Bigger carb...still runs like crap.

**Yamahauler** · 03-04-2006, 02:07 AM

The Z was runnign like crap with the stock carb, it had a 490 main. It wouldnt rev right out.

I got a 38mm Mikuni TMX carb off an 92 YZ250 for it. The jets that were in it were 320 main and 45 pilot. I got it hooked up, and started it, It revved way up. Full throttle. I checked to make sure the slide was all the way down, it was.
So, then next thing i did was check for air leaks. I sprayed water all around the boots and it didnt rev down at all.

I tried bigger jets tonight. First I put in a 350 main and a 55 pilot. Started it, revved way up again, so P.O.'d as I was, I put in a 420 main, and a 65 pilot. Started it, revved waaaay up again. Whats going on? MTS thinks it may be the left crank seal sucking air.

Why would it idle with the other carb then?

**Louis Mielke** · 03-05-2006, 12:37 AM

Sounds like you're barkin up the wrong tree. There has got to be an air leak somewhere. Spraying won't alwys find the leaks. Check the crank seal.

**Yamahauler** · 03-06-2006, 12:50 AM

Yea, thats what I thought.

How can you check the crank seals? We have a leak down tester at work, does that work?

**Yamahauler** · 03-06-2006, 12:51 AM

Also, is it possible to change that left crank seal without splitting cases?

**TeamGeek6** · 03-06-2006, 12:45 PM

Leakdown is for the rings, thats not the problem. Seal off the intake and exhaust and put about 2-3 psi on the spark plug hole, with a gauge, then watch the gauge. If theres a leak, the pressure will bleed off. A bad crank seal can leak a lot of air.

It will rev high because theres no load onthe engine.

if its a bad seal, itll be one that doesnt have oil, otherwise the cylinder would be fouling with oil.

**Ryah** · 03-06-2006, 12:51 PM

I've seen a cigarette used. They put the cigarette near the left crank area and see if the smoke is pulled in. Obviously this only works when there is no wind.

**Yamahauler** · 03-06-2006, 02:34 PM

I'm also going to put the stock carb back on and try that, because it would run and idle with it before. It wasnt until I put this 38mm on when it started to rev up like that.
When I had the stock carb on, you couldnt run full throttle, it would just bog when you pinned it. The plug was also gloss black

**Yamahauler** · 03-09-2006, 08:29 PM

Originally Posted by TeamGeek6

Leakdown is for the rings, thats not the problem. Seal off the intake and exhaust and put about 2-3 psi on the spark plug hole, with a gauge, then watch the gauge. If theres a leak, the pressure will bleed off. A bad crank seal can leak a lot of air.

It will rev high because theres no load onthe engine.

if its a bad seal, itll be one that doesnt have oil, otherwise the cylinder would be fouling with oil.

So, the piston has to be at TDC for this?
Its not possible to change crank seals without splitting cases, is it?

**Bryan Raffa** · 03-09-2006, 08:43 PM

I put a right side in my 85 without splitting the cases you got to remove complete clutch and gear and seal keeper.as far as the left im not shure i almost want to say you can but dont take my word for it take your flywheel and stator off and look at it?

**Yamahauler** · 03-09-2006, 08:47 PM

I know what it looks like in there, is pretty well the same as the right side (seal is pressed in from the outside of the case), but I phoned Yamaha and asked them if you can replace the seals without splitting cases, they said absolutly not, hahha!

Kind of a relief to hear that it is possible to replace them without splitting cases though

**Bryan Raffa** · 03-09-2006, 09:09 PM

dude what are they telling you ive never seen a seal that has to put in from the inside out there both changeable with out spliting the case look at the micro feish on bikebandit and you can see the lip where the seal butts up aginst the right is a SW-type and the left is a 38-w type they might be saying that because it might be tricky getting the old one out but who cares your replaceing it!
trying to find my manual on cd but i cant find it!!!! I think its at work.

**Yamahauler** · 03-09-2006, 09:13 PM

Yea, I have another Tri-Z bottom end apart right now, so i can see how the seals go on. Do the new ones slide in fairly easy? or does it take some work to get them on?

**Bryan Raffa** · 03-09-2006, 09:19 PM

do you have a socket the same size as the outside of the seal use one to tap it in evenly it uasally goes right in no prob. on the left side is there a keeper holding it in or is it just the seal there, is there a lip in the crank case holding it in or does it look like it will slide right out

**Bryan Raffa** · 03-09-2006, 11:29 PM

well how did you make out?

**Yamahauler** · 03-09-2006, 11:40 PM

Yea, it looks the exact same as the right side. Should come out no problem...dont see why not!
Thanks

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Bigger carb...still runs like crap.