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General Category >> Rubber Side Down! >> Bucking / missing at 65 mph
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Message started by 49mack on 03/06/14 at 12:41:02

Title: Bucking / missing at 65 mph
Post by 49mack on 03/06/14 at 12:41:02

Help! I bought a decent 1996 Savage, 19,ooo miles. I had a problem when hitting about 60 mph. The bike bucks and snorts like it is running out of fuel. Here's what I've done: adjusted the valves, cleaned the tank and fuel lines, checked and gapped the plug (running a nice tan color), changed the air filter, removed the carb and installed a new float needle seat and float bowl gasket. It improved slightly - the bucking does not start until I hit 65 mph and also backfires when downshifting. I am at my wits end! One other question. . . there is a small line the same size as the line that connects under the gas tank. It seems to go nowhere. I don't believe it is a battery overflow. Any advice, please? I am retired and don't want to drop a wad at the nearest dealer, 45 miles distant. Any and all advice is gratefully appreciated. Thanks!

Title: Re: Bucking / missing at 65 mph
Post by LarryP on 03/06/14 at 12:50:42

Mack, I noticed that you did not say anything about cleaning the carb, re jets , passages. Perhaps ? Hope some of the other guys will weigh in with valuable advice. Larry

Title: Re: Bucking / missing at 65 mph
Post by HondaLavis on 03/06/14 at 13:27:04

Our petc0ck - the fuel valve under your gas tank - is vacuum operated. If you have a small vacuum leak it may be starving your engine and not providing enough fuel. Perform Serowbot's petcock test, found here: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1251932429/1

You are not alone, it's a pretty common problem. If you determine that to be your problem, simply purchase a genuine YAMAHA Raptor 660 petcock. Do a little research, the part number can be found variously throughout this site ;)

Title: Re: Bucking / missing at 65 mph
Post by verslagen1 on 03/06/14 at 13:34:03

This identifies the carb hookups...

http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1098869040

Title: Re: Bucking / missing at 65 mph
Post by old_rider on 03/07/14 at 05:13:06

Mack... I did the white washer needle valve mod and adjusted the air/fuel ratio on my wife's LS650 and the bucking has settled into a mild surging and the backfire on shutdown went away, still backfires a bit on hard downshift , wife never gets it past 60 so she doesn't feel it.
I'll be watching this thread to see if you solve it completely... oh and I also changed that vacuum petc0ck out.
Does that small line come off of your carb? or tank? sounds like an overflow.

Title: Re: Bucking / missing at 65 mph
Post by 49mack on 03/07/14 at 10:46:57

I did not rejet. I did let the carb soak / sprayed passages in carb cleaner for four days. This morning I tried the vacuum line bypass test with no success. I am thinking my next move should be a COMPLETE carb rebuild and the Rapptor fuel valve. Any additional comments are appreciated. Thanks!

Title: Re: Bucking / missing at 65 mph
Post by bobert_FSO on 03/07/14 at 11:25:41

Before tearing the carb apart, I would try a Raptor petcock, or at least run on PRIME. My stock petcock developed a stiff diaphram and would not open the petcock under low vacuum conditions. This manifested itself under high speed/high load conditions like attempting to drive 65mph into a 20mph headwind. My bike would act like it ran out of gas. It would stumble a few beats and then actually quit. Switching to PRIME while coasting down would allow the engine to start firing again.

Under run-around-town conditions I never experienced a problem.

Title: Re: Bucking / missing at 65 mph
Post by 49mack on 03/07/14 at 11:35:49

Gents, many thanks for replies. I just ordered a Raptor petcock even though the bypass was not successful. The stock petcock seeps a tiny bit anyway. A new one will be good. But cannot find a source for a complete rebuild kit for the Mikuni BS40SS. Any advice?

Title: Re: Bucking / missing at 65 mph
Post by 49mack on 03/07/14 at 11:37:01

Old Rider, what is the white washer repair or mod? Thanks!

Title: Re: Bucking / missing at 65 mph
Post by Arnold on 03/07/14 at 12:29:11

Also make sure the gas tank cap is properly vented.

Title: Re: Bucking / missing at 65 mph
Post by old_rider on 03/07/14 at 12:31:06

Here ya go... follow this post to do the mod...

http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1104205157

Title: Carb woes and fixes
Post by 49mack on 07/19/14 at 14:26:21

I'd posted about my Savage spitting and coughing at 60 mph and got some advice. Seems the main fix was to upgrade main jet size from 145 to 155. In being highly frustrated getting the float bowl off, I determined to make it easier. Replace your float bowl screws with socket head (Allen) screws from Home Depot. 5mmx12mm, SKU # 387480032789. The best tool is a flex shaft reversible screwdriver. Mine is made by Allied. The flex shaft allows you to get the bit into position and install / remove them. Getting the cheap tin can screws out was a headache. Putting in the new Allen heads was a breeze. I can change jets in 10-15 minutes. Oh, by the way, thanks to the rider who advised cutting one full circle of spring off the reversionary valve assembly. Magic! No more backfiring.

Title: Re: Carb woes and fixes
Post by engineer on 07/19/14 at 18:27:21

I remember your thread, did you ever get around to doing the white spacer mod? Yep, stainless steel Allen head screws make a whole lot of jobs easier. They should sell them that way.

Title: Re: Carb woes and fixes
Post by Todd James on 07/19/14 at 22:08:55

I replaced all of the external screws on my carburetor
with Allen head screws.
Here's a picture that shows the location, sizes, and
quantities of the screws.

Title: Still coughs and stumbles like running out of gas
Post by 49mack on 07/20/14 at 10:47:23

Engineer: Please tell me again about the white spacer fix. I can't find it. Last night I installed a 155 main jet (up from 145) and it still coughs and sputters like it's running dry at about 61 mph, level ground. I've adjusted valves, gapped the plug, new air cleaner, Raptor petcock. . .
I like this bike but it's getting close to becoming a trade-in!
Thanks, Engineer!
49mack

Title: Re: Still coughs and stumbles like running out of
Post by verslagen1 on 07/20/14 at 11:03:32

155 is quite a jump from 145

what made you do this?

And breaking up all your questions into several posts won't help you solve your problem.

I spliced your 3 threads together, now I can see whats going on.

Title: Re: Bucking / missing at 65 mph
Post by verslagen1 on 07/20/14 at 11:28:30

White spacer mod won't fix your cut out at 65.

There are 2 possibilities that I hope you don't have... electrical or cam.

and it could be just a safety acting up... bypass your kickstand safety as if the spring is weak and allows the stand to drop at speed for some reason it will cut out the ignition.

Electrical... I not sure how to determine this (the following is all vapor), a bad TDI or coil might cut out when pushed or maybe the starter signal to the TDI is still on keeping the advance off.
But a bad sparky will fail at higher pressures, so you might try a new one.

And finally, Cam... if the PO replaced the cam chain and did not set the cam right, previous posters have said it won't go pass 55.

Title: Re: Bucking / missing at 65 mph
Post by Dave on 07/20/14 at 18:42:01

Could a sticky carb slide cause a problem like this...or does a sticky slide just a cause a lack of speed without the bucking problems?

Title: Re: Bucking / missing at 65 mph
Post by verslagen1 on 07/20/14 at 18:54:29

Haven't had anybody describe it to do so.

When I had (no don't clean it... no don't clean it... ok, that's it, clean it) a sticky slide, you'd twist the grip and nothing would happen... till suddenly it'd open and whoa nelly she'd take off.