Throttle stays wide open

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wrx2bike

New Member
Oct 31, 2010
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california
Hello again my friendly MB coummunity.. So heres the Deal I just bought and installed a Sick Bikes HD throttle assembly Sick Bike Parts

Im by no means an expert but I think I did it right..

The cable did seem to be a lil short for my chopper tho and now the when I get it started the throttle stays wide open and revs really high. There doesnt seem to be much play in the handle. I barley get a 1/4 turn out of it. almost as if the cable was the wrong size but I got the largest one they had available. So Im just looking for some ideas on what you think may be the problem.. Thank you in advance .shft.
 

MEASURE TWICE

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Jul 13, 2010
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I bought a twist grip throttle assembly and I had the opposite problem. I made stops to the cable movement to be sure it would not put undue stress on the carb linkage. In addition I added a spring linkage to the final connection to the stupid plastic part on the carb throttle butterfly valve, so when it goes to min or max throttle the spring just bends a minute amount and the plastic does not bend.

Where does this leave you with just the opposite problem? There is a fix, because when making all the linkages with big return spring for the twist grip throttle I had to figure in the amount of total cable movement and match that to the amount the throttle on which the carb butterfly valve could move. The hinge for a door I cut up and used with return spring and that worked for me. I added a length of metal to extend out the movement range of this hinge piece. Then with another stationary piece of metal that the end of the throttle cable came though, I tried various distances from the axle on the hinge metal extension to try and see how much movement I would get. When closer to the axle then more movement with the same range the twist grip has. When further out from the axle less movement with the same range the twist grip has. I will try to get a picture for you to see, but note eventually this will have to be encased with a metal cover to protect it which I will be making as well. The size of this all seems a bit large and a more compact design could obviously been made, so I encourage you to do a little looking around.

But remember the important here is that the angular movement is what makes this adjustable to match the carb butterfly valve range of movement with any twist grip throttle.

One more thing to note is that I had some much movement to the throttle of this twist grip that my wrist could not go that far around to get to go full throttle and that is why I put a stop for maybe around 80 degrees of a full 360 degrees rotation.

What I built works, but it is just the way I did it. If you can find what the manufacturer has to add to the problem you encountered I would start there first. I only had this way of making my setup since the carb that I got was to work on a lawn mower engine and the engine I had even though it was from a lawn mower had a different type of carb so all new linkages had to either be bought or made by myself. I looked at the stuff that was at the go-cart/mini-bike/atv store and nothing would work with my setup.

See in the attached picture where just to the left of my index finger is a hex nut for which a screw fastens that "J" shaped piece of metal to which a powerful return spring is attached. Now just below the hex nut not shown is a fine drilled hole for which the end of the throttle cable goes through and one of those cable stop barrels that has a set screw to clamp down on the cable. Then for where the cable comes from with the sheath stop, look just above that to the stationary piece of metal that has the knurled cylinder with threads and a hex nut holding it in place. The starter recoil pull is a bit close to all this and so a rigid cover I will make to prevent the cord from snapping back and hitting the throttle workings I made.

The black plastic, is butterfly valve on the carb and so it does not get stressed there is a connection to it with a spring underneath the rectangular block of metal. That spring’s hollow center is on a vertical screw attached to the plastic butterfly valve part on the carb. The stops are the other long threaded screws for idle and full throttle stops. When the transfer of the rotational movement from the hinge goes to either stops end, the fine spring underneath I described but you cannot see in the picture, bends slightly, insuring that the full movement for idle min and full throttle max is attained.

Measure Twice
.spr.
 

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DuctTapedGoat

Active Member
Dec 20, 2010
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Well, I'd first have to ask if you set the throttle adjustment screws on the grip and on the carb are all the way down. Then I'd have to ask if you put the slide barrel in backwards. Lastly, make sure your idle screw is pulled out enough.
 

MEASURE TWICE

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Jul 13, 2010
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I wrote before more than necessary on last post, sorry about that. I had just found the previous other post on throttle problem from 5/17/2011.

Since now I understand you already had a good throttle set up at one time and it worked, you just are replacing the twist grip.

The travel ¼ turn 90 degrees is quite enough, I have limited as I said my home brewed design to put stops on a twist grip that went further than 90 degrees.

Rohmell has mentioned things that are good to look at.

There are also carbs that have a idle jet screw that are aft of the jet controlled by the throttle butterfly valve which is not to be mistaken for the other idle screw right on the throttle butterfly valve. Some carbs have both and both can be adjusted.

If the cable is too short then I would really presume you would see that as you hook it up to the throttle butterfly valve. When this was done if you were able to see that the twist grip was at idle and the connection to the carb showed at idle then it should work.

In the case that you re-route the cable afterward, then you may cause the cable to become shorter if the cable bends too much. This though would not account for but a little increase in throttle not full throttle.

If and only if there is enough of the total length of cable and covering available and you need more cable coming out by the carb end, cut off some of the covering, that will give you extra at the carb end.

Check to see if the cable move freely and does not stick. I use the dry graphite power that are used on locks to coat the cable then I put the cover back over the cable, works great.

Hope that helps.
 

wrx2bike

New Member
Oct 31, 2010
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california
Thank you guys for all your great advice to my lil problem. Hopefully I get some time tomorrow to put all this good advice to use and fix the problem so I can be up and riding again
 

MEASURE TWICE

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Jul 13, 2010
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I have thought of a possibility that may be the cause.

I remember when I had an English racer type bike that on the top frame bar the one between the seat post and the head set/handle bars), it went straight front to back. Some of these bikes had the rear brake cable routed along there with the cable bare. They only used cable covering for the portions of the cable forward and aft of that bar, but not along that bar itself. This allowed a rider to niftily grab the cable and pull on the cable to apply the rear brake with the same results as using the rear hand brake. The rear brake was applied.

Now understanding that, if that was for a throttle, then the throttle would be applied to go faster. I do not suggest anyone have this done intentionally, but I can see how existing throttle cable systems could approximate that happening. Here is how.

If you were to bump the cable for a throttle and the covering was not secured tightly enough with clamps at both ends by the carb and at the twist grip, then the cable covering could come away from the end stops for the cable covering.

This then allows the cable inside the cable covering to pull on the throttle to go faster.

If this were to happen and let us say that once after bumping the throttle cable and the cable covering came away from either or both of the end stops at the carb or the twist grip, but then return spring was not strong enough to have the cable covering return back into their respective end stops, the throttle would still remain applied.

If the amount that the cable covering slipped was enough to cause full throttle and the return spring did not make the cable covering go back to end stops at all, full throttle would be indefinitely applied.

To fix this problem the cable covering would have to go to its end stops, adjustment of the throttle, and better securing of the cable covering at the end stops.

If tie wraps had been used as securing method and they were not tight enough, but just tight enough to prevent the throttle return spring from having a slipped cable covering to return to the end stops, throttle would continue to be applied even after the twist grip was returned to what otherwise would be idle.

Measure Twice
 

vincent713

New Member
Jun 2, 2010
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Dallas
I have the opposite problem, my throttle moves freely now, it won't twist back like its suppose to. I have a 66cc Grubee kit, can anyone help?
 

MEASURE TWICE

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Jul 13, 2010
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Vincent713, Measure Twice here…..

Check to see if the cable moves freely and does not stick. I use the dry graphite powder that is used on locks, since to coat the throttle cable with it is another good use of the stuff. I hold a towel with a small amount cupped in the towel and draw the cable through it. It gets a good coating. Sort of meshes into the strands, giving it a dull grey color. I then put the cover back over the cable, works great.

Also are you using a big enough return spring and a good cable routing without too tight a radius bend anywhere along the length.

By the handle bar to upper bar on the frame, I use a lot of cable to allow for turns. I let it sort of bellow out to the front of the handle bars above the headset. If for some reason the throttle cable needs to connect to the carb with a 180 degree bend, then again a large radius is necessary to avoid any extra stiffness with the movement of the cable.

It would not be a good idea to have it have to go bend 180 degree bend, but since I had to make my linkages from scratch with my particular choice of carb and manifolding, I made sure that it just has nearly a straight path from the head set along the top bar and the over to the right just 6 inches. The movement outward to the right, to come in straight to the carb linkage happens along about 18 inches, so there is little resistance from the cable inside the covering.

Maybe some other people have found ways to fix this problem your noticing now. Did you do a search on this and other sites for a way to solve this issue?

Hope this helps.

Measure Twice
 
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vincent713

New Member
Jun 2, 2010
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Dallas
Hi Measure Twice,

I had to open the throttle assembly and upon close inspection I see that the plastic that holds the end of the cable was broken. I just ordered the whole right hand throttle assembly which means no riding for about 2 weeks! boohoo In the mean time, I can do what you suggest about greasing the cable with graphite powder. I made sure not to have a sharp bend on my cables as it would ruin the cables quicker. Thank you so much for your help, I'll be spending more time on this forum since my ride is down. :-||
 
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MEASURE TWICE

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Jul 13, 2010
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I'm beginning to think that maybe I ought to have a spare throttle cable and also a twist grip as well. I’d carry it with me and the tools to work on it if it happened to break.

I remember riding a bicycle (non-motorized) on a month and a half AYH trip from upstate NY Grand Isle to Bar Harbor ME and then ferry to Nova Scotia. It was not fun for about a week period while in New Hampshire in a mountainous area with a broken shift cable for the 5 to 10 gear shift on a 10 speed. No granny gear 1 to 5, stuck in 6 to 10 is what I had to ride with.

You know now that I think of it, I probably could have rigged something to pull the 5-10 shift inward and having it left in position so I would then be only stuck with 1-5 while riding to get close enough to a big town with a bike shop.

Glad you found out what had broken. I suppose JB Weld and a Dremel to grind to shape a part to fix the problem might hold depending on what happened inside the grip on your throttle. I had initially before a buying a twist grip from the shop, hacked an old bike by the trash with a twist grip shifter. I removed a part inside that made the detents and had a shifter turned analog (a twist grip throttle).

The thing I did not like so much about the shifter was that you could only twist it on the 1/3 inside of the grip with thumb and fore finger which is not as useful as a throttle control. Thinking I could modify that too, I finally got the proper part at the shop.

Just to not gore you out, but for safety sake, forget using one hand reaching for the throttle at the carb while riding. I did that and it was not too difficult, till the flywheel shroud, with a small enough gap let one of my fingers hit the flywheel fan blades. I probably should have had stitches as it kept coming apart for two weeks with a band aid. Butterfly stickies and a band aid I know about now, but best left to a doctor to get it right.

Measure Twice
 

vincent713

New Member
Jun 2, 2010
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Dallas
Yeah these cheap plastics break easy and the part was too little to even consider JB weld. I just ordered a new assembly on ebay for 8 bucks. I might even JB weld the whole surrounding plastic just so it won't break again. What kind of bike do you have? Mine is a Raleigh hybrid 12speed, I'm at work right now but I'll post some pics when I get home.