78 DT175 Heat seize

[laavalancha882012]

hello everybody, im beginner in this Blog, but in need help, i have one DT 175 but i need know if is compatible the Pulsar Coil of MX 125 whit DT175

[laavalancha882012]

is compatible the electrical compounds of IT 175 wiht Dt 175

[flyday58]

Update:

New piston came today so back together she goes. Fired on the 2nd kick and let it tick over with the Autolube held wide open to get the oil to the cylinder, at which point the beautiful blue cloud surrounded me. Great to have at least one bike that runs again!

I've fitted a 160 main jet and gone back to the mid clip position as I try to sort things going forward. I rode maybe 2 miles just up and down my neighborhood's road keeping it under 4000 revs and everything went fine. Seems boggy right now but how much can you tell from an initial run?

I will experiment with the jetting as I get the time. Unfortunately, in the West we have this thing called "jury duty", and my tour came up for next week, so the DT may languish again. Languish? Hell, the CS5 won't even look at me anymore and the RT3 just screams, "why did you even buy me, you ?" 70s Yams, so needy!

Paul the Fabulous, I fitted your temp gauge/gage/gay ja but only saw 180˚C on my short ride. I am going to be paying alot of attention to it as I go along. It's a great addition, thanks for the post about it.

[Cynic]

I just wonder why some OEM pistons on fleabay are 150 bucks but the parts houses have them for 60 to 70. Just hope the piston I ordered are genuine OEM and not Chinese knock-offs.

I thought that untill i had 2 pistons on the bench for comparispon. The yam piston is a LOT lighter and has been through far more machining. The ports are trimmed etc. I would imagine they are made from a better quality alloy too.

They really are just a better product. I have used both. They both work but going from one to the other is deffinitely noticable.

[Airhead]

yeah I weighed a standard against a pattern one and the pattern was heavier, I do believe though that some pattern ones are good quality...perhaps as good as OEM

[blackhat250]

Heat seizure"s may be a thing of the past, hows about alloy liners, with nickasil coating, disperse heat 4x better than cast iron ,,

http://www.exbilletengines.com/Specialparts/specialparts.html

[Airhead]

Great to see the old Girl 'smokin' again Richard

[Ventura]

Have you ever done any jetting tests and set up? mine was standard at 130 and is now fitted with a 155 , may even go to 160 yet if it doesnt cock it up...(I do have a gianelli pipe on though)

I've fitted a 160 main jet and gone back to the mid clip position as I try to sort things going forward. I rode maybe 2 miles just up and down my neighborhood's road keeping it under 4000 revs and everything went fine. Seems boggy right now but how much can you tell from an initial run?

I will experiment with the jetting as I get the time.

Good to hear that you seem about sorted Flyday58 and that the bike is a runner again.

Ive been struggling a little to fine tune the jetting and tuning on my '79 DT175 since rebuilding it and find the above comments about jet sizing very interesting.

While I was running mine in, with stock 130 main, it was fine and dandy up to 4,500 rpm, but when I took it over this I first started to experience very"boggy" (rich) running then at 5500 rpm the dreaded "flappy" over-lean noises!! Not good!!

As I had a spare Gianelli silencer I welded in a bung and fitted the A/F gauge I have for tuning my other bikes.

This is when the sniffer screws in.....

The A/F results I got were very interesting.

At tickover to 4500 revs, while riding in all gears, the A/F was spot on around 13:1 which is roughly what we aim for.

Very soon after 4500 the bike went suddenly ultra-rich (around 10.3:1) and bogged down to the point it was 4-stroking.

Feathering the throttle got it thro this, but at just over 5500 revs it then went ultra-lean (15:1) till the revs went over 6200 then went rich again to the point at WOT where it was running at 11.5:1

This sudden over-rich and then over-lean running, in such a short rev range, must have been a product of some strange resonant harmonics going on in the airbox and/or exhaust as it came and went in such a short time. Not something that would happen if down to just jets and needle position.

I couldn't get the mid-range bogging sorted until I removed the top cover of the air box which, altho it still goes rich, now doesn't badly effect the running too much.

The over-lean part at 5500 revs has been much improved by raising the needle.

But the interesting thing is that the stock 130 main is, if anything, a bit on the rich side already.

The way Im running, and the results Im getting, at the moment I could easily drop down to a 125.

If you guys are running 155/160's then from the above you must be running very rich at WOT.

Unless of course you have a pod filter or the likes and have binned the airbox?

I have recalibrated the A/F gauge so no inaccuracies there and have now refitted the stock silencer which hasn't seemed to effect things too much.

The running-in, lean running, problems I was having were obviously due to the fact I was limiting the bike to run in that short 5500 - 6000 rev range which was causing all the lean issues!!

More food for thought!! ..................

V.

[Airhead]

Good to hear that you seem about sorted Flyday58 and that the bike is a runner again.

Ive been struggling a little to fine tune the jetting and tuning on my '79 DT175 since rebuilding it and find the above comments about jet sizing very interesting.

While I was running mine in, with stock 130 main, it was fine and dandy up to 4,500 rpm, but when I took it over this I first started to experience very"boggy" (rich) running then at 5500 rpm the dreaded "flappy" over-lean noises!! Not good!!

As I had a spare Gianelli silencer I welded in a bung and fitted the A/F gauge I have for tuning my other bikes.

This is when the sniffer screws in.....

The A/F results I got were very interesting.

At tickover to 4500 revs, while riding in all gears, the A/F was spot on around 13:1 which is roughly what we aim for.

Very soon after 4500 the bike went suddenly ultra-rich (around 10.3:1) and bogged down to the point it was 4-stroking.

Feathering the throttle got it thro this, but at just over 5500 revs it then went ultra-lean (15:1) till the revs went over 6200 then went rich again to the point at WOT where it was running at 11.5:1

This sudden over-rich and then over-lean running, in such a short rev range, must have been a product of some strange harmonics going on in the airbox and/or exhaust as it came and went in such a short time. Not something that would happen if down to just jets and needle position.

I couldn't get the mid-range bogging sorted until I removed the top cover of the air box which, altho it still goes rich, now doesn't badly effect the running too much.

The over-lean part at 5500 revs has been much improved by raising the needle.

But the interesting thing is that the stock 130 main is, if anything, a bit on the rich side already.

The way Im running, and the results Im getting, at the moment I could easily drop down to a 125.

If you guys are running 155/160's then from the above you must be running very rich at WOT.

Unless of course you have a pod filter or the likes and have binned the airbox?

I have recalibrated the A/F gauge so no inaccuracies there and have now refitted the stock silencer which hasn't seemed to effect things too much.

The running-in, lean running, problems I was having were obviously due to the fact I was limiting the bike to run in that short 5500 - 6000 rev range which was causing all the lean issues!!

More food for thought!! ..................

V.

wow thats impressive venture, I've though in the past that it would be great to have a tool that analyses the exhaust gasses but this is the first time I have seen anyone reference one in a forum...

so A/F...is this air to Fuel then?

Tell us more about this tool, make / model / etc

I recently tried with my airbox lid jacked up because for obvious reasons I didnt want to drill it, maybe you'd want to do that too if you're running without it now?

I removed the seal and placed 2 off 1mm plastic washers on some slightly longer mounting screws drilled small enough so that they had to be screwed down the thread so they didnt fall off

I gave up in the end because I couldnt seem to be getting anywhere with it...perhaps I needed an A/F gauge...who knows?

anyway the airbox lid unadulterated

[Ventura]

Hi Paul, sorry if I wasn't clear but it was this top cover I removed........

The inlet hole is so small on this stock cover that it badly effects airflow

Since taking that off the 4500 rpm over-rich bogging has disappeared altogether.

With it on the bike was almost unridable as it was bogging just at the point that the power band seems to start!

The lean band at 5500 is still there a bit, but I now know I can safely ride thro it.

Ive had a few of these wideband A/F (Air fuel ratio) gauges in the past, some permanently installed on the bikes and some portable.

They really are indispensable if your setting up the fuelling / jetting on any bike. Ive used one on everything from my racing C90's to vintage Brit-Bikes and modern litre bikes.

The first one I bought was when I fitted flat-slide race carbs to my Triumph twins. With so many points of adjustment on those things it was near impossible to set them up blind. The only other option were visits to the Dyno man, but that ends up very expensive!

What Im using now is one of these, bought from Burton Power......

http://www.burtonpower.com/parts-by-brand/brands-g-to-i/innovate/innovate-mtx-l-wideband-air-fuel-ratio-gauge-3844.html

I have it all installed in a tank-bag, along with its own little 12V battery. No messing with wiring, just plug in and play!!

For anyone who's interested in tuning and modifying set-ups then one of these must be one of the handiest tools around.

Highly recommended!!

V.

[Airhead]

Haha yeah that thing, I removed mine years ago, I bet theres not many of those around these days! By removing the lid, you have effectively removed yours too now

I'm tempted by the meter I must say, £160...whats that? about two dyno runs these days?

£145 on fleabay

http://www.ebay.co.uk/itm/INNOVATE-MTX-L-AFR-Wideband-Air-Fuel-Ratio-Gauge-3844-/300506017816?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item45f78df018

[Ventura]

I'm tempted by the meter I must say, £160...whats that? about two dyno runs these days?

£145 on fleabay

http://www.ebay.co.u...=item45f78df018

The beauty of the A/F gauge is that your getting readings, and doing your adjusting, on real road (or track) riding conditions, rather than a 4th/5th gear dyno pull roll-on.

There's a BIG difference between the two.

Its amazing to watch the A/F change as your riding, and what effect the differences in throttle position, engine load and even wind direction has!

Ive bought from that Ebay seller before Paul.

Very good comms and very quick delivery. But be aware that the item will come from Latvia.

Burtons are good too, but you'll pay a few quid more.

V.

[flyday58]

What fancy posh airboxes you MX guys have! I guess the Japanese were getting back at Americans and just bodged together the snorkel-looking intake on the State-side DTs. Mine was missing, found one on ebay but when I installed it, the bike started 4-stoking between 5500 and 6000 rpm and wouldn't rev higher.

As it sits now, the bike is very spry up to 4000 revs. At that point it suddenly hurls itself forward similar to what I had on an RM125 back in the day. I back off at 4500 as I'm still breaking in the new ring set, but I'm itching to find out what's going to happen in the higher revs. I'm also going to keep an INTENSE watch on my Autolube feed tube as this seems more and more like lack of oil causing the seize. Stay tuned...

[Ventura]

Mine was missing, found one on ebay but when I installed it, the bike started 4-stoking between 5500 and 6000 rpm and wouldn't rev higher.

Interesting Flyday58.

Can I ask, does that mean you're presently running with no airbox , and just a pod filter? Or even no filter?

With the kit I have I could run a test to see how much difference it makes and how much leaner the bike will run.

That could help quantify exactly what jetting you'd likely need for that set-up.

From what Ive found so far, the awful "flappy" combustion noise starts when the mixture gets to 14.8:1 and above, which is definitely lean enough and hot enough to fry a 2-stroke piston if left running at that for any time.

V.

[Cynic]

What fancy posh airboxes you MX guys have! I guess the Japanese were getting back at Americans and just bodged together the snorkel-looking intake on the State-side DTs. Mine was missing, found one on ebay but when I installed it, the bike started 4-stoking between 5500 and 6000 rpm and wouldn't rev higher.

As it sits now, the bike is very spry up to 4000 revs. At that point it suddenly hurls itself forward similar to what I had on an RM125 back in the day. I back off at 4500 as I'm still breaking in the new ring set, but I'm itching to find out what's going to happen in the higher revs. I'm also going to keep an INTENSE watch on my Autolube feed tube as this seems more and more like lack of oil causing the seize. Stay tuned...

No i am in the same boat. They are the nasty restrictive airboxes that only lasted 12 months. Can see why now. I have a more traditional airbox and tbh it hasnt had a filter of any kind for years.

Ooops ha ha.

[dt502001]

without quoting and re visiting all you have mentioned Ventura...You point on jetting on dyno or anyother method your's best ..without a doubt. but without the o2 sensor ..I have tried to mention why it's so important to do wfo plug chops, as that when any 2t will run lean and blow.

The rest of tuning can be done without a o2 sensor to suite your riding style.

Altuitde is so important we try to run 14.7:1 in summer and lower in winter here in South western Ontario if I try to run my bike in say North Bay I have to re jet as i am 500 ft more above sea level. hence why fi bikes work better.

[Cynic]

Do you not think its going a touch too far.

Stock jetting with maybe a clip up or down is it.

These engines were never ment for wot. They are low rpm tree pluggers. Town centre traffic killers. These bikes on fast roads is like a morris minor (google ) at the nurburg ring.

2 rules for a dt. No wot and use the oil warning light as max cruise rpm. Thats about 55 on mine (i think). Done me for the last 25 years.

[Ventura]

Do you not think its going a touch too far.

Stock jetting with maybe a clip up or down is it.

Your probably quite correct Cynic.

Problem is when you either mod the airbox (or exhaust) as some have done, or experience problematic running as I did, then these bits of kit are invaluable as its actually showing you if you have a fueling problem and what it is, as it happening.

After fiddling about with carbs, jets and needles for over a month I eventually welded the bung in the exhaust and fitted the gauge.

Twenty minutes later I had the full picture of what was going on and it was all sorted!

The other thing that became apparent is that with stock airbox/filter and stock jetting these bikes actually run overly rich.

Fine for keeping the engine cool, but not good on performance or fuel economy!

Opening up the airbox on most bikes would require upping the jetting. On mine anyway, this wasn't required.

It actually brought the mixture closer to where it should be, but at the same time still running on the rich side.

I agree that WOT is not the place many of us would often be on these little bikes, but they do like to be kept buzzing.

As you say, 55-60mph or around 6500rpm is a comfortable limitation.

You do tho need to go to WOT to determine the correct main jet size, as its only here that its fully in play.

Its also good to know that if you do have to give it the bifters, your not really doing any harm.

Everyones greatest fear with these little strokers must be running lean and seizing/burning as many have done.

When I had my first DT back in the 70's I didnt know what a jet was, never mind where to find it!

Happily rang that things neck for 1000's of miles without going near airbox or carb (or probably near the air filter either!!) but it never let me down.

So your right, they're happy leaving all well alone!

But if you don't!...................

V.

[Cynic]

Well said. Couldn't agree more....

[Airhead]

Well said. Couldn't agree more....

me neither, well said 'V'