• Husqvarna Motorcycles Made In Sweden - About 1988 and older

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

Insufficient fuel from tank to carb ?

S

subarumy98

Husqvarna
AA Class
HI All

Here are the symptoms:

Accelerate hard 1,2,3. Half-way through 3rd, the motor will die. You can throttle back, and she will pick up again and accelerate some more. Then I ran out of road.

Go to 3rd, and keep the throttle on half, accelerate gently, will pick up speed at a constant rate then suddenly accelerate harder as she goes lean, then die.

In both cases, as you throttle back, the sound is the boowang, banggg bangg boowang.

So here's what I'm thinking:
The fuel is not flowing fast enough. Somewhere between the tank breather and fuel tap.

  • If the fuel level was too low, then by accelerating slowly, you would not induce the condition, as the fuel will replenish fast enough.
  • If the main was too small, it would not accelerate to top revs in 1st and 2nd.
  • If the main was too large, it would not rev cleanly in 1st and 2nd.

Please check my logic and post your thoughts..

btw:
1983 500XC
45 pilot
430 main
std needle and jet
new needle & seat
everything is clean
2000m altitude
 
No. The suply hose will suply more than the bike can drink. My guess is main jet fuel starvation. Does the cap for the main jet removal have holes drilled around the perimeter on the threaded area? If not drill some and see if it fixed the issues. Does not seem like this would matter but several report it does. the thought here is the main sucks fuel quickly at WFO and cavitates this small cavity the main sits in. Sure is fills from the bow and should be under fuel at all times (I made this argument as well) but many reports that is does fix that issue. Nothing to loose trying it.

Part shown here lower left...

48-9021.jpg
 
Had the same problem on my 430 once. Found-finally- that the floats were sticking on the guides under hard acceleration, let up and they would free and let fuel in bowl. Took me awile to find that one. Just another thought........
 
Hmm:
1. There is a brass plate with 4 small holes around the edge that the main jet holds onto the bottom of the carb section. Did read somewhere that these holes should be size x, will go find the info. The plate is there for sure.
2. @Moto, do you want holes in the drain plug ?
3. @Husq, I can hear the bowl fill up as I hold the carb in my hand, fills quite quickly and steadily. floats seem loose on the pins. How did you solve the sticking floats ? I will go polish the pins in the meantime...

Questions:
Do you guys have the plastic end-caps on the float guides ?
Do you have the standard fuel taps, (mine is the repro item from Husqvarna-parts) ?
 
@Motor, that's what I also wanted to ask.
My fuel level stops at 16mm from the top of the bowl. tested by assembling, letting the carb fill up, then remove the bowl to measure.

I found an archive doc here that says one should measure by turning upside down, and the measurement from fuel float to the underside of the carb (upside remember), should be 17-22mm.
Going to strip again and check that.

I seem too remember a value of fuel being 10mm from the top of the bowl - cannot find that again.

Will also post the time to fill a cup from the fuel tap later tonight. Just as a reference.

Thanks for all the ideas so far.
I even wanted to calc the fuel flow required based on 480cc swept volume, 6000 rpm, and a 16:1 fuel/air ratio :)

T
 
I installed new floats. In removing the float bowl to check fuel level that is going to be somewhat inaccurate. Reasoning is. When you shut the petcock off and remove the float bowl you are allowing the needle to open on the needle/seat assy allowing the fuel above it in the carb and fuel line just below the petcock to drain into the fuel bowl. Keihen (sp) are nice with the bowl drain and tube on the float bowl, can install tube and point it upward with drain open and it gives you the fuel level, wish Mikuni had that. Mikuni recommends the float arms to be level with the carbs float bowl mounting surface without compressing the needle spring.
I also assume you are using NON-ETHANOL fuel? If using an ethanol blend you fuel is going to be leaner than non-ethanol because of the alcohol content. Basicaly need twice the volume of alcohol as gas for same energy. Ethanol blends also are more prone to fuel boil and airation. Your pre-mix ratio will also have a big effect on jetting for proper air fuel ratio. More oil the less fuel in the engine and vise-versa.
 
Mikuni recommends the float arms to be level with the carbs float bowl mounting surface without compressing the needle spring.
I reckon that's where I am going wrong.
Mine will be level once all the weight is on the bottom of the needle & seat assembly.

What does confuse is that in the 500XC manual, it shows the orientation of the brass float level assembly as the opposite to the picture in the Mikuni manual:

Husqvarna500XC-40mmMikuniexploded.jpg


Husqvarna500XC-Ownersmanual40mmMikunisetup.jpg


I am assembling according to the parts manual. Pic 1.

Trevor
 
I have this EXACT same problem with my 84 500XC. I set the float arms level to the bowl mount surface, and still have the problem. I only notice it when I can get it on a very long stretch of road as well. I'll look at the float drain plug as well as if the floats are sticking. Anyone ever try or know of an oversize float bowl?
 
Yes the needle will just close and the spring will then absorb some float bounce WITHOUT opening and closing the needle valve and flooding the carb! Sounds like you found the problem. I'd go by the Mikuni manual as the 500 manual I'm assuming is a parts manual.
 
When it does that just stop and pull the plug and take a reading if you were leaning it it would rip until it seized. Sounds like to mush fuel.
Think more like the hold down plate for the needle is on wrong side, should be on top of needle with spring on top.
Later George
 
If you guys look at the parts diagram, item 41 is bending down into the float bowl. making it engage earlier with the pins on the floats.

In the owners manual, the bend is upwards, away from the bottom of the carb, toward the throat.

Problem is, I have just had a heat seize, at 1 and 7 o'clock on the piston, (looking from top with exhaust at 12 o'clock). This was caused by an air-leak on the barrel intake manifold face. As such, I am being very careful, and and have discarded all my previous jetting notes as these were being influenced by the air-leak.

I started at a 450 main, and finally got to the 430, when this "fuel starvation" started. It would burble all the way through the mid-range, and was super-rough on top.
I will do a plug check next, but was holding off on doing that till it at least felt reasonable... :)
 
Well, with the brass float lever installed, and the tab horizontal, I am at either 13mm or 27mm, depening on which way you orientate the float lever.
The 17-19mm is basically inline with the pivot on the brass lever.

Getting the legs of the float to be horizontal AND 17-19mm - not going to happen in this lifetime.
I am looking at a whole different shape for the float lever / the little tab being way out of shape.

Have some more work stuff to do, so probably attack it again tomorrow.
 
Tested again today.
bottom end fine.
mid-range good.
top of 3rd she runs out of fuel again.
Its consistent, every time.

Plug chop as it happened shows dry, not moist, not wet - but also not burnt white. There's an even grey colour. Light ash I would describe it as.

Next:
Going to find another float level, and flatten the whole assembly - test that.
Main up to 450, and test that.

Comments and solutions welcome....
 
My experience is if I turn off the gas and forget to turn it back on and start riding I don't notice anything until half a mile or so. I know there is a lot of talk about how critical the float level is however it really doesn't correspond with my experiences noted in the previous sentence.

The origional settings would be for the origional spark arrester/silencer packed the origional way. I rode one of those 1983 xc 500 for a long time on the origional setting it worked ok for my purposes 700 to 1000 feet altitude mostly. It rarely would come onto the pipe with a hit and lots more noise but it really didn't matter unless I was in a sand pit.

Your descripiton in the first post sure sounds likie a main jet issue if you had the manual from a 1960's bmw to read.

You didn't state if the piston which got seize marks was a cast or forged one or what brand.

Fran
 
Had that happen to me. Kept going bigger on the main and couldn't get to rich. Finally went way to big and still not rich. Pulled the in-line filter and solved the problem.
 
Hi All

Thanks for the input.
New short fuel hose and NO filter at the moment to eliminate 1 variable
Have tested with an open fuel tank to eliminate the breather too.
Piston is Woessner, so that should be forged.
Am very particular about warming up now, (even more than before) before applying load.

Next step:
Will pull the petock and check.
Have flattened out the float lever completely now. No step, and that gives me a more reliable 17mm from the carb body as per the Mikuni diagram in prev post.

Hold thumbs :)
 
You must log in or register to reply here.
Back
Top