Hi

For a leakdown test on my 1980 dt175mx, I need to buy some rubber plugs for the inlet and exhaust. Could someone help me with the diameters of these 2 'holes' ? (save me having to strip the bike before buying)

BTW, If anyone in the UK knows where we can buy the expandable rubber plugs? (See attached pic). They only seem to be in the U.S and the postage makes price ludicrous




Cheers

Adrian

Hi, can't help from here [nz] as to where to buy bungs, but i've never found the need to do a leak down test. Think i'd loose sleep if i tried that idea on any of mine lol but they run ok regardless. I'm interested though to know if you're chasing a problem that won't go away or just purely doing it because its a good thing to do. [& absolutely nothing wrong with that]. Cheers.--& Welcome.

Intake 35mm

Exhaust 38mm

If I remember correctly, you can use the same size on both... You need to find one that the smallest size is under 38mm as the port gets smaller as you go in. The ones I have just fit the port at their smallest... Very tight fit.

They are expandable freeze plugs so maybe a Halfords has something.

If not, I'd do what I used to do... Make a simple plate to cover the exhaust port and clamp something round into the intake. A piece of capped pvc pipe works or even a hardwood dowel.

thanks Mark,

I bought some wine makers rubber bungs to prototype. One has a hole in the middle and I intend to fit a shrader valve into it. let you know how it goes.

You may remember we were discussing an ongoing weird one where the bike runs perfect except when hot the idle stays high for about a minute. We came to the conclusion it could be a vacuum leak. Well I discovered the left hand crank seal was leaking so replaced that. It was hard and brittle and almost fell out! Got a genuine Yamaha replacement and popped it in and .... still have the problem.
Lubed it up but stupidly, I forgot to give the crank a quick cleanup where the the seal runs. Im not convinced the new one is sealing so Im going to give it a full leakdown/vacuum test
The other thing I noted was the old seal was flush with the crankcase (it was so loose though it could of moved) where as I pressed in the new one in until it seemed to 'butt up' and is recessed into the crank case by a couple of mm. (so the seal would be now running in a new spot on the crank)
Can I check, is the seal supposed to be pressed in until it stops or should I of left it flush with the crankcase?

cheers
Adrian

yeah its unbelievable just cant find expandable plugs anywhere in the UK. Plenty in the US including some plumbing options that look good - www.mcmaster.com/expansion-plugs
www.lawsonproducts.com/lawson/Rubber-Exp...tment-35Pcs/LP212.lp

I'm thinking its not seal related or i think it'd be doing it similar hot or cold. I'm wondering if its a combination of idle mixture too rich & the idle speed is wound up to counteract the richness pulling it down to idle, so richness fighting slide lifted a bit. That theory probably doesn't work though as i think if set rich when cold it'd be even worse when hot--so ignore that. But if it was set too lean at idle & the speed has to be screwed up to stop it faltering & stalling then that would only get worse when motor warms up. Also is the fuel flow restricted into the carb so motor is using about equal or a fraction more than the flow into the bowl so as it drops quite low its leaning off & revving higher--doesn't explain it then dropping down though. Something out of the ordinary going on. Be interested in your test results though. Thanks.

cheers for the ideas. Thing is I cant emphasise enough how well the bike runs other than this. And idles fine when it settles.
Anything with fuel flow would probably impact it at higher loads/speeds.
I've had the carb off a few times and think its pretty well set up and clean. Im on std mikuni jets and the air screw adjustment is in tolerence. I did go 1 groove leaner on the needle but that made it run perfectly, I put it down to adjustment for 40 yrs of wear and modern fuel!
The only thing wrong on the carb is my float height may be a little out because it pukes fuel out the overflow when moved around quite often. But I'll put right and check everythign as the carb'll have to come off for the leakdown test

Seal should be flush with the case... also use the IT175 seal as it's double-lipped to seal vacuum and pressure... Stock seal is only single lip on ignition side.

Link to seal with part number: www.partzilla.com/product/yamaha/93103-25125-00



.

How good is the motor for compression. If its down on comp you end up screwing the idle up more than normal for it to keep running, so then it comes down slowly. sorry if you've said motors good for compression in an earlier post, but if low comp it could still run ok at revs within reason but struggle to idle. If you back the speed screw out slowly does it keep idling lumpy like a good pulsing compression or just fade & struggle. I remember when the monoshock dt175's got a lot of miles on them the rings gave up--got caught in the exhaust port & all that. Rings were made out of cheese--well cheese might've been better. Rings could be wound around like a cork screw without breaking by memory [was a long time ago].

Cheers, local dealer has them in stock and its cheaper than the stock seal!