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Persistent left cylinder misfire


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9 minutes ago, footgoose said:

just a little note here.... the XS will perform better with the earlier 38mm carbs. The ones from the '75 model are set up the best imo

Interesting, I know the bs34s are hard to get right. That's why I went with modern CVKs from a Kawasaki Ninja, modern carbs feel leaps and bounds ahead of the originals.

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Oh, bugger. It's idling over 1000 on the tacho, haven't checked in GuzziDiag. Might have to go over this again.... Have I invented a new procedure, BTW? 😉   Thanks for all your help.

Do it now while they can't come over . . .  

Hi Grim, I know I'm late to the party but FWIW my '02 Scura would backfire then spit off the RH inlet rubber after 100 miles. Replaced the inlet rubber & issue resolved, even found the low fu

Gotta love it when an OP drifts his own thread just to recover some perspective. ;)

We're not giving up on your left cylinder, Grim!  :luigi:  :nerd:  :drink:

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Thanks for believing in me (or at least my left cylinder)

Positive steps.. I'm going to check compression tomorrow.

I'm going to try resetting the throttle plates and get them aligned somehow....

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6 minutes ago, Grim said:

Thanks for believing in me.

Positive steps.. I'm going to check compression tomorrow.

I'm going to try resetting the throttle plates and get them aligned somehow....

I had been thinking how important it is to make sure the high idle mechanism is not fouling the throttle stop.  And that the fussy right side idle stop screw did not interfere with your TPS baseline . . .

Compression test (or even a leak-down test) will set some heavy concerns aside.

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1 minute ago, docc said:

I had been thinking how important it is to make sure the high idle mechanism is not fouling the throttle stop.  And that the fussy right side idle stop screw did not interfere with your TPS baseline . . .

Compression test (or even a leak-down test) will set some heavy concerns aside.

The high idle follower was flapping in the breeze, and the right throttle stop was way out (someone had been here before and was only using the left for idle) it initially read 84mv. When I got 157mv the butterfly was sticking in the bore. I feel I definitely got that bit right.

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I'm gonna reach sideways here and ask what relays (make/model) are in the last two positions (at the back)?

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That may be an opportunity. The Panasonic are good relays, but are under-rated for the fifth position (fuel injection/ignition), especially.

True High Current (micro) Relays have become hard to come by, but worth sourcing.

As a minimum, swap your middle relay (Neutral Switch Relay) with the fifth (FI/Ignition) and repeat your hand-flapper test . . .

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5 minutes ago, docc said:

That may be an opportunity. The Panasonic are good relays, but are under-rated for the fifth position (fuel injection/ignition), especially.

True High Current (micro) Relays have become hard to come by, but worth sourcing.

As a minimum, swap your middle relay (Neutral Switch Relay) with the fifth (FI/Ignition) and repeat your hand-flapper test . . .

Thanks, I've tried to find Omrons to no avail. I actually bought the set of Panasonic's and replaced all 5.....

I still have the old Siemens and Tyco mix in a bag, not sure which ones you would recommend?

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Your Panasonic are the best of your mix. So sorry that the true High Current OMRON are NLA. They are amazing in this application.

So, I also have pondered how your exhaust system is groomed and sealed.  Asymmetry, and even small leaks could affect your Flapper Test. Even without materially reducing any performance.  Can you ride it and get a feel for its real world performance?

 

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Maybe it was the other forum, but I recall some long threads about one cylinder misfires that were maddening. It was Tonti bikes, but perhaps the same applies here.
On my '85 LeMans, I had a weak cylinder- don't recall left or right but to make the long story short, the positive feed to the coils came in on one terminal, then there was a short jumper wire from there to the second coil. A significant number of bikes had that jumper fail, which killed the secondary one. A simple replacement of the jumper wire fixed the problem, but it was a bitch to discover. If your coils are set up this way, a simple measure of resistance in the jumper wire might tell the story and make for a simple fix.

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13 hours ago, docc said:

That may be an opportunity. The Panasonic are good relays, but are under-rated for the fifth position (fuel injection/ignition), especially.

True High Current (micro) Relays have become hard to come by, but worth sourcing.

As a minimum, swap your middle relay (Neutral Switch Relay) with the fifth (FI/Ignition) and repeat your hand-flapper test . . .

docc, going off topic for a second

Just asking a question, why are the Panasonic underated?

I haven't when through the whole spec, but providing the Panasonic are the sealed type, which look like the type Grim has, both relays are rated for the same same loads 35A NO 20A NC

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Sorry to barge back in Weegie.

I got about 135psi cold on each, but could only rattle off about 5 cranks on the battery before it slowed. Also, this was a universal rubber tip compression test, not a screw in.

You just hold it on with your third hand!

Main thing is, both sides exactly the same. 

So onto the next thing....

 

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1 hour ago, Weegie said:

docc, going off topic for a second

Just asking a question, why are the Panasonic underated?

I haven't when through the whole spec, but providing the Panasonic are the sealed type, which look like the type Grim has, both relays are rated for the same same loads 35A NO 20A NC

@WeegieYeah, we could take this back over to the (lengthy) Bet Relay thread, but in short the NO contact of most micro relays (Panasonic included) is 20 amps. The NO contact on our #5 carries the injectors, coils, and fuel pump coming in at some 22.5 amps. Check how hot yours gets as an indication how well it's working.

@Grim  Those compression numbers seem fine. Certainly symmetrical. If your battery went flat that quickly, perhaps getting it well conditioned and swapping the relays (3<->5) is worth the small fuss. Otherwise, I still ponder about grooming your exhaust, getting all lined up and fully seated at every joint. The last time I had to set my air screws very much differently, I found the intake vacuum taps had loosed up enough to cause trouble.

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