1973 DT250 cafe racer

[Catbird]

Started her again today. Fired on the first kick after I remembered to turn the fuel on.

Rearset geometry is going to be tricky with the kick starter. Going to have to get creative.

Brought her around the block once. Surprising amount of pickup, even off a cold start.
Soon on the agenda:
-Replace the damaged cylinder head
-Replace dented pipe
Projected time of completion for repairs:
Tuesday, 4PM

[Von Kirk 75 dt250]

whats wrong with the head?

[Catbird]

It's the older style head with two ports for spark plugs. One of the sockets has a large chunk broken off and I'm sorta surprised it hasn't gone kaboom yet.

THe radial-finned heads look cooler and in fact provide better cooling action to the cylinder, and I have about three spares of that style. I'm going to try decking one some time soon to ramp up my compression a bit.

[Catbird]

UPDATE:
ENgine runs surprisingly strong after carb tuning. CUrrently it'll push 8,500 RPM without load just fine, after burnishing and adjusting the points.

I'm a little leery of some extra noise in the case, however, and the clutch is just "there" enough to move. Will probably be swapping the jug, the charging and ignition system, and a new cylinder head onto another motor case soon. Not going to lie, I've been afraid to look inside this one to see what kind of timebomb I've been riding. XD

[Catbird]

Hey, question.

How much does anyone here know about the Hooker DT250 expansion chamber? I have an opportunity to possibly bag one and am wondering how much it's realistically worth.

Also... It turns out the bike is actually a 1974.

[Von Kirk 75 dt250]

Well from what i've found its a pretty rare header, so if you can get it for under 125 your solid.

[makotosun]

The Hooker chamber for that year is not too common. Bassani made them for the '74-76 models, but I don't know that I have seen one from Hooker. Lots for the earlier years out there.

If you add a chamber, to get optimal performance, you should improve the intake a bit - maybe a uni-filter or a K&N pod type. You will likely need to richen up your mix (larger main and Pilot) to handle the greater air flow.

You may also need to add or fabricate a silencer for it if it is not built with one. An in-silenced chamber sounds cooler than almost any pipe, but will put dollar signs in the eyes of your local constabulary.

Post up a pic when you get it, as I would be curious to see the design.

_

[Catbird]

It's already got a K&N pod filter on it and a richer mixture to match.
My issue right now is that what it seems like is that the DT was designed to have a wide, flat peak around mid-throttle operation given that it's an enduro-type bike. I'd like to have *some* full-throttle response, since I will *not* be using this particular machine off road.

Plans are to do the eyebrow port job, match up the exhaust, and either use that Hooker pipe or make my own for 6-7K peak output. I may drill the head for booster ports but I'm not sure yet. My carb should be big enough to handle the load, I shouldn't need to do anything but fidget with jetting.

EDIT:

Is it realistic to expect 30-35 horsepower after porting and an expansion chamber?

CUz...

[makotosun]

The 73 mx250 put out a claimed 31 hp from the factory. The motor you have is a similar design.

If you could match the porting of the MX, get a similar design pipe and add more carb (the MX used a Mikuni VM38SS carb) you may be able to obtain similar numbers. The MX bikes did have a spark arrester, but were not "silenced" and would likely get a noise complaint in most urban environs.

I have project based upon a DT400 frame with an MX400 motor on the bench right now, which should have the potential for about 38 hp. I just need to clean the garage of other projects so I can move it forward.

Following your build with interest.

[Catbird]

This is very exciting. I can't quite put it in words how happy I am to hear that this at least appears to be a realistic goal. It'll go a long way toward extending the service life of this particular motorcycle in my ownership, which is awesome, because I *really* like the dumb little thing, but I just need the extra power for longer-range trips where I'll need a steeper drive gearing for highway speed, in order to keep up with my father on his '99 FXD Superglide and my brother on his new '06 Buell XB9.

The obvious answer would be to sell my DT stuff and buy an RD350, but I'm a sentimental sonofabitch and I've been on DT250's literally since I was 13.

[Catbird]

I've come to a conclusion most of you may find facepalm-level obvious. My carb is outdated.

I've heard whisperings on the interwebs that one can use a YS250 carb on the DT250 with minimal modification, but I'm wondering which year I should go with to provide maximum benefit and minimum need for alteration.

[makotosun]

Not sure which carb to interchange with. I believe your bike (if the same as the 360/400 series) injects the oil into the carb instead of the cylinder. If you are using the oil pump (I would recommend it as it varies the mixture for optimum ratio) you will need to ad an injection port to the replacement carb.

The pumps are actually very reliable - most of the tales do failure were highly overblown.

You would probably get the best results by installing an MX carb if you can locate one. There is nothi g really wrong with the carbs these came with if properly cleaned and jetted.

[Catbird]

Yeah, I like the autolube system. Even if it was fidgety I'd take it over having to mix oil with my gas every time I stop for fuel.

I've got carbs for both systems currently, inject-in-carb and inject-in-head.

[Catbird]

Henry sent me some drag bars and they look tits.

[Von Kirk 75 dt250]

Im really diggin your bike Cat, go check out my lil yammy, i painted her.