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Message started by maxbowersox on 09/21/15 at 18:41:39

Title: Timing advance and backfiring
Post by maxbowersox on 09/21/15 at 18:41:39

Does anyone know if advancing the timing a few degrees helps with the back firing? Before anyone asks, here is what I have done so far.

So far I have done the following:
-Installed a Screaming eagle2 exhaust, from the head pipe back. I have also slotted some of the holes in the baffle, It still makes decent back pressure but has a good flow at WOT

- Opened up the stock airbox a good bit and installed K&N filter

- 155 main jet, 52.5 pilot jet, removed spacer on needle and added 2 washers, mixture screw worked best for me at about 1.75 turns out.

Bike runs great, but back fires, Loud now with exhaust on it. Seems to back fire a little less if I keep the idle up, but i don't want to ride like that all the time. SO, I was wondering if anyone has advanced their timing and did it help with back firing? Also, does anyone know of an aftermarket ignition module, maybe with programable advance curves? I put one on my sportster and it made a huge difference.

Thans for any help.

Title: Re: Timing advance and backfiring
Post by Dave on 09/21/15 at 19:25:43

The backfire is not a timing issue, it is a fuel mixture issue. When you close the throttle, the fuel circuits are closed, and the mixture goes so lean that the spark plug cannot ignite the mixture. When that mixture enters the hot exhaust system and the temperature of the mixture rises, it can ignite in the exhaust system.

You can learn to ride so that you don't create the conditions that cause the backfire. Don't let the throttle close completely when you shift, and when you slow down.....just keep the throttle open enough to stop the backfire - but not enough that you are accelerating.

Your jetting is already on the rich side.....no jetting change is going to make the bike stop backfiring when the throttle is closed and you have created a high vacuum in the engine intake......the main jet and tapered needle do not flow fuel when the throttle is closed (the pilot jet is flowing enough fuel for the engine at idle - but cannot flow enough fuel to an engine that is revving with a closed throttle).

Title: Re: Timing advance and backfiring
Post by verslagen1 on 09/21/15 at 20:31:35

2A32323D23612B590 wrote:

[quote author=7C42434F5D41402E0 link=1385903883/0#11 date=1386093533]
Quote:

I am building a custom bike with a Savage engine - I think it's an early engine , the serial number is P401-106734. I wired it all up, and had it running . I now have the tank etc all fitted, so I tried it again - but this time, NO spark. It has a new coil and a new ECU. I have an idea what might have gone wrong, perhaps a loose connection - but when wiring up, I wired a lead from the ignitor to the starter solenoid as shown in the diagrams, BUT it only started while the starter motor ran! so I wired that lead to another power source and it ran OK. But I don't like the idea that I have in reality not wired it right, and now it won't go. I intend to re-wire the whole ignition now. I tested the coil, it is OK, so now I will try to test the ignitor.

Keith,

I just went back and reread the above from one of your earlier posts. I'm having second thoughts about your pickup coil despite the fact that it apparently tested OK.

Has the bike ever run except when you had power to that lead between the igniter and the starter solenoid ? It looks to me like that wire supplies the signal to the igniter while the engine is cranking and then is disconnected as soon as the solenoid disengages. At that point the signal comes from the pickup coil to switch the transistor in the igniter on and off.

You said this is a custom build. Does that mean you are not working with a stock wiring harness ?

I found this in the tech section:

http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1173898705

May be some help if you are wiring the bike from scratch.

yes, I only could get it to run with the wire full time live - BUT when done the right way , it DID fire up, only when the starter was running! It is a custom build, all non ignition I have done from a similar diagram, except I have no decompressor. The rest of the wiring works OK - it's done with a Zenith brainbox , really easy. I am ready to give up and call a travelling electrician to sort it.[/quote]

1429252D2F28190C292E28460 wrote:

Finally got done with the Magneto and ignition pickup remove and replace! Started up and ran fine after putting juice in the battery and charging it for 30 minutes. Looked to be bone dry on gas too, that always helps them run, so I got my mower gas can and filled up for a little test ride in the rain. Took a few pictures under the carport when I got home:

http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/99_savage/P4130007.JPG

http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/99_savage/P4130008.JPG

A whole file full of pictures if anyone is interested:

http://www.catoosatrading.com/images/vehicles/cycles/my_ls650/99_savage/

The bike ran out really well. At least as good as the old '87 with only 6.5k miles, and this one has 27k on the OD.

Kid (err young man) I got it from said the he "had the head done" whatever that meant to him and his mechanic. I'm hoping maybe they made sure the cam chain was in good order when they did that, but I'll check it soon just to make sure.

Lots of misc. notes:

First, the spots on the driveway are NOT leaks from this bike. Some are from my wife's car, but most is water from my having just returned from a ride in the rain. After riding it hard for 10-15 minutes, and letting it sit for 30, I didn't notice a single oil drip (yet).

Yes, those forks are 4" over, and ~no~ the frame rake (steering head angle) wasn't changed from factory 35º.
However, the rear shocks seem to have been shortened by about an inch. By measuring with a level / plum and a carpenter's roof rise gauge (angle), and by mathmatic calculation, I've arrived at a new rake of 39º-40º and a trail figure of between 6.5"-7" (under 7" for certain).

Anything over 40º rake is considered "extreme" and street bike trail is normally between 4" and 6"... So... by the math, this setup is pushing practicle limits, but it felt real good to me on my little 8-10 mile ride. No mountain twisties (yet) due to rain, just street corners and straightaways. Slow speed handling was really good too, considering the frame geometry. That is with the exception of having to zig-zag back and forth about 10 times in the driveway to turn it around. :-/

I think the five-speed gearbox is probably worthwile

Several small knit-picks: The 23" drag bars are WAY too narrow, and combined with the short stem mirrors, you don't get much of a rear view. Think I'll try my 26" flat drag bars on the super tall straight risers already on there first. Hope all the wires and cables will reach another 1-1/2" per side. If that doesn't work, it will just give me an excuse to try one of the pairs of Z-Bars I've been saving. And those really thick leather grip wraps? Those gotta go. The clutch cable needs adjusting.

Thinking I'll put the big loud turnout on this bike. But the short sportster muffler is louder than the too-quiet Dyna on my '87. I might put the Sporty muff on the '87.

Then there's the custom headlight and o-ring pegs still in the boxs; which have had to wait on the electrical repair. So many toys... so little time 8)

Title: Re: Timing advance and backfiring
Post by maxbowersox on 09/22/15 at 02:11:32

Dave, thanks for answering my original question. I suspected as much, since it back fired less with the idle set high. But I guess I should have had two different posts, would also like to hear from anyone who has slotted the stock pickup sensor and advanced their timing. Was it worth it, did it work? Also are there any aftermarket ignitions available?