Rd350 won't rev under load when warm

[raptormeat]

I can ride it for 15 minutes, once the bike gets hot, it won't pull anymore. I can rev it till redline with the clutch pulled on, but once engaging the clutch the revs drop all the way down and it stalls.
It can idle forever, I figured this is symptoms of running rich on the main jets or possibly the needles are way off, but taking the air filter off did nothing. Was intermittenly firing on the left cylinder so I'm thinking fouled plug as well. Idk. Just looking for opinions I guess.

 

[mydlyfkryzis]

Don't assume rich without checking plug color.

I had a similar problem. the rubber intake boots were cracked. Very subtle too. The bike ran great cold, but after 15-20 minutes, it would stop running and be impossible to start. The rubber was hard and didn't leak when cold, but softened and leaked after warm-up.

There are plenty of posts for checking air leaks. WD40 on boots when problem is occuring may help see if that is the issue.

 

[raptormeat]

fantastic. thanks mydlyfe. will check this weekend.

on a related note, my crossover tube (running modified banshee carb boots) kept vibrating out of the rubbers after a very short distance even with clamps on the upper ports, so much so that i had to epoxy the sucker into place across both boots. wondering if anyone else had a similar problem or fix for that.

 

[runmikeyrun]

Install fresh plugs, ride and see what they look like to know what you're dealing with (rich/lean).

i second with suspect cracked rubber parts. You can use a variety of sprays to check for leaks. I prefer starting fluid- I use an extension wand (you know, the little red tube that always gets lost) and I spray very small bursts directly onto the boots, joints, crossover tube, etc a little at a time, waiting a second in between bursts to make sure the last burst evaporates before spraying the next one. If you spray and the idle ramps up, you've got a leak there. Just be sure to do it when its hot and exhibiting symptoms of your problem. If you find a leak PLEASE order a new part (hvccycle.com and economycycle.com are great RD part sources) and don't just glob silicone over the area. Only asking for trouble.

Also, don't forget to make sure the rubber gasket is inside the top cap of the carb. IIRC there should be one there. Can be a source for leaks as well.

Another possibility are loose clamps on the boots. It happens. Been there, done that.