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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> dies under acceleration /cgi-bin/YaBB.pl?num=1549935265 Message started by fang on 02/11/19 at 17:34:24 |
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Title: dies under acceleration Post by fang on 02/11/19 at 17:34:24 So I'm at a bit of a loss about what the problem could be A friend of mine has a suzuki s40, 2008 i believe The bike starts and idles fine but when accelerating it sputters and won't accelerate beyond 15 miles an hour We've cleaned the carbs with the exception of the accelerator pump? or maybe it's a decelerator pump, it's got 3 stuck philips head screws holding it in I didn't have my impact driver on me at the time so that will have to be cleaned within the next few days all ports and jets have been cleaned The petcock has been tested, somewhat, the fuel will run from the line when it is in the prime position, it will also run in the on position and reserve (checked by disconnecting the vacuum line from the petcock while idling and it died) we also pulled the petcock off and verified there wasn't anything blocking it, clean as could be Nothing is blocking any air ports including the one in the front of the carb, the port that lets air into the upper diaphragm, I know sometimes aftermarket air filter housings can block them The bowl float moves freely as well as the needle that the floats actuate The upper diaphragm area has been cleaned and i cannot see any holes or anything in the upper diaphragm We also checked the spark plug and verified it worked as well as the wire I also checked the voltage at the battery thinking maybe it could be a charging issue with the battery voltage dropping but that checks out too I disconnected the decompression cable thinking maybe the valve was stuck open, nada double checked all the lines from the carbs and tank the tank vent line is clear the the vacuum line from the carb to the petcock is working and is pulling fuel into the carb I verified the fuel flow by opening the carb drain bolt, gas came out so I know that is working i also tried to run it with the gas cap off in case there was a vacuum issue with it, nothing I'm not sure what else it could be, it was running fine until it was parked for a few weeks, had a little rain that probably got under the bike cover but it wasn't like soaked I assume if the rain did something to the wires then there would be a blown fuse or something I also pulled the exhaust to check the gasket, that was good as well Could this accelerator pump be related to the issue? Or is the piece on the side of the carb a decelerator pump? To me it feels like the carb slide isn't reacting the way it should, almost as if it had a hole in it but i can't see one :o |
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Title: Re: dies under acceleration Post by Yoshi on 02/11/19 at 22:11:30 You said you cleaned the carburator but did you clean the jets? What's your air filter look like? I'd rejet the main a step or 2 higher if you're going intonthe carburator again |
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Title: Re: dies under acceleration Post by Dave on 02/12/19 at 07:07:41 The diaphragm behind the 3 screws is the TEV (Tranient Enrichment Valve), it is supposed to provide additional fuel when decelerating to help prevent backfiring noise. Have you tried riding the bike with the petcock in the prime position? The petcock diaphragm can become stiff as it ages, and fail to allow fuel flow at speed as the engine vacuum decreases when the throttle is opened. Have you checked the battery/charging system for voltage? A weak ignition system can cause these kind of symptoms. When you had the carb apart....did you take the needle out of the slide....and put the spring and plate back properly? The spring needs to be on the top of the needle pushing it down, and the plate needs to be installed so the holes in the bottom of the slide are not blocked. Did you remove the float seat from the carb body and clean the screen on top of the brass seat assembly? |
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Title: Re: dies under acceleration Post by youzguyz on 02/12/19 at 07:59:13 With all that I have read and all that has been said, I don't see a lot of mention of the carb slide. Sounds to me like it is stuck/sticking. Check one: Tap around on the upper carb body while opening the throttle to see if it helps. Check two: Take the boot off the carb intake so you can see inside it with the bike running. When you open the throttle, the slide should rise up. If it doesn't, it could be a hole in the upper diaphragm (yes, I know you said you checked it), or just stuck (from dirt, finger print, whatever). Try giving it a nudge up with a clean wood/plastic stick (or something that won't leave a scratch). |
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Title: Re: dies under acceleration Post by batman on 02/12/19 at 08:05:13 The brass plate also has to be positioned ,with the dimple (right next to the needle) protruding down into the slide-(which should be clean and free of even fingerprints) and you should be able to see light through the two tiny vacuum ports in the bottom of the slide. In the bowl, besides what Dave and Youzguyz said, you should check to see if the washer is on the main jet , it holds the needle jet body tightly up into the carb body and MUST be in place. you should also set the float level last before closing up . |
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Title: Re: dies under acceleration Post by ohiomoto on 02/12/19 at 09:56:14 7F69737C61737F7C060 wrote:
This... It happened to me once. |
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Title: Re: dies under acceleration Post by norm92de on 02/12/19 at 10:25:15 I had the exact same symptoms but it was my fault since I had taken the top off the carb and got the slide spring cocked or something. It sounds like you had the problem before you touched the carb so it is probably not what happened to me. Just a thought. |
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Title: Re: dies under acceleration Post by justin_o_guy2 on 02/12/19 at 11:08:46 One year mine did that. It would idle, but would not take throttle. Puke and die.. I dumped the gas, and it healed up. That was after sitting a few months. |
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Title: Re: dies under acceleration Post by fang on 02/12/19 at 12:35:15 7F44495E4F43585E454D405F2C0 wrote:
Thank you for clarifying that, on my yamaha road star it is labeled as a deceleration pump and it does the same thing 7F44495E4F43585E454D405F2C0 wrote:
Yes I have tried riding it in all 3 positions with the same results each time 7F44495E4F43585E454D405F2C0 wrote:
Yes i've checked it while running, twisting the throttle does not effect the voltage 7F44495E4F43585E454D405F2C0 wrote:
When I had the carb apart I didn't end up taking the needle out of the slide, i just removed the diaphragm /slide assembly along with the needle and sprayed the needle and slide body off with carb cleaner, my friend who owns the bike had just cleaned his carbs out a few months prior so when I go check it out tomorrow I will take a look at the needle/slide assembly 7F44495E4F43585E454D405F2C0 wrote:
I didn't end up taking the float needle out i just verified the needle was moving up and down, i didn't realize there was a screen on the top of the seat I just assumed since the bowl was filling/ able to idle that it had sufficient gas flow How would i go about testing the amount of gas coming out per minute for the on and reserve position of the petcock? As for testing the flow rate per minute on the carb, I think would I just leave the petcock on prime, allow the carb bowl to fill up, then after it is filled open the drain screw on the carb and measure how much pours out in ten seconds, then multiply that by 6? Giving me the flow rate per minute? I will take a look at the float seat and screen when i go look at it tomorrow I need to talk him into just getting a gravity feed petcock, seems much easier to deal with |
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Title: Re: dies under acceleration Post by fang on 02/12/19 at 12:46:58 7667764F434D4754554D4F260 wrote:
The air filter is good, it's basically a velocity stack with a mesh screen on it and it is clean The main jet he has in there now is a 147.5 and it has been riding good up until a few weeks ago That's what has me confused seems like it would be acting up when we re jetted it for the first time years ago |
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Title: Re: dies under acceleration Post by fang on 02/12/19 at 12:50:29 3E28323D20323E3D470 wrote:
That sounds like it could be the issue, It hadn't occurred to me that it could simply be getting stuck What would you recommend for cleaning the top rubber portion? I had just wiped it off gently with a paper towel but there is a good chance it could be dirty I will try to clean that and check the needle and slide tomorrow |
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Title: Re: dies under acceleration Post by fang on 02/12/19 at 12:55:08 27243128242B717D450 wrote:
I can't remember if we did the washer mod on the needle but I would assume so, I will be looking at it tomorrow to see if the plate is mounted up correctly, my friend who owns the bike said he cleaned the carbs a while back so maybe he put it in up side down Thanks for all the info, I will be double checking on the floats as well |
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Title: Re: dies under acceleration Post by fang on 02/12/19 at 12:58:23 504F494E53546555655D4F43083A0 wrote:
That was my first thought and I had him dump the old gas from the tank and the petcock and get new stuff in there, no luck with it though :-/ |
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Title: Re: dies under acceleration Post by verslagen1 on 02/12/19 at 13:29:46 696E61683737393E360F0 wrote:
A dirty rubber :-? won't cause a problem. Clean it with the wrong stuff and you'll have a problem. It's made for a gas environment, gas on a paper towel shouldn't hurt it. |
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Title: Re: dies under acceleration Post by batman on 02/12/19 at 19:33:09 OMG! A velocity stack is terrible !!!!!! ( even a cone filter-which isn't great- would be better) it will never work with a main jet as small as the stock 147.5 and the stock 52.5 Idle jet, the bike is running dangerously lean !!!!!! It's no wonder it stalls when the throttle is open! You'll need to get a proper filter , do the spacer mod and go to much larger jets , and I'd hate to ask what you're running for a muffler , (but I hope it's not a straight pipe) you should tell us as that also affects jetting. |
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Title: Re: dies under acceleration Post by fang on 02/15/19 at 07:35:55 3C3F2A333F306A665E0 wrote:
The velocity stack has worked for the past few years but I'll let him know the cone filter is a better option I'm not sure what numbers he was reading me but I now have the carb and i'm looking at the jets, here are the numbers 152.5 on the main jet 55 on the pilot 230 on the main jet in the upper diaphragm 45 on the smaller jet in the upper diaphragm i cleaned the slide, not much residue on it i checked the needle in the slide, the plate was put on correctly, i can see how it could block the holes in the bottom if put in incorrectly, the spring was installed correctly and there was one thin washer under the clip on the needle the float seat was removed and the screen was cleaned, i found a decent sized chip of aluminum in there! seemed like when the carb was made a small piece was lodged in there, it could have been blocking the fuel flow I got access to the transient enricher, it was kinda dirty but it's clean now! I have verified all the ports in the carb are clear and free of debri When i initially cleaned it i didn't realize the needle jet under the main jet could be removed, it has been cleaned as well He has open pipes with the exception of a baffle at the end of the pipes What im thinking could have happened was maybe he put the top jet from the diaphragm in the bowl, they appear to be the same thread size The enricher was removed and cleaned Hopefully i can get it back on his bike to test it today |
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Title: Re: dies under acceleration Post by batman on 02/16/19 at 18:52:08 So a velocity stack and a drag pipe with a baffle at the end , Jetting doesn't get much harder. Even if you do a good job ,the bike may only run well at a narrow power band near Wide open throttle. The jets you use will need to be more like 55 pilot -155 /157.5/160 main jet and 2- #4 steel washers for the needle jet (spacer mod).Don't expect mileage to be more than about low 40's. If the velocity stack has been on the bike 3 years ,I'd be doing a compression test/and /or pressure test, to check piston .rings ,cylinder walls and valve guides . A low reading would indicate wear/damage caused be poor air filtration , as these stacks are meant for racing only, bikes that are rebuilt often, not street bikes which log thousands of miles. |
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Title: Re: dies under acceleration Post by fang on 03/18/19 at 10:05:58 686B7E676B643E320A0 wrote:
The velocity stack was supposed to be temporary but getting this guy to buy parts is like pulling teeth Luckily fate has left him in a situation where I now have full control of the part ordering/installing The first order of business was getting a pod filter, it's on the way in the mail I replaced his stock petcock with an aftermarket one from ebay, the pill shaped o ring sealed up just fine and it's now gravity fed, 3 position, on off and reserve I also installed a small inline fuel filter I'll be ordering some mandrel bent pieces as well as a small baffle soon to make him a new exhaust I took off the exhaust pipe and cranked the engine a few times to verify the valves where all moving, looked into the carb inlet and they where all functioning as they should The problem kept pointing at the carb slide, i verified there was no leak from the top diaphragm cover by lightly blowing into the overflow tube while sealing the other outlet holes with my fingers, it went up like i expected I started researching jet sizes and stumbled across a picture of the slide needle with the spring under it.......wait.......spring under it....... I took the top cover off, pulled out the slide and took the needle plate out of the slide body, there it was, the spring, sitting ON TOP of the needle.... I had taken the needle out a few weeks ago and thought nothing of it, i guess my buddy must have put it on top of the needle the first time he cleaned the carbs a few months back Thinking about it, the needle would have excessive pressure down on to the main jet, which would starve it i assume Only time will tell, I'll be picking up a few gallons of gas today to try it out and hopefully get him back on the road |
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Title: Re: dies under acceleration Post by batman on 03/18/19 at 23:07:48 The in line filter can cause problems (CAN BECOME AIR BOUND STOPPING FLOW) and is basically unneeded , the fuel is filtered in the tank and above the float bowl valve. |
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