Carb angles for dummies

[reimair]

After looking at all the detailed info regarding carb angle settings it appears to me that it has been overly complicated. Secondary opening angle and accelerator pump angle are pretty much hardwired in place and should be correct except for physical damage. This leaves only adjusting the cables for fully closed and fully open and then making sure the Port valve opens shortly after the accelerator pump starts to move. Then possibly minor adjustment with cable on the Port valve setting to eliminate the lag.
This doesn't require removing the carb or measuring angles and should get the machine running decent unless there are other carb issues. Relying on cables alone for such important settings seems like a poor design.
The above approach worked well for me in a very short time, surprised how strong and smooth the RE5 can pull. 

Inviting "experienced criticism" of the above idea/method. 

[wayne]

The original factory spec was accelerator pump and port valve both opening at the same time, 35 degrees. Using this method, there is no need to use angle gauges etc, you can, as you say, do it on the bike.

EDIT: Assuming an otherwise perfect carb, the above will work to time the AP and PV as long as the AP hasn't been modified to Bulletin 9 spec. But how do you know, without angle gauges or removal of the carb, whether your accelerator pump setting has been changed to Bulletin 9 spec ? If it has, aligning the AP and PV will have the PV opening too early (13 degrees before the earliest the secondary can open) and I don't think you'll end up with a smooth transition through the rev range.

Try aligning them. If it works, to hell with the theory. It takes 10 minutes and you won't lose anything.

More typically though, if you got a smooth running carb with no hesitation or flat spot doing that on your first or early attempts, you have no idea how lucky you are. I'm genuinely pleased it worked for you. A hesitation or flat spot has much less to do with the setting than with other issues in the carb.

For the majority of us, it generally doesn't fall into place that easily. I've only managed the miracle you speak of once myself and considered it sheer "arse" as we'd say down here. I felt at the time that the bloke I did it for would walk away thinking "that was easy, what's all the fuss about ?". Don't fall into the same trap, just appreciate you've been lucky with a carb that has no other issues.

If the accelerator pump angle of activation was changed to the Bulletin 9 spec, it's a bit harder to get it right by eyeballing as there's 7 degrees of difference between when the AP starts to work and when the PV is supposed to start opening.

As I've mentioned in the past, I've ridden 100% hesitation free bikes that used the PV/AP aligned both at 35 degrees and ones that have the AP set at the 28 degree point. Either can work, but I'm afraid to say both methods more often than not don't respond that quickly or easily and it's not the setting, but other issues with a very complicated motorcycle carb.

[reimair]

Thanks Wayne. I was not aware of the Bulletin 9 spec. Probably a good thing as it would have voided my having a "arse day."

In my case I found the cables where not set to allow for full throttle and PV valve was opening way to soon. When I got the bike it was a non running project but had had the carb rebuilt. (Looks like he got it right)

Very pleased with how the rotary starts, runs and pulls. Did not expect that much power from the bike. This from a guy who has a Kawi H2

Heres to hoping we all have some more "arse" days in our future

[wayne]

I wish I could "arse" a few more things around here. Keep using that saying, you'll fit right in down under : )

They've got fabulous torque. It'll leave the MAB waterbottles dead in a 5th gear roll on from 80 kph. I don't think it'll lose against the earlier JKL's either (Mac B ?)

Given a twisty road with 15 to 40 mph corners, there's not much from the era of that size that'll stay with it. The neutral handling is a big plus, but mainly the ground clearance is outta sight for the vintage.

[reimair]

Have now changed my original plans for the RE5 from just riding it to shows to now planning on putting some miles on it. It rides much better than expected. Hopefully score a luggage rack to make it more useable. 

Got up to speed on the term "arse" and now you throwout "MAB" to describe the kettle??

Here in Canada this is a seldom used term for "Mad Australian Bloke"

We are buying into the new PC culture fairly fast so we have been encouraged to not use it any more. 

[ap951]

I believe Wayne is referring to GT750 model designations. First year was a "J" model (1972) followed by K, & L.
These early models had standard round-slide carburetors. The "M" model came out in 1975 (just like the RE5M), followed by A & B model.
These had lower compression & CV (constant velocity) carburetors

[reimair]

That makes a lot more sense in hindsight. Still left wondering what a Mac B is. 

[Jess]

MacB is the definition of a "MAB"

Just my non PC opinion...

Best

[wayne]

Indeed, MAB, Mad Australian Bloke and MacB are freely interchangeable down here if you're struggling with these acronyms Remair.

MacB, board prowler and bike fiddler extraordinaire, owns both an L model waterbottle (the last of the "torquey" versions) and an RE5 so would have an opinion on this.

And most other things.

[pmcburney]

I'm sitting right here, you know...


The 'L' model (1974) GT750s are torquey-er than the later models being the last model fitted with the crossover pipes and the milder porting - they can't stay with an 'M/A/B' model (1975 on) with the wilder porting and higher compression once wound out.
An RE5 is altogether a torquey-er beast than any GT750 IMO, and will easily romp ahead a good few bike-lengths in a roll-on between the two and will continue to pull strongly long after a GT has done its best.

Well, that's my SotP (seat of the pants) experience, anyway.

Besides, I'm not mad, just a little cranky is all.