Single carb

[Nathan]

Having now ridden Andy230's DR i now know why you would fit a single carb.

To mod an SRX is this a bind? or fairly simple. any recogmendations?

Nathan

[andy230]

Hey Nathan

Good to see you at the weekend.

SteveL fitted a big Amal to his.  Can you elaborate Steve??

I noticed when riding a stock SRX again how gentle the delivery is, with the 2 standard Yam carbs.  Presumably to take a bit of the "thump" out of it when fresh riders whip the throttle open...

YDIS:   You Do It Slowly!!

You can get round it by fitting 2 big identical carbs (ie. Keihin CR33s) like wot racers do, but its not a cheap option.

Alternatively the aircooled Yam quad (Raptor I think) which used the same top end on different cases has a single carb, and the manifold bolts straight on (apparently...).  I did a bit of reading about this with the intention of converting but can't remember why i didn't...  Seizure?  Fell off again??!  Not sure 

SteveH, wasn't there a Kwak 250 (ZZR?) carb mod??

andy

[squirrelciv]

Bit confused over here ;-? What was it abour riding a DR that made you want a single carb on a SRX??? Changing the carb wont alter the riding position :-)

[peterj]

The air cooled quad was a Grizzly I think, the Raptor being the 660 water cooled version.

I tried to do the ZZR mod after getting a cheap set of 30mm ones (I think some years had 32mm ones which would make more sense), but gave up when I found that the throttle linkage wouldn't fit under the tank, and that the carbs I had needed new float needles.

From what I've heard, the common single carb mod uses a DR carb on a Grizzly manifold, but requires the tank to be lifted up at the back, and (don't quote me) perhaps the oil tank modified/moved/replaced. I think there's stuff on SteveH's SRX page.

I'd definitely agree about the power delivery, particularly compared to the SR I had quite a while back. I always put it down to number of valves, but if a single carb does the trick, I'd be interested in giving it a shot.

[Nathan]

No no no, the riding poisition is perfect for me on the SRX

 I was amazed at just how quick the DR took off, the power is just there, with my SRX you can open it up and it chugs for a while and then speeds up, (i only know the basics on carbs) but andy reckons the delay is due to a double carb.

And if there is a cheapish way of swapping it for a single carb im sure the little mechanical experiance i have will allow me to do so.

Nathan

[Steve Lake]

Well, yes, I did.....this was what i had to do

1. get a manifold made up, had ond done in alloy by local fabricator, cost me £50 ish (can send you a pic if you're interested)
2. buy/obtain carb. I bought a 40mm dellorto with accelerator pump , cost about £120 (suppliers were very helpful, setting carb up to what they thought would be ok and included a bag of jets and needles in case i needed to change anything.
3. cut out front of airbox to accomodate the big bellmouth (you could make up a plastic plate to incorporate the carb into the box/filter assy)
4. with a rubber mallet, GENTLY concave underside of tank to make room for top of carb and cables, (I managed to split my tank 'cos i'm a pillock, so needed welding up, so at this stage the tap assembly was removed and the hole welded up, and a 1/2" pipe welded to the inside of each rear lobe of the tank as main and reserve outlets.
5. modify choke cable to fit dellorto choke slide, modify throttle cable to fit main slide.
6. blank off breather in top of oil tank, and weld in one near to filler (carb will foul the original), depending on the size of the rubber collar and depth of the manifold you may need to file off some of the top ridge on the oil tank.
7. As my manifold/carb didn't have a vacuum pipe take off, i blanked off the equivalent port on the fuel tap, (these taps have a diaphragm in them that is activated by the vacuum from the inlet port) so, my 2 pipes welded into the tank supply the main and reserve of the tap, but the tap has to be run in the 'prime' position, so there is no reserve function.
I have to ask myself if it was worth it, well, yes it was, not as difficult or long winded as it seems, so easy set up, SO easy to start (cold or hot), lovely tickover, not as economic, lovely inlet sound from the dustbin sized bellmouth, and better performance over the standard setup.
Am I still using it....no, trying out twin 34mm dellorto's at the moment on standard short yamaha rubber manifolds, the jury is out on whether there is any improvement
can you borrow the single carb/manifold to try it out...yeah sure

[Nathan]

That'll be going to the end of the queue then... the SRX needs that money elsewhere 1st
Cheers for the info.

will do some more looking into this on google...

Nathan

[Steve H]

Not sure how Andys DR is setup but I suspect it has lower gearing than the SRX. You may find a DynoJet kit and K+N filter would improve throttle response.

[themoudie]

Thanks to SteveL, I have his drawing and dimensions for this conversion. However, due to other 'commitments' (don't ask), self inflicted grief etc. still haven't given it a try.

Despite the Clubs name and the perception about these machines, they don't!!! THUMP.

I tried the Yam 350 YPVS rear sprocket of 39 teeth on Sally and it just made it uncomfortable to ride above 60mph, revs, tingling, like holding a horse tight back on the bit.

However, reverted to standard 37 tooth sprocket and rev to 5500 at least through the gears and off you go! Try a downward change and a handfull!

I'm still thinking dark thoughts about a 38mm Amal or Wal Philips on a Griz' manifold and will publish the outcome on here. Just don't hold your breath whilst I'm thinking, you'll go blue!

Cheers, Bill

[andy230]

I was amazed at just how quick the DR took off, the power is just there, with my SRX you can open it up and it chugs for a while and then speeds up, (i only know the basics on carbs) but andy reckons the delay is due to a double carb.

Or more accurately the YDIS method:

1) Whip the throttle open
2) Small primary carb opens up via butterfly
3) Engine begins to draw hard as it begins to make power
4) Subsequent vacuum then opens up the secondry (CV?) carb
5) Hey presto, you (eventually) get "full bore"

Just makes it a bit gentler lower down...

cheers

a

[Steve H]

4) Subsequent vacuum then opens up the secondry (CV?) carb
5) Hey presto, you (eventually) get "full bore"

Fitting the DynoJet kit involves drilling the CV slide air hole, this hole essentially dampens the acceleration of the CV slide. Bigger hole means a sharper throttle response, the needle has to be changed to match. Obvioulsy if it gets too big it all goes pear-shaped so dont get the Black and Decker out and randomly drill holes.

[Nathan]

This may be off the wall...

could you mod the carb so both open at the same time?

[Steve H]

This may be off the wall...

could you mod the carb so both open at the same time?

You can but it will restrict the full throttle performance, as the butterfly on th CV carb will go over centre and partilaly restrict the carb choke. I adjusted mine so that at full throttle the butterfly was horizontal in the CV choke.

[J Hop]

I looked into getting a dynojet kit but was put off by the £85 cost for a few drills for drilling out CV slide,secondary main jet, a 136 primary main jet, a CV fuel needle, and a new spring for above the diaphram on the CV carb.

Call me tight but that seems a bit steep.

[Steve H]

Call me tight but that seems a bit steep.

Agreed, but you need to bear in mind your not just buying parts but paying for the development time and knowledge to put the kit together. That said its still quite a lot of money.