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bike nut
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I am look into fitting 43mm Honda CR 250 fork stantions running in Varadero lower legs & damper rods. You read it here first!!!!!
Amazing thread!

Fantastic write up Firedero!

Wish i could come have a blast on your dero to see the difference compared to mine!

Now to find some VTR carbs......
 

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Discussion Starter #22 (Edited)
Hi,

Thanks,


Some on the Bay tonight (21-04-13) Item number:171027685099.

He might do a deal for the carbs, inlet rubbers, airbox & trumpets ??

If intrested I can post some pictures of the modified carb plate holes, also the intake shorkel.

If you go for it I will try my best to iron out any problems you might come across.



Good luck.
 

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Discussion Starter #23
Hi everyone,

I thought I would update on the carb mod & the settings that I finally settled for.

After quite a lot of carb fiddling, I finally settled for Hawks setup that was mentioned previously in the thread & original paper air filter. It runs really well.

It is still my daily ride & since the fitting of the Blackbird front & CBR rear wheels it’s a proper hoot to ride.
I have been gathering the parts together to fit VTR cams into it & I am just waiting to get some manual cam chain tensioners to fit whilst doing the exchange.

The next thing I started to look at for a bit more go was velocity stacks.

I had read about the Moriwaki & HRC velocity stacks that were fitted on the VTR race bikes & found a chap from Canada who has the original Honda cad drawings & is making some accurate cnc copies for around $200.

So, with that price in mind & the large amount of positive comments on various VTR / Firestorm forums from people who had fitted them (5 bhp in the midrange), I decided to have a go & make some myself!

I started looking into what bikes are fitted with high performance 48mm ish intake diameters (not many by the way) & decided on using Ducati 916 velocity stacks. They are 50mm internal diameter & all over eBay for around £20 a pair. All I did was remove the original Ducati trumpet mountings by grinding/sanding the trumpet bases to the thickness of a coke can. I did this using a 4” grinder fitted with a Roebuck flap wheel to remove most of the material then an upturned belt sander held in a vice to sand the trumpet base to a wafer thin tube capable of fitting into a short VTR trumpet.

What you end up with is the original Honda fool proof trumpet to carb fitment, then the Ducati aluminium velocity stack with a far superior bell mouth. The transition from one to another is minute due to the carefully sanded wafer edge. Lightly tap together & use a glue of choice to stick them together.

I was a bit worried it would play havoc with the fueling but that has not been the case, the difference is unbelievable, it pulls so hard, you have to recalibrate, beware of second gear power wheelies! All this from such a simple modification.

It has cost me £15 for a pair of Honda trumpets & £15 for a pair of Ducati trumpets then about an hour to sand & glue. The biggest job was stripping the bike down to gain access to the air box!

If anyone does have a go at the VTR carb modification then you must do this modification. You will be shocked.

20uy6gw.jpg


This is the bike Honda should of built.

Regards.

 

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yet another Dave
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Will an SP2 engine fit?
 

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Discussion Starter #25 (Edited)
Hi,

I fitted a Yamaha R6 throttle tube yesterday, it’s a tried & tested quick action throttle modification for various Honda’s.

I thought I might get away with a quick swap…. no chance. Fairing & tank off to gain access to the throttle cables & remove all the slack. Then remove the Barkbuster hand protector to slide the throttle tube’s on & off.

The diameter of the original pull & push (throttle tube) cam is 34mm, the R6 is 37mm. Also the width of the cam’s are different, 5.6mm for the original & 7.3mm for the R6 tube.

It was time to get the flap wheel & grinder out & reshape, initially taking the width down to the required 5.6mm so it fitted into the housing, then hand filing the inside of the top aluminium housing (to allow room for the cable due to the increased diameter).

I tried to assemble again but the 90° ptfe insert needed reshaping also….. Finally Into it all went together.

What a job.

Is it worth it? Not sure yet! Why do it? Why not?


I can still put the original tube back if it's not to my liking & I think the 125cc model uses the same throttle assembly & they are in abundance on eBay for around £15 posted.

The rain started as soon as the tools were put away so the only test so far was riding it 10 feet to the garage, the word responsive came to mind though.

Will update soon.

Regards.
 

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bike nut
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So if i want to do this now tried and tested mod (thanks for being the guinea pig!) I will need the following?

VTR carbs and inlet rubbers

Ducati 916 velocity stacks

And thats it?

I will happily change my carbs out but i cant be bothered playing with the carbs every week getting the set up correct

this is the set up for the carbs?

The main jets fitted are 170 front – 175 rear. (The 170 main is from the rear XL1000 carb).

Standard VTR springs.

Pilot jets are #48 (from a VTR w,x or y model).

The needle jets have their washers removed.
Pilot jets are 1 1/3 out front – 1 2/3 out rear.

Both vacuum holes are open.

Ram air filter mod fitted. -
Please explain this air mod?



 

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Discussion Starter #27
Hi,

This is what I wanted from the bike, it might not be for you.

If you are thinking of following the instructions on the thread, then please read them. Do not just skim over quickly & hope for the best, you will be disappointed with everything you do.

This has taken quite a lot of time to get it right, like a recipe, miss one ingredient & it will not work.

There are lots to this modification, you will need:-

VTR carbs,
VTR inlet rubbers,
VTR airbox,
washers for the needles,
Plugs for the pair system,
2 VTR short velocity stacks,
2 Ducati (748,916,996) velocity stacks.
Lots of patience.


Then you have to cut holes in the carburettor mounting plates for the Varadero fuel lines. And shape the VTR Throttle position sensor (TPS) so that it fits into the Varadero TPS plug.


The first step is to install a set of #48 pilot jets. Then you need to shim up the needles. Around .040" is a good starting point but will need to be tuned to each bike. Also there is more to it than just shimming both needles .040". One of the set up tips from HRC is to use one more shim on the rear needle than you use on the front. So what I do when setting up a set of carbs is remove the stock thin washer that is under the front needle and leave it in place on the rear. With this method you actually end up with the front needle approx. .030" higher than stock and the rear .040" higher than stock which seems to work well. The pilot screw set at 2 1\4 turns in the front and 2 1\2 turns rear as a start and the bike will work pretty good.


There is nothing new here, it's all in the thread if you read it.................


Regards.
 

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Discussion Starter #29 (Edited)
Hi Jamie, some photo's of the snorkel & a few others.





This is the hole that's required for the fuel pipe to go through.





These pictures show the pipe from the pair system sealed & the fuel pipe & various carb vent pipe routes.











Here is one of the TPS sensor that has to be modified to fit the loom. The plugs wires are the correct orientation, its just the connecting plug that's different. You can't just use the Varadero TPS, it will not fit.



Hope they help, a picture is worth a thousand words.

So they say :thumbup:
 

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Discussion Starter #31
Got my act together & ran her on the dyno, here are the fruits of all my work :thumbup:

My Big day & here are the specifications


Pilot
Front------1 turn out.
Rear-------1 1/4 turns out.

Pilot jets
Front------#48
Rear-------#48

Needles
Front------no washer at all.
Rear-------1 Std washer.

Mains
Front------#175
Rear-------#178

Slide holes
Front-------1 open.
Rear--------1 open.

Air filter------Std.

Ducati stack mod.

Varadero cams.

No porting.





The discrepancies are down to me! Because I was the one running it on the rolling road.

The runs are 4th gear full throttle power rollons from 2000rpm to limiter.
 

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Discussion Starter #32
I have been busy reading about various jetting setups & thinking about what step next.

I am not too sure about the hole in the fueling @ 6000-6500rpm so will leave that for the moment.

The fueling is definitely rich across the range, so this is what I'm thinking.

I think the Ducati stack mod has vastly increased air flow into the carb mouth & is causing the engine to run rich.

The pilots are around a turn or so out, the needles are as low as possible & the mains are Std & its still rich.

This is the plan.

Pilot
Front------2 turn out.
Rear-------2 1/4 turns out.

Pilot jets
Front------#45
Rear-------#45

Needles
Front------no washer at all.
Rear-------1 Std washer.

Mains
Front------#172
Rear-------#175

Slide holes
Front-------1 open.
Rear--------1 open.

I plan to refit the #45 pilot jets, purchase & fit a #172 main for the front & around 1~1.25 extra turns out on the mixture to compensate the smaller pilot jets.

This will be the new base setting & I will take her for another run to cross reference & report back


I think the rule of thumb is if you are 3 turns or more out on the pilot screw, go to the next larger sized pilot jet, or 1 turn or less out, go down 1
size.
 

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Discussion Starter #33
I decided to leave the needles/mains & run it with the free flow (homemade) Ram Air filter instead.

All back together now with #45 air jets fitted, Pilot~ 2 turns out front, 2 1/4 out rear.

Seems easier to start & snappier throttle also. You could say it sounds raspier, nastier too


Had enough today so will update with a seat of the pants test asap.

Hopefully it will run okay & will be interesting to see what's what on the Dyno again


 

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hiya still working on mine but could you please tell me what power/torque increases this has yielded the graph you posted seems to show an identical trace ?
 

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bike nut
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The claimed figure from Honda is 93BHP, although not sure if that is from the crank or rear wheel?!
 

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Discussion Starter #38
hiya still working on mine but could you please tell me what power/torque increases this has yielded the graph you posted seems to show an identical trace ?
The top graph shows power & torque :thumbup:

The lower graph shows power & fuel mixture :thumbup:

There are more gains to be had, the fuelling was way too rich.

It looks as if the stoichiometric ratio is averaging 11-1 & it should be around 12.5-1, correcting this should bring me closer to the 100bhp goal without the cams & head porting :thumbup:

Below is a graph that shows the increase in power & torque only from correcting the stoichiometric ratio.

The bike was an XR650 I think.

 
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