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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Carb Leak Diagnosis /cgi-bin/YaBB.pl?num=1176142433 Message started by vroom1776 on 04/09/07 at 11:13:53 |
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Title: Carb Leak Diagnosis Post by vroom1776 on 04/09/07 at 11:13:53 Hey all, My 38 mm Mikuni VM rounslide carb keep spitting gas out the overflow tubes. This is NOT the stock carb... Also, I stuck the stock carb (40 mm Mikuni BS40) back on, runs fine. This implies that it is not an issue with the petcock. So, step 1) Make sure the float needle valve closes 2) Make sure the floats themselves do not leak (they float) 3) Make sure the float arm is not getting stuck. 4) Check float height. It usually spits gas when I come to a stop. Ever since I got the thing on there, I've more or less had to run it on "PRI" at the petc0ck in order to keep it from stalling... THAT part may be related to the idle set screw & spring. The vacuum line seems to work properly, though. If I set it to "PRI" and disconnect the vacuum line, it dies (no vac to pull gas into engine). If I put my thumb over the vacuum port {edit ->} on the carb, and restart, it will run, so the vac's okay. Am I missing anything? Also, I am very unsure how to check the float height. Thanks gang! V |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/09/07 at 11:34:36 My simple rule of "thumbs" is to adjust the float to where the float arm is parallel with the flat edge of the bowl when you hold the carb upside down. Just bend the tab and eyeball it... Also, try blowing into the fuel inlet while moving the float up and down. If the float needle valve is working right, you'll know. That's what I do when I don't know the measurement, don't have a manual, get lazy, or don't give a crap :P |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/09/07 at 11:37:09 my plan to test the float needle was to fill the fuel line with gas, gently push up on the float arm (i.e. seat the needle valve), and see if gas leaks... float height... okay, that's about where it was last time I checked (months ago). Ug, now I remember posting on this... Thanks greg. |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/09/07 at 11:37:32 vroom1776 wrote:
That seems strange to me. PRI should not require vacuum at all. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/09/07 at 11:48:59 Savage_Rob wrote:
He didn't mention if he plugged the hole in the carb intake when he disconnected the vacuum hose. It could have gone lean and died then... Just a guess... |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/09/07 at 12:09:38 sorry, me not being clear enough. edited above. response was going to be: "PRI" doesn't require vacuum to deliver fuel, but the carb still needs an internal vacuum to pull up fuel from the float bowl spray it into the engine. leaving the vac port on the carb open to air will kill the bike (no fuel delivery). |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/09/07 at 13:38:23 I can see that. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 05:27:58 But you can run the bike with the vacuum hose off, and the hole plugged, and the Petc0ck on PRI. That we know. I can't remember the original problem now... |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 07:49:10 sorry just trying to be clear... maybe for nubes? anyway, everythiung seems to be in good shape, but one of the floats seems to occasionally stick... no, for my own sanity. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 08:48:18 vroom1776 wrote:
How do one of the floats get stuck? Mine are connected and move together. This forum helps your sanity? :P |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 09:40:17 this aint the stock carb, and the floats are independent. They are hollow (of course) plastic disks with brass pins that push on the float arm. They slide up and down on vertical brass rods with stops at the ends. They are free to rotate around the pins, until they hit the sides of the float bowl. I had the bowl about 3/4 filled with carb cleaner, so that the floats were not all the way up against the stops. pushing one down should push the other up. occasionally, one would bind a little and not move. I cleaned the heck out of the bowl and pins, gonna stick it back in tonight, see if it was just gummed up. Also, the floats did not appear to leak. Also, a 250 W heat lamp is my friend. The stock carb-engine rubber flange needed some heat lamp love to get the carb back in there. diagram: http://www.motorcyclecarbs.com/images/mikuni/carbs/explview/vm20_44explview.gif my floats are round. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 09:46:37 vroom1776 wrote:
What is the purpose of independent floats? Geez, how to take an overly complicated carb and make it even better :P |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 09:59:54 That carb is very similar to my Amal Mk2, though the Amal uses a single float. http://rob.savageriders.com/images/Amal_MK2.jpg |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 10:03:34 Greg_650 wrote:
hmmm... that's a good question. I don't know. Actually, I like this carb... when it's running well. VERY responsive. First gear is pretty ridiculous. Also, the throttle attachmetn is way better (easier to get on & off) than the VM28s that came with my RD350... |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 10:06:09 They seem to be yoked together by item 23. That looks like they function as a single item. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 10:08:30 vroom1776 wrote:
Do both of the floats act on the same part that works the float valve? I keep an old hair dryer in the garage. (I borrowed it from my spouse, but when I returned it a little dirty, she bought a new one)...that's what I use for removing stickers and heating things. |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 10:11:45 there is no attachment mechanism. 23 is what I've been calling the "float arm." The pins on the floats that point toward the center push up on the float arm, but are not "yoked," but ideally, they both push on the float arm the same amount, at the same time (I imagine). To try and be more specific, they separately push on the arms that extend towards teh bottom left corner of your computer screen in the diagram I posted. The center tab on the float arm pushes on the needle valve, or course... Hope i made that clear. |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 10:14:36 Item 23 is one solid piece so that the two floats cannot move independently, is it not? |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 10:16:12 23 is a solid piece. But if one float is binding and not pushing on 23, I don't think the other float will push on 23 enough to close the needle valve. |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 10:18:32 That makes sense and it functions the same as a larger single float. If one side of my single float were to bind, I would expect the same effect. |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/10/07 at 10:26:17 one thing I've noticed about our VM & Amal (from another post by you, Rob) carbs is that they both have starter, or cold start, plungers, not chokes (enrichment circcuits). As far as I can tell, they operate very differently than chokes. Get the bike started, lift the plunger after a bit. If you put that plunger down again, kills the bike. On a stock carb, engaging the choke effectively ups the idle (and may make it run like garbage if you leave it out). |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 10:47:49 I can verify that I only use mine for initial start. Once she's running, that lever is flipped back. I intend to convert that to a cable actuated version with a thumb lever on the handle bar. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 11:07:16 vroom1776 wrote:
That theory would almost make the 2 float design just about stupid though... Seems like either one should be sufficient to close the needle. Could it have anything to do with leaning the bike over? |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/10/07 at 11:17:27 I honestly think it's just a matter of how they decided to get it to fit around the jet and into the overall package size they wanted. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/10/07 at 13:45:01 Savage_Rob wrote:
Why do you like the carb? |
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Title: Re: Carb Leak Diagnosis Post by vroom1776 on 04/11/07 at 07:23:47 Greg_650 wrote:
maybe... uh, I noticed it almost always happened when I cam to a stop. Occasionally though, I did smell gas as I was motoring along... I don't think it particularly had anything to do with leaning. I'm gonna reinstall the VM tomorrow evening... |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/11/07 at 07:55:31 Greg_650 wrote:
My Amal? Mainly, I like the simplicity and the responsiveness. I like having the movement of the needle being directly related to movement of the throttle instead of being tempered by a rubber membrane. It's also kinda cool that I need simply remove a threaded brass plug and have easy access to the main jet (though a special tool makes changing it simpler). |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/11/07 at 09:28:44 vroom1776 wrote:
I just wondered if the floats might seek different levels if the angle of the carb changed... Just trying to understand the purpose of independent floats. Could be like Rob said too. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/11/07 at 09:31:30 Savage_Rob wrote:
There you go confusing me again...:) I knew you had the Amal, but I thought that you were running the 38 MM Mikuni too. |
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Title: Re: Carb Leak Diagnosis Post by Savage_Rob on 04/11/07 at 11:19:04 Greg_650 wrote:
Ahhh... Nope, I have the BS40 as an emergency standby (and another BS40 I bought for spare parts off eBay for $35 a long time ago) but I use the Amal full-time. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/12/07 at 14:24:22 Savage_Rob wrote:
Good. I was right, and I was confused. :P |
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Title: Re: Carb Leak Diagnosis Post by tuxedo on 04/12/07 at 15:46:43 On a completely thread-hijacking note, would a busted choke cause the stock Mikuni to overflow through the vent tubes and airbox? Assuming I modded the petcrock like bobo described in his post? |
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Title: Re: Carb Leak Diagnosis Post by Reelthing on 04/12/07 at 16:22:47 Doubt it - if you did the Bobo383 mod - you only have the gas line going to the carb right? sans vacu line - so a float that is not closing the needle seems the only way it could happen in your case - now the why - worn needle, worn seat, improper float height, or a float that has a hole in it and doesn't float anymore - boy those are fun |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/13/07 at 11:13:10 tuxedo wrote:
Since you hijacked it, I'll comment. No. The fuel line leads directly to the float needle valve. From there, gas goes to all other parts, including the ground, crankcase and airbox :P |
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Title: Re: Carb Leak Diagnosis Post by tuxedo on 04/15/07 at 09:50:58 I would like to thank Greg_650 and Reelthing for the help. Yanked my carb for the...10th time, I think? I thought the slide needle was clean whenever I cleaned the carb last time. Turns out, it's not supposed to be deep gold in color. Polished it up really well, put it back in, and voila. After all the cleaning and tuning I did on the carb, Glen's running like a MF-ing CHAMP! Yes, my bike's name is Glen. |
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Title: Re: Carb Leak Diagnosis Post by Greg_650 on 04/16/07 at 10:57:01 Let's try this out..."I'm going out to ride ol' Glen"... Glen is better than Bobby, I suppose :P Glad he's fixed and running good now. |
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Title: Re: Carb Leak Diagnosis Post by tuxedo on 04/16/07 at 11:16:00 Yeah, got ol' Glen dialed in and running on all cylinder. |
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