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Discussion Starter · #1 ·
My mito evo 96 has mikuni tm35, and standard pilot jet there is size 45, however it was running insanely rich - even with air screw fully out. Trouble starting, completely wet spark plug, juices coming out of the exhaust.
The cylinder I had at the time (now seized and destroyed, oops) was unmarked mitaka(i guess it is a0401, will try to check today), but from the factory the bike had 73037 cylinder(at least the manual says 130 transfer and 190 exhaust). Everything else afaik is standard from the factory.

So I got some jets, and re-jetted it with size 20 pilot and upped main jet from 310 to 350(standard mikuni jetting for tm35), to keep the total fuel flow unchanged. Aaand it seized after running wide open throttle for quite a bit and closing the throttle fully before a turn.
I suspect that this happened because I was running too lean pilot jet, causing detonation (there is a small molten spot on the piston). Contributing factor might be tight clearance between piston and cylinder (yes, rookie mistake to assume that cylinder kit comes with matched piston).

I get the idea behind rich pilot, it is exactly for extra cooling when going from full throttle to closed throttle, however now I dunno if it was designed to idle like crap.

Now I am thinking that port timings (124 degrees for a0401 and 130 for 73037) affect air velocities - same amount of air is to be delivered in a shorter time - increasing air flow through the carb.

I will get my old 73037 replated and new vertex piston, see how it goes.

So, question:
Why would cagiva use such a rich pilot jet, that can not (in my case) be leaned out with air screw? What might be the reason for this rich situation?

Pics here: https://photos.app.goo.gl/7rWuxXodtZir6F4y7
 

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My mito evo 96 has mikuni tm35, and standard pilot jet there is size 45, however it was running insanely rich - even with air screw fully out. Trouble starting, completely wet spark plug, juices coming out of the exhaust.
The cylinder I had at the time (now seized and destroyed, oops) was unmarked mitaka(i guess it is a0401, will try to check today), but from the factory the bike had 73037 cylinder(at least the manual says 130 transfer and 190 exhaust). Everything else afaik is standard from the factory.

So I got some jets, and re-jetted it with size 20 pilot and upped main jet from 310 to 350(standard mikuni jetting for tm35), to keep the total fuel flow unchanged. Aaand it seized after running wide open throttle for quite a bit and closing the throttle fully before a turn.
I suspect that this happened because I was running too lean pilot jet, causing detonation (there is a small molten spot on the piston). Contributing factor might be tight clearance between piston and cylinder (yes, rookie mistake to assume that cylinder kit comes with matched piston).

I get the idea behind rich pilot, it is exactly for extra cooling when going from full throttle to closed throttle, however now I dunno if it was designed to idle like crap.

Now I am thinking that port timings (124 degrees for a0401 and 130 for 73037) affect air velocities - same amount of air is to be delivered in a shorter time - increasing air flow through the carb.

I will get my old 73037 replated and new vertex piston, see how it goes.

So, question:
Why would cagiva use such a rich pilot jet, that can not (in my case) be leaned out with air screw? What might be the reason for this rich situation?

Pics here: https://photos.app.goo.gl/7rWuxXodtZir6F4y7
As i saw photos the problem is from piston quality. Usually Mitaka cylinder is ok but pistons coming together are crap. If it's this type that's one of the reason .
Also small pilot can do this but it needs time and not at the time you are closing throttle next minute seize.
Always companies tune richer all high performance 2 strokes bikes, just for their engines to be accurate and have longability before failure.

Btw check carb specially air chocke, if when is close has small flow then it will be like you have rich mixture at low throttle opening or idle
 

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Discussion Starter · #3 ·
As i saw photos the problem is from piston quality. Usually Mitaka cylinder is ok but pistons coming together are crap. If it's this type that's one of the reason .
Also small pilot can do this but it needs time and not at the time you are closing throttle next minute seize.
Always companies tune richer all high performance 2 strokes bikes, just for their engines to be accurate and have longability before failure.

Btw check carb specially air chocke, if when is close has small flow then it will be like you have rich mixture at low throttle opening or idle
Thanks mate! Getting my 73037 recoated and vertex piston to go with it :] hopefully no more destruction and pain.
Do you maybe know if (like on probably most automotive carbs) there should be a gap (and how big) between throttle slide and carb body? Should the bike even start with say fully closed slide?
 

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Summink seriously wrong with the Engine or/and setups..... the Evo1 Tm35 can run even #300 main jet. "Equimania" even made the landspeed record in 125 Stock Class with his '95 Evo1 at Saltlake hotness.

#310 in northern Scandinavia tends to be on Rich side. but Aftermarket TMX35 #350 size would be an overkill.... about same viceversa issue compering idle jet #20 into #45.

that Pilot #20 and closing from WOT killed it, but im seriously wondering an deeper issue like "AirLeak" on intake manifold/crank seals...No matter if it doesnt Hang Rev's/idle Rev's for a while as a 1st Symphtom

Throttle slide's "CutAway" depends on Carb specs (richer or leaner function.... more or less Vacume needed for idle jet side.....".
iirc "Dellorto basics principals" carb pdf book explains this and shows some photos etc...linked on this forum too....

Engine starting with or without fully closed throttle depends various matters, like is it cold engine, is it running temp, using or not using Choke circuit. etc

if the slide has a "Medium" or smaller "CutAway" , healthy engine should start with closed throttle with using Choke circuit, from cold stand still, sea level ~+20Celsius. with clean good plug and strong sparg etc Healthy specs.

some 2T carbs at least from dellorto moped carbs, iirc, do not have slide "CutAway"....
 

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Discussion Starter · #5 ·
Summink seriously wrong with the Engine or/and setups..... the Evo1 Tm35 can run even #300 main jet. "Equimania" even made the landspeed record in 125 Stock Class with his '95 Evo1 at Saltlake hotness.

#310 in northern Scandinavia tends to be on Rich side. but Aftermarket TMX35 #350 size would be an overkill.... about same viceversa issue compering idle jet #20 into #45.

that Pilot #20 and closing from WOT killed it, but im seriously wondering an deeper issue like "AirLeak" on intake manifold/crank seals...No matter if it doesnt Hang Rev's/idle Rev's for a while as a 1st Symphtom

Throttle slide's "CutAway" depends on Carb specs (richer or leaner function.... more or less Vacume needed for idle jet side.....".
iirc "Dellorto basics principals" carb pdf book explains this and shows some photos etc...linked on this forum too....

Engine starting with or without fully closed throttle depends various matters, like is it cold engine, is it running temp, using or not using Choke circuit. etc

if the slide has a "Medium" or smaller "CutAway" , healthy engine should start with closed throttle with using Choke circuit, from cold stand still, sea level ~+20Celsius. with clean good plug and strong sparg etc Healthy specs.

some 2T carbs at least from dellorto moped carbs, iirc, do not have slide "CutAway"....
Thanks!
The bike I have is was abused a lot in the past, however I have fully rebuilt the engine, new crankcase gaskets should be tight, will check anyway. I will double check for leaks on the intake, and with new cylinder kit definetely will go first with factory spec jetting.
Carb slide I have now if I recall correctly is 6.0, and factory should be 5.5, I guess should be fine.

With air leaks isn't it supposed to run leaner?
 

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Yes, any CrankSeal or intake manifold airleak will cause running Lean. on Cagiva's the CrankCase pressure is known to sometimes PopOut crank oil seal at Magneto side.

with Cagiva, the intake manifolds are famous to perish and leak. full of minor cuts in them.....Tm35 manifolds are also relatively thin, and especially under the Jubilee clip, they are most weakest. ive seen some seriously broken ones 180degrees around under jubilee, and cracks all over on top at manifold.

better be sure than sorry. "SikaFlex 221 polyurethane compound" is Brilliant to fix/ re-coat them manifolds, that are still FixAble worth fixing.

Tm35 manifolds have been factgory NLA for like past 10years.....Some NOS have poppedup every once in a while at germany/italy. last time i bought qty:5+4 Tm35&VHSB manifolds.....

ohh and like "strgr" said, take extra notice into Choke Plunger, into its rubber tip, that it is sealing and not leaking when Choke closed.

ALSO !! Tm35 choke cable isnt same as PHBH28xx choke cable. difference in stroke lenght !!!!

Must do is also to check and measure:
-Float height
-Fuel level
-Float Grams weight
-Floats being sealed, not leaking into them weighing more Due fuel inside them...

brake fluid could soften and swallen hardened Plunger rubber tip (as a DIY tip trick). but its worth buying new Plunger if the Aftermarket TMX35 is the same as Cagiva's OEM.

ive had about 12 Tm35's as OEM evo1, due re-selling them in past and using them on my bikes.....
 

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Discussion Starter · #7 ·
Yes, any CrankSeal or intake manifold airleak will cause running Lean. on Cagiva's the CrankCase pressure is known to sometimes PopOut crank oil seal at Magneto side.
Thanks! I believe there is a stopper/holder for the seals, but anyway, how do I check if the seal is in place? Preferably without splitting the engine :)
 

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Discussion Starter · #8 ·
Quick update:

Fitted 73037 cylinder, standard jetting/settings, 5.5 slide instead of 6.0 - idles almost perfectly. My guess is that mikuni + any other cylinder than 73037 will run rich :] Thanks everyone!

Did not ride it yet, the bike still has to be fully assembled, but I guess it will be fine.
 

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as a side note as a info, the "stop plate" wont prevent oil seal popping out. commonly seal popsout about 180degrees and in 30~40 degree angle....

for a such oil seal the Tolerance for not to leak is 0.1mm, to be in correct angle/to be at Level.
 

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My mito evo 96 has mikuni tm35, and standard pilot jet there is size 45, however it was running insanely rich - even with air screw fully out. Trouble starting, completely wet spark plug, juices coming out of the exhaust.
The cylinder I had at the time (now seized and destroyed, oops) was unmarked mitaka(i guess it is a0401, will try to check today), but from the factory the bike had 73037 cylinder(at least the manual says 130 transfer and 190 exhaust). Everything else afaik is standard from the factory.

So I got some jets, and re-jetted it with size 20 pilot and upped main jet from 310 to 350(standard mikuni jetting for tm35), to keep the total fuel flow unchanged. Aaand it seized after running wide open throttle for quite a bit and closing the throttle fully before a turn.
I suspect that this happened because I was running too lean pilot jet, causing detonation (there is a small molten spot on the piston). Contributing factor might be tight clearance between piston and cylinder (yes, rookie mistake to assume that cylinder kit comes with matched piston).

I get the idea behind rich pilot, it is exactly for extra cooling when going from full throttle to closed throttle, however now I dunno if it was designed to idle like crap.

Now I am thinking that port timings (124 degrees for a0401 and 130 for 73037) affect air velocities - same amount of air is to be delivered in a shorter time - increasing air flow through the carb.

I will get my old 73037 replated and new vertex piston, see how it goes.

So, question:
Why would cagiva use such a rich pilot jet, that can not (in my case) be leaned out with air screw? What might be the reason for this rich situation?

Pics here: Mito noname piston
I had the very same issue:
I am just running a Raptor with 35mm Mikuni, Vforce4 and full Arrow pipe.
The 40 pilot was way to rich on tick over - I drilled a small jet to make a calculated 25
Matika piston (18miles old) thought a 100m sprint was needed . Seized and removed my chrome 😕.
I was thinking not enough oil but it was all bled.
Grampion motors in Liverpool are the importer direct from the manufacturer Matika and they checked and sized my 3,600 mile old barrel.
Very disappointed and will be giving Matika a very wide berth from now on.
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There is summink wrong at the bike SetUp if you get the Mitaka to Seize like that....
take into notice also that the Mitaka's are very very Symmetrical regarding Bore shape.

Mitaka's are not as much Conical and Oval as OEM Gilardoni's. this causes big difference on Clearence.

i could write exact 0,00/millimetres specs how they differe from eachother.

top to that Gilardoni's also prefer bigger than 0,04mm~0,05mm clearence. -> into RealLife empirical 0,06mm for Cast pistons and then its safer....

Also Mitaka has much better Honing than OEM Gilarodni's. like 3-times better. Also Port edge chamfering varies.....to Scrape of 2T oil......

Mitaka's are uber Tight like the 0,04mm, so that is exactly how they melt distruct like yours 4-corner seize-melt, if Engine SetUp is not correct (carb-airbox-exh-cts etc details)
But often what comes to Nature of 2T's nothing can save engine from fully Closing Throttle from WOT top rpm's, no matter properly setup engine or not...


What is commonly said from Stock mitaka parts regarding piston kit, is that the Stock piston rings are too soft. the piston itself is good ! iirc PJME for example changes the stock rings on the kit's. ( "Riken" was the OEM ring brand or not ? )

on past we did a lot of Beating on Mitaka parts on Sp series 6 level Cagiva 5P engine. Mitaka piston was indistructable.....
What cannot be OverLooked is the correct-safe Piston/bore clearence..........



ALSO people dont understand/realise that Aftermarket Mikuni TMX35 is very very Different Vs Cagiva factory special custom made TM(X)35.
Basically nothing is SetUp-Compere able between them.
(Wrong Slide, wrong needle, wrong pilot jet , etc)

For example, at Cagiva's own TM(X)35 , the needle is custom made and only available from Cagiva, not sold at anywhere else on Planet.

at Aftermarket TMX35 the stock needle causes stutter-hesitation etc issues. but there is 1 good aftermarket Needle to compensate the issue. but what ever you do the carb it wont be same or even close to OEM Cagiva's.
 
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