The Stache's '76 RD400

Re: '76 RD400c -- 2smoker "Ginger"

Waiting on some advice in getting rid of this chugging when i close the throttle. To reiterate: Jetting is all stock save for the 120 main jet and the needle at 2. The problem occurs when I let out the throttle while cruising. It only happens below 4,000 rpm. Above that she's relatively smooth. Below 2,700 rpm (in high gear, which I don't usually do) she is also relatively smooth. It is quite violent at speed.

I'm thinking of going down one size on main jet to stock 115. Was also thinking of going up one size to 27.5 pilot. I've read RD's are notoriously lean at closed - 1/4 throttle. I'm going to reset air screw/idle tomorrow using the jetting guide posted earlier to verify that I need a larger pilot.

Any suggestions would be greatly appreciated.
 
Re: '76 RD400c -- 2smoker "Ginger"

Those videos bring back memories of my RD400G, bought new in 1980, just another of those 'I wish I'd never sold it' bikes :)
 
Re: '76 RD400c -- 2smoker "Ginger"

Stache, what is this bike like at higher speeds? 50-60 mph range. Does it feel like the 2 stroke is working hard, smooth, loud? theres a local RD I'm thinking about picking up. I really like two strokes in dirtbikes, yz etc, but never trail rode it like a constant ride on a road. Generally just flying through the gears on and off.

Sorry I'm not help on the tuning troubles. Videos are sweet man, hopefully you get the carb figured out.
 
Re: '76 RD400c -- 2smoker "Ginger"

McBrenner said:
Stache, what is this bike like at higher speeds? 50-60 mph range. Does it feel like the 2 stroke is working hard, smooth, loud? theres a local RD I'm thinking about picking up. I really like two strokes in dirtbikes, yz etc, but never trail rode it like a constant ride on a road. Generally just flying through the gears on and off.

Sorry I'm not help on the tuning troubles. Videos are sweet man, hopefully you get the carb figured out.
Click to expand...

She is beautiful at speed. I can cruise down the highway 80+ without pushing the engine too hard. Just remember to tuck behind those guages haha. She is only truly happy when accelerating though.

Edit: also since it is a 2smoker you do have to vary your throttle at speed to avoid potential damage.
 
'76 RD400c -- 2smoker "Ginger"

Installed new pilots, went up one size - #27.5. Completely eliminated the "chugging." Also installed new float bowl gaskets hopefully to fix the slow leak i had on both carbs.
 
Re: '76 RD400c -- 2 stroke monster

The_Stache said:
No premix. I haven't touched the pump.
Click to expand...
so you running the pump correct. well what is the ratio set at
 
'76 RD400c -- 2 stroke monster

I don't know how to check the ratio on the pump, bradj. Haven't done that yet.
 
'76 RD400c -- 2 stroke monster

During a ride today i started to notice a slight vibration (more than usual) in the seat when accelerating through 3500-4500. As soon as i hit poweband it went away and was as smooth as butter. Not sure where to even start looking. She seems a bit sluggish in the range, too.
 
Re: '76 RD400c -- 2 stroke monster

One place to have a look at for the vibration are the engine mounts, check that they are torqued to the right settings. This was always a source of strange vibes on the Kawasaki 500's (at least it was on mine).
 
'76 RD400c -- 2 stroke monster

kiwi60 said:
One place to have a look at for the vibration are the engine mounts, check that they are torqued to the right settings. This was always a source of strange vibes on the Kawasaki 500's (at least it was on mine).
Click to expand...

Thanks i will. Its only sometimes. At a certain rpm. Resonating? Anyway...

Going to pull and replace the reeds with tdr reeds. Replace stock manifold with a crossover manifold linked with a boost bottle.

Also glassing the new seat this weekend. :)
 
'76 RD400c -- 2 stroke monster

While riding tonight i payed attention to how the engine was responding at the vibration spot. Engine sounds awful, lacks in power until rpms build to powerband... Than she runs great (from 5,000+). The exhaust note sounds dull at this problem spot. So based on what i've read I'm getting conflicting possible causes.. Dull sound = rich. Lack of power + (she doesn't necessarily bog, but) she "struggles" to dig out of 4,000 if I'm just cruising there, i have to give her a little extra to dig out.. Not very snappy = lean. I'm going to adjust needle from 2 -> 3. Besides.... Its better than running too lean. Thoughts?
 
Re: '76 RD400c -- 2 stroke monster

The_Stache said:
While riding tonight i payed attention to how the engine was responding at the vibration spot. Engine sounds awful, lacks in power until rpms build to powerband... Than she runs great (from 5,000+). The exhaust note sounds dull at this problem spot. So based on what i've read I'm getting conflicting possible causes.. Dull sound = rich. Lack of power + (she doesn't necessarily bog, but) she "struggles" to dig out of 4,000 if I'm just cruising there, i have to give her a little extra to dig out.. Not very snappy = lean. I'm going to adjust needle from 2 -> 3. Besides.... Its better than running too lean. Thoughts?
Click to expand...

fixed
 
Re: '76 RD400c -- 2 stroke monster

So I'm making this:
972225_10152058241584622_2003131124_n.jpg


but this is in the way:
0



ideas?
 
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