The Strangest thing

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Hi

I have been riding my 1977 interstate for about three or four months, apart from a sticky clutch (Norman White)type everything has been going ok in fact very ok....the bike runs a lucas rita ignition and a mikuni vm36 carb. Last Sunday while I was out riding it I became aware that the when the throttle was closed the bike ran on,a sticky cable I thought but no the cable is ok it returns and I can hear the slide dropping to the bottom and seating ok. sometimes it will do it sometimes it won't (intermitent) it can be cleared by blipping the throttle but not always. The revs usually hover at 2-3 thou. Anybody had a similar problem?....all suggestions gratefully accepted.... :shock:
you don't want one of these with a stuck open throttle....
 

MichaelB

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Mikuni's have chrome plated brass slides that don't usually stick.
However, it could be slightly gummed up.

It could also still be the cable.
The angle of the cable entering the Mikuni is very sharp because of the frame backbone tube. Sometime it kinks here.
As you lower the slide slowly, the spring tension doesn't allow the slide to seat, when you blip it, the sudden up and down motion frees it.

1. Remove slide and clean, also the carb body.
2. Check cable for kink and smooooth operation.

Cheers
 
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Iv'e cleaned the carb it was like an operating theatre in there, the cable is a venhill cable and has a metal tube that takes the cable at almost a right angle away from the top of the carb.....the slide is all clean and moves smoothly, the other thing that occured to me is the needle valve that controls the amount of fuel into the float chamber may not be cutting the fuel off....both floats float and move ok....can't think of anything esle :cry:
 
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strangest thing

Sounds like an air leak to me,idle the motor and spray some starter fluid around the intake manifold joints,the revs. should increase if there is a leak. Ride safely. James.
 
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inclined to agree tried the trick the wd40/starter but no difference,i'm inclined to think the air leaks after the engine has been reving....and it's been sucked past the spigot of the carb, the clip/clamp that holds it on is pathetic with the weight of the carb and the K&N all hanging on it i'm supprised it hasn't fallen of..... :roll:
 
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Don't discount the slide sticking just yet. Why not try a stronger spring, or another smaller diameter spring inside the original.
Best of luck.
 
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It might be worth replacing the o rings on the idle mixture screws. They can be the cause of an air leak.
 
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Have you taken the handlebar throttle assembly apart? I dont know what kind of throttle you have but ive had the cable wear the plastic types to wear it binds.
 
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I just had a similiar problem this weekend - i removed the carb (left the tank in place just loosed the screw on the manifold pulled it down w/ aircleaner and unscrewed the top part where cable goes in) then disassembled the carb - removed the idle and mix screws and sprayed carb cleaner through all the passages, wipped off the slide with a lttle gas which did have a liitle gum on it (i think the cable lube worked its way down from lubing the cables to much) - reassembled and started the bike up and readjusted - ran beautiful and only 45 minutes.
probaly easier to jut do the carb cleaning thing and make sure not a dirty passage/gummy slide and then think about the other stuff of no change
mike
 
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I new this had to be simple but it always difficult to see the wood for the trees....after spending a Saturday morning fitting a new needle valve and going over everything I had already done and fitting a new stainless clip around the rubber manifold,checking the spring length I decided that the cable at the carb end although free looked a little dry. So I deadjusted the cable 8" below the twist grip pulled the rubber sleeve back to pump some oil down and low and behold the ****** ferrule came away from the outer cable I mean it it was so lose it hadn't been crimped.....it's now wire bound and so are the rest of them...... :oops: Thanks for all the suggestions and help......P.S this wasn't an old cable It had been bought a while ago but only fitted recently... :!:
 
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not-ron said:
I new this had to be simple but it always difficult to see the wood for the trees....after spending a Saturday morning fitting a new needle valve and going over everything I had already done and fitting a new stainless clip around the rubber manifold,checking the spring length I decided that the cable at the carb end although free looked a little dry. So I deadjusted the cable 8" below the twist grip pulled the rubber sleeve back to pump some oil down and low and behold the ****** ferrule came away from the outer cable I mean it it was so lose it hadn't been crimped.....it's now wire bound and so are the rest of them...... :oops: Thanks for all the suggestions and help......P.S this wasn't an old cable It had been bought a while ago but only fitted recently... :!:

I've run into a few crappy cables lately too. Had a throttle cable a while back where the round soldered end just popped off!! Don't want that to be happening on a long road trip!! If anyone has suggestions for a source of quality cables for British bikes, I'd love to hear about it!! Does anyone have experience with Barnett? Their speedo and tach cables seem pretty good quality.
 
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Phoned Allens R&D somewhere in deepest Nottingham (really nice people
)and they have supplied a stronger spring from the mikuni Vm38 part number (VM34/152) appx £4.50 + vat it gives the throttle a much more controlled feeling and seems to slow the rate of opening and make the whole business of hard accelration much better. The spring itself is about 3/8" shorter and but the actual wire is twice as thick also at low speeds it doesn't seem to be so prone to slight movments.....anyway time will tell haven't done any distance on it yet..... :D
 
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