Throttle feel

[Zombie Master]

While working on my 1984 R100 I noticed the throttle feels a bit rough. Kinda lumpy. It works all right when riding. My other bikes are perfectly smooth. Is it the design of the chain and cam throttle mechanism that feels different? How does yours feel?

[ME 109]

Put up with it as long as you can, then change the whole lot, throttle tube, gear with the chain, upper cable, lower cables, splitter.
Check the throttle tube housing for wear....it may still be ok.
I changed all mine out not long ago and the throttle now snaps back. Feels like there's another ten horse power.

[Rob Frankham]

The problem is that the bevel gears in the twistgrip wear and what you are feeling is the worn teeth catching against each other. Lubrication might make it temporarily a bit better but won't fix it... in fact the only thing that'll fix it is to replace both the twist grip tube and the bevel gear. Be aware that, on some models, replacing the bevel gear also requires the replacement of the cover that goes over it due to a design change... not sure of the date. The old type bevel gear is NLA.

It's a job well worth doing as soon as you can because a) it makes a big difference to the feel of the throttle and b) if it is a nuisance, then the gear is very worn and wearing very quickly. The next stage is that it'll start slipping teeth (very soon)... the effect of which is that you go for full throttle and only get half... which can be quite embarassing to say the least. Needless to say, the part of the rotation where it slips is the part where it gets most wear... i.e. the first quarter of the turn.

Not a cheap fix but an essential one with no alternative unless you got for an aftermarket throttle assembly with all of the issues that brings...

Rob

[Zombie Master]

Hmmm sounds spendy, but then again, throttle control the most important riding skill. I've always, since I got my first airhead in 1972, pulled apart that mechanism, and kept it lubed. The four airheads I've owned never had the smoothest throttle feel. I guess there is no way of measuring the wear on the teeth?

[Airbear]

I replaced just the gear and throttle tube about 12 years ago in an attempt to cure the lumpy feel. It made very little difference because the body and cover were also badly worn. I put up with it until two years ago when I bought a whole new throttle and cables from Motobins. I also fitted lighter return springs from a vendor whose name I can't remember. The difference is amazing - the first couple of rides were a bit scary in fact. As ME109 says it feels like an extra 10 HP. I recommend the $pend.

[Zombie Master]

Thanx! Not easy to find these parts. Moto bins seems to be down. Is the throttle cam disc the same part on all the models?

[Rob Frankham]

The wear on the teeth is normally quite visible if you clean off all of the grease... but if the feel is as bad as you say, then there's no need to see it, it needs replacing.

Thanx! Not easy to find these parts. Moto bins seems to be down. Is the throttle cam disc the same part on all the models?

No the cam and chain are model specific. They also the differ dependant on whether the bike has one or two cables at the control. You need to get the set that fits your machine... Motobins and Motorworks websites are both up this morning but I'm sure there are shops your side of the pond that can help. BobsBMW comes to mind, they seem to get a good press though I've never used them.

Rob

[Zombie Master]

Wonder if this would cover it?

Screen Shot 2021-02-19 at 12.03.40 AM.png (46.14 KiB) Viewed 1920 times

[Rob Frankham]

Three points...

1) Do you know if you require a replacement cover for the bevel gear recess? The designed was changed, not sure when, and the older style cam disk and cover are no longer available. The later type work perfectly but only if you replace both.

2) I'm a bit confused about the cables. You either need three cables if the handlebar mount only accomodates one (i.e. one from the handlebar mount to the splitter under the tank and one to each carb from the splitter) or, if your mount accomodates two, you need two longer cables one for each carb. The arrangement varied by year. I think yours should be the arrangement with a splitter but I'm not sure.

3) If you do have a splitter, it's worth examining it to see that it's in good condition while you're changing everything else.

Rob

[Zombie Master]

Yea I should only need one cable to get to the splitter, I have to determine which part number that is. I'll have to measure the cam disc to see if I need a new cover. I'd like to get the OEM heated grips. I wonder how well they work. I could always install undergrip heaters. Are there switched accessory jacks in the headlight?

Thank you !