Seizing 430 motors

[Husq.fleet]

Any more 430 jetting going on?

I wish!! Have a new RetroRocket pipe and Mossbarger reeds for my 82-430XC. I was looking forward to getting it dialed in but a ruptured disc in my lower back is now dictating my future.

 

[stormer254]

The guys who say to tune the main jet first and then do the lower revs are exactly right A point to remember is our older bikes have been "tuned etc" over the years so the original carb settings are often no longer correct. 2 strokes are famous for seizing on the overrun, climb a steep hill, get all hot and bothered, coast down the other side, no petroil to cool and lubricate motor and bingo loads of ali skid-marks. Another point is our motors were designed for R vegetable oil. I run all my racing bikes on R (Greeves and Stormers) and even when I take a broken engine to pieces it will still be oily, not something you find with modern oils they simply can not fill the larger clearances we run at.Also the smell of an engine running on it is simply brilliant, I even use the stale fuel in my lawnmower,

 

[Picklito]

Good info, Stormer. And so true... sometimes I can't believe the state of tune I find these bikes in.

 

[stormer254]

I have found the best way to go faster is to pull the wire harder, not grind away ali and steel

 

[Trailridernut]

I agree with Picklito in jetting technique - you have to go until it blubbers and then back off on size... I have forgotten my jetting other than a 3-3.5 slide. Also, unless Vance has rewound the motosplat(yes, I spelled it correctly...lol!) go with the MZB... 1-2 kicks hot/cold makes no difference! $500 BUT it starts without kicking 4-6x's. MZB is the only coil that actually holds a small charge as opposed to kicking to charge the coil(motoplat/pvl/etc). All of my bikes either run mzb or pvl.

 

[Ron]

Testing with the main jet first is a very dangerous proposition.
The various circuits in all carburetors are cumlative and over riding in effect.
This fact is not debatable.
However all jets in the carburetor should be considered as restricitons to fuel flow.
The pilot circuit draws fuel at all times, the size of the jet restricts its flow. The needle jet and the tapered needle combo together create a variable restriction until the wide open restriction becomes the main jet.
Working with the main jet first does not consider these cumlative, over riding effects.
Consider this, when you decide you have found the correct main jet size and then reduce or increase your pilot jet size, you have altered the fuel flow supplying the main jet and your back to square one.
The first thing to do is to mark your throttle housing and twist grip so that you can see where the throttle is.
What your really seeing is where the slide is.
The throttle position (actually the slide) controls the various circuits at each throttle position as follows:

throttle closed to 1/4 = pilot jet and slide cutaway
throttle open 1/4 to 3/4 = needle jet and needle taper
throttle wide open = main jet

You should always start with the pilot jet.
With proper size pilot jet the bike should start and idle smoothly with the air screw no more than 2-1/2 turns out. If more than 2-1/2 turns are required the pilot jet is to large. If the motor dies at less than 1 turn the pilot jet is to small.
In addtion, if you have to go more than 2-1/2 turns out, the spring tension on the air screw will not be sufficiant to hold its setting and will allow it to vibrate and fall out.
When you have the pilot jet size sorted out, the next step is to move to the needle and needle jet combo.
Put the clip in the middle position on the needle and remove the main jet from the carb.
Next, without the main jet installed, take a short test ride and notice the throttle position when the engine starts to blubber.
What your looking for is accerleration up some where between the 1/2 and 3/4 throttle position, as the main jet starts to take over.
Don't worry about a smooth transistion off idle or smooth accelleration at this time. Just verify the needle jet and needle combo are not restricting fuel flow past the 3/4 throttle position.
If the engine continues to rev out past 3/4 throttle, your needle jet size is to small. If it starts to blubber at 1/4 throttle your needle jet size is to large.
Now you can start searching out your main jet size.
Start with a main jet that is to large and work your way down.
This will prevent you from having a a lean condition that would cause a piston seizure.
When you have settled on a main jet size, you can now go back and work with the slide cutaway and different needle positions and tapers to clean up any transition problems you may still have.

 

[suprize]

when i was racing, i used to be 1 clip rich on the needle as long down hills can see high revs with little throttle. saved me once whenthe base gasket cracked. ran lean butgot me home with nodamage. agree with the tome above.get themain rightand play withthe rest!

 

[jimspac]

I have even heard your premix ratio affects jetting as well

 

[Husq.fleet]

Yep, oil displaces gas so the more pre-mix the less gas.

 

[Velocette]

-82 430: MJ 420, needle jet R2, needle 6DH2 clip in the top, slide 2.0 filed to get it idle, PJ 45, plug NGKB8ES, result white plug...bu not seized yet.

 

[Kartwheel68]

I agree with Ron, starting with the main first is not a good idea. When tuning the main, you DO need to go richer until you find the "blubber jet", but that should be done last, after the pilot and needle/needle jet have been set. Also something to keep in mind, if you are in the US and you are using straight pump gas DO NOT USE PLUG READINGS TO TUNE!!! Modern pump fuels with their current blends DO NOT give accurate plug colors like they used to. Unless you are using at least a mix of pump/race fuel only jet by the behavior or sound of the engine, not the plug color.

 

[suprize]

thats an interesting obs as thought some thing was notquite right. we have 95 unleaded here in aus

 

[Velocette]

460 main and clip in the second from top, allmost there. 100m above sea level and 25celsius. I ran 98 unleaded with Shell 2T castor oil, the plug colour doesn`t change much with this modern petrol.

 

[Kartwheel68]

I thought I'd add my bike, an '82 125XC with the 175 kit on it, to this jetting discussion. I've been slowly getting the bike ready and this weekend started working on the jetting. It had the stock jetting for the 175, a 400 main, but it was blubbery rich on the pilot and needle. Once I got those cleaned up the main seemed fine, but in an '83 Dirt Bike magazine article on the 175s they sent the bikes to Pro Circuit and had them ported. The jetting PC put in them was a 460 main, so I tried richer mains to try to find the point it started to blubber. I tried 410, 420, and the biggest main I had was a 430. It still ran clean, so clearly a 400 was super-lean, which is probably why the bike was seized when I got it. I've ordered 440, 450, 460 and 470, but I get 450-460 will end up being right, much much richer than the stock main. Not sure why Husky had them blubber rich low/mid and lean on top.