I am having an intermittent problem with my 175 MX. It will not run smoothly above 1500 RPM right up to 5000 RPM. Once it reaches 5000 RPM everything is fine. It will also not idle. It sounds like it is suffering from fuel starvation. It might do this for 20 or 30 miles and then it will revert back to running absolutely fine. The carb has been completely stripped and cleaned around half a dozen times (including the tiny hole in the float bowl) . The CDI side crankshaft oil seal has been replaced and I have tried a couple of new plugs. The little oil ring around the nozzle/main jet is worn. Could this be the problem or could it be something to do with the electrics?

Any help or advice would be greatly appreciated.

Thanks,

I am confused can you post pictuers( read FAQ in new members),there shouldn't be any hole in the float it's self.

Right. The float should be completely fuel proof. If the float fills up it will cut the fuel off too soon. Take ou the float and wiggle it around to hear if there's fuel inside it.

Could as well be an electric failure. I had some bad connections and possible shorts on my DT. It did all sorts of funny stuff that at first seemed to be carb related. I undid all the wire harnesses just to be sure. It helped.

he means the hole in the bottom of the bowl lol, the one that feeds fuel to the choke cct

That makes sense

Thanks for all the comments. I am about to check the whole electrical system.

what's the exhaust header like?

has it got a restrictor tube in there?

Not checked to see if the exhaust has a restrictor tube in there. Going to have a look this weekend. If I find one do I have to cut and re-weld the pipe to remove it?

On another note... My friend who tinkers with RD's says the Boyesen reeds I installed maybe causing the problem. He mentioned my bike could be suffering from fiber "reed flutter". Does this make any sense? Should I try putting the stock Yam reeds back in there?

Any help would be sincerely appreciated.

Thanks,

Paul

Reed flutter indeed.

Your bike uses a 2 coil ig system. One controls the cdi to 4500 to 5000 rpm the other then takes over.

A bad connection from the low speed coil cause everything you mentioned.

So all the stuff about "reed flutter" is nonsense?

Braking for a 2g turn on a 150bhp race bike maybe.

On a dt175. Yep.

LOL! Thanks

see here for exhaust restriction elsie

Problems that come and go are rarley mechanical faults and can be traced back to faulty electrics 99% of the time. Or fuel supply but fuel supply problems are normaly noticed at high rpm not low.

If your bike has the restriction in the exhaust removing it most likely won't fix this problem but will make your bike run better once this is sorted.

It sounds like it is sucking air in from the mag side crank seal. A new seal was fitted soon after I found the bike. The seal looked like it had slipped off center so I tried to push it back in line and the problem got worse! Their is no lip for the seal to rest against on my case. I have just ordered a new seal, how far should I push it in? I am also going to pull the carb rubber and re-install it with a little silicone.

yeah mate just tap the seal in flush with the casing face

It sounds like it is sucking air in from the mag side crank seal. A new seal was fitted soon after I found the bike. The seal looked like it had slipped off center so I tried to push it back in line and the problem got worse! Their is no lip for the seal to rest against on my case. I have just ordered a new seal, how far should I push it in? I am also going to pull the carb rubber and re-install it with a little silicone.

Well you answers your own question,if it got worse then you should have started there.Or did you just recently adjust the seal?

Check that the seal hasent worn a grove in the shaft,yes rubber seals can cut groves in steel, if it has than dont push the seal in as far so it can ride on a smooth section of the crank.

What colour is you spark plug? if it is black sooty then I would be checking the low speed coil as cynic pointed out,it would make more sence than the crank seal giving this problem alone,mainly because it shouldn't come and go if it was the seal alone if the seal is leaking then it should be a constant problem,you can spray some wd 40 at it while running and if the rpms chang then for sure its leaking.

Thanks fellas. I checked and cleaned all of the electrical connections yesterday (I am crap with electrics, I have testing gear but don't know how to use it). leaning all of the connections made no difference to how the bike ran. That's when I noticed the crank seal was off center. My seal is now pushed in 5mm. I only ran it up and down the street once after I tried to push it back inline. It definitely sounds like it is sucking air or rubbing against something. My plug is black in color (not wet or sooty). When I think about it I have had this problem for quite a while now (it never reverts back to running ok). I couldn't really notice a difference after I tried the WD40 test.

The coil with the copper wire wrapped around it has a couple of spots on it that kind of look like dried glue. The largest is about 10mm long and 1mm wide.

The coil with the copper wire wrapped around it has a couple of spots on it that kind of look like dried glue. The largest is about 10mm long and 1mm wide.

yeah thats epoxy insulation covering the solder joint it should look like that