Xt350 low top speed

[*Neo]

What it feels like to me. is that it’s geared to high and the motor doesn’t have the power to push past that speed but if it was geared to high ... wouldn’t it be going faster than its original top speed before something like this happens. also pretty sure the sprocket sizes are stock... it just feels odd

[*Neo]

Also appears to be running pretty lean... that could be the whole issue.... What should I do ? Shim the needle in the cv carb.. or drill the jet in the cv something like that ?

 

Also I forgot to list the jet sizes. The main carb has :135main and 42pilot

The second carb has:106 main and 14pilot.

I’m assuming it’s called a pilot .. the 14 is the jet under the diaphragm of the secondary carb

[*Neo]

Any ideas ?

[*Neo]

.... well I feel stupid for not checking this more thoroughly before .... it’s a vacuum leak on the intake boot?‍♂️. I didn’t check it before because it didn’t really pop.not like I’ve had bikes do in the past anyways but I decided to check it. And sure enough. thank your for all the helpful advice. Hopefully I won’t have to get back on here with anymore dumb questions. But it’s nice to know there are people on here that seem to know this model inside and out .

[William1]

Glad you got it sorted. Those manifolds are a real weak spot. No idea why. I have assume Yamaha ordered 100,000 at once and they are all crap. Going to sell until they are gone.

[*Neo]

I haven’t replaced the boots yet. Just haven’t had time. I did inspect them closely however and they look brand new. The rubber isn’t dried out.. no cracks that I can see. I jut assume that’s where the leak was because Of how often everyone says they go bad. I test by spraying a Generous amount of carb cleaner in between the carbs while bike was idling and the rpm took a noticeable drop. If it isn’t the boot is there another common leak area ?

[*Neo]

So the saga continues.. I managed to get the bike up to 70mph indicated after replacing boots. I had to rev the snot out of it in every gear to get that speed tho i Checked with my gps and my speedometer seems right on!... anyways I finally got around to replacing the boots but I still have a leak. Next on my list was the two small black tubes connecting the carbs. and the primary carb cap so... I changed them and just for good measure put a small amount of high temp silicon on the cap gasket. And still!...... Vacuum leak?‍♂️
it spits and pops and will die if try to let it idle For to long. I was checking with carb cleaner again, and I think I’ve got it pinned this time, I think it’s leaking around the axle for the butterfly valve in the secondary carb ... I removed the spring assembly and butterfly but the rod still won’t pull out. Is there a trick to this ? I’m thinking there must be a bad o ring/seal there but I can’t find anything about it. ... just when I think I’ve got this bike figured there’s something else lol

[scarumanga]

I had a 1994 xt350, I struggled to maintain highway speeds with it, hills were a challenge even in 5th. Had it for 2 years, replaced all kinds of stuff, had a mechanic have a peek at it. Seemed fine otherwise. I ended up selling it and buying a fuel injected crf250l, in comparison it hits highways speeds and keeps going, does everything my xt350 did and then some. My buddy had a older 80's xt350 and it seemed to actually have some more guts than mine did, he ran it dry of oil and scored the cylinder and ended up going with an oversize piston, he said it had more power after that. I have heard of using a xt600 jet in it to squeezer more out of the top end, I never was able to try that out myself but searching online showed that was a option.

Specs say it has 31hp, and 22ft-lb of torque, but its only felt down low. Whereas my 23hp and 16.5ft-lb is a lot more even, peaking higher than the xt350 can even rev.

Pull up XT350 on gearingcommander.com, as the chart's are based on M P RPM, not redline, technically that is your reachable top speed. But it doesn't reach those speeds. Makes no sense.

It doesn't help that there are no aftermarket parts like exhausts or jet kits. You can however buy a UNI air filter for it and delete the spark arrestor...I found that to help a bit...max speed i ever hit was 110kmh downhill. Struggled to maintain 100.

Edited July 8, 2020 by scarumanga

[Daren Harben]

I'm interested in this topic my self ? I've got a 86 just rebuilt the top end. Good compression, new timing chain and tensioner. 

Ignition timing good. Set float level to 6mm all cleaned out changed main to 135 to get rid of a lean the bike had before.

Now bike starts and runs great up to about 5000rpm and starts skipping and sputtering. Right where the secondary should come in?. Drive easy and it runs great.

Just no big throttle or it falls on its face. Tried putting bigger and smaller jet in the secondary and it's made no difference either way.

At part throttle it will rev to red line without skipping.

I don't want to take it to my local shop ? because they mostly work on Harley's and will probably charge more than the bike is worth.?

[scarumanga]

There is a company that makes replacement carbs for these bikes,  my buddy was telling me about it actually. Apparently they are an upgrade from stock. Might be worth looking up. With specs on paper in mind.. these bikes should perform almost like a drz400... only 2 hp less... and 50lbs lighter 

Edited July 8, 2020 by scarumanga

[Jens Eskildsen]

Theese bikes are plenty rich stock on the mainjets.

A stock bike should easely go 80mph, and clutch up wheelies in 2nd gear.

[*Neo]

I ended up getting it running quite well.. I replaced the carb assembly with one from a newer xt350... I did finally discover the cause of my poor running condition tho, it was a vacuum leak. the fiber washer/seal on the transfer spindle for the cv carb butterfly. I couldn’t find a replacement seal. But that was okay because I needed to replace the carb, do to some damage anyways on the original carb. after that the bike ran great for a commuter. Tho it never made enough power, in my opinion.... I owned a dr350 before my xt, and the performance between an XT and the DR were night and day.  It would get to 50-60mph quick enough but anything past that it was just gutless. But the 50mpg was worth it for me in the trade off... however I ended up selling the bike to get a road bike. Seeing as 90% of my riding was on the rd anyways. And the xt wasn’t spectacular in the dirt and the seat was uncomfortable after only 30min... I think the xt is good for dedicated Yamaha guys and somone just looking for a commuter.  but if I ever get another 350 dualsport I’ll be going for the DR.  More available parts, more power. Electric start option And much MUCH! better suspension for dirt..  

[maim]

mine will not red line in 5 or 6  either and i have done a bunch of motor work that raised the red line in all the lower gears.

[Secondchancecycles]

I know this is an old thread but I would like to leave this here to help anyone in the future. I own a bike shop and had an old honda rebel that had been neglected I pulled the carb and put it on a xt350. It idled and ran reliably around and I returned the carb back to the rebel and ordered a $50 rebel 250 carb. The out put side was as big as the xt350 carbs and the inlet size was a bit larger so air volume will be enough. You will have to use some larger runer hose to run back to the intake box. After installing the new carb and fine tuning the idle adjustment to enrich the fuel mixture the bike runs flawlessly. More could probably be had by a carb rejet. Since the original carb that was on the bike when I got it was beyond repair and a replacement was not much less than the value of the bike I had to try this. The bike will do a bit over 70 per it's factory gauge so if factory it was faster then a rejet will be required. However for puting and trail riding the carb out of the box will do. The carb outlets are the correct distance apart to fit in the xt350 factory boots that bolt to the head. The only two modifications to the bike for this is the aforementioned intake tubes from the airbox and you will need a choke cable which can be sourced for $10 on amazon. In total without a rejet you are looking at $75. For the exact parts I used let me know and I will find my receipts and post PNs