Mikuni Carb trouble - fuel line routing

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rgla

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I've been having trouble with my 850 since I took the mikuni apart cleaned it and put on new fuel line. Rough idle, need the choke to start the bike, choke off it starts to die. I rerouted the throttle cable thinking this might be part of the problem. I cut the fuel line a little shorter and that seemed to help a bit. Does anyone have a photo of the proper way to route the fuel line. Maybe it's fuel starved when I take the choke off.
I routed the fuel line almost exactly how I had it before. but used a different kind of line and fuel filter.
if i knew how to post photos here i could show a photo of what I have going on?
 
I'd put a filter in the line before the carb as well since Mikunis do not have a filter. I use a Pingel 2 into 1 filter that works well. See below. I don't like how the left hand feed line has to make such a sharp bend so plan on replacing with a 90 degree feed from the petcock to ease the bend a bit. But it works fine so far. The disposable inline jobs work fine too and are much cheaper. Have you cleaned out our tank and made sure that both your petcocks have mesh filters that are functioning? It took me a fair while to get my fuel system sorted out when I first bought my Commando. It had been sitting around for a long time.

Mikuni Carb trouble - fuel line routing
 
thanks
how did you post a photo?

from the looks of yours - mine should be fine. In fact there might be less extreme bends in mine. i'll try and post a photo
 
If you go to the Old britts web site there are good pictures of how they do it & it's a clean job. I did mine that way. The only thing I don't like is that puting the small filter just befoe the carb makes it very hard to get to the side cover zeuse fitting. I like the 2x1 pingle idea that would make it easier.
 
rick in seattle said:
Buy one of these. It only fits one way and works very well. Pre-built to perfect lengths. Get the clear version and you can visually confirm the fuel flow. It works great on my Mk3/MikuniVM34.

http://www.oldbritts.com/13_065192m.html

Rick
Click to expand...

I bought the black pre made Mikuni version from Old Britts and it nowhere near comes close to fitting. I made my own out of cheap, red coloured gas line instead. I'll sell my unused one cheap.
 
Hey coco
why didn't it fit?
Not sure I'd want to purchase something that doesn't fit correctly
also these seem easy to make with just a tee
how much are u asking
 
You can avoid any kinks in the lines if you use two 90 degree fittings. One at each of the gas taps. It eliminates the loop in the fuel line for a more direct feed.


Tim
 
here is the routing i use although might be the source of some problems currently

Mikuni Carb trouble - fuel line routing
 
rgla, your photos are correctly tagged, but they don't show in your message?

I suggest you go to your User Control Panel >Board preferences> Edit display options and check that Display images within posts: is set to YES?

If it is set to NO then change it to YES and press Submit. All five display Yes/No options are usually set to YES by default.


Mikuni Carb trouble - fuel line routing


Mikuni Carb trouble - fuel line routing


Mikuni Carb trouble - fuel line routing
 
The Old Britts fuel line setup for a single Mikuni is NOT symmetric, as you can see from their photo. If you put it on backwards, the long line will crimp and the short line will stretch. If this is the case, switch the connections to the petcocks. My Mk3 is perfectly stock, as is my Mikuni VM34. Once I got past the WTF moment and reversed the connections, it fit perfectly.
 
rick in seattle said:
The Old Britts fuel line setup for a single Mikuni is NOT symmetric, as you can see from their photo. If you put it on backwards, the long line will crimp and the short line will stretch. If this is the case, switch the connections to the petcocks. My Mk3 is perfectly stock, as is my Mikuni VM34. Once I got past the WTF moment and reversed the connections, it fit perfectly.
Click to expand...

Mikuni Carb trouble - fuel line routing
 
Since the petcocks have screen filters, why would you need additional filter in the fuel line?

What could get past the fine mesh petcock screens that could cause damage?

I have the pre made Old Britts fuel line set up for my Mikuni, fits and works beautifully.
 
highdesert said:
Since the petcocks have screen filters, why would you need additional filter in the fuel line?

What could get past the fine mesh petcock screens that could cause damage?

I have the pre made Old Britts fuel line set up for my Mikuni, fits and works beautifully.
Click to expand...

Another filter is insurance in case the petcock screen fails. I'm going to not put any additional filters on and see how it goes.
 
Screens on the petcocks are pretty coarse so don't provide much protection except from fairly large chunks of crud. I have had too many fuel feed problems with old bikes so I don't take any chances now and always fit some sort of bronze filter in the fuel line. Mikunis have no filter at all so I think you need something in the line before it reaches the carb. Amals have screens but they are pretty coarse as well so I don't depend on them. An inline filter could be overkill but it can't hurt!
 
so I got the bike to idle. Both idle screw and air mixture screw are about 1.5 turns out.
here is the current problem. it is idling around 1.5 but will jump up to 2 for a few seconds and then drop back to 1-1.5. so it jumps on its own and then will suddenly drop down below 1 after awhile and die out. it will start now when warm without the choke on.
does this sound like an air leak? the pilot air mixture doesn't do alot it seems more affected by the idle screw. also hear small pops from exhaust sporadically but not too often
 
rgla said:
so I got the bike to idle. Both idle screw and air mixture screw are about 1.5 turns out.
here is the current problem. it is idling around 1.5 but will jump up to 2 for a few seconds and then drop back to 1-1.5. so it jumps on its own and then will suddenly drop down below 1 after awhile and die out. it will start now when warm without the choke on.
does this sound like an air leak? the pilot air mixture doesn't do alot it seems more affected by the idle screw. also hear small pops from exhaust sporadically but not too often
Click to expand...

What ignition?
 
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