Author Topic: running issues  (Read 480 times)

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Offline hmmmnz

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running issues
« on: December 30, 2016, 07:21:51 AM »
hi guys, well the bridgestone 200 is back together, and running-ish
its a bit of a pig to start, and when its running has no power to speak of, not really even enough to even get moving with out riding the clutch,

it also has a few back fires when starting and a bit of a pinking noise when running,

where should i be looking??
im guessing its timing related.

cheers
logan
mini buffalo (chibi copy) 68' mkII 200

Offline skiri251

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Re: running issues
« Reply #1 on: December 30, 2016, 06:23:55 PM »
I just had similar experience with my BS200 rebuild.

In my case, it was carbs.

I tried to clean old carbs as best I could (used Harbor Freight ultrasonic cleaner, thin wire to unclog small passages) but they never delivered.
Powerwise it felt like Honda CL125A (4stroke 125cc twin). Had a hard time taking off even the slightest uphill in 1st gear. Had terrible gas mileage (35MPG).

I ended up installing brand new VM18-144 carbs. They are almost like stock VM17-18 except the choke lever. But the stock choke mechanism fits perfectly. Came with #78 main jets which were much smaller than stock #100 but it was the correct size. Moved the needles to the lowest to get rid of mid-range hesitation.

Now it runs strong with 50MPG gas mileage.


Offline hmmmnz

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Re: running issues
« Reply #2 on: December 30, 2016, 09:09:29 PM »
hmmmm,

ok, ill definitly look into that, ive also soaked the carbs in my ultra sonic cleaner,
but it'd been sitting un started since 73 :D 

i reset the timing tonight, and i seemed to be a few degrees out and the point gap was too small,
so ill give it a start up in the morning and see if thats made a difference.

where did you paick up the carbs from??

cheers
logan
mini buffalo (chibi copy) 68' mkII 200

Offline skiri251

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Re: running issues
« Reply #3 on: December 30, 2016, 10:24:26 PM »
I bought the carbs from ebay.
Search for VM18-144 and you will see several. Around $70 including shipping.
Not sure the situation in the UK.
Apparently Mikuni still make these carbs.

Offline hmmmnz

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Re: running issues
« Reply #4 on: December 31, 2016, 09:46:50 AM »
well its running much better, still a pig to start but revs cleanly
but typically the carb started over flowing,
it must be a sign from the gods.

couldnt find any suppliers out of the uk,
so ill have to order a set out the US and pay the stupid exorbitant UK import tax. grrr :D

i was going to try and go for a ride but its started pissing down, so ill flag that for now, and try tomorrow
mini buffalo (chibi copy) 68' mkII 200

Offline Sye

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Re: running issues
« Reply #5 on: December 31, 2016, 10:08:41 AM »
Before you go down that path contact Steve at Motocarb. He's a Mikuni specialist in the UK and will sort the carbs you have with new needle valves, check and set float height and whatever else you need. He can be found here:

http://www.motocarb.com/
Be nice - feel good

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Re: running issues
« Reply #6 on: January 02, 2017, 06:44:59 AM »
            Before paying out for new carbs, try these fixes.
       The starting problem is likely to be a blocked jet at the bottom of the cast tube in the float bowls, quite a common issue with old Mikunis. Clear the slant drilling in the bottom of the main float bowl first, if that doesn't do the trick use a piece of very thin piano wire or a needle to clear the jet down the tube and blow through.

         Check the float valves while the carbs are off and use a sealant  (Hylomar) on the float bowl gasket when you reassemble. The float bowl flanges warp for fun.

   Brian.
Growing old is compulsory, Growing up is optional.

Offline ddog71

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Re: running issues
« Reply #7 on: February 18, 2017, 01:19:56 AM »
On the VM18-144 carbs you need to remove the throttle valve (slide) that came with it. It has a Cut Away (C.A.) of only 1.0. The throttle valves in the old VM17-18 carbs have a C.A. of 2.0. It should fit in your new VM18 carb. I think the Pilot Jets in the VM18 and the old VM17-18 are the same (#17.5) and also the Needle Valve and seat assembly are also the same (#1.5). Needle Jet for the 175 should be O-0 ("Oh-zero") and for the 200 should be O-6. I think the Main Jets should be #90 or #95.

 


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