Sorry, but a really basic carb jetting question!

[Gr8uncleal]

Why are the carb jets often different from market to market (eg between Europe and North America)? Are there always other associated differences, such as air filters?

On my Canadian GT550J I have the original set of carbs that came with it, but I also have a set of European market carbs and I was wondering if these can be used without any mods.

Again, apologies for it being such a basic question.

Many thanks.

Alan

[barney01]

The carbs are jetted differently because of two reasons.
1. USA had much more stringent emission laws
2. Different climate affects the fuel/air mixture. Higher altitude means more air pressure so more fuel is needed and vice versa.
Both sets of carbs will work but adjustments will be necessary.
There is a number stamped on the car body below the choke to denote the country of destination
Look here for other differences
https://www.oldjapanesebikes.com/mraxl_ ... s/page-A51

[Gr8uncleal]

Thanks Barney.

The emissions reason crossed my mind (I know, a very short journey!), but I thought it might be a bit too simplistic.

I also pondered the atmospheric reason, but wasn't sure about this, given that North America has so many different altitudes at which the bikes (and other vehicles I suppose) would be operating at. I read on another forum of a rider changing the main jet on his 2 stroke single trail bike once he got to a certain altitude.

You or another forum member kindly provided me with the carb model codes on another of my threads.

Thanks again.

Alan

[Alan H]

UK market carb details. If you'd like a copy of that service manual from 1972, PM me.
Click the pic and it grows like magic!

[Gr8uncleal]

Thanks Alan H, that's really useful.

I am mulling over whether to stick with the Canadian carbs that the bike came with or make use of the European set that I got with a load of other parts. One strand of logic says stick with what the bike came with, whereas another says that, as the bike is in Europe now, go with those!

Thanks again.

Alan.

[barney01]

I've had USA carbs on my J for 22 years and 40 thousand miles. I've lived in UK most of the time but also 10 years in the South of France which is a temperate climate. Worked fine in both
Would just fit the best condition set.

[Gr8uncleal]

Thanks Barney.

[teazer]

Just a slight correction there. As altitude rises, pressure and available oxygen drop so the carbs need to be leaned out. And with less air and fuel, you get less power. That's always an issue going over high mountain passes and if teh stock jets stay in, the thing is running rich to add insult to injury.