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Author Topic: fire and melted carb overflow tubes  (Read 892 times)

flyboy

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fire and melted carb overflow tubes
« on: October 06, 2013, 06:09:27 PM »
'99 Bullet 500 w/stock Mikarb - After a quick stop following a 20 minute ride, I started again...went to pull away and a large backfire blew the carb off the head AND yanked the fuel line from the petcock. Fire started and burned from the fuel that collected on the crankcase...before shutting down the tap. Anyhow, the only appearent damage was to the overflow tubes coming from the carb, which completely melted. It also appears the nipple (plastic) at the bottom of the bowl melted and broke off in the old tube, so I can't re-connect a new tube to that position.

Any advice? Thanks!
TDS

QUESTION...how important are these overflow tubes? I'm assuming they just re-direct the excess fuel to dump on the road and not your hot exhaust/engine. Can I purchase another nipple for the bowl? Looked everywhere on-line and can't seem to find the right part.

cyrusb

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Re: fire and melted carb overflow tubes
« Reply #1 on: October 06, 2013, 08:56:57 PM »
The part is available, 30mm flat slide will do....nicely

ROVERMAN

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Re: fire and melted carb overflow tubes
« Reply #2 on: October 06, 2013, 09:39:14 PM »
Nice one Cyrusb,  ;D ;D ;D. But seriously, at this point i would have to agree.
Robert.

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Re: fire and melted carb overflow tubes
« Reply #3 on: October 06, 2013, 10:39:57 PM »
+1

That backfire and inferno was the Mikarb killing itself.  Replace it.

Scottie
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ace.cafe

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Re: fire and melted carb overflow tubes
« Reply #4 on: October 07, 2013, 02:28:22 AM »
No problem running without any of the overflow tubes.
I always pull mine off right away when installing a new carb anyway.
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baird4444

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Re: fire and melted carb overflow tubes
« Reply #5 on: October 07, 2013, 12:39:30 PM »
but what caused the backfire in the carby?
   I'm guessing timing is a little off....
   points rubbing block worn causing points to be off...
   jetting a little lean....
« Last Edit: October 07, 2013, 12:44:01 PM by baird4444 »
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ace.cafe

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Re: fire and melted carb overflow tubes
« Reply #6 on: October 07, 2013, 01:21:50 PM »
I always found that the bike backfired on starting when the jetting was lean, or if there was a hole or tear in the manifold rubber hose. Every time my OEM manifold rubber was starting to go bad, I got those incidents with the carb blowing off the manifold. I switched to a piece of radiator hose, and it was solved, as long as my jetting was right.
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flyboy

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Re: fire and melted carb overflow tubes
« Reply #7 on: October 13, 2013, 12:46:09 AM »
Thanks Ace...I failed to mention that I had already replaced the OEM rubber with a section of radiator hose...and there are no leaks. I think the Mikarb's days are numbered. Eventhough, it throttles smooth for the most part...there are those occasional farts and backfires at pull away AND those frantic kickstarts at an intersection (after waiting for a light to change for a while) when it just decides it doesn't want to work!

Scottie is right...the inferno was the "Mikarb killing itself".

Any suggestions regarding replacing with either the "real" Mikuni or "true" Keihin? 30mm seems to be the answer with KN cone filter and unrestricted pipe?

Chuck D

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Re: fire and melted carb overflow tubes
« Reply #8 on: October 13, 2013, 01:42:45 AM »
Get a Mikuni flat slide (30mm). Treat yourself to an "ACE" air canister while you're at it. You'll wish you'd done it years ago.
Chuck.
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flyboy

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Re: fire and melted carb overflow tubes
« Reply #9 on: October 13, 2013, 01:25:33 PM »
Thanks Chuck. Mikuni is what I was leaning towards. I have them on my CB550 and never an issue with over 30,000 miles. Although, I have heard good things of the Keihin's...if you stay away from the clones. I'm shopping now!

D the D

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Re: fire and melted carb overflow tubes
« Reply #10 on: October 13, 2013, 05:07:26 PM »
Get a Mikuni flat slide (30mm). Treat yourself to an "ACE" air canister while you're at it. You'll wish you'd done it years ago.
Chuck.

Genuine Mikuni Flat slides jump from 28 to 32 mm with no 30.  30s all seem to be Keihen copies.  But I have to say yes to the Mikuni/Ace Canister set up.  Best thing I did to my RE followed by EI and new shocks.
Another reason to go to Mikuni 32mm Flat Slide is that all the ground work has been done for you. Just go to the flat slide threads or ask Ace and you'll have a starting point for rejetting it that may be spot on from day one.
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ace.cafe

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Re: fire and melted carb overflow tubes
« Reply #11 on: October 13, 2013, 06:37:10 PM »
Be aware that when you go to a 32mm, you will need a bigger intake manifold. Sudco has hard rubber ones, and Ace or Hitchcock have alloy ones.
« Last Edit: October 13, 2013, 11:00:53 PM by ace.cafe »
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flyboy

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Re: fire and melted carb overflow tubes
« Reply #12 on: October 13, 2013, 10:57:29 PM »
Is there any issues jumping to a 32 from the stock 28? Too much? This bike is totally stock, no performance mods other than KN cone filter.

ace.cafe

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Re: fire and melted carb overflow tubes
« Reply #13 on: October 13, 2013, 11:20:07 PM »
Is there any issues jumping to a 32 from the stock 28? Too much? This bike is totally stock, no performance mods other than KN cone filter.

No real issues with the 32mm carb. The port is about 32mm too, so it's a good match.
You will get better top end rpm and better throttle response with the TM32 Mikuni flat slide, and it doesn't cost much more than a VM32 round slide. You will need to re-jet whatever carb you pick.

It would be advised to move to a more free flowing exhaust, to make the most of the breathing improvement.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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flyboy

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Re: fire and melted carb overflow tubes
« Reply #14 on: October 13, 2013, 11:53:50 PM »
Thanks Ace.
Mikuni 32mm flat slide it is. As far as the exhaust goes...the bike came with an unrestricted shorty, but that was way too loud for my liking so I went back with the stock exhaust. Which would you recommend for performance, but not too loud? Is there a semi-restricted?