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yamaha ag 175

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Yeah Eric gorr has written similar things more recently. I know a guy who races but I've done a lot of reading and a bit of experimentation so that helps.

No updates really. I still need to modify the head to high compression. I've been sorting the jetting out I was having problems with an in line fuel filter causing the bike to lean out on low tank. Took me a while to figure that out. I removed it

I'm pretty happy with it definitely gonna up size the carb when I can afford. It's the worst the aussie dollar is worth shit now. Should have bought one three months ago.

Have lots of little things to do on the bike but I've been playing with a puch magnum X

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just a quick update - I've been riding the bike a fair bit, I've put 1,500 km on it since I got it registered in November last year which is a decent amount considering its just on historic rego!

anyway I've been having problems with the bike just randomly not wanting to run (running very lean), it's almost got me stranded 2 or 3 times and the only way to make it home was to pretty much ride the bike flat out RPM and I reckon I've almost seized the motor 2-3x lol

So I hadn't got around to looking at it all until this morning, so I pulled the carb because I knew the fuel was getting to the carb but didnt seem as if it was getting to the cylinder and did the usual, pulled and inspected the main jet, pilot jet and needle jet - all good.

Anyway so I thought that maybe the needle and seat had some crap in it and it wasn't letting enough fuel through, well it was just the opposite! the needle and seat which is screwed into the carb body was about 3 turns loose! so fuel was slipping past the threads!!!! what the!? I'd never pulled the needle an seat before so it must just have vibrated loose.

Anyway put it all back together the bike runs better an throttle response is loads better too! I actually need to buy a new plug and do a chop and get the jetting right as well, but I will probably wait until after I modify the cylinder head. waiting for my mate with a lathe to have some free time, hopefully feb!

still a few things to do after the cylinder head

- definitely new clutch which I cant get to hold despite shimming the springs and roughing the existing friction plates which are still within spec! (going to need new ones I guess) worst case scenario I will fork out for RD350 springs which are meant to be pretty dang stiff.

- new chrome rear shocks

- bigger carb - think I'm going to go 34mm flatslide

then i'll either pass it on to a mate for his learner permit or sell it

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I bought a set of 5 new OEM friction plates off ebay today, will fit them with the 5x brand new steels I bought a while back... hopefully this will once and for all fix my slipping clutch. I am going to use type F Auto trans fluid in the trans, and will soak the plates with that... I will use the stock springs with some shims to stiffen them up a bit.

need to do this before I'll reap any more rewards out of mods such as going to a bigger carb etc!

woopie won a 32mm mikuni roundslide (ol and used) off ebay for $15, might see if I can jet it to work!

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bought a brand new in box mikuni flatslide for $55 from ebay! woop! it will be interesting to see which is better! the 32 roundslide or the 28 flatslide

pumped as !

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55 $" that's a steal, is there enuff room for the exhaust crossing over carb ? or is yours the side hung pipe,,

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yeah I have an expansion chamber so plenty of room! :)

fitted it today I will have to jet it out properly but it seems great... its hard to gauge how much throttle response etc is better because the clutch is slipping I will have to fix that before I get anywhere.

seems its best with a 170 main jet pops the front up a bit in 2nd 3rd with the slipping clutch - but feels lean on the bottom end so might have to raise the needle jet a notch or two to fix the bottom end.

will do a proper tune once the clutch gets replaced.

I am waiting on the 32mm, will be interesting to see if that brings anything different to the table, the true comparison wil be done once I fix my knackered clutch.

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Yeh " if you go too big , it will bog shurely . what rubber manifold you using ?

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I'm wondering if its actually rich not lean, it has a 175 series P8 atomiser in it which is for 4 strokes and supossedly works ok with reed valves, but I'm thinking I might put a 169 p0 atomiser in - the 2 stroke guys say the difference is obvious even with reed induction...

it seems to be lean at partial throttle with the 170 despite needle position, I need to plug chop the 170 main, I tried a 180 but the bottom end is far too rich then an now i'm wondering if the atomiser will solve the bottom end and 180 is in fact the right jet.

i'm using a dt175 rubber boot, the 28mm mikuni is only 33mm flange so same as the standard DT carb as far as I know.

I am looking for a boot to buy that has the port for the boost bottle as I would like to retain that feature on the bike.. because i've changed carb I cant readily tell if I've lost performance as a result of removing it. are the later dt 175 intake boots the same sizing as the earlier ones?

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havent done much on the bike lately

put type F ATF in and the clutch is slipping a lot less haven't bothered replacing that stuff yet

made a new fuel tap gasket out of nitrile bonded cork sheet (10 bucks for A4 sheet) - no longer leaky fuel tap

carb bleeds fuel out overflows when on side stand, have to turn tap off to prevent this. will have to fabricate a more straight side stand (It does lean way over as its an ag bike stand)

still waiting to modify the head.

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Howdy S900t8v - love your post.  I just bought a 75 Ag 175 for my good wife (Birthday present...)  Here's a pic (if it works) - only done about 5 thou kms.  Have learned a heap from your post, including that my (her) motor likely needs new crank seals.  I'm curious, if it's not giving too much away, as to what bearing shop you got all your seals etc from, early in your build.  I'm also in Vic and if you've got a good bearing/seal man I'd be keen to use him and pay postage etc.  Was also interested as to how you established what bearing an seal sizes?  Were you working from those removed or did you have a reference at hand.

Thanks for any help you can give.  Cheers.


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finally cut a high comp squish band head for the yam, took 1.5mm -1.7mm off, squish set at 50% and 0.5-0.7mm

havent putit on but it should rip!

MINTY fresh

also did a bit more porting work, cut down the transfers and reangled the boost port, chamferered the transfers a bit more

Edited by s900t8v

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Hey your back,,,,:wavey:,,,,good work,,,,

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hey thanks blackhat ! 




opened up the reed cage a bit more, about 15% should flow a little better at peak RPM 


I actually put the 24mm carb back on while I order a bunch of spare parts for the 28mm flatslide. the 24mm carb setup retains the boost bottle setup which I think does really improve on/off throttle!  I never did get the 28mmm jetting right, the needle jet is the wrong type and too rich, it bogs at mid throttle, probably also to do with the throttle slide cutaway as well. 


I took it for a spin today! 


holy cow the bike just shreds the clutch again and it pulls hard and quick despite a lot of slip! 

prior to the new head i';d got the clutch to a point of non slippage with a 6 disc pack, and shimmed springs! now ive upped the power it cant handle it! just shreds. 

plan now is to throw in the set of new clutch plates and steels I was keeping for a rainy day. it may just be that the ratios are too short and I should lengthen them to reduce the slippage... but should be able to get the clutch to hold irrespective of gear ratios. 

heres a comparison of the windows on the piston 
CT (mine) 


probably gonna throw one of these kits in soon


Edited by s900t8v

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took it for another spin today! its great! I've got the stock 24mm carb on again, I am looking at making a custom stubby flange for a 34mm flatslide instead of just using the 28mm flatslide. rechecked the squish, set at 0.7mm which is fine. the bike is just nothing like it used to be. 

 the clutch is  slipping like mad after the upgrade haha so I will have to throw another new clutch pack in. think I will buy a set of new OEM springs and shim them up, and maybe even add a 6th plate in to the pack to try and lock it down for good! 

I am running points, I am thinking about trying a transistor ignition pack to see if it will improve engine performance, basically turns the points into a switch, so they dont wear out, and also eliminates problems associated with points bounce or coil lag at high rpm. be interesting to see if it would help top rpm. I think now the limiting factor is probably the carb! 

to do list is now 
- throw in a b8es plug and check the jetting is ok 
- reset the timing think probably around 2.5mm btdc 
- throw in new OEM frictions/steel pack 
- grab a new piston kit - the bigger windows will be beneficial, and I will shorten the piston a bit as well to lighten it up. 
- install the lighter flywheel I have and examine the advance mechanism on it. I think its actually a start retard system but could potentially be reversed to retard at higher rpm (with a heavier spring) could be an idea!  
- install transistor ignition module

after I knock over most of these mods I think I'll dyno the bike and see where I am at power wise.  

after that I think I will be going silly with even more porting! I probably really need to pull the engine and open up the transfer bases in the crankcase.  

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adjusted the timing to 2.5mm the other day, - filed the points they were sitting at about 2.5ohms resistance closed, got it down to 0.5ohms which is factory spec acceptable. after about 1000km of riding.

still putting the bike back together after doing a heap of servicing

ordered a bunch of new parts
- new piston kit $35
- new levers chrome $16
- new handlebar grips $4
- new rear shocks $100
- new wiring loom insulation $5
- 12v regulator/rectifier $3
- 12v flasher relay $3

going to convert to 12v and at the same time trial one of the early style pulserless CDI units from a later model yamaha ag175 it used the 4 wire CDI box also found on RXS100, will be interesting to see what it runs like if it runs at all.

hopefully pretty straight forward wiring wise! I dont know if this CDI box works but I watched a cool video on youtube showing how to service them!
1976 Yamaha rAG175

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So the first stage of converting to CDI is done! SUCCESS!  :woop:

Bike started first kick, I checked the spark before I kicked it over and it barely requires any effort to kick! revs out well! wont know until I ride it if its helped the top end at all (8500-9000) rpm. 

I cant believe I had some plastic 6 terminal conncetors and crimp on spades in my utilux kit that actually were the same as the OEM yamaha ones. I just had to change the pin layout on the stator plate to match my pre CDI wiring loom, very simple took about 10 minutes. 

its a 4 wire CDI box 
red/white - cdi input from stator 
black/red - ignition kill 
orange - trigger to coil 
black - earth to chassis 

stator is a pulserless CDI stator - I just matched the colours up! 

yellow - ac lighting 
red white - CDI coil output 
green/red - nighttime charging 
green - daytime charging 
blue - neutral light 


Once I convert to 12v I'll be throwing an electronic tach on and EGT/CHT probes. 

Just waiting on the 12v regulator and flasher units, then have to go globe shopping then It'll be ready to test.

The biggest downside of this CDI stator plate is that its not adjustable, it doesnt have slotted holes, I might have to pay a machinist to slot them for me so I can adjust the ignition timing! its set at 2mm I think or slightly less, very retarded for my setup. 

Once I do boost ports through the piston I might even be able to advance it up to 3mm without increasing crown temps too far. 


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Ha  900"    for every  +  theres a  minus eh "   the power is up, but the clutch slips,  bugger,  with these stiff springs, hows the lever pull ?

And what CDI  did you use, ?.  the  iggy box may have the curve built in, [ see Rex speedshop website,]  ,  and you can beadblast the steels for more friction,  but this  increases wear on  fibre splates,,,, + & -  again eh, :rolleyes:

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hey blackhat I'm going to try blasting some used steels and use them with used good frictions within spec. 

I guess blasting them without warping may be a bit tricky. 

lever pull is ok! I am getting new levers cos the current clutch one is heavily worn. 

 I used this stator/rotor kit - see it uses the same stator plate as the points ignition ct/at/early dt series 


The AG series CDI is interesting, it used a single stage coil setup with pulser mounted on top of source coil to trigger the CDI unit which makes it look similar to the 2 stage DT CDI... and the CDI box is a 4 wire static timing box like found on the RX100 series, however the RX100 use a pulsar coil mounted in a different location as well despite having the static box which I find weird. 

The AG series CDi seems to make use of the early CT/DT100 stator plate with the opposed coils whereas the later DT CDI uses the V shaped CDI setup.
The AG uses 130mm stator - the same as AT,CT, DT100
The 78 and later DT125/175 uses 120mm stator 

Here is a DT175 stator setup with pulsar coil, 2 stage CDI coil and lighting/charging coil - the two stage coil is meant to be better for higher RPM. 

Here is comparison of the variable timing and fixed timing boxes 

here is the 4 wire cdi (RX50,100, AG100,175) 

vs the later 6 7 wire cdi (IT175, DT175 mX etc) 


you can see the 4 wire has fixed timing, the 6 and 7 wire has a variable timing curve. 


I am looking to see if I can adapt a variable timing box to suit. I'd love to be able to computer tune the CDI 

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so I threw on the 28mm flatslide mikuni I had on a while before doing all the head mods etc...  I could never get the jetting right from 1/3-3/4 because even on the leanest needle clip it was still boggy, if I went down a main jet it ended up too lean at WOT. 

but I found a few atomisers in the shed !!! woop. so I mounted it back up! 

the pilot jet was too lean at 30 so upped to 40. 
main jet 170 - needs to go up to 175, 180 is too rich at WOT peak rpm which is about 10-11k before it comes off the pipe. 
the atomiser was a 175 series Q4 which is very rich, I substituted it for a P8 which is WAY better, still too rich but no bog. I'm thinking a P4 or O8 would be good to try. O8 is about the middle in terms of atomisers or needle jets 
needle middle position but I will drop this leaner and see if I can pick up the performance in this range.  

I've got the jetting way better with the leaner atomiser, the thing rips and you really notice the throttle response difference of the flatslide carb, it just jerks (and slips the clutch like mad) 

Always thinking about how to grab a few more ponies with this bike.  I have to take a bunch of measurements before I go any further with port adjustments. 

I've got a 34mm flatslide carb in line to try 

And now I picked up a banshee reed cage wit boyesens an te rubber intake boot or $15! there will be some extensive work required to make this work. 

The boot has the spigot for a boost bottle an this just stretches large enough to fit the monster 34mm flatslide I bought for this bike! The rubber mount has stuffers which is good too. 

I am going to epoxy around the inlet and fins and see if I can fit the banshee cage it's 9mm wider than the DT175 cage I have in there. Originally it was the super tiny ct cage!  

The banshee cage is about 20% bigger an with a bit of modification should flow really well. 

I am going to widen the boost port a bit and re angle the transfers flat acros te crown they're aimed up as is the old style. 

I've hydroformed a few chambers for another project and have a laser cut template ready as an upgrade of te current chamber I'm running. 

Once all this is done I'll probably look at cutting down the combustion chamber even just a bit smaller. 

I bought the later DT style piston to replace the  ct piston with the much larger piston windows I still gotta fit it when I get a chance. I want to be happy with the state of tune and porting and fuelling cos I'll have to break in the new rings. 

My cylinder has a bit of wear probably needs a bore oversize but Inwont borer in case i kill the cylinder with a mod or porting idea. I still have to plug the decomp hole above the exhaust port. 

Finally figured out my end game to sort the clutch
- New OEM CT springs - shimmed 2mm 
- New steels + frictions 

will install this with the CT3 gearset I have with the evenly spaced gear ratios. I need a CT shift drum if anyone has one lying around they're willing to sell for cheaps i'd be interested. 


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