Help Rqd DT175 uneven running

[vambo]

Firstly apologises as i know some of this has already been covered elsewhere but would just like some advice.

I've just picked up a 1979 DT175MX (the one with the tubular swingarm)

The bike has stood for the past 20 odd years and i'm trying to get her going. Would like to get some rides out of her before i undertake a restore over the winter (well the TV is always cr@p and you need something to do lol)

Here's what's been done so far.

Petrol drained and refilled. Oil drained and refilled. Oil line bled so no air.

New battery, spark plug and air filter.

Carb removed and cleaned, jets pilot holes etc blown through with compressed air (the stuff you get in tins for cleaning computer keyboards)

Here's the problem

She will start no probs usually first kick from cold, with the choke out and will idle quite happily.

It will stutter a bit if you ride it like this and not really pull (like you would expect once it was warm but with the choke still out)

If you push the choke in the revs will increase slightly then it will die, if you try revving it while you push the choke in it will be like its just sucking on too much air.

If you try screwing in the pilot screw (this has been set at the 1 and a half turns in the manual) there,s no real change in engine running and she'll still die if you push the choke in.

I can't find anywhere in the UK where i can get a carb refurb kit so i guess i could order from the US if anyone thinks it worth it.

I've seen in other posts about hardened crank seals. I don't really want to tear the engine down unless absolutely necessary. I can borrow a compression tester if this would prove it is or isn't the seals. Similarly i haven't changed the gearbox oil as yet just in case she's got to be stripped down.

I don't have much experience of 2strokes so all help gratefully received.

Many thanks in advance

Glenn

[Cynic]

Firstly apologises as i know some of this has already been covered elsewhere but would just like some advice.

I've just picked up a 1979 DT175MX (the one with the tubular swingarm)

The bike has stood for the past 20 odd years and i'm trying to get her going. Would like to get some rides out of her before i undertake a restore over the winter (well the TV is always cr@p and you need something to do lol)

Here's what's been done so far.

Petrol drained and refilled. Oil drained and refilled. Oil line bled so no air.

New battery, spark plug and air filter.

Carb removed and cleaned, jets pilot holes etc blown through with compressed air (the stuff you get in tins for cleaning computer keyboards)

Here's the problem

She will start no probs usually first kick from cold, with the choke out and will idle quite happily.

It will stutter a bit if you ride it like this and not really pull (like you would expect once it was warm but with the choke still out)

If you push the choke in the revs will increase slightly then it will die, if you try revving it while you push the choke in it will be like its just sucking on too much air.

If you try screwing in the pilot screw (this has been set at the 1 and a half turns in the manual) there,s no real change in engine running and she'll still die if you push the choke in.

I can't find anywhere in the UK where i can get a carb refurb kit so i guess i could order from the US if anyone thinks it worth it.

I've seen in other posts about hardened crank seals. I don't really want to tear the engine down unless absolutely necessary. I can borrow a compression tester if this would prove it is or isn't the seals. Similarly i haven't changed the gearbox oil as yet just in case she's got to be stripped down.

I don't have much experience of 2strokes so all help gratefully received.

Many thanks in advance

Glenn

Sounds like there maybe some issues with the carb still. Float height possibly or one of the filters in the fuel tap may be restricting the flow.

When the crank seals go it generally makes them a bit of a bugger to start and the idle generally goes all screwy(well mine did).

A quick test for the crank seals is when the engine is idling squirt some WD behind the flywheel and see if that affects the idle at the same time pop the crank breather into a glass of water, if you see a constant stream of small bubbles that indicates seal troubles. Olgit told me that one and it proved a reliable test on my engine.

[Airhead]

Hi Glenn and welcome to the forum.

It does sound like a fuelling issue from what you describe, first with this bike standing for so long, pull off the fuel line from the carb and verify a good flow, the symptoms you describe may be blockages in the carb or even a slow feed of fuel to the carb. There is a filter screen in the bowl of the fuel tap.

Where are you based?

...Paul

Edit

Oops you beat me to the tap Cynic...

[vambo]

thanks for the info guys

I'll be hitting the garage latter on and let you know how i get on.

I'm based nr solihull

[vambo]

Ok Guys

Quick update from the garage.

Checked the mesh filter in the petrol tap - looked fine but cleaned it anyway. There's an inline filter that looks quite new (no disscolouration at all) if its not really needed i can take it out. I took of the petrol hose and there's good flow on main and on reserve.

Bike started 2nd kick and after half a min to warm up was ticking over quite happily on full, 1/2 and 1/4 choke. Try to push it in the last bit and the revs rise before it dies (and sounds like its sucking on air). This is better when its on the prop stand. If you stand it up straight it needs full choke and will still need a blip of the throttle to keep her going (not sure what that proves mind)

put the crankcase breather hose into a glass of water as suggested and nothing not even a bubble.

Cynic you mentioned about float height, can see any settings in my book, what would you suggest?

[Airhead]

Cynic you mentioned about float height, can see any settings in my book, what would you suggest?

Hold the carb in an upside down position. While holding the floats so the tang is just touching the float needle, measure the distance from the top of the float to the float bowl gasket surface. Bend the tang on the float arm if adjustment is necessary. BOTH FLOATS MUST BE AT THE SAME HEIGHT.

[YPVS TONE]

Did you remove the pilot jet as this sounds like it could be still blocked.The jet unscrews with a small flat bladed screwdriver and although the hole is quite small you should be able to just see through it. Tony.

[vambo]

well the plot sort of thickens

cured the difference in running when leaned over and upright by getting shot of the inline filter. Don't know if this was put on by the last owner or the dealer, but a can't see the point so its gone.

stripped the carb again and this time took out the pilot jet rather than using compressed air in situ. couldn't see any light so used a pin then the compressed air, can now see sunlight through it. (Thanks for that one Tony)

put it all back together and hey presto tickover with no choke :-)

problem is now she won't pull much over 4000 rpm. Anything over about 1/2 throttle is doing diddley. Stationary she'll rev quite happily to the red, but nothing when you ride it. It gets worse as you go up the gears (1st is happy till about 6000, 2nd to about 5000 etc but still around the 1/2 throttle mark)

i'm guessing this is the main jet?

now this is where i get confused.

i've looked at some previous posts and was looking to get a keyster refurb kit.

i've looked in the haynes manual i got with the bike and for the 175E 175F and 175MX there's no data for main jet and the pilot is 25. Carb ID is 2H500 mines 2H501

the parts catalogue for the 1979 175F gives 140 for the main and 20 for the pilot. Carb id is 2N500.

the keyster kit from sirius for 78,79 and 80 has a 140 main and a 22.5 pilot.

I spoke to NRP in Manchester who where the only place i could find in the UK to get a kit from and they said their info for a 79 DT175 is a 130 main and a 25 pilot.

so what's the collective wisdom on why the lack of pull and what's the correct main/pilot jet sizes and will it make much difference either way.

[Airhead]

The main jet on a uk bike is 130, try the sunlight test, use a nylon bristle pulled from a brush to clean out as well as carb cleaner spray. Seems like youre on the right track now but now the problem is the main jet circuit. Come to think of it if the pilot jet was blocked its likely that the main jet may be blocked and its possible that the needle jet may also need cleaning, if you unscrew the needle jet you will see a series of tiny holes along its length in the side of the tube, may as well have a look at these too.

...Paul

[vambo]

thanks for that paul

I've just dropped the carb round at a friends. Its had a good dose of carb cleaner in it's various holes (note to self carb cleaner stings if you get it in your eye lol) and blown through with a compressor.

everything seems fine but he's going to put it through a sonic cleaning bath at work to see what that will do as it cured his LC250 when that wouldn't run smooth

i should get the keyster kit sometime next week so i'll put it back together with that and see what happens and report back.

thanks again all for getting me this far.

[vambo]

Still No Joy :-(

She will start 2nd kick from cold and once warmed up will happily idle at 1500 rpm.

She just won't pull over 4000 to 5000 rpm (depending what gear your in) and you get nothing beyond 1/4 to 1/2 throttle

Got the carb back form its Sonic bath

rebuilt using the keyster kit.

used the new 25 pilot jet and pilot screw. Pilot screw 1 1/2 turns out.

used the 130 main jet and new needle. Needle clip position 3 (from the top).

used the new float needle and seat. Float high checked at 21mm.

the B8EV plug that was in her has been replaced with a new B8ES and the air filter is brand new.

any ideas?

I've ruled out coil as it starts so easy and the ignition as past experience has shown me CDI either works or it doesn't. i guess she has stood since 1983 :-) but she should have woken up by now.

[Airhead]

Still No Joy :-(

She just won't pull over 4000 to 5000 rpm (depending what gear your in) and you get nothing beyond 1/4 to 1/2 throttle

any ideas?

Apply the choke when its struggling, then what?

[Cynic]

How about going out with a plug spanner handy run for one or two miles as flat out as you can, kill the motor then have a look at the plug.

The following model to yours used a 160 main. What side of the bike is your oil tank?

[vambo]

Ok once more into the breach

choke out made no real difference, in fact it was a tad worse.

Got back and noticed there was a slight drip of petrol from the overflow.

was going to take the carb off again to check the float height and also checked the needle and found i'd managed to put the clip into position 4 not 3 (oops old age and bad eyes)

put that right and put it all back together. Tried it and its quite a bit better but still wont really pull past 5500rpm.

i've also looked at the main jet and needle i took off, the needle is the same but the main jet is a 140.

I've put the 140 jet back in and tried again, felt a bit better but that could be just wishful thinking.

either way just on a paddock stand you can start it, rev up to the red line then with full throttle it will slowly drop back and the rev at 5000rpm with the throttle back to the stops.

now here an interesting bit. I was just showing this to a friend of mine and i'd forgot to switch the gas on.

it did exactly as before till just before it ran out of gas then it started revving perfectly (for about 10 sec before it cut out all together) now i'm sure that should tell us something just no idea what. I tried raising the float height to 23mm and that really didn't change things. I also put back the fuel line with the inline filter still no change.

can't do any more today as its p**sing down again :-(

here's a couple of pics of the plug after about a mile with the 130 jet in.

it's slightly blacker along the whole of the electrode with the 140 jet in but i'm putting that down to the extra mile or so running. Its not particularly wet or sooty or anything.

for the record the oil tank is on the left and the model number from the engine and frame numbers (which match) is 2k4

over to the experts then :-)

[vambo]

Just for id here's the little bugger

[Airhead]

Oil tank on the left and round section swing arm, thats an early one. It should have a carb as follows

Mikuni VM24, Number 2H500

Standard Set up with factory porting, standard exhaust and air filter

Throttle Slide, 2.0

Needle, 4j13 Clip position 3.

Needle Jet, 249 0-2

Main Jet, 130

Pilot Jet, 25

Reed side diameter, 35mm

Filter side diameter, 43mm

Length, 85mm

Float Height, 21mm

Sounds to me like its running rich, it gets worse with choke so isnt lean, if fuel is running from the overflow then the level is too high, this will cause a rich mixture and may lead to (four stroking)...firing every other rev instead of every rev. you need to re check the float height, as I posted earlier, did you check from beneath the gasket and with tang only touching the needle valve without compressing the spring? Perhaps the float needle valve is worn and is passing fuel, examine with a magnifying glass for wear around the pointed end. Rather than test on a paddock stand you would be better riding it to test as its under load then. besides its safer and wont have your chain whipping about so much.

[vambo]

well lawns, work and weather finally let me back in the garage so the saga continues.

Carb off and put the 130 jet back in. Made a note of everything with a number.

Mikuni Number 2H501 (don't know if this has any bearing or not)

Throttle Slide, 2.0

Needle, Original 4j13 Clip position 3. One from keyster kit is just stamped Y with 2 faint rings. However checked them with a mic and there the same as best as i can tell. Tried them both and no difference

Needle Jet, 249 0-0 (this is the original one that came in the bike)

Main Jet, Original 140, keyster 130. 130 is back in

Pilot Jet, 25 (from keyster kit)

Float, Marked A-10

Float needle, new from keyster kit.

Float needle seat, has 25 stamped on the base and is new from keyster kit.

Float height set from base of gasket seat (not top of gasket if that makes sense) and is 21mm (actually 21 and a bit)

so off for a road test and guess what next to difference (maybe a bit better but prob just wishful thinking). Only thing i found (and again this is probably wishful thinking) was when i was sat stationary for a bit the bike would rev quite happily when i pulled away (even when whacking the throttle back to the stops) well for about 4 or 5 seconds anyway :-(

got her back after about a mile and checked the plug, looked the same as the photo's above. black but not sooty or wet

old git the four stroking bit sounds just about right for the way it sounds when it runs, and as i said before if you shut the petrol off she will starts to rev and sound like a 2 stroke just before it runs out of gas

assuming it is that its running rich for an experiment i change the needle clip position to 2 instead of 3 (as in 2 down from the top) this made quite a bit of difference (still no where near right) but i can just about get 30 out of her on the flat :-( but she still wont rev like a 2 stroke. Still ticks over quite nicely at 1250rpm and starts 1st or 2nd kick, so i kind of ruled out coil or electrics (less anyone says otherwise) but he only things different from oldgits info is the carb is maked 2H501 not 2H500 and the needle jet is 249 0-0 not 249 0-2

getting really peed of now :-(

[Cynic]

well lawns, work and weather finally let me back in the garage so the saga continues.

Carb off and put the 130 jet back in. Made a note of everything with a number.

Mikuni Number 2H501 (don't know if this has any bearing or not)

Throttle Slide, 2.0

Needle, Original 4j13 Clip position 3. One from keyster kit is just stamped Y with 2 faint rings. However checked them with a mic and there the same as best as i can tell. Tried them both and no difference

Needle Jet, 249 0-0 (this is the original one that came in the bike)

Main Jet, Original 140, keyster 130. 130 is back in

Pilot Jet, 25 (from keyster kit)

Float, Marked A-10

Float needle, new from keyster kit.

Float needle seat, has 25 stamped on the base and is new from keyster kit.

Float height set from base of gasket seat (not top of gasket if that makes sense) and is 21mm (actually 21 and a bit)

so off for a road test and guess what next to difference (maybe a bit better but prob just wishful thinking). Only thing i found (and again this is probably wishful thinking) was when i was sat stationary for a bit the bike would rev quite happily when i pulled away (even when whacking the throttle back to the stops) well for about 4 or 5 seconds anyway :-(

got her back after about a mile and checked the plug, looked the same as the photo's above. black but not sooty or wet

old git the four stroking bit sounds just about right for the way it sounds when it runs, and as i said before if you shut the petrol off she will starts to rev and sound like a 2 stroke just before it runs out of gas

assuming it is that its running rich for an experiment i change the needle clip position to 2 instead of 3 (as in 2 down from the top) this made quite a bit of difference (still no where near right) but i can just about get 30 out of her on the flat :-( but she still wont rev like a 2 stroke. Still ticks over quite nicely at 1250rpm and starts 1st or 2nd kick, so i kind of ruled out coil or electrics (less anyone says otherwise) but he only things different from oldgits info is the carb is maked 2H501 not 2H500 and the needle jet is 249 0-0 not 249 0-2

getting really peed of now :-(

Now i'm sorry to put you off in a completely different direction but. Myself and OG have just found our primary ig coils are down on spec by nearly 25%, this will have the double whammy of giving you a weak spark at higher rpm due to the weak coil and afect the timing of the spark due to the cdi referencing the voltages generated to fire the spark.

Its an easy check, between black and brown and red and black, you should get 420ohm and 13.8 ohm. You may have the later 5wire mag (6 wire cdi) and then the prob doesent appear to happen but it sounds like it could be worth checking before you go at the bike with a gallon of gas and a match.

[vambo]

I'll try anything once cynic :-)

i'll let you know what i find, i'm a bit cynical (sorry for the pun) as if it was that, why would moving the needle have helped, mind you it could be part of the problem so be good to find out if only to rule it out.

Like is said as far as i know its not been run since 1983/84 ish

[Cynic]

I'll try anything once cynic :-)

i'll let you know what i find, i'm a bit cynical (sorry for the pun) as if it was that, why would moving the needle have helped, mind you it could be part of the problem so be good to find out if only to rule it out.

Like is said as far as i know its not been run since 1983/84 ish

A weak spark can give the impresion of a rich mixture as the spark struggles to ignite the fuel so it doesent burn properly and soots up the top end. Leaning the mixture out will help it run but ultimately at higher rpm you will lose out.