The beast is back! (TZR125 Pit bike, Setting it up now)

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

I've got the engine back together now. It's been re-bored, New oversize piston, New crank seals, New gaskets where I could get to. So the engine should be in tip top condition now.

The compression is noticeably better when I kick the engine over, or put it in gear and roll it forward.

I am now running a Delorto PHSH 28mm Carb from an RS125. Running a 126 main jet.

I've got it all back up and running, It started 3rd kick! Well impressed.

Took it out for a gentle ride to warm it up. Throttle response was noticeably better too.

But once the engine had fully warmed up, And I started to open it up.
It didnt really like it.

It is flat until it hits the power band. Obviously expected of a 2 stroke.
Up into Second, As I close the throttle off, It dies/bogs down.
And then once I open it up again, WHAM, power kicks in after a second, And it pulls hard up to the top of second.
Close off for 3rd, And it dies. And so on.

I've also tried riding it by keeping the throttle fully open as I go up the gears. Obviously not red lining it because its a fresh engine. But it runs ALOT better when I dont shut off the throttle.

Now I am running a K&N filter because I have no choice. So Please dont tell me to fit an Air box. There simply is NO room. It's a KLX110 sized pit bike.

Exhaust is a custom made jobby, From "Big One", FOR the TZR125 engine.
So its the right exhaust.

The carb is a little bigger than standard, But no where near as big as the standard carb on the imported TZR125 which runs a 32 Delorto I believe.

So I am assuming this niggle can be jetted out?
I've held throttle fully open for a good 3/4 mile in 6th gear. Pulled into my street. Done a plug chop. And its burning a little black and sooty.

But IMO the symptoms are saying its running lean, Not rich?

Any advice appreciated.

Cheers

Ben

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

https://i902.photobucket.com/albums/ac227/pitbikeben/Photo0858.jpg

RudiRulez · Two Stroke Sniffer Joined: 24 Jul 2009 Karma :

from my experience.....plugs don't lie, so maybe down jet, give the bike a run see how it goes and then do another plug chop.

Edit: just had a thought drop the throttle needle down a notch. (move the clip one notch up)

chris-red · Have you considered a TDM? Joined: 21 Sep 2005 Karma :

Maybe put an airbox on it Laughing

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satelliteone · Nitrous Nuisance Joined: 08 Feb 2007 Karma :

agreed.. looking a bit rich... here is a plug after 2000 miles on my DTR125. Same engine.. it running a little lean..

https://i31.photobucket.com/albums/c357/satelliteone/DTR125_1990/IMGP2710.jpg

no detontaion tho..

https://i31.photobucket.com/albums/c357/satelliteone/DTR125_1990/IMGP2716.jpg

Also recheck the autolube settings..

Why not go back to the original TZR/DTR carb?..

Blau Zedong · Banned Joined: 26 Jun 2006 Karma :

Standard carb for standard porting methinks. Go up a few sizes on the main jet to start to compensate for the cunt filter (I'd consider running a bellmouth with some mesh over the end in preference to a pod). Might need to go a size up on the pilot jet too. Certainly don't think there is anything to be gained with a bigger carb other than it being a twat to set up.
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binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

I cant revert to the stock carb any more because I had to destroy the end of the cable holder to get it out of the carb cap.
It's now fitted to the Delorto Carb.

Also the Delorto carb is a Piece of P*ss to do the jet on.
14mm bolt in the bottom and the jet comes. Dont even have to remove the float bowl, Carb or anything. Just catch the petrol.

Thanks for the help. It was running rich.
I've dropped the needle down (Clip to the top setting). And its ALOT better.
Although it still splutters at top RPM.

As for the standard carb, The 26mm carb was fitted to the restricted UK TZR's with the power valves Pinned shut.

The Import TZRs ran the power valve servo, And ran the bigger carb. Same as the DT125 really. They dont run a 26mm.

My Power Valve is pinned open at the moment. Once its running right and I can sort out the charging system, I will fit my VPVS.

I think I need to go down a jet size, And bring the needle back to the middle setting, And fine tune it from there.

As for the power, OMFG! When it hits the power band, the front end just glides up in 1st, 2nd and 3rd. But it wont rev high enough to keep it in the power band for 4th >.

I'll let you know how I get on tomorrow after I've down Jetted.
As for the pilot jets. There are two. Low and High Idle I think?

Be

satelliteone · Nitrous Nuisance Joined: 08 Feb 2007 Karma :

would`nt mind a TZR RR carb !.. Keep it at the middle position for now, down jet a little. till u get a light tan..

yup u might have 2 jets , being one of them..(low speed) circuit. the other im not sure, you carb might have another circuit for mid. The needle main jet for mid to High speed.

IF you can get it right for the mid to top, then adjust pilot jetting.

Another thing is the filter. Dont use a end capped filter, use a tapered cone type. Somthing to do with resonance in the intake. DTR/TZR`s hate them. Foorks up airflow or somthin..

You will get there in the end m8..

stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

Just to get the carb jetting spot on, and without the possible complication that a pressure reflecting pulse from a cap ended clamp on filter could be having, then id do the initial jetting with no filter on at all.

TBH every time i re-build a modified 2stroke engine with new parts, and different carbs, exhaust from std spec, id pay to have a new engine jetted by an experienced tuner with a dyno, and exhaust gas anyliser to get quicker and safer tuning carried out, Also by the time the bike is properly set up with a good few dyno runs, and a bit of road testing, it's ready for a power run to see how many ponies have been liberated.

Regarding the filter, then id either try an space it away from the carb belmouth as far as possible on a peice of hose, or else fit the biggest physical filter that you can get in the space available.

If a pod filter is big enough and or otherwise spaced far enough away from the carb inlet, then it won't cause jetting or carburation problems. Most pod filter troubles are caused by insufficiantly small filters, and or fitting them too close to the carb, where as all airbox's are fitted further away on a rubber hose normally.

Hope you get it running well soon!

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

Well I've got a K&N Style filter, With the rubber grommet at the carb end pulled off.
Glued to the stock TZR Air box Snorkel,
And then pushed onto the carb.

So the filter / intake is about 5" away from the Bell mouth already.
Would I be better off with a massive foamy filter on there then?

Ben

stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

As long as it's big enough which im sure it probably is, and that the inlet pipe is the same dia as the carb entry, then i can't see it causing problems. The change of carb, filter and exhaust set up will mean some fairly different carb jetting from std spec will be needed to get it spot on everywhere.

When i built my speedfight 100 motor, i had a bigger carb, that i guess jetted at a 100MJ. This was within 2 sizes of the final jetting used, but the pilot and needle jet supplied with the carb was so rich that the midrange was terrible, and the motor would struggle to pull through and pick up any revs.

To me it sounds like you jetting is rich, as the plugh colour shows, but to get the main jet right you might need to lean out the mid range circuits, so that they don't mask the true jetting required for full load.

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

So can I get different tapered needles too then?

RudiRulez · Two Stroke Sniffer Joined: 24 Jul 2009 Karma :

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

I read somewhere that foam filters are better than the pod filters because the flat end cap reflects the pressure pulses back down the intake which makes it very hard to tune.
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lllN30lll · World Chat Champion Joined: 12 Jun 2005 Karma :

silly question, aren't you running then engine in?
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stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

Yes the engine is in its running in period.
But you shouldnt run an engine in at low RPM anyway. It needs to be used right through the rev range, Just not held on the red line for ages. Which I'm not.

Just letting it ring up to the powerband, And changing gear.

It's better to get it set up well asap, And then run in, Rather than run it in while its running very rich or lean.

Anyway, I managed to get some replacement Jets off a mate who recently built an RS125.

I've dropped the main to a 120, And the needle is still on the top clip (lean setting).
It runs 99% spot on now.
Very high RPM it splutters, But Thats after the powerband has gone dead anyway, So I will never be revving it that high.

However, I noticed the exhaust was blowing tonight, right out of the manifold, And quite badly too.

So I've sorted that. Which may well iron out the splutters.

It doesnt really have any flat spots now either. Obviously its flat as a fart until it hits the Band.
But once its in the power, It's a rocket. Stupidly fast!

The gearing is too short though, The front wheel lifts, but by the time its like 6" off the floor, The bikes ready to change gear.

So I've put the 17t front sprocket on. It's made it better, I may drop to a 37t rear (rather than right down to the 35t that I have in the garage).

I had 75mph out of it in 6th, And it had a bit to go. Thats on 17/39 gearing.

Really impressed with it. I need to sort the electrics out, And then fit the power valve servo so its usable at low RPM too.

https://i902.photobucket.com/albums/ac227/pitbikeben/Photo0865.jpg

bladerunner · World Chat Champion Joined: 09 Sep 2006 Karma :

the bigger the carb the worse the mid range but an RS 125 carb on a tzr 125 should be able to work with a bit of jetting
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binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

Well the Imported TZRs are fitted with 32mm carbs. So a 28mm carb cant be that bad?

I've looked into the PHBH28 Carbs and they seem to be a popular choice.

I've managed to get it running quite well to be honest.
Surprised at how fast it is. Laughing

twotakt · World Chat Champion Joined: 25 Oct 2007 Karma :

binge · Emo Kiddy Joined: 03 Jul 2004 Karma :

There were TZR's with the 2RK engines fitted, Which ran full power with the Power Valve servo and a bigger carb.

They were rare, Which is why people fit the DT125 power valve servos to the 2RK engines. Because you simply cant buy the 2RK power valves.
You need a control unit and a servo.

Ben