Bump start 426 with Decomp?

10 replies to this topic
  • LBZYZ426

Posted June 03, 2004 - 06:00 AM


Those of you with a 426 and decompression lever. Whats the best technique to use when rolling down an hill in order to bump start?

Might be a silly question but I have never attempted it due to fear screwing up valves.

Yes I know about the 450 cam mod :thumbsup:

  • Vibeguy

Posted June 03, 2004 - 06:17 AM


I never used the decomp lever (when I had it) get it going down hill in neutral, pull in the clutch 2nd gear then dump the clutch, even then it can be a *****. The 03 e-cam is the way to go!

  • Stumpy

Posted June 03, 2004 - 08:14 AM


If I stalled and was still rolling, I just pulled the decomp to bump it past tdc and it usually fired right off. It got to be second nature after a while.

  • DrThumper

Posted June 03, 2004 - 09:27 AM


I do it like Stumpy...it becomes second nature. A lot of times I don't actually bump it, I kick it over when rolling.

  • LBZYZ426

Posted June 03, 2004 - 09:51 AM


DrThumper- Thats what I've always done.

Stumpy- I'll give that a shot this weekend. That doesn't harm anything by doing it that way???

Thanks guys :thumbsup:

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  • skthom2320

Posted June 03, 2004 - 01:27 PM


I pull in the decomp lever to bump start it too...

  • grayracer513

Posted June 03, 2004 - 02:55 PM


Like they said...

Pull the clutch, pull the decomp lever, shift 2nd or higher, and let the ckutch out as it rolls. You'll hear the compression being released through the exhaust system. After the engine is turning (2-4 cycles)ease off the release and it should pop off pretty happily.

's what we all did way back in the day.

Rememeber, the comp release holds one of the exhaust valves off its seat, so it's "less than cool" to go yanking on the thing at any speed above idle.

  • LBZYZ426

Posted June 03, 2004 - 04:27 PM


Grayracer513- "Rememeber, the comp release holds one of the exhaust valves off its seat, so it's "less than cool" to go yanking on the thing at any speed above idle."

Thats what I was looking for, thanks :thumbsup:

Now I'll only bump start it when I'm good and pissed :awww:

  • holeshot426

Posted June 04, 2004 - 08:55 AM


Before the 450 cam, I always used to bump start with a little pull on the decomp. lever. Hell with my old XL 600 I used to use it as a jake brake... never &%$#@!ed anything up then or now.... btw the new cam feels like I have a new bike...

  • Fastest1

Posted June 04, 2004 - 03:22 PM


Great avatar! :thumbsup:

  • grayracer513

Posted June 04, 2004 - 07:00 PM


You don't need to be afraid to use it to bump start the engine, in fact, back in the day, the decomp was often used as a kill switch, but only at an idle.

When you realize what it does (lift an exhaust valve), you can understand that it will temporarily increase your valve clearance from 0.2mm to over 1mm. Fool around with that at higher speeds, and it's pretty much like banging on your cam with a hammer.

Besides, the decomp in a four stroke will not produce the braking effect that top cylinder releases do in two cycle engines (diesels included). The internal dynamics of the two are entirely different.

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