PICTURE_MAN36

I bought a cheap DT125MX from EBAY 2 years ago, with the intention of refurbishing it, and putting it back on the road. I've had a few yamaha's, DTR125, RD125LC, TZR250, and my current ride which is a '93 FZR600. I always wanted a DT125MX when I was a teenager, but went down the path of driving lessons, car etc, and whilst learning to drive I ended up with loads of 100's.... I am now at the stage where the DT is stripped, and my first project is to rebuild the top end. I've checked the con rod, and the bottom end, and it is sound, and I am therefore not looking to split the crankcases. I am however going to explore the age old myth of swapping the 125 barrel for the 175 barrel, as I've passed my test, and I am reliably informed that the 175 'went' better. Not having experienced the 175's performance I am not sure, but I have the following questions for anyone who may have attempted this modification; a) The 125 will be restricted somewhere? I guess that its in the front pipe, or was it restricted in the carb? I want to use the stock 125 carb, so I guess that the main jet will need to be changed, assuming that the 125 & 175 shared the same carburettor? I will be using the stock air box & air filter, and I am looking to put it back to as near standard as possible, albeit, being a 'big fella' I have fitted a jack up kit to the end of the monoshock to the rear to raise the suspension (my kit modifies the length of the shocker, and not the backet on the swinging arm), and I have a similar kit for the front forks. I've read quotes from lots of people who 'knew' someone who did this, but I've never spoken to someone who has actually done it. I had considered grafting a DT125 LC mark 1 front end onto my frame, as I beleive that the LC mark 1 had a disc brake front end? I would appreciate any comments from anyone who owns an MX, or owned one, and carried out the 125 / 175 barrel swap.. Cheers

Its a DTR for sure... I bought one of these in the 90's as box of bits, and put it back on the road, and it was very quick. It cost me £ 200 + another £ 300 to make it mint. Reluctantly I sold it when someone offered me £ 900 for it. I would recommend puuting the powervalve servo kit on it as they respond very well to this modification. When I did mine, they were quite new so I paid top dollar for the bits, but you should find plenty in the breakers now, and the parts are cheap. If you're looking to put it back on the road, try Yamaha UK for the registration. A lot were registered by Yamaha, and they keep records of all the registration numbers. Mine was a field bike, but luckily had come from a local dealer, who just happened to have the registration number. It makes it a lot easier than having to have it registered at your local DVLA centre, or 'Q' plated. Cheers and good luck

Correct. The floats work like the float in your toilet cystern. There's a brass tube that runs verticaally up the middle of the bowl. If the fuel rises higher than the top of the tube (Normally if the floats are damaged or they're not set properly) the fuel drains down the tube, and exits on to the pavement!!! In my halcyon teen days, if someone had dodgy floats on their '50' you had to make sure that you switched the fuel tap off when you switched the engine off, which was fun when you set off chasing your mates, as if you'd forgotten to switch the fuel back on you'd get about 30 yards, and the engine would start to die!! Hope this helps.... Cheers

Hello. I think what Wild Foamy is saying is that they're overflow pipes. I've had it before with other small Yamaha carbs. If the float's in the chamber are not set properly, the level of fuel goes past the overflow point, and it drains out through the hoses you refer to. I haven't found my manual yet, but I'm reasonably sure that these pipes perform this function. If I could get to my bike (its buried behind the lawnmower etc in the garage) I'd have a look. Cheers

Hello. I run a '93 FZR 600 which I believe is the '3HE' model. I will have a look when I get home for the manual, and will try to scan it for you. Cheers

Great I'll have a scout around now. Much Appreciated. I've done nothing with my 125 barrel and head yet so I just need to source a barrel, head, and carb. Cheers

Thanks for your response. I need to make a list now I think. I guess other than the obvious things like barrel, head, piston, rings and little end bearings, I'm looking for a 175 carb as i believe that the carb listed has a different part number. I'm also looking for a front pipe, tail pipe, and may be a CDI unit? (I'm sure that the guy at Yamaha said that the ignition timing was different. I guess that it would be pointless sticking with my carb, front and tail pipe as the '83 MX would have been restricted to 12 BHP by the carb and exhaust? Thank you

Hello. I don't know this engine well, but if its a derivative of what I have in my FZR600 I don't think so. I have a similar problem with the sight glass on my engine; the sight glass appears to be stained or discoloured which makes it very difficult to read the oil level properly. If your's is like mine, it seems that its pressed into the right hand side casing when the casing was manufactured, and its not removable. Cheers

Thanks for the replies. In the first instance my apologies. I had my car head on at the time. I meant to put CDI not ECU (This is what comes of trying to have a sneaky look at a forum, whilst at work, when your supposed to be being productive!!!). I have the Haynes manual for the DT125/DT175MX and it lists the part numbers, bore & stroke etc. There were many models made, for many countries, and I would guess that looking in the book a good 85 / 90% of the bits are common, with the exception of the engine, carb, exhausts (both front & tail) and the CDI unit I believe. I guess I am better sticking with what I know works. If I decide that the 125 is a bit gutless, I might look to swap the complete engine for a 175 engine. It would seem that the 175 is more common than the 125. (the model I have was the final variant of the air cooled motor before Yamaha went to liquid cooling). As with most older machines (I won't use the word classic so I don't offend the old gits on the nice BSA's and Royal Enfields that always seem to be broken down at the side of the road in a pool of oil), finding good parts is getting harder and harder and I didn't want to spend potentionally £ 100 plus on a barrel, head, piston, rebore etc, if the myth was a load of old tosh!! When completed, it will be only be used locally anyway (gone are the days when I want to do 1000's of miles on a 125, screaming along the road at 69 mph, flat out!!!) but I had considered rebuilding the top end with 175 bits if the myth was true. I think in essence, what actually happened in the past was someone sneaked a 175 engine in a 125 frame, and made all of their mates look naff on their stock 125's. Does anyone remember anyone doing this with the RD125MX & RD200MX???? They were identical, but for the fact that the 200 had an electric start! Thank you for your responses.

Hello Sorry to sound an old sod, but we did all this in the 80's with AR50's AP50's, DT50MX's, TS50ER's et al. We found that yes you could fit 60 & 80 kits, but the bottom end got knocked out in months. Some of the guys we hung around with ran FS1E's with 60 kits, and they could get nearly 50 - 55 mph out of them. Buy far the easiest mod is to change the front pipe, and tail pipe. I had a Honda MT5 (does anyone remember them!!!) and I had a mate fillet the front pipe, and take out some of the restrictor. I also changed the tail pipe for a 'JAMMA' I think it was called, and I managed to get it up to 45 mph without touching the barrel. Changing the gearing only works it your built like a race horse jockey. If you like most people are not 8 stone wet through, changing the gearing will make the gearing taller, but will mean that top gear will only be useable in a back wind down hill!!! If you go down the big bore kit road, it might be worth investing in new big ends, and main bearings dependant on how many miles the engine had done. Personally I'd avoid it as its a quick fix which ends in tears!! Cheers

Hello Can someone possibly dispell a popular myth for me. I have an 83' Y DT125MX which I am currently restoring. When we were in our teens, we were always told that the DT125MX & DT175MX shared the same bottom end, and that the barrels could be interchanged, i.e, we could put a '175' barrel on a '125' bottom end and v.v. Is this true? I've spoken with Yamaha who say no, but I've also been told by many previous owners that this is possible. They've never done, but always know someone who did, and in the immortal words 'Cor! it went like stink afterwards'. I've never actually ridden a 125MX, but the popular concensus I have been given by a number of people who did, says that the 175MX is quicker excellerating, and does not run out of breath as quick as the 125MX I do know that it is possible to drop a 175 engine in a 125 frame, but I understand that you need to change the carb, the ecu, and both front and tail pipes, and I guess there is no way that these items will be available at a reasonable price anymore. Any info would be grately appreciated.. Thank you

Hello. Having previously done this with a DTR125 in the 90's when I was a teenager, I recently bought a DT125MX field bike with the intention of restoring it to road use. I applied to DVLA for the log book in the same way you did, and got the same help you did. Unless you have the VIN/Chassis Number / Engine Number and Registration number, the DVLA will not issue a V5. Having spoken with my local dealer, he asked if I'd tried contacting Yamaha UK to see if they had recorded the Registration number, as it was likely that my machine was first registered by Yamaha. I contacted, them and a very nice lady informed me that they did keep records of the vehicles they first registered, and if I wrote to them, they would reply with the registration number given to my bike at import. There was no cost whatsoever. I faxed a letter through from work one day, and a letter was faxed back from Yamaha the next day giving me the reg number. I do not know the age of your bike, but it might be worth a try. Mine was bought as an 1980 model, but when I eventually got the registration number it was in fact a 1983 'Y' plate. I too contamplated going to my local licencing centre, but the thought of having lovely restored my bike to pristine condition, and not being able to get an age related plate, frightened me to death. I also considered that my bike might have ended up being a field bike for a reason, i.e., it had been 'borrowed'. I do know of someone who did a similar exercise with a bike, and upon inspecting the bike at the local licencing centre, it was found that it had been stolen at some point in its life, and was still listed as missing, and the bike was subsequently confiscated. Not only that, he got his collar felt by the plod. Unless you're confident that your machine is 'straight' I would err on caution, and would avoid the SRA test unless you really have to. Hope this helps. Cheers