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#851373 06/11/21 11:06 am
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Was a bit late for my eye test so I charged off, got down a couple of short roads and then the throttle stuck open a bit and it was a bit frightening. I pulled the clutch first and the engine revs went a bit high and I bashed my hand down on the kill switch when I remembered it! My 67 has one of those big ones that sit upright on the bars. It was fine last time I rode it. I have washed it since the last ride and I remember some water went on the air filter. Maybe some got in the cable at the bars but washing the bike has never caused this before.

I will investigate today.

Dave

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Doesn’t sound like you have done any recent Carb removal/install work, so over tight mount Fasteners and bore distortion not the likely answer. Any additives in the fuel? I have had AvGas get gummy and stick the slide years ago, and stopped using it.


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Thanks, KC. No I hadn't dismounted the carb.

Here is where I am now. When I got back from Chichester I tried the bike again and it went straight to highish revs. I shut it down and took off the air filter (a palavar on a single carb 67 650. It requires taking off piece by piece) I felt the throttle slide and it seemed to be closing down and clacking on to the stop. I started it up again and it behaved perfectly normally. I don't know why removing the air filter would do anything!

I still don't trust it so I am changing the throttle cable as the one on there was starting to fray at twist grip end anyway. The return spring should be 2 1/2 " but is slightly shorter but I don't think enough to matter. There are two strengths of springs available the lighter for twin carbs, apparently.

Changing the cable involves taking off the carb (Monobloc) as the top is too close to the frame. I also had to remove the tank because I had used ties on it. Is it possible to thread a cable through without removing the tank? Should I leave the ties off?

By the way can air leak past the manifold studs and cause any trouble? Mine is actually held on with allen screws.

Dave

Last edited by dave jones; 06/11/21 5:32 pm.
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All back together. No idea what was wrong with it. Will ride to my death tomorrow.

Dave

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Might be worth checking/lubricating cable.

Steve


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Originally Posted by dave jones
All back together. No idea what was wrong with it. Will ride to my death tomorrow.

Dave

If it has to happen Dave: Beachy Head! Not far from you, and it would make the local papers.

Is the throttle slide return spring OK? Closes with a decent "snap" ?

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Yes it all seems fine. I fitted a new cable and hopefully all well now.

My resleeved carb is usually ok but i wouldn't mind a new one. I thought maybe i could just buy a body and slide and reuse the rest to save some money but no go it seems.


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I learned a long time ago, the more I try to save money, the more it costs me in the long run. Those carb return springs are pretty weak when new. Did you lube the new cable?


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The spring is supposed to be 2 1/2" long but mine is about 3/32" shorter but it seems quite strong.. Yes I lubed the new cable and it seems ok,


Dave

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Went for a 30 mile jaunt and all fine.

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Mine does this occasionally. Usually when left sitting for more than a few days. Might also be associated with rain. Corrosion around between the body and slide perhaps. This is for Premier Concentrics which I'd have thought would avoid corrosion pretty well. Usually happens when half warmed up. Fully hot or fully cold seems OK, with no 'sticking' .

Differential heating of body and slide? But this doesn't seem to make logical sense?

Carry a spare nipple for the throttle cable/twist grip. Easy to lose the nipple if this happens.


My poor solution.: Carry a large screwdriver to tap the body.
My best solution: Ride everyday. smile

Ray


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I've been watching this topic with interest too see if there's a magic bullet.

I've a '65 TR6 with new Monobloc, but have had the sticky throttle thing. The problem I see is that the top of the carb and under tank area, is a very busy, congested space. I first of all replaced the wiring ties with looser ones, but there's no getting away from the cable coming out the carb, almost immediately having to go through a right angle, then fight other utilities for space under tank. I also wondered whether the choke mechanism didn't help either. What about nylon lined cables? Maybe they're all of this construction these days. Also wondered whether there was enough slack in the cable - I've TR6C bars.

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Originally Posted by DUHC
but there's no getting away from the cable coming out the carb, almost immediately having to go through a right angle, then fight other utilities for space under tank.

I have this issue with the OIF thunderbolt A65, the carb is so near the top of the frame. I found that the modern repo cables don't flex very well, kink easily and cause issues like overcoming the spring. the inner length was also way too long. So out of desperation I bought some NOS BSA cables, the outer is so flexible it goes around bends easily and the cable doesn't get bound up (why the heck can't the modern repos be like this?) So no longer does the cable touch the top of the frame but it happly bends out of the way and through the head steady mounting lug on the frame without touching anything, the slide also moves much free'er.

One other thing I can add, I am not sure what others are using as carb spacings. I always use the tufnol spacings (1/4" minimum) and bolt the cab against it flat. I have seen/used those thick fibre spacers/gaskets and they do compress quite easily making it just as easy to over tighten the carb and pinch the slide. I have had stale fuel issues causing the mazak slides to stick but never with a hard anodised slide. If your using anything other than the tufnol spacer its worth spending half an hour whipping the carb off and checking its flatness of the flange against a sheet of glass. Can you get a feeler gauge or some fag paper under it?


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
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Yes the cable does have to bend sharp ly on my bike. I have to use a tufnol spacer less that 1/4" because of a lack of space. I can only now just about get the airfiler off by dismantling it in situ. It is stll hard to squeeze the element in and out of place. Also on mine the little tab that makes the top stay in the right position when I do up the top ring has quite a lot of side play so maybe it ends up slightly squiffy.



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What is everyone using for cable lube? I recently used Marvels mystery oil on front brake cable because it was closest to me and seemed runny enough to work down into outer sleeve. 🤷🏻‍♂️


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Not cable drag for me. Its the slide sticking in the body. Tap with screwdriver handle to the carb body works to unstick the slide. Carb nuts not overtightened and I use a tufnol spacer as Allan mentions. I donr belive the body is warped, just seems to do it after rain mostly and it's very infrequent. No wierd looking wear on the slide or body, but a bit of carbonaceous reside on the slide and sometimes a bit of white salty stuff that could be oxidised metal. The cable goes slack and the nipple at the twist grip will fall out (and get lost) if not careful. Dab of silicone fixes that. But indeed a sticking cable gives a similar effect. Had that recently. My warning from that is: don't lubricate nylon lined cables (as I had been advised, but ignored). If a new cable fixes it, it was probably that.

For cable lube I use bicycle chain lube with nanotechnology. This or another like it that is pink and smells real nice smile Its vefry this so will run down into cable.
https://cycleinn.co.nz/products/joes-nano-chain-lube?_pos=1&_sid=006d08ab3&_ss=r

Ray


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Hi Splash, For clutch & brake cables I use Mobil 2 v-twin 20-50 same as in motor. I lube about once a year. Ride 5k miles a year on average. I always lube new cables before installing.

Got throttle cables I use very light oil such as Singer sewing machine oil. I feel 3-in-1 oil is too thick once solvent flashed off.

Marvel oil s fine for brake, clutch cables.

It will never really wick in fully. I do like shop Manual. Disconnect upper end. Cut small hole in baggy. Tape baggy to cable with electricians tape. Hang cable, baggy with wire to rafter in garage. Put some oil in baggy. Leave overnight. Next morning oil is dripping out bottom. Remove baggy, but let cable hang some hours so excess drips out. If I ride in rain, I’ll lube much more often. I never wash bike with hose so never get water in cables or carb when cleaning. I wipe with wet cloth & dry. Spray nozzle on hose gets water where rain won’t. On your island salt air may demand hosing bike. In that case more cable lubing needed.
Don


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An alternative for cable lubing I’ve used for decades (yikes I’ve been motorcycling a long time) — get a Motion Pro or Yamaha cable luber— it’s a little split fixture that goes on the end of the cable and has a thumbscrew operated clamp to seal it, with a little port in the side to insert a spray can tube. It’s made for this job and works really well. I usually put a rag around each end of the cable to catch the excess flow, and first I spritz WD40 through the cable to clean it, then spray in aerosol white grease to lube it— it’s actually quite thin— or one of the proprietary cable lubes from your local motorcycle shop. Takes about 2 minutes to do. Works on my vintage bikes, modern bikes, dirt bikes, race bikes. Easy peasey. I don’t think I’ve removed a cable, hung it up, and taped up a paper cone or baggy to run oil through a cable since the 60’s, but you can certainly do it that way if you choose, it works fine too, but time has long since marched on to quicker and easier methods.

On the original post, to me this sounds like carb slide galling issues, what with mentions of rain, oxidation and white powdery deposits, loose throttle cable, etc. You might check the slide and body for signs of galling, they should show. Whatever it is, you need a real fix, this can be hazardous to your health. Of course, you may have fixed it with a new cable already. Another possible thought—perhaps make sure the tank sits high enough it doesn’t deform the cable where it exits the carb top? Also, cable ties can sometimes cause problems. Cables like to find there own way, and routing them carefully to be free without cable ties under the tank may also help.

Finally, one possible problem with plastic carb spacers is they compress and allow the carb flanges to bend, deforming the body. My DBD34 Goldie had this very problem, leading to the same throttle sticking excitement.

No fun to figure this problem out but important to do.

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Thanks for all new replies.

Linker48x- I have one of those cable oilers made of ally and rubber but it is so messy to use! I looked up the motion pro one and it has much better reviews. I went back to using a hypodermic needle and 30 weight engine oil for my new cable. I have since learn't that engine oil is not suitable!

The trouble with the single carb 650 is that the frame top tube is right above the carb top so the cable immediately has to bend sharply as it exits.

Dave

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Originally Posted by splash
What is everyone using for cable lube? I recently used Marvels mystery oil on front brake cable because it was closest to me and seemed runny enough to work down into outer sleeve. 🤷🏻‍♂️
NOTHING! Most modern cables are nylon lined, which do not wish to be oiled.
I have a few clutch cables hanging on the wall which refuse to move, even though I used synthetic PTFE lubricant.


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