I posted this on reddit this morning, but I thought I'd post it here as well. I'll try to sync the replies in both places. Here's the reddit page:
Hey all- so, I have this 1975 RD350 that I got a few years ago, non running, and it's taken me a while to get through different systems and get it up and running. Tank rust had fouled the carbs, and the previous owner eventually gave up and sold it to me. The mileage is high, over 40,000, but the bike is all stock and seems to have been well cared for. Apart from the rusty tank and a seized front brake caliper, everything has been in really impressive shape.
Rather than sort out the rust issues (so many options, all sort of scary), I made a small tank from a stainless steel water bottle with open fuel lines running straight down to the carbs (no petcock or valve). I decoupled the oil feed system and I'm just running premixed fuel for now.
Two weeks ago I pulled the carbs again, futzed with them a little, remounted then and finally got it running! After adjusting the idle screws, it idled nicely around 1300rpm (not sure if this is the correct idle rpm, but it felt nice and comfortable). It makes all the characteristic pops, and revs beautifully. Here's a video:
So, I was pretty stoked, the thing sounds amazing. But I noticed a problem. The fuel level in the homemade fuel tank drops WAY too fast. Where was the fuel going?
Also, after a few sessions like the one in the video, I started to notice some percussive ringing sounds from the cylinders. Piston slap, I thought.
Thinking it through, the missing fuel would have to be in the crank case. I'm thinking the homemade gas tank setup just flows too much fuel, or maybe my float valves need replacing, something like that.
This weekend I pulled the engine from the bike, took off the cylinders and tipped the engine over. Sure enough, a good amount of fuel poured out.
So, here's what I'm wondering:
Does it make sense that oversized fuel lines and lack of a petcock could overpower the float valves and cause the fuel to overflow into the engine?
With the heads off and the cylinders still on, the pistons seems comfortably snug in the cylinders, no play to speak of. So, why the piston slap? Does it make sense that the fuel in the crank case would cause the piston slap sound?
With the cylinders off, I did notice some slop in the conrod bearings. They're definitely not rock solid. Is this normal/acceptable? Given that the piston and crankshaft are retained firmly by the cylinder and case, maybe it's ok for the bearings to have some play.
I tried to pull the wrist pins, but there's some chowdering of the piston casting where the spring clips fit in, and although wrist pins slide back and forth and can spin, they won't come out, they interfere with the spring clip seat in the edge of the piston. I have some bolts and nuts that I could use for mechanical advantage to pull harder on the wrist pin, but I think they might get scored in the process when they drag past that lip where they interfere. Should I try anyway, so that I can inspect the small end bearings? New wrist pins are pretty cheap, probably just $50 for a pair.
One thing I could try, to stop the fuel overflow, is to bend the brass tab on the carb float arm where the float valve plunger seats. I know there are some engines where this is a normal thing to do. I'm not sure its meant to be done with these carbs.
If I start replacing carb components, where can I get good parts, particularly the float valve elements? I've heard that the aftermarket jets for these carbs are no good, and that if you do buy a carb rebuild kit, you should just throw the new jets away.
Thanks for taking a look! I'd appreciate any advice.
(why the \[code\] tags for links? I couldn't get the URL tag to work properly :\)
Code:
https://www.reddit.com/r/motorcycles/comments/70a5rg/working_through_rd350_issues/
Hey all- so, I have this 1975 RD350 that I got a few years ago, non running, and it's taken me a while to get through different systems and get it up and running. Tank rust had fouled the carbs, and the previous owner eventually gave up and sold it to me. The mileage is high, over 40,000, but the bike is all stock and seems to have been well cared for. Apart from the rusty tank and a seized front brake caliper, everything has been in really impressive shape.
Rather than sort out the rust issues (so many options, all sort of scary), I made a small tank from a stainless steel water bottle with open fuel lines running straight down to the carbs (no petcock or valve). I decoupled the oil feed system and I'm just running premixed fuel for now.
Two weeks ago I pulled the carbs again, futzed with them a little, remounted then and finally got it running! After adjusting the idle screws, it idled nicely around 1300rpm (not sure if this is the correct idle rpm, but it felt nice and comfortable). It makes all the characteristic pops, and revs beautifully. Here's a video:
Code:
https://www.instagram.com/p/BYW41lhhbXZ/?hl=en
So, I was pretty stoked, the thing sounds amazing. But I noticed a problem. The fuel level in the homemade fuel tank drops WAY too fast. Where was the fuel going?
Also, after a few sessions like the one in the video, I started to notice some percussive ringing sounds from the cylinders. Piston slap, I thought.
Thinking it through, the missing fuel would have to be in the crank case. I'm thinking the homemade gas tank setup just flows too much fuel, or maybe my float valves need replacing, something like that.
This weekend I pulled the engine from the bike, took off the cylinders and tipped the engine over. Sure enough, a good amount of fuel poured out.
So, here's what I'm wondering:
Does it make sense that oversized fuel lines and lack of a petcock could overpower the float valves and cause the fuel to overflow into the engine?
With the heads off and the cylinders still on, the pistons seems comfortably snug in the cylinders, no play to speak of. So, why the piston slap? Does it make sense that the fuel in the crank case would cause the piston slap sound?
With the cylinders off, I did notice some slop in the conrod bearings. They're definitely not rock solid. Is this normal/acceptable? Given that the piston and crankshaft are retained firmly by the cylinder and case, maybe it's ok for the bearings to have some play.
I tried to pull the wrist pins, but there's some chowdering of the piston casting where the spring clips fit in, and although wrist pins slide back and forth and can spin, they won't come out, they interfere with the spring clip seat in the edge of the piston. I have some bolts and nuts that I could use for mechanical advantage to pull harder on the wrist pin, but I think they might get scored in the process when they drag past that lip where they interfere. Should I try anyway, so that I can inspect the small end bearings? New wrist pins are pretty cheap, probably just $50 for a pair.
One thing I could try, to stop the fuel overflow, is to bend the brass tab on the carb float arm where the float valve plunger seats. I know there are some engines where this is a normal thing to do. I'm not sure its meant to be done with these carbs.
If I start replacing carb components, where can I get good parts, particularly the float valve elements? I've heard that the aftermarket jets for these carbs are no good, and that if you do buy a carb rebuild kit, you should just throw the new jets away.
Thanks for taking a look! I'd appreciate any advice.
(why the \[code\] tags for links? I couldn't get the URL tag to work properly :\)