke OFF and will start and idle perfectly from there.

[@neilgildenhuys3370]

I don't understand you correct, if I search TT350 secondary it has a #122 main jet and the XT350 secondary is #106, the XT600 primary main jet is #130 and XT350 primary is #125. Is that the correct sizes and will going from a #42 pilot jet to #48 pilot jet be too big. Thanks, Neil

[@chowmurphy]

Have you changed the jets at all since this video? Did you change out the pilot jet to something bigger? How many turns out are you at now for the a/f mix?

[@ericsacco7406]

Jets are all the same... I think I'm out 2.5 turns on the slow needle cant remember I just turned it until I had good reponse and was not loading up.... I ended up taking the air box cover off as it was a little too rich... is not perfect. To start I give it full choke and usually 2 kicks until it pops. Choke off and one kick has it purring.

[@ericsacco7406]

Just to clarify.... XT350 made from 86 to 2001.

[@ericsacco7406]

Correct!! that was my bad!

[@johnflack3686]

You are actually wrong I have a 85

[@mrnihad170]

Nice mods, any idea where to find the exact measurements of Main jets TT350 & XT650 ? (otherwise I'm into buying whole restorations kits just for the main jet)

[@ericsacco7406]

130 jet for the xt600 and TT350 secondary jet.. get them at the dealer or Partszilla.

[@KryslerKid]

Finally have my carbs off to go through. Just wanted to confirm #'s with anyone. #130 main to replace #125, Secondary jet to a #122, mine is #100 in kit, and pilot jet from 42 to 48? Any help appreciated. Thnx

[@latenightlosers420]

How much of a power difference? And do you compromise anything doing this? Maybe like creek crossings? Can it take water now that you did that to the airbox?

[@ericsacco7406]

I would say you get a 10-15% boost in power. Runs a lot cooler easier to start. I would never ride a bike like this hard off road but if you are worried just mod the top of the airbox instead of the sides like I did.

[@KamenKachev]

I'd like to do the exhaust mod that you've done. Mine has the original exhaust cut at some point and it was redone, but it is too quite and it is not possible to remove the bafle, so it is a good idea to cut it anyway and redo it once again. I also have some holes in the diaphragm of the secondary carb. Do you know what is good for a replacement? It is no longer available at Yamaha. Also mine has adjustable needles and I raised both of them a single notch but now it is too rich.

[@ericsacco7406]

I would not shim the needles that is not needed. Look for aftermarket on the diaphram that needs to be in good shape. I only cut a hole at the back of the pipe I do not touch the spark arrestor.

[@ThatSB]

Idk, my XT runs fine. What ran wrong with yours?

[@ericsacco7406]

Takes too long to warm up with choke... less power stock and runs hotter.

[@ThatSB]

@ericsacco7406 well yeah if you remove the protective box to allow more air in youre gonna make more power that goes for any vehicle. It is a trade off though. Those types of mods can be bad for offroad. As for the choke it does take a little to warm up but you dont really need to let it get that warm either. Just ride and pop it off after a minute

[@marccawood]

Remove the air filter and backfire screen. Are you kidding? Do you want to clean your jets after every ride?

[@ericsacco7406]

I have not had any issues at all. Most other bikes with a carb do not have the screen like my XR600. Just more restriction.

[@marccawood]

OK, but you say "remove the filter" and I can see the red replacement filter through the hole you drilled. So I guess you mean - replace the filter.

[@ericsacco7406]

@@marccawood Correct. I used a Twin Air.

[@ericsacco7406]

@@marccawood yes Mark... you need the air filter of course. You can use the stock one or Twin Air like mine... it costs less than stock also.

[@Englishman-mz8vy]

I would not recommend doing this to your bike. This is silly, how he is quick firing anwsers.. Do you think YAMAHA would make a bike that needs this to be done to it,.... to much grinding and drilling and breaking things... just a mod flex video. If anyone has a real problem with their YAMAHA XT take it to an "older Mechanic". These bike were made by professionals who are of the highest quality your bike does NOT need this! Paitence and brains will fix an XT.

[@willhutton1516]

Eh. People don’t always use bikes for their intended purpose. Look at torture test magazine’s video series on a road trip with the cheapest bikes they could find. One even used a gs550 as an off-road dual sport😂

[@ericsacco7406]

Your point is well taken. These bikes come so lean from the factory. They will run as they come stock. If you wish to run them that way that is totally fine. I prefer starting cold one kick and not having to wait until the bike runs correctly only when warm. I also like more performance and longer engine life due to lower operating temps.

[@kitvexed8229]

you know what would make this bike better>? SELL it and get an XT600.. all the power in the world without ANY mods and it's hardly more expensive!

[@ericsacco7406]

@@kitvexed8229 I have one!!! THey need the TT600 main and 2nd jets as well as an open airbox. Mine ROCKS!

[@TheIrishAmish]

This guy is telling you to do STUPIDITY.

[@ericsacco7406]

Anyonne that states that is describing themselves... I have owned over 170 bikes and have a shop... your loss if you like a lean running bike.

[@BurnerJones]

@@ericsacco7406 It runs fantastic with these mods. Found this video last year and just happened to find it again. The before and after is massive, the front wheel lifts off with no effort now and you can actually start it, crazy how lean these are stock. I'm going to be welding in a bung for a wideband o2 sensor next week just to see exactly what numbers it's running at.

[@ericsacco7406]

@@BurnerJones Awesome!!! SO happy it helpped out!! Doing a DR431 now... did the same mod to the exhaust. Thanks again!