Whats sizes do you think I need?

turbowrenchhead

turbowrenchhead

Member
Jul 13, 2011
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Customer brought me an 89 blaster with burnt rings. Its too lean. It has a 72mm piston in it with a vito's jug and head. The head is not re designed. Just the larger diameter. I'm going to put in a 73mm piston. It has the stock carb. Going to eliminate the tors and re jet it from him. Whats a good starting point for a needle, pilot and main.
 
Also depends on the elevation and Above or below sea level heights , I'm fairly new to jetting and doing it properly but from what I've read you need to do a leak down test and plug chops to confirm jetting
 
It has a full fmf, stock air filter. we are at 900 ft above sea level. I looking for a general size to get me started to i can fine tune it with plug chops
 
Id start with 280- 310 i think ive heard people say with similar mods , If I'm wrong someone will chime in , did you say air box lid on or off , that adds a size to the jet if removed
 
Gotcha , Well I would try and contact somebody that carries them , You don't want to bore more than you have to , Might as well keep some life left in the Jug , just my .2C
 
FMF Fatty or SST..???

Fatty #290, #300 safe bet. SST, not sure but prolly round about the same.

Needle middle clip, pilot #32.5.

Correctly set idle before trying to jet and ride for the plug chop.

If using a different pre mix than 32:1, jetting will change also, more oil larger main jet.
 
Yeah, I found the next overbore size but it was $159 and I had already made my quote with the $109 piston. I got the engine back together and its making 160psi. I can't talk him into a bigger carb. He wanted the tors eliminated and go back to thumb throttle. Took the carb apart and here the cap threads on the carb are bad. Found a replacement carb for $25. The stocker had a 340 main in it and a aftermarket needle. I didn't look at what size the pilot was yet. The story is that the guy bought it running, his kid washed it and thinks that water may have got into the airbox, since there is no lid. After riding it for 10 mins it fried. It looks like a lean burn down, can water intrusion cause the same kind of damage?
 
havin troubles understandin but your saying the bike your fixing now had a 340 main in it?? or the replacement carb had a 340?? which is the "stocker"???? cuz u just said the bike ur working on has a 72mm which is a 240 not stock. sorry just confused

the reason i ask is it that puppie had a 340 main in it and leaned out something deffinitly went wrong. i wonder if the guy let in run low on 2stroke oil, maybe had a bad airleak and kept running it, water could lean out the mixture but the guy would of noticed everytime you would hear the motor missfire.

even tho quote was made you really shoulda mentioned it considering 240 cylinders dont have many bores and they arnt cheap. skippin a bore cuz that size is too pricy

160psi sounds like lots did you leak test it?
 
The customers bike has a 240 vitto's big bore on it. It has a stock carb with a 340 main in it. The guy doesn't have a lot of $ so he probably wouldn't of went the more expensive piston.
 
Yeah, water can ruin the rings. I've done it. It takes a lot however.
Probably more than a cup of clean water in the air filter box.
I completely submerged my 125 bike in silty muddy water to scuff my rings.

When you say "the rings were burnt" what do you mean?
Water wouldn't do that.
 
turbowrenchhead said:
The rings are melted into the piston on the exhaust side. It must be lean burn down condition then.
Click to expand...

Yeah, doesn't sound like water damage.
I submerged my 125 three times over the years, all in the same general location, deep muddy water holes with hidden rocks and logs.

The water damage to the piston was a pinched and broken ring in the worst case, probably from hydro-locking. The other two times showed fine scuffs on the ring surface and a rounded edge. Nikasil cylinder was highly polished and didn't seat the new ring very well, even when it was lightly scuffed with a hone pattern with paper for a second ring. I suspect most of the damage was done by the abrasive silt, not the water. In all three cases (including broken ring) the bike was rode home on its own power after a cleaning and a push start.

Engines that have a coolant gasket leak will show a very clean piston and chamber and a high degree of ring and (iron) cylinder wear. Pouring a few glasses of water down a running worn out, smoking, low compression engine is an old trick to restore some of its vigour. It will occasionally restore some compression and reduce smoking.

Rings fused on the exhaust side do not sound like water damage. Lean or overheating (exhaust side always gets hottest). Exhaust leaks will cause localized leanness independent of jetting and will burn and pit the exhaust side of the piston. Richening up the jetting will not solve this.
 
best said:
. Pouring a few glasses of water down a running worn out, smoking, low compression engine is an old trick to restore some of its vigour. It will occasionally restore some compression and reduce smoking.
.
Click to expand...

Not that I am going to advise you to do the above, unless you know exactly how to do it.

I have been using this little trick for many years now. It is surprising just how much crap is blown out of the exhaust.

Some years ago I did a lot of experimenting with water injection on my speedway motor.
 
Blaaster said:
Not that I am going to advise you to do the above, unless you know exactly how to do it.

I have been using this little trick for many years now. It is surprising just how much crap is blown out of the exhaust.

Some years ago I did a lot of experimenting with water injection on my speedway motor.
Click to expand...

I used water injection on high compression motors back in the 70s when we couldn't get high octane fuel. There was never any carbon on those motors when you took them apart! I ran am 11:1 1970 Torino 351C on regular 87 octane. In fact this motor below is a 351C running slightly over 10:1 on regular octane fuel with water injection:

271_29545085802_5231_n.jpg


271_29545090802_5614_n.jpg


That ain't steam coming off the tires!

You kept using the Cleveland engine down under after we stopped, I dreamed of being able to work with your closed chamber small port Clevelands and your cross flow six cylinders.
 
ok , so turbowrenchhead is working on a big bore kit with a full fmf exhaust the airbox lid off, i mean im still learning here, but on a stock carb, 340 jetting sounds like its a possibility to be lean isnt it?

on a stock motor he would have to jet like 300

doesnt the bigger displacement of the vitos affect jetting by alot more then your average upgrade?
 
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