Seizing 430 motors

[Dave J]

I am wondering was the 430 jetted lean? I am in the UK at sea level and bought a 430 motor from a guy in California to fit into a 83 cr500 when it arived it had the big seize at some time so we rebored it and before a local twin shock meeting took it out to run it in, it ran great untill after a couple of hours we gave it full throttle and it seized instantly, It hadnt done much damage to the piston and none to the bore, it had seized between the exhaust port and transfers both sides. we then ran it in 6 motos at the meeting and towards the end of the day stalled a couple of times while braking for turn, having removed the barrel again I can see it was nipping up . We are now building up another bike the same for a freind and have purchased another low use 430 motor from the USA to go in it, I removed the barrel tonight to check it over an it is on standard bore and looks like it has had a seizing time over the years with scuffs up the piston and bore on the thin side of the transfer port where it must get hot and clamp the piston, a previous owner has drilled the piston in rows about 3mm holes about 1.5mm deep that coinsides with the thin area between the ports. Any advise on what I should be doing for a couple of reliable motors would be much appreciated.

 

[Leftcoast leftkicker]

I have a lot (unfortunately) experience with the jetting on these motors & seizing them. I think because they're set up so fat from the factory back in the day that most guys start leaning them out so they'll idle. In my experience they'll run crappy in the morning on cold days then bitchin in the afternoon when it warms up (chased pilots, arirscrew settings, slides, needle jets, clip settings, etc. and nothing seems to work) I will say that unless you pressure test the motor for air leaks you're never going to start to solve your jetting issue.

 

[Picklito]

Very good question. I had the opportunity of starting my Husky "thing" in 1982 with the purchase of a new, crated 430. Got to assemble it myself, break it in myself, and then tune it myself. I was a lot younger and a lot less experienced, and there was tons of stuff to learn along the way.

First, the dealer told me up front I'd find the jetting too rich, and I was not to lean it out for "3 full tanks of gas." He must have said that to me a thousand times. Interestingly, there was almost always a new Husky in his shop getting a new top end. I'd ask him what happened, and he'd say "they didn't wait 3 full tanks of gas." So, the motors were set up tight, and they needed plenty of break in time. But that's only part of the story. The other part is the way they were too rich...

Mine was, in fact, a blubbering drooling mess, just as he said it'd be. It was difficult to ride 3 full tanks of gas without leaning it out, but I did, and I rode it conservatively. Once it was "ready to go" I found something interesting: Jetting was way rich everywhere... except on the main jet. The bike would sputter and spooge and foul plugs at all other throttle settings, but if you took it out into the sand wash and ran it at wide open throttle for more than just a few seconds, the plug would turn a scary blistering white. How did I know? Because I looked at it. Doubtful many riders do that. Most likely, they just rode... and seized. Right there in the sand wash did a bunch of WOT plug chops to get the main correct. If I had just gone like blazes it would have CERTAINLY seized. No way it could have been taken from the crate and raced. Would have seized for certain.

Mine had the "correct" 440 main in it. At sea level I ended up with a 480 or 500 in order to get the correct burn. THEN, and only then, did I start to jet down the other brass to clean it up. I've learned to go through this process with EVERY bike ever since.

The bikes end up running quite nicely, and I don't think they could be said to have "a seizure problem." In fact, that top end on those motors will last a long, long, time. I bet most owners rode a full lifetime and never took the top ends off... unless they got caught by the issues above. JMO.

 

[Leftcoast leftkicker]

Good info because I've been running jetting from 2 very well-known Husky shops and still seizing. Admittedly some was my fault (not always air leak testing) but still... Sounds like I need to start with a 440 MJ, 45 pilot, #3 clip and work backwards.

At one point we had a discussion thread on jetting, perhaps HuskyT can resurrect?

 

[Blazes]

Many moons ago i used to race Huskies for 11 years here in South Africa. Common problem we had here was that All the Huskies came from Sweden jetted lean. Ended up with the 430 on a 480 main jet 2000m above sea level--The other problem we had was--this is lion country and it gets hot here. Eventually i moved over to putting in Slick 50 through the motor-teflon based coating----Used to do it after that with all my Huskies--never siezed one again. Do not know if it was the Slick 50 --or just that i got wise to how to jet the bikes. Tip i learnt form Ralph Tiblin from Husqvarna was to slightly machine the arch at the back of the mikuni carb a fraction bigger and to drill a small hole in the front bottom of the slide on the inlet port side. He said it helps when you close the throttle when you have been riding at high speed to suck fuel through and still lubricate the motor cylinder. Well i just did it and it worked-----

 

[Picklito]

Sounds like I need to start with a 440 MJ, 45 pilot, #3 clip and work backwards.

Oops. Maybe I confused you. When I said that the 440 was the "correct" main jet, I only meant that my bike had the jet Husky had intended. I meant that I didn't have some assembly "mistake" in my carb. So, no, don't start with a 440.

I'd start 480, 6DH3-3, R-4, 2.5 slide, 45 pilot at sea level.
I'm currently at 460, 6DH3-3, R-2, 3.0, 40 pilot for 2500 feet.

 

[jdaatwebco]

81/82 430 xc

I have 3 of the 430's. They run great from bottom to top end and idle very well. The only issue that I have is starting; and yes, I know how to start a big bore 2 stroke ( I hace ridden Huskys and KTM's for 40 years). It is difficult to start, hot or cold.

I have heard of a slide modification whereas the slide is cut a small amount to help airflow. Have any of you heard this and might have the spec?

I have also heard of drilling an oil relief hole in the piston where the exhaust port brace is located. Amy specs on the hole size and location?

 

[Dave J]

Thanks for all the advise guys I will have a look again at the carb spec, I am sure you are right and it is a mixture thing, I remeber riding severe events back in the 80s forestry going bog after bog lots of revs with no air flow on air cooled bikes with no overheating/ seizing problems.
The 430 motor that I have just taken the barrel off has drillings in the piston, that must of been the oil retaining mod, I will post up pics, did not work though as the problem must have been that it was lean and getting so hot and seizing

 

[Husq.fleet]

Oops. Maybe I confused you. When I said that the 440 was the "correct" main jet, I only meant that my bike had the jet Husky had intended. I meant that I didn't have some assembly "mistake" in my carb. So, no, don't start with a 440.

I'd start 480, 6DH3-3, R-4, 2.5 slide, 45 pilot at sea level.
I'm currently at 460, 6DH3-3, R-2, 3.0, 40 pilot for 2500 feet.

Thanks for te jetting help, I'll start in-between, I'm at 1200 feet, Thanks Scott

 

[Leftcoast leftkicker]

Yeah I think I'll swap the TM Mikuni out for my round slide VM and start with your specs

"I'd start 480, 6DH3-3, R-4, 2.5 slide, 45 pilot at sea level. I'm currently at 460, 6DH3-3, R-2, 3.0, 40 pilot for 2500 feet"

 

[Picklito]

The point is to GO BIG on the main, big enough to make it blubber and so that peak RPM is limited by the richness, no matter how long and hard you hold it wide open. On a tight 430 at sea level, that might require a 520-560 main. Then slowly bring the main jet down, with full throttle tests each time. Pull the plug each time, and you'll see the changes. Once the blubbering JUST stops and the RPM comes back... the plug should be a clean mocha brown and that's the one.

*NOTE - you could go several more sizes down, and the plug will get whiter and whiter... don't do it!!

So, guys, post up your feedback after you do some trials.

 

[Leftcoast leftkicker]

OK this is backwards from the Mikuni jetting manual which says to start at the opposite end (air screw, pilot, then slide, then main & then fine tune w/needle clip and air screw). I've been doing that and never getting the main larger than a 410-420. With the results I've had perhaps I should try your method instead?

 

[Husq.fleet]

Glad I took the carb apart on my 430 tonight, havent ridden it since buying it last summer but around the block a couple of times. This is what I found, 2.0 slide, R-4 needle jet, 410 main, 6DH3 needle-2nd from top and 45 pilot. The slide looks like it has been ground down on the cutout side, that would lean it out wouldn't it? I didnt have another to check it to without pulling another out my other bikes-tomm. project. The larger the cutout the more air for throttle position would make it leaner I assume. 2 stroke jetting is new to me as my best friends dad when I was a kid had the Husky shop and always tuned my bike "so I wouldnt screw it up".
I have drag raced for a long time and I always jet for WOT then adjust the other circuits for idle quality, acc. pump squirt, mid range. like Picklito practices. Used to run WOT then shut down crossing line and check plug color. Idling back to pits then looking at plug was useless other than trying to impress to other "pit stars". Being a diesel tech for my whole career I use the exhaust temp as fuel/air mixture indicator. I then put EGT's on my drag car to tune, no more looking at plugs just check temp at WOT then adjust carbs other circuits. I haven't found anyone to ever tell me what the stoich exhaust temp. should be on a two cycle? Easy on a four cycle without the oil being a factor. I think the variable with having different expansion chamber/head pipe designs would have a big effect on EGT's. Wouldnt it be nice to just have a small 2" guage to look at rather than the plug ritual? When tuned take the guage off and leave probe in or plug hole in headpipe. Sorry to get windy, just lazy and it would save alot of time and dead parts.

 

[Leftcoast leftkicker]

You can measure the slide cut-away by flipping it upside down onto a completely flat surface, put a straight edge across the top then measure the distance from the lowest point on the curve's cut-out upwards (perpendicular) in mm. Most all 2.0s have been ground to make them leaner so NEVER assume its a 2.0 because it's stamped 2.0.

 

[Husq.fleet]

You can measure the slide cut-away by flipping it upside down onto a completely flat surface, put a straight edge across the top then measure the distance from the lowest point on the curve's cut-out upwards (perpendicular) in mm. Most all 2.0s have been ground to make them leaner so NEVER assume its a 2.0 because it's stamped 2.0.

Thanks for the tip on the slide cutout, I'll check mine. Another thing I was thinking about was not running leaded fuel. I believe these engines need leaded fuel for lubrication. I run 114 Purple Plus in mine.

 

[Picklito]

OK this is backwards from the Mikuni jetting manual which says to start at the opposite end (air screw, pilot, then slide, then main & then fine tune w/needle clip and air screw). I've been doing that and never getting the main larger than a 410-420. With the results I've had perhaps I should try your method instead?

What do you mean that you've "never getting the main larger than a 410-420?" You've never tried one larger? Or are you saying that running a larger one screws up the other circuits, that you already thought you had set correctly via Mikuni's method? If it's the latter...

I think Mikuni's method is fine... to start with. Say you use their method, and you get it nice and crisp and clean at idle, off-idle, and small throttle running. Then you go put my monster main in there. Ya - I wouldn't be surprised if the previously crisp small throttle settings became sloppy. IGNORE THAT - for now. Go and do the WOT blubber runs and plug checks and work down and get the "safe" main in there. Big enough that (provided we're good enough riders) we could just hold it wide open at 100MPH across Baja for 20 minutes at a time. If you never find your motor's WOT "blubber jet" then you never went big enough.

THEN - go back through the other circuits and clean things up. "The main only works at wide open throttle." Ya - blah blah blah. It begins to flow pretty early and has significant effect by 1/2 throttle, and becomes ALMOST the entire effect at WOT. The pilot is still flowing, too, but is minor compared with a 500-ish main. But the pilot does have to be considered for FINAL main jet selection. IMO.

So after you clean up the low end, then do the plug runs and get your perfect main, you'll probably be running a pretty big main and you'll probably need to go back and clean up the low end again... then ONE MORE TIME go out and make sure that your main is STILL large enough, now that you've reduced your pilot and maybe increased your slide cutaway and/or changed your needle or clip. They all overlap. And if you've reduced their contribution to WOT fuel flow, you may have to increase the main one more small amount to compensate. Trust me, this works.

I just skip one step and start with the main. In fact, I'd prefer to be fat on the pilot while I'm doing all this high speed stuff anyway. Only after I know I've got a big enough main to cool the motor do I want to start cleaning up the low end. Why? Because it's very common to seize these bikes at the END of a high speed run AFTER you chop the throttle. Why is that?

Because it was too lean at large throttle settings and the motor got too hot. Maybe not hot enough to seize at WOT, but hot enough that what "should have been" a rich enough pilot jet can't keep up when you close throttle and the motor's that hot. Seizure. Get a sufficient main jet in there that's doing it's job, and the throttle can be closed safely.

Sorry for the book, guys. This is important in order for us to protect our dwindling supply of vintage pistons and cylinders!!

 

[Dave J]

Piclito, this may be a bit basic but I have never adjusted slide and needle jet before,am I correct an increase in slide number from 2 to 3 will weaken the throttle opening from idle to main and an increse in needle jet will make the motor run richer across the full rev range off idle.
I have looked at my settings today and notice that the slide no2 is cutt the radius is about 2mm more than the uncut 3 that is in my other engine, I need some new parts

 

[Picklito]

By the way, if you're jetting for play, easy MX, or plunk-along trail riding, you may not need nearly as large of a main jet simply because you don't have the extended WOT periods of time. It's all about time. Time for heat to build. But I still recommend finding the blubber jet for your typical track, and back down just a bit from there.

 

[Picklito]

DaveJ
The greater the slide cutaway, the weaker is the signal to draw fuel up past the needle. So more cutaway = leaner, in the effective range, which is a tiny bit at idle, and mostly just above idle to 1/4-3/8 throttle or so. If your 2 has more material cutaway than your 3, then your 2 is now leaner than your 3.

The way the factory cuts them is to increase the angle of the cutaway, but not the width of the arc. The corner angles are in the same place on 2, 2.5, and 3, but the cutaway gets steeper as you go 2 --> 3. Some guys who cut their own don't do it that way and they just make the whole arc larger. This wouldn't match Mikuni's calibration, of course, and it's anybody's guess what that might do to mess up the mixture.
It's good that you have a "real" 3 around to use as a reference.

"Increase in needle jet?" I assume you mean going from R-2 to R-4 or similar? That increases the internal diameter of the needle jet at all needle ranges, but again the effect is greatest off-idle to probably about 1/2 throttle. There's a chart in the Mikuni tuning manual. But remember, all the circuits overlap and the chart is just a generalization.

 

[Leftcoast leftkicker]

Picklito- thanks for the clarification. I believe what you've described is exactly the problem I've been having because it seizes on short straight w/throttle chopped. When I pulled the cylinder yesterday it was pretty ugly and basically confirmed that I shouldn't be trusted with anything sharper than a dull butter knife.

Jetting 101 next Saturday!