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Message started by denistheruski on 11/14/12 at 08:06:18

Title: Still searching for source of jerkiness
Post by denistheruski on 11/14/12 at 08:06:18

So my bike is still being "jerky" when I give it low-mid throttle and also under deceleration (engine braking). I'm currently riding in Serowbot's petcock "test mode" (I think that's what you call it) where I've pulled the vac line off the carb, capped the vac port and the hose (with a golf tee), and set the petcock to Prime. I've only been riding like this for a few days, so I'll give it at least 2 tank fulls before I make the final call on whether this problem is caused by my petcock.

One thing I noticed the other day is that if I ride with the choke out, the jerkiness goes away (almost completely). But with the choke in, the bike becomes jerky again. I think what I mean by jerking is "lurching" but I'm not 100% sure what lurching is.

Anyway, does the fact that the problem improves with the choke out point to any possible issues that I should look at next?

Title: Re: Still searching for source of jerkiness
Post by Dave on 11/14/12 at 08:29:34

I am not familiar with what you have done to your bike, what you have tried, or any history.

The symptoms you have described tell me the engine is running lean just off throttle. Mine did this until I removed one additional washer from the top of the needle. I originally did the mod where you removed the white spacer and put in the 3 washers - and my bike had a bit of the "surging" just off idle. I tried larger main and pilot jets and it did not help reduce the surging. When I removed one washer and only ran 2 washers the surging problem went away and the bike became smooth - but it became too rich elsewhere and I ended up with a 150 main and 50 pilot. I also dropped my float level to 29mm from the bowl gasket surface which is the minum level (27-29mm recommended).

Title: Re: Still searching for source of jerkiness
Post by denistheruski on 11/14/12 at 08:37:30

Dave, you're right, I didn't really give any details about the bike. It's a 2005 Savage which is bone stock. I've changed the oil, replaced the air filter and I'm doing the Serowbot petcock test right now. Other than that, I haven't done anything.

As for history, before I reconfigured my petcock, it would always need choke when starting, even on very warm (over 90 deg) days. This surprised me. Once started, if I put the choke in too soon (with the petcock set to "on" not "prime"), it would die. Lot's of moving parts so I started with the petcock, knowing that many have issues with it. Additionally, it almost stalled on me at a red light a few weeks back. This was after having ridden for ~15 min at highway speeds so the engine was warm.

I haven't heard of removing washers from the top of the needle. Are you referring to the float needle? What does this mod do, exactly?

Title: Re: Still searching for source of jerkiness
Post by Dave on 11/14/12 at 08:47:14

It sounds to me like you need to do a carb cleaning - combined with the brass plug removal and needle washer mod.

The idle mixture screw that is behind the brass plug controls the idle fuel/air mixture. The Pilot Jet controls thei mixture from about 1/8th to 1/4 throttle, the slide needle controls mixture from about 1/4 throttle to 3/4 throttle (my experience shows it to come in sooner), and the main jet from 3/4 to full throttle. Your bike sounds like it is running too lean from idle to 1/4 throttle.

Here is a link to the suggested carb mods - you can use the search feature in the Technical Section to read more.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1309246277

Title: Re: Still searching for source of jerkiness
Post by justin_o_guy2 on 11/14/12 at 09:05:34

Once the source of Jerkiness is located & the solution found, it needs to applied to Many, & mankind will be much improved.

Title: Re: Still searching for source of jerkiness
Post by Serowbot on 11/14/12 at 09:08:14

What Dave said,... plus, one question,.. How low is your idle?...
Got that lumpy thing going on?...
I ask because you mention "on decel" as well...
:-?...

Title: Re: Still searching for source of jerkiness
Post by denistheruski on 11/14/12 at 10:04:04

I can't give you my idle number in RPMs because I've never hooked up a tach. But when I first got the bike, I was afraid it was a bit low so I adjusted it to be higher. I *believe* it's on the high side, but I can't say for sure.

Title: Re: Still searching for source of jerkiness
Post by ToesNose on 11/14/12 at 10:35:40

+1 to Dave's suggestion of a cleaning, that was the first thing that popped into my head after reading your description. Ethanol really helps to gum up a carb when fuel is left in it, especially for a period of time like over the winter.

Title: Re: Still searching for source of jerkiness
Post by denistheruski on 11/16/12 at 08:41:05

Thanks for the suggestions. I'm still a noob, so just for my own knowledge/curiosity ... let's say the pilot jet is a bit gummed up in my carb. Why would I experience less jerkiness if (1) the choke is opened up and (2) as the bike warms up? This is what I'm seeing and, in my simple view of things, I would thing that if the jet is gummed up, it would continue to cause jerkiness regardless of the choke position or as the bike gets warm. Any theories?

Title: Re: Still searching for source of jerkiness
Post by Serowbot on 11/16/12 at 09:33:25

Engines need a richer mix at start-up... that's why we have choke/enrichment valves... and that's why the problem is showing up more when cold...
Once the engine is warm it can run on a leaner mix...
With a partial blockage in the pilot,.. the enrichment is compensating...
... but the fix,.. is cleaning...

Title: Re: Still searching for source of jerkiness
Post by Oldfeller on 11/16/12 at 09:46:31

2B343235282F1E2E1E26343873410 wrote:

Once the source of Jerkiness is located & the solution found, it needs to applied to Many, & mankind will be much improved.

:D

Yep, Justin is correct. Bad gas, bad plastic float assembly, it makes no difference --- once you find the source of the Jerkiness you have to eradicate it.

Title: Re: Still searching for source of jerkiness
Post by ToesNose on 11/16/12 at 15:13:52

Also Denis if you plan on leaving the bike idle for any period of time like over the winter don't forget to turn the petcock off, run all the gas out of the carb and add fuel stablizer to the tank ;)

Title: Re: Still searching for source of jerkiness
Post by denistheruski on 11/17/12 at 11:23:18

Sounds good, Toes. Good to know. I'm in Austin, TX, so the weather is still great for riding here - just gotta layer up. Hopefully the bike won't sit for long.