RD350 in Denver Fort Collins elevation at 5000 feet

[LexPaul]

Good morning,

I brought my 1974 Yamaha RD350 to Fort Collins, CO from Knoxville, TN and it does not like the thin air. HP is down and it's clearly running rich. The carbs on this RD350 are very difficult to get on and off the bike. Having said that, what would be my best one off adjustments to get the carbs tuned for this elevation? I'm probably going to sell or trade this bike, looking for a DT250 or something, but I want it running top notch for the next owner if I do get a buyer.

I've read some good suggestions in the forum, but still looking for a solid confirmation on this particular model and the changes I might need to make.  Does anyone live in the Fort Collins area? Any good mechanics if I needed one?

My RD has Dyna S ignition, rebuilt oil pump and top end, running new air boot with OEM type filter.

Thanks for the advice! LexPaul

[SoCal250]

Since your altitude increased by just over 4000ft you're going to need to rejet for the thinner air.
Decrease the main jet size by 1 or 2 steps.
Assuming you've got a 140 main in there now you'll probably need a 130 or 135, and you're going to need to tweak the airscrews as well.  See how 1 step in size works and if it's still rich go another step.

Removing the carbs from a 350 is pretty easy.
-Disconnect the fuel lines and oil lines.
-Remove the Y-boot from the carbs & airbox.
-Loosen the manifold clamps and pull each carb out. As soon as the carb is free you can unscrew the carb top and carefully set it to the side so the needles do not get damaged.
On the bench, remove the carb bowl and then replace the main jet.
To reinstall, reverse the process. Before putting the Y-boot back on make sure the carbs are in sync. You can use a mirror, your fingers, or pieces of zip tie inserted into the throats to be sure they're opening together.

The main jets you need are Mikuni large hex 4/042. Be sure to only buy genuine and buy from a reputable dealer.

The attached should help dial it in. Good luck.

[m in sc]

as an addendum, its easier to putt eh airbox out completely IMHO than fiddling w the y boot on the bottom of the airbox.
leave the y boot in tact on the airbox, pull the battery, batery box, set to side, then pull airbox and y boot out the back as one unit. my 0.02

[RDnuTZ]

LexPaul, are you original owner of that bike, or have detailed history on it? If I'm not mistaken that is the correct color bodywork for 1974, but they came with disc brake front end. Might want to check the VIN matches for 1974. Could be a 1973 bike with 1974 bodywork, or pre disc brake front end on the 1974 there. Lots of these things are compatible for swaps.

[SoCal250]

LexPaul, are you original owner of that bike, or have detailed history on it? If I'm not mistaken that is the correct color bodywork for 1974, but they came with disc brake front end. Might want to check the VIN matches for 1974. Could be a 1973 bike with 1974 bodywork, or pre disc brake front end on the 1974 there. Lots of these things are compatible for swaps.

All years of the RD350 came with front disc.
Definitely a '74 RD350A with the correct body parts. The VIN listed in the FB ad is for a '74 350. Someone swapped that front end.

[LexPaul]

I appreciate all the good information. I'm hoping to pull these carbs today.

I always thought the drum brake was an early model before they swapped to disk. There's some signs of foul play as well. The right side tank has a ding and the blinkers on that side are a slightly different length than the ones on the left?? It's almost unnoticeable, but the handle bar seems slightly out of square. Maybe it was damaged and the front end swapped?? Bike really runs good, if it has oxygen, lol.

Thanks all,