Why manual decomp with auto?

[wickedsprint]

If the 650R has an auto decomp, why does it need the manual one? I am used to kicking singles that have either or, but not both (unless it had an auto as well and perhaps I was not aware of it?) I know the proper technique for a manual, but with the auto and manual, can you just kick it like it is always past TDC since the auto does the work, or is there a different technique altogether? Forgive my ignorance, but I hav long since learned if you have a question hang it up and ask ? -Tony

[qadsan]

You can kick it from anywhere in the cycle and the auto decomp will prevent the lever from harshly kicking back at you by lifting an exhaust valve if the engine rotates backwards. Kicking from TDC or just past it will give you the best chance of starting your bike and you don't have to use the manual decomp lever if you don't want to, but it makes the job easier. The auto decomp mechanism was a source of problems for my bike, so I removed it, but it generaly functions pretty well.

[BWB63]

I removed the stock perch and went with the CR perch. The stock perch is not a cheap replacement like a $6 CR perch. I hold the thottle wide open to start after a spill and others hold the decopression lever in and cycle the bike several times to help clear the extra fuel.

[wickedsprint]

So does the auto decomp actually do anything when the engine is rotating the correct way during a start attempt, or is it only for kickback. Does it work the same way as the one on my old XT350 did..I could start that engine with my hand.

[qadsan]

So does the auto decomp actually do anything when the engine is rotating the correct way during a start attempt, or is it only for kickback.

It doesn't do anything when the engine is rotating correctly once the engine is running, but it does aid in the starting process and prevents the kick start lever from harshly kicking back by lifting an exhaust valve if the engine rotates backwards.

[smashinz2002]

The auto-decompressor mainly keeps the engine from kicking back on you. I have found it useless for starting, since I prefer to use the standard drill utilizing the lever.

I don't like auto anything, so I have never tried to start the bike with the auto-decompressor. In fact, I have no idea how to do that. I'm so used to the old 4-stroke starting drill, that I just use the lever every time. Sometimes, however, you may notice that the auto-decompressor makes it to where you can't get it to come up on compression for several kick throughs, which is annoying. I have plans of removing the auto device. Otherwise, the bike is awesome and it freakin' rips!!!!

L.L.

[wickedsprint]

So it does release passively when slow kicking? Is the starting technique the same? Or doy ou still find yourselves going to tdc and popping the release, moving it over tdc then doing a full through kick?

[qadsan]

I don't have the auto decomp mechanism on my camshaft anymore, so I have to bring it to TDC, pull the decomp lever, move the kick start lever just pas TDC, release the decomp lever and kick...vaarooom! I'm from the old school like smashinz2002 and have always done it this way on big bore four strokes whether the bike has an auto decomp mechanism or not.

[wickedsprint]

I want to remove the auto decomp, one of the nice members posted about something ont he cam you need to plug..or just get an aftermarket cam..seems easy enough. I would much rather have it removed.

[qadsan]

If it's working fine, you may want to leave it alone, but here's a quick post I wrote that has more info on this topic.

https://www.thumpertalk.com/forum/showflat.php?Cat=0&Board=UBB9&Number=1236051&Forum=UBB9&Words=decomp%20cam&Match=And&Searchpage=0&Limit=25&Old=1month&Main=1235861&Search=true#Post1236051

[frogman]

Another great thing about the lever is you can pull it in and bump start the Pig on a downhill.

Pull in the clutch and de-comp lever, get rolling and let out the clutch and bump out the decomp and your running.

[Mikie1]

Hmmm... mine makes kind of a loud "ticking" noise (like a bad lifter) at about mid rpm's, & I can feel a pretty hard pulse in the manual decomp. cable. The cable got pinched really bad between the stabilizer tower & triple clamp- got another cable on order- but it seems to still be working ok.

The bike starts really easy (Edelbrock carb) & runs so good I'm hesitant to remove it. Maybe it just needs an adjustment or the cable is sticking a little bit. I did a quick search for "cable routing" but couldn't find anything... anybody come up with a good solution?