Undercarburetted?

[sund]

Reading the manual (Haynes) for the GS fourcylinders, it is stated that they are undercarburetted. As well is the GS two cylinders.

If that's true it should give me some more power switching to a bigger bore, eventually flat slides.

Will that give more power or do I need to punch the engine out to bigger cc's and a different bumpstick to gain more power?

I have both two and four cylinder machines about to be restored.

This is for the street, not all out racing, just a little more fun.

carsten

 

[hampshirehog]

GS750?

10 characters

 

[Big T]

Probably a translation error to Danish (or even English)

You can gain power without changing to another carb, but switching carbs alone will net almost nothing

If you want real power, figure to spend 1500 euros or more

 

[sund]

Thanks for the replies.

No, there' no translation error. I might live in Denmark, but I'm bilingual, and only quoted the book.

I do not look for more power, as much as a better running engine.

Searching various sources I've found out that it's not just a matter of undercarburation, it's also a matter of wrong/lean jetting from the factory.

I'm gonna try some different setups, and will be posting the results as they come.

I've also come to suspect the CV carbs as being somewhat sluggish in response, I'll try some of the old kind and see if that's the case.

 

[Steve]

I have a suspicion that when they said "undercarburetted", they actually meant "jetted lean". :-k

Depending on what size bikes you have and what years they are, they probably have very adequately-sized throats in the carbs, but might be able to benefit from some slight jetting changes.

.

 

[hampshirehog]

What's a bumpstick?

 

[Nessism]

Bump stick is a cam.

 

[tatu]

If they're undercarbed, then fitting bigger bores will make it worse, no?
Bumpstick?

 

[hampshirehog]

If they're undercarbed, then fitting bigger bores will make it worse, no?
Bumpstick?

See Ed's reply Chris - apparently it's American for cam.......

 

[duaneage]

Depends on the engine.

The 550 - 650 - 750 - 650 engines used 32 mm carbs at one time, some 850s had 34 I think. The 650 was just about perfect at 673cc for these carbs and most agree they ran the best. But in reality if you want to go faster then buy a larger bike, like a 1000 or a 1100, and be done with it.

Nothing against smaller rides, I have one myself, but it's all about expectations and personal preferences. I happen to love my 650 and it's enough bike for me.

 

[koolaid_kid]

I agree with Steve. From the factory they came a bit lean, so simple jetting changes should help. A larger carb will hurt your bottom end; you won't like it.

 

[duaneage]

I learned a lesson about carb sizing long ago and that is the carb should be appropriate for the majority of driving you do. A larger carb WILL flow more air and fuel at very high RPM, and if you spend all your time at 8000 RPM and above this works for you.
Most of the time your bike runs 3000 to 6000 RPM. A larger carb will have difficulty metering fuel at that range and the crossover from different stages will be problematic.

 

[Steve]

Depends on the engine.

The 550 - 650 - 750 - 650 engines used 32 mm carbs at one time, some 850s had 34 I think.

To the best of my knowledge, all 850s from '80 on, only had 32s, at least in the US market. Can not vouch for the rest of the world, though.

.

 

[duaneage]

To the best of my knowledge, all 850s from '80 on, only had 32s, at least in the US market. Can not vouch for the rest of the world, though.

.

i parted out an 82 that had 34mm carbs, might have been a mod but they looked correct. I think they would work on an 850, maybe better than 32mm carbs