Low Idle After Revving Engine

[Guest]

I have just installed a Dyna S DS3-1 onto my 550 last night. All seems Ok except when the engine is revved to 4 or 5 grand the idle drops to about 800rpm and sounds like it is about to stall. It then increases in idle speed up to the normal speed of 1100 or 1200 rpm. I have not ridden it on the road yet after installing the Dyna S so it might not happen under riding conditions.

I have timed the engine with an xenon timing light. The idle and advance marks line up correctly as they are supposed to do, etc. at appropriate rpm.

Any ideas what the problem is?

[Flaming Chainsaws]

Did you let the bike warm up completely? Same thing happened with my GS450 and that was the problem.

[Suzuki_Don]

Did you let the bike warm up completely? Same thing happened with my GS450 and that was the problem.

Thanx Flamin', logical suggestion I guess. The engine was warmish, but not really fully warmed up as I was doing this in the shed after fitting the Dyna S. The engine took a while to start as well after fitting the electronics, actually had a momentary thought it was not going to start and then it immediately burst into life.

Just had another thought that maybe the idle is a bit lean and that is why the idle speed rises after closing the throttle. Maybe some more fiddling with the mixture screws is required. We'll see.

I have a ride tomorrow of a couple of hundred kms so I'll see if that settles things down a bit. Our winter here and they predicted 23C deg for tomorrow (that's 74Fdeg) so that should be OK for riding.

[Nessism]

Don,
Make sure the rotor doesn't bind up the advance unit. Twist the rotor with your hand and then let go to make sure it snaps back.

[Flaming Chainsaws]

Wow! Winter is 74*F? You guys can ride year round!

[Suzuki_Don]

Don,
Make sure the rotor doesn't bind up the advance unit. Twist the rotor with your hand and then let go to make sure it snaps back.

Everything is OK there Ed. I actually turned the large crankshaft nut clockwise until the advance mark on the advance unit lined up with the index mark, turned the ignition on and rotated the rotor by hand to get the continuity light to come on and it does snap back with no issues. I had read somewhere where it could bind once torqued down - so checked that out early in the piece. I also gave the advance unit the once over when it was off, cleaned it up with fine wet & dry (800) and oiled the shaft and bushing with light oil before putting it back together with fresh springs after modifying the advance curve a bit for my application.

I will see how it performs tomorrow on the road run. Although I will give it a quick run this afternoon when I get home from work to make sure there are no nasty little surprises for me on the run tomorrow. Nothing worse than being 3 or 4 mile down the road from home and find that something is not as it should be.

Thanks Ed.

[trippivot]

too rich

when revving the engine a well jetted engine will rev and fall to the set idle quickly. Vroom,Vroom,purrr.. quickly. Recovering from a rev will tell you how the needle and pilot jet circuits are balanced to a specific tune


the rev hangs up at a high rpm and dosen't recover to set idle immediately== too lean


the rev falls below the set idle and then recovers (or dies) back up to the set idle == too rich.

not a perfect science but it is the first step to understanding "engineese" which is the language your bike speaks. it will tell you when it needs attention- if you listen

[Suzuki_Don]

when revving the engine a well jetted engine will rev and fall to the set idle quickly. Vroom,Vroom,purrr.. quickly. Recovering from a rev will tell you how the needle and pilot jet circuits are balanced to a specific tune


the rev hangs up at a high rpm and dosen't recover to set idle immediately== too lean


the rev falls below the set idle and then recovers (or dies) back up to the set idle == too rich.

not a perfect science but it is the first step to understanding "engineese" which is the language your bike speaks. it will tell you when it needs attention- if you listen

Thanks. Valuable info. Then it seems mine is a bit rich.

Does this science tell us what part of the circuit is too rich. Pilot (mixture screws) or needles, etc.

Any help would be appreciated.

Thanks.