Thumper Club Forum
Club House => Chatter => Topic started by: Nathan on September 19, 2006, 03:18:44 PM
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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
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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
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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 :-)
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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.
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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
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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
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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
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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.
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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
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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
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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.
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This may be off the wall...
could you mod the carb so both open at the same time?
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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.
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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.
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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.
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As an option to improve performance its still cheaper than buying a single carb and having a manifold fabricated.
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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.
Yes but should have recouped development costs by now (its a 20 year old bike).
Time to drop the price IMO.
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The other option is watching out for a pair of Keihin CR33's on eBay, not tried mine yet but being a slide carb, throttle response should be improved. That said since they are quite a bit bigger than standard carbs the air velocity for any given revs will be lower and therefore may not carburate as well at small throttle openings. That said the DR carb has to be a reasonable size and since its a single carb the air velocity will be even less.
Or am I talking complete b*****ks ?
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Yes but should have recouped development costs by now (its a 20 year old bike).
Time to drop the price IMO.
True but bearing in mind the total number of SRX's is low (compared to say a Fireblade) they cant have sold many.
But I agree and if it wasnt for the fact that my bike came with one fitted I would probabaly think hard before buying one. Still cheaper than a few hours on the Dyno,
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Development costs - perhaps 10 hrs on the dyno with a good tuner (if they were that consientious), not many parts required, say total development cost in the region of 500 quid. At 85 a time sold direct, that sounds like good business to me.
My objections to dynojet are that unless you are modding exactly as per the development bike, ie same pipe, filters, no internal mods, the stuff they sell you could still be way off for your bike.
I bought a set of drills for about 8 quid, the other 77 would buy a reasonable amount of dyno time. I don't object to lightly modding a needle with a file on a single, so all I'm missing is the CV spring, and I wonder why you need that if you alter the damper hole correctly.
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Again agreed, but if it were that bad a value people wouldnt buy them and Dynoject would have gone out of business years ago, also if it were that simple we'd all be doing it. I wasnt justifying the cost just indicating that its not as simple as shippng a few jets and springs.
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Again agreed, but if it were that bad a value people wouldnt buy them and Dynoject would have gone out of business years ago, also if it were that simple we'd all be doing it. I wasnt justifying the cost just indicating that its not as simple as shippng a few jets and springs.
Can't agree with you there SteveH. Take a look at Joe averages machines, (be they car or bike) And they will be filled with very expensive goodies sold as performance enhanceing, but not justifying the expense. Sometimes I get the feeling that if you have a crap/ordinary product, but hike the price enough, Mr muggins will snap your hand off.
I also firmly believe Dynojet price product in accordance with their percieved status. Market leader, needs/can get away with inflated prices.
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If its easy money why arent there more companies doing the same thing ?. If there was that much of a markup it would be very easy to undercut them.
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hi ,ive been looking for info on converting to a single carb on my srx 400 monoshock
reason why ?? well the honda xr's have single carb and seem quite raw with power
also the price of air filters and diaphrams from yam dealers !
and lastly cuz i cant leave anything standard pmsl
ive converted the bike for offroad/enduro type use as something to mess about on ....lost my bike license years ago and not gonna pay silly money to get back into riding bikes on the road....well overpriced now!!
anyway good to see more srx owners!
any pics of a manifold would be great !!
happy ridin
simon