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General Category >> Rubber Side Down! >> Intermittent throttle response and backfire
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Message started by shugarsca on 09/24/12 at 03:54:05

Title: Intermittent throttle response and backfire
Post by shugarsca on 09/24/12 at 03:54:05

Hey guys I'm riding... well was riding an 87' Savage that I bought about a year ago. I live at a high elevation about a 5500ft, and the bike was burning really rich as evident by really low mpg (about 30-35), a lot of carbon build up on the plug(s), and the stock air filter reeks of gas.
I also read somewhere on here that the mixture on old savages was pretty rich from the factory. I'm not sure if previous owners ever did any adjustments on the carb. Anyway I'm new to working on engines, so after reading many posts (apparently not enough) I decided I would take out the stock air intake box and install a K&N air filter. This install went really smooth and she ran great! for about an hr. I ran the gas tank down lower than normal stopped filled up with premium started back on the road and within about 5min I started getting no throttle response. The bike would hesitate and lunge forward like its wanting to stall out. It does this for about 30secs then seems to level off then starts right back. Every once in a while it will build up and backfire through the muffler.

I put a new spark plug in when I added the K&N filter, so I pulled the plug and it actually looks better than it ever has its light tan in color. I put another plug in and I'm getting the same problem. I replaced the in line fuel filter thinking that maybe it could be impeding the flow of gas if there was any sort of sediment, but that also did not help. Ive ran sea foam through the carb also no luck. I have a buddy that said maybe the coil was going back and I'm getting extra gas in the cylinder??? If thats the case can someone point me in the right direction for a new one? Or do I need to rejet the carb even though the plug looks good?

Sorry for the long post, but background information always helps.
Thanks in advance!

Title: Re: Intermittent throttle response and backfire
Post by Oldfeller on 09/24/12 at 05:02:09

3B3B28353429322F3D3B28295A0 wrote:

We have lots of experience with your issue, which fits the symptoms of a vac petcock going bad starving your motorcycle for fuel while running while also leaking some fuel down the vacuum line which dribbles down to the air box (the reeking you mentioned).

First question -- do you still have the stock vacuum actuated petcock on your motorcycle?

If so, please perform this test and tell us the results after running the bike in prime (follow the arrow cast into the lever to find prime please) while the vac line is blocked with a golf tee and the vac nipple on the carb is capped off.

go here for the test http://suzukisavage.com/cgi-bin/YaBB.pl?num=1251932429/0

Title: Re: Intermittent throttle response and backfire
Post by Gyrobob on 09/24/12 at 05:40:58

OF, how many times have you explained this issue to individuals posting about this problem here? I would think you'd have a canned response in an MSWord file that you could just copy/paste as necessary.

Title: Re: Intermittent throttle response and backfire
Post by RidgeRunner13 on 09/24/12 at 06:22:33

You forgot to mention the problems the cone type air filters may cause, that premium may cause issues from sitting in the storage tanks, & there could be water in the tank. Anytime mine suddenly runs crappy after a fill up, I drain the carb bowl into an old glass & check for water. 8-)

Title: Re: Intermittent throttle response and backfire
Post by Gyrobob on 09/24/12 at 06:47:13

"premium may cause issues" says Ridgerunner.

It might,.. but the main question is why would anyone want to use premium in a motor designed for 87 octane?

Title: Re: Intermittent throttle response and backfire
Post by justin_o_guy2 on 09/24/12 at 06:52:21

Premium? Why? Its just a big old lawnmower engine,,

Title: Re: Intermittent throttle response and backfire
Post by Charon on 09/24/12 at 06:54:13

"Ive ran sea foam through the carb also no luck."

My Heavens! A problem Seafoam didn't cure? Unbelieveable.

Title: Re: Intermittent throttle response and backfire
Post by RidgeRunner13 on 09/24/12 at 06:58:41

I didn't say you SHOULD use it!! But good premium gas WON'T cause the problems the op described. ;D

The only thing that gets "special" gas at my house is a 2.3l race engine that has the head shaved .110, & premiun won't cut it. It gets VP 110 octane race fuel. 8-)

Title: Re: Intermittent throttle response and backfire
Post by justin_o_guy2 on 09/24/12 at 07:24:51

If I put gas in somethjing & it starts running bad ( & I have run w/o the fuel line to the carb, it will run a few minutes) I first suspect the gas. Id dump the tank into a gas can, drain the bowl, put a gallon of fresh Refular in it & see what happens/

Title: Re: Intermittent throttle response and backfire
Post by verslagen1 on 09/24/12 at 08:19:46

From the members running at high altitue, I would recommend the stock jets for a '96 or later, 145 & 52.5, a 155 is definitely too rich.

The leaner jets should clear up the rich issue.

Did you use the K&N drop in or pod filter?

A wet filter will choke the air.

Title: Re: Intermittent throttle response and backfire
Post by Oldfeller on 09/24/12 at 08:40:04

1729223F323F32500 wrote:

Serowbot wrote it and I added to it -- it lives in the Tech Section.

However, each new person deserves to feel like we pay individual attention to their issues as stated, so everyone gets a personalized lead in to the Serowbot Test.

What amazes me is how very few times I have been WRONG on calling the shot -- you can't be right that often by pure chance or by luck. Serowbot's Test is very definative and useful.

Next, I am also amazed at seven (7) posts from different helper people suggesting all sorts of "stuff" before the new person has even completed the Serobot's Test (which cuts the world of problems in half and always is the VERY FIRST THING we ask a new person with fuel system issues to do).

You don't even theorize bad gas until the Serowbot's Test is done. No other alternate nothings until the Serowbot's Test is done. Let the new person focus on getting the test done.

You certainly don't overload the new person with "aging premium gas" or any of the rest of it until you know what the Serowbot's Test results are.

You are wasting the new person's time and attention with something that you are gonna shift away from just as soon as you hear the results of Serowbot's Test (no matter which way the results go, over half of these suggestions will instantly become invalid).

Just wait for the new person to come back on the Serowbot's Test .....

Title: Re: Intermittent throttle response and backfire
Post by justin_o_guy2 on 09/24/12 at 09:32:59

This install went really smooth and she ran great! for about an hr. I ran the gas tank down lower than normal stopped filled up with premium started back on the road and within about 5min I started getting no throttle response. The bike would hesitate and lunge forward like its wanting to stall out. It does this for about 30secs then seems to level off then starts right back. Every once in a while it will build up and backfire through the muffler.

I still think that sounds like bad gas. Its so easy to find out. I would start there.

Title: Re: Intermittent throttle response and backfire
Post by Gyrobob on 09/24/12 at 09:54:01

JOG said, "I still think that sounds like bad gas. Its so easy to find out. I would start there. "

Good point. It's always a good idea to check the easy stuff first,.. before you start tearing things apart, buying parts, doing damage, etc.

Title: Re: Intermittent throttle response and backfire
Post by Digger on 09/26/12 at 19:40:51

4A594E4F505D5B59520D3C0 wrote:

FWIW, I live at =6500' ASL. The jetting in my bike (see signature block) is stock. The bike runs great up here....averages over 56 mpg in urban riding.