More Grunt!

[Recycle1]

Hi, I am new to this forum and would like to ask for some advice. I have a much modified R100 which started life as a R100rs,
it has been twin plugged, and fitted with 38mm Del-orto carbs. I am not happy with low end performance and am considering fitting heads with a 32mm inlet and amal mk2 carbs. Has anyone done this? I was advised to put the bike on a dyno first!

Thanks in advance for any help offered
Recycle1.

 

[Kenny]

Revert back to normal OE carbs for best low down grunt.

 

[Rob Farmer]

Do you know what cam is installed?

I do know a couple of people who ran Amals on their airheads. Both run very well.

I went down the dellorto route but really wish I'd gone for amals instead. I may well change.

 

[timeandtide]

Revert back to normal OE carbs for best low down grunt.

Tautology old boy!!!

 

[Beemerboff]

Mk 2 Amals are stub fitting and the Amal carb company sell a molded rubber adapter which fits 32 mm carb inlet stubs perfectly, so fitting isnt hard, if you have the correct inlet stubs.
But the RS came with 40 mm and 32 mm carbs so if yours was originally a 40 mm bike you might have bit more work/ bodging to get them to fit. They also had 135/2.66 jetting but with my set up 150/2.68 works better.
You dont mention you air intake and exhaust arrangements either, they can make a big difference but everyone seems to get different results.
No mention of ignition system or timing , but IMHO the OEM mechanical system cannot be made to perform as well for twin plugging as a digital system which can advance and retard the timing as required. My twin plugged G/S goes OK with around 26 full advance.
Yoe dont state what you consider to be low end either - I like to keep above 3500 revs at all times so if low end to you is 2000/ 3000 revs you might find good advice hard to get.

 

[solidstate100]

Welcome to the site recycle1, lots of advice expertise experience and humour here.

Probably need more info on the engine really, you say "much modified' If you have a really wild cam in there and are running high compressions big valves etc etc simply downsizing the carb might actually have a more overall detrimental effect. In my experience a motor in a higher state of tune can tend to be a bit more top endy at the experience of the bottom end.

The advise to dyno it first it sound - start with a known data set, and work from there - could just be a simple as a re-jet needed.

 

[Ras Thurlo]

... also what exhaust system do you have?

Its possible you have a free flow system for the modded engine which prioritises top-end over low grunt

I changed the exhaust on a modded bike to a (quieter) system with more compression and the difference at the low end was big