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#1 Raz

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Posted 14 April 2005 - 05:23 PM

:saywhat: Got a problem with my carb........I have a mini 1000 based trike That i baught anyway when it was started for the first time it shuved black smoke out so we decided to strip it down and do the head... after refitting we decided to fit a cooper crowsfoot manifold and a metro alloy inlet, the trike already had a su hif 4 fitted but we decided to change the needle winsu sugested a BFY instead of the ADS with the setup i have... anyway when restarted it would not run without holding a hand over the air intake and on full choke it also stoped if left to idle and chucked out blue smoke this time mmmmmm.... ok we stripped the carb again and when we cracked the carb from the manifold oil ran down the manifold heatshield.. on inspection we found that the needle was holding the pison up slightyly in the carb it also stcks when it comes down hard

here are a dew pics can anyone give me some advise

cheers Ray

picture 1

picture 2

picture 3

#2 Bluemini

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Posted 14 April 2005 - 06:29 PM

Is it a HIF44 that you have? If so then you might find a HIF38 works better as the 44 is for the bigger engines realy.
Have you put the right grade oil in the dashpot, if its too thick the needle wont rise very well and will stay risen, if its too thin it will have the oposite affect.
When you stripped the head did ou put new valve stem oil seals on?
Also, try taking the over-run valve off the breather on the side. If that doesn't make any differance, try holding your finger over the beather it was attached to so you block it off. Sometimes they work better if they are blocked off for soome reason.

#3 Raz

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Posted 14 April 2005 - 06:58 PM

Yes i believe its a hif 44 its 1 3/4 rs anyway but there are no markings on it that i can see unless somone can tell me where to look or maybe redocnise the carb from the pics and i used engine oil in the dashpot thanks for your help

#4 Dan

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Posted 14 April 2005 - 07:12 PM

Is that an overrun valve or is it a servo for a cruise control or something? If so it would work much better if it was attached to a vacuum source rather than an emmissions inlet, and that may be causing some of your problems.

Oh and Blue is quite right, an HIF44 is far too big for a 998.

If the needle is sticking in the jet then it's probably got the wrong size jet fitted. There are different jets for SU's as well as different needles. It may have an HIF 38 jet fitted or a small sized HIF44 one.

Or it could just be that the jet hasn't been centered which is important in HIF's I believe.

#5 998dave

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Posted 14 April 2005 - 07:38 PM

heya,
To start the carb in the pic is an HIF, you can tell as the float bowl is integral with the carb.
The HIF44 is too big for a standard or even a stage one 998, you'd be better with an HIF38, or an HS4, both 1.5" carbs.
The needle on both SU carbs is held down by a spring so centring the needle in the jet isnt a problem, it self adjusts, keeping the two clean and checking for wear is needed though.

Dave

#6 Guess-Works.com

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Posted 14 April 2005 - 07:46 PM

HIF44 uses a .100" jet where as the HIF38 uses 0.090", so there is a possibility that an undersized jet is installed, but more likely..

If the needle is failing to rise, there could be a number of causes, but most likely is a lack of vacuum. As has been said above, a 1.3/4" carb on a 998 is too big, there is just not enough airflow in the engine to pull a decent enough vac and not enough airflow through the venturi to 'suck' the petrol out the jet. What happens is you need to use a realy rich needle and low jet to compensate for the lack of lift by the needle.

You'd be far better of with a 1.1/2" carb, either HS4 or HIF38.

#7 Raz

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Posted 14 April 2005 - 08:05 PM

the pic showing the piston with a small gap under it is with the needle fully down isent the piston suposed to reach the bottom?????

#8 Guess-Works.com

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Posted 14 April 2005 - 08:13 PM

pretty much so...

#9 Dan

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Posted 14 April 2005 - 08:14 PM

No, how would you ever get any fuel or air into the engine if it blocked up completely? Take the dashpot off and see if the piston is touching the body inside there, if it is then it is fully down.

Edited by Dan, 14 April 2005 - 08:15 PM.


#10 Guess-Works.com

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Posted 14 April 2005 - 08:38 PM

Yes, If there is no vac present ( carb removed or engine not running ) then the piston should sit on the base of the bridge. When the engine is running there will always be a draw of air through the carb, this will cause the atmospheric depression in the suction chamber and cause the piston to rise.

#11 Dan

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Posted 14 April 2005 - 10:12 PM

OK, I really must actually look at pictures before making comments in the future! :P

Yes, that gap is far to wide!

As Guessworks says, it should contact parts of the bridge.




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