1998 fe600s pop thru carb

When does it happen? I see you said when revved, does that mean speed increasing, steady, or when you rev and let off?

How do you know the carb is a little rich? Compared to what?

I dont have a backfire thru the carb but it does have a slight rough idle. I plan to rebuild the top end hopefully next month.
My carb settings: PHM 40
Start Jet- 45
Needle Jet DR 272
Needle-K51-2nd from top
Pilot Jet- 33 or 35? (I forgot)
Main jet- 170
Slide 4.0
Sparks Stator
It has been awhile since I tinkered with it, I recently installed a 190 main jet and have been tinkering with the timing. I figure get the top end rebuilt and go from there.
It starts 1st kick and 80% of the time on the button. There is just a little pop on idle. Plug is coming out black no matter what my settings are so I am thinking it may be time for a rebuild. I have been avoiding it due to cost but what the heck, might as well go for it!

when i got my 600, the timing chain was off one tooth from a rebuild that the previous owner did, it would start fine but would start misfiring BADLY at 4500-5000 rpm or so, would really not go past the start of its mid range before it fell on its face when accelerating, i also get a gunshot type of noise out the exhaust sometimes when starting, i guess i just considered it normal but it will start fine on the next kick, i have never gotton the loud backfire when running only when starting.
when i kick start it i will put on the chock and kick it through two times slowly, turn the choke back off then kick it hard and will usually start, the loud backfire out the exhaust happens sometimes when kicking through the second time slowly, or when using the electric start if i just tipped it over or stalled it or something it may happen,
i also sometimes get a slight backfire out the carb when i dont kick it hard enough or when cycling it slowly with the choke on, i think that is the only time i notice it, i guess its not bad though and never bothered anything so i never worried about it, mine also hasnt ever backfired from carb happened when running.
fwiw, i too had a rough idle that seemed to go away when i lowered my pilot jet from the 45 to the 40 and got even better and snappier off idle when i dropped it to the 35. my elevation is about 1000ft. in below 32F temps it seems to start better with the 40 than the 35 pilot.

scott600 said:

Then the pop thru the carb is on start up or when it low idle and dies.

Click to expand...

actually now that i think about it more i have gotten a slight backfire from carb when it stalls or is about to stall occasionally,but not a bad backfire, have you adjusted your valves to spec? if you havent yet, you should and then you can look at your valve springs but you probably wont see anything obvious or it would run like crap, research the owners doc for the 1/6th turn method? or 1/8 turn method? i forget which one on how to adjust the valves more accuratly than with a feeler guage.
same with you timing chain being off a whole tooth, it would run like crap at some point through the rpm range, or just not start at all, it could be stretched you could always set it to tdc then removed the timing chain tensioner to see how worn it is, if it is at its max adjustment then you may have an issue with that, if its only like 6-8clicks out your chain is not stretched....

So Scott

If I understood correctly you only have a pop thru the carb when you are trying to start it, or it is when you are runing the bike ?? If that is the case its under aceleration or on decelaration ?

:cheers:
ZAGA

what you guys are describing is what my stock '98 600e did when it was new. off idle performance was bad in the tight stuff. if you used a lot of throttle, no problem, went like a bat out of hell. flame outs were common, but who cared with estart? when i looked into rejetting, i was told by a dealer that it was not advised because it was likely to cause serious backfiring that would kill the starter. :roll: one of the popular mods was the qwiksilver carb, but never heard of a permanent solution.

Mine came with a Qwiksilver carb. Seemed pretty good in the single tracks but in the wide open stuff the carb seemed to run out of fuel! I would have to wait 2 minutes and it would fire right back up. I may try it again this spring just for the hell of it once I sort the other stuff out.

Scott

From what I've heard pop thru the carb it can be a usual thing, specialy on older 4 stroke and the big ones like yours, even to pop the carb out of its place.
For me its easier to understand the pop tru the exhaust, but thru the carb can have some explanations: spark timming, valve timming, cam overlap, intake valve not sealing very well, too high idle, bad jetting possibly too rich.
I just never experienced this problems, only the exhaust ones, hope there is someone with more experience than me to give you a better advice than check everything
:cheers:
ZAGA

The only time I can remember any back-fire through the carb issues on any of the 4-strokes I've owned was when I temporarily installed the Mikuni VM38 carb off my 2-stroke Husqvarna 500XC on my new '96 Husaberg FE501 without changing any jets and actually had it back-fire hard enough to blow the carb out of the rubber intake manifold. I'm sure, in this case, it was because the pilot circuit was too rich with the carb jetted for a 2-stroke since 4-strokes have significantly higher intake vacume than do 2-strokes and so require smaller jets to get the proper amount of fuel into the combustion chamber. It seems to me that back-firing through the carb is the result of pre-ignition which could occure if the timing was too advanced or the fuel mixture too rich and igniting via compression (think dieseling). If the float level is too high and a minor bit of flooding is occuring it could possibly cause it to back-fire also. Back-firing through the exhaust during decelleration is usually a result of the fuel mixture becoming too lean when the throttle is suddenly closed .

My '96 FE501 ran the best with a 35 pilot jet in the 38mm flat-slide Delorto it came with and my '02 FE650 had a 33 pilot jet in the OEM 40mm round slide Delorto carb (bigger motor - higher intake vacume).

Yes you will have to remove the valve cover and water pump cover, the valve cover can be silicone sealed back on using a small amount of good quality engine sealant, water pump cover gasket i reused but could aslo be siliconed back on, the engine will need to be at tdc then there are two bolts on the camshaft sproket that should line up paralell with the top edge of the head when at tdc. you can check to see if the timing chain is stretched by setting the engine to tdc then removing the timing chain tensioner and see how far pushed out the plunger is, if its a long way out then the chain is stretched if it is only pushed out 6-8 clicks then the chain is like new. the tensioner also has a gasket that could easily be made if you cant reuse the old one. you can go to husaberg.com, click the service tab, then dowloads, and download the service manual. the 1999 manual has much better pictures and you can see how the alignment of the head to cam sproket bolts should be. the 1999 engine is the same as yours except that the ignition stator is a different style so that section of the 1999 manual will not help you there. from you description i do not think that you timing chain is off one tooth, if anything the timing chain strethed or ignition timing off maybe it is just a jetting issue? like i said earlier mine was really bad with the timing chain off one tooth, i would think it would either do what mine did or not run at all if it was off one tooth the other way. if you pull the valve cover though when doing a valve adjustment its really not that much more work though and you can see a lot more of the valve springs and rockers etc, it would be like killing multiple birds with one stone, and who doesnt like killing birds with stones

I thought that too the first time i took off my valve cover....the rockers shafts are built into the valve cover so when you remove it it stays with them and you can't actually adjust the clerance because of this with the cover off...but you can still see everything, i agree with you on downsizing the pilot too. i havnt replaced the chain and never looked into finding a replacment so i dont know if they are even available. search the 1/6th turn method or you can find it in the doc under valve adjustment for the best way how to accuratly adjust them without a feeler guage. it is easy to do through the inspection covers, just a flat screw driver or preferably 90 degree or bent flat screw driver and a 10mm wrench.... also when you reinstall the valve cover you will want to make sure the axial or side to side play of the rocker shafts is within spec before you tighten down the valve cover bolts all they way. i think the spec is .5mm or something very small, just basically put your sealant on the valve cover then put all the bolts in finger tight then take a 13-15mm or so socket and tap on the black circle end of the camshaft on the right side of the valve cover head untill they are in spec (should be able to feel a microamount of movment but wont be able to check with feeling guage either) then tighten downt the valve cover bolts.

Hi Scott

I don't think you are one teeth off, its hard to miss that much with this type of chains, but check it anyway. This way you can see how things are in there. Since you are opening it, check the spring of the ADC, when its on the bottom open it and it should close fairly fast without loosing speed until it thouches the small bolt.
Also if you can, get wurth super rtv (red is the best) silicon, to close it.
If need anything just ring.

:cheers:
ZAGA

The popping on decel may be the result of the needle a bit lean - try raising it one notch.