new here with an RD 400 drag bike project

good to see you made it here Al.. this is gona be fun to watch!!!!

Cheers Rob, thanks for pointing me In this direction.

Glad you got it ok
Good luck - hopefully you will get the gearbox working ok now

Dusty

Great stuff , result .

If your looking at changing the ignition system I'd recommend the vape race version probably the best ignition on the market! I love mine.

www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/electrical-ignitions-lighting/ignition/mzb-rd350-rd400-race-ignition/

Oh yes, it runs. Crackles and barks like a demented beast, I won’t be popular on my road when I get it out for a test ride

Unfortunately the throttle cable broke at the twistgrip so no riding today.

So spent the afternoon making a new cable end with solder.
I drilled a 6mm hole in a piece of wood, cut a slot for the cable go in so its cleaned and frayed end is In the middle of the hole, put a 6mm drill tail back in the wood from below to set the required width of the cable end and then filled it with solder….. worked a treat So might try and see if it will roll tomorrow

Good news is I have tracked down the original Tuner (Harry Barlow) who did the original work in 1988, and more good news is that he still has his 400 drag bike and a supply of parts alongside his current scooter tuning business.

So Harry asked me to strip it all down and measure the key parameters to help him understand what he did back then and from there we can work together to get it set up and racing. ….. so rather than rushing to the dyno its all coming to bits and getting measured.

In the process of doing the measurements I have built up a leak tester and I just tested that on the RH cyl, as I haven’t taken it apart ….. it leaks like a sieve .

So I just took the primary drive gear off and can see a few problems with both the seal at the end of the keyway, and the washer on the end of the crank.

I will post some pictures later and go back and look at Dusty build thread so I can see if I am missing anything here

Part #26 is the seal I need, but it’s showing as unavailable so far.

I notice that dusty350 didn’t have one on his 400E rebuild, so perhaps I can work round this with some sealant on the joint and key.

Found the seal (assume a pattern part) on yambits, so will get that and also add the sealant to the key.


I will get a new Belleville washer, as the one i took out it was dented on one side so not the normal cone shape

Since my last flurry of activity and posts, the project went off teh boil for a while, but it is now back as a focus and i intend to get to the Straight liners Run What You Brung meeting at Santa Pod on April 7th.

So the work now completed is
- a full rebuild of the air shifter,
- rear shock removed and a a lock up bar in its place.
- structural bracing to make sure the chain adjusters don’t get bent under an aggressive launch.
- purchasing some seriously expensive high octaine C16 fuel.
- full day on the dyno at 2T engineering in Banbury to get the jetting and ignition dialled in.

The main jets that were in the bike when I got it were 500’s, but we ended up back down at 280 to get it revving through with a good AFR at all throttle openings, we then advanced and retarded the ignition to get the best compromise of peak power and overrev.



Power is 65bhp at 10,700rpm and 33ftlb at 9700rpm and the curve looks good. I had hoped for over 70, but this looks like a safe tune and should be more than enough for a a starting point into drag racing.


What still needs done is:
- work out how to pull down the front forks to reduce the tendency to wheelie off the line.
- sort out some kind of chain guard so the bike will comply with the regulations for the RWYB class.

I know it will be only full chat for a few seconds but I’m interested that Andy was ok with revving to 11.5 with a 400 crank. That’s TZ350 revs…
Or is that just dyno exploration?
I would have thought Rev limiter at 10.8 would be prudent . Should still be plenty of power across the gear spread you need.

Well that’s a huge step backwards!

With the 1st drag outing less than a month away, I thought i would start her up, get her up to temperature and make sure all the basics are still working.

After wam up, did a couple of hard starts from about 3 to 4000 revs just to see it it wheelies or spins (it spins) and then the engine note changed with a new metallic sound from the left hand pot.

Back on the bench and took the L/h head off to see some metallic particles in the combustion chamber



Further strip down to find the back of the piston has broken up



So now I need to split the engine to get the rest of the bits out and also the joy of tracking down a 40yr old piston which may or may not be from a DT175.

The engines out and on the bench and I have spent hours on the internet tracking down Yamaha pistons that are marked like this one





anybody know how to decode the piston numbering 2A700?   Is it DT175 or IT175 and what year?




Let’s see how far get before the deadline of April 7th

As Dusty said, 2A7 is prefix for Dt175, though parts could also be used across a range of machines, ie piston also for It175, but the prefix is for DT175, yamaha do this s lot.

HTH