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FCR CUSTOM. YZF450 QUAD. Lots of pictures.

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I guess I should start at the beginning.

About 4 years ago when I first bought my DRZ SM I knew very little about the bike in general and the FCR carb other than the fact that it was the one to have!

So while looking on E-bay I came across an FCR listed for fitting a DRZ straight swap for the stock carb. with only a few hours left and zero bids I won it for £46. Alarm bells should have rang but I knew nothing of FCR carbs and bought it on impulse.

 

I quickly learnt that it was not in fact a straight swap and after some research on here and the UK DRZ forums found out it was from a YZF450 quad bike and would require some serious modification to work.

So with that it was relegated to the back of the wardrobe and there it sat for a good few years.

 

Just recently with all the talk of modding variants of the FCR to fit the DRZ it sparked a passion for me to drag out the old girl and give her a chance. I always knew that it was possibly to fit the carb but I was unsure if I had the means of doing it my self. 

 

So what will follow is every step I took to achieve the carb to fit, its going to be a long read so sit back and settle in for the ride.....

 

The carb in Question. YZF450 QUAD

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First thing was to get some dimensions of the stock carb

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The stock carb has an intake bell diameter of 58.23mm

and an exit bell diameter of 41.11mm

 

The YZF carb has an intake bell of 55.49mm

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and an exit of 48.24mm

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The over all length of the stock carb is 95.52mm

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While the over all length of the YZF is 86.45

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I needed to know these figure for reference later on when I made the velocity stack.

 

First thing I did was remove the TPS housing but in doing so you lose the idle stop and adjuster

The TPS housing case unscrews with security torx heads revealing the throttle shaft and idle stop.

 

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Remove the nut on the end of the throttle shaft.

 

Next remove the screw holding the slide plate to the throttle shaft.

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Next remove the idle stop arm from the throttle shaft.

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and finally remove the throttle shaft. as you pull the shaft out the return spring will unwind rapidly.

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Once the throttle shaft has been removed the TPS housing can be removed.

First unscrew the center screw. Thread lock holds it in place.

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next remove the outer casing screw, again thread lock holds it in place.

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With the two screws removed the housing will pull off away from the carb body.

 

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Next the throttle shaft needs to be cut down. You will need to make your own measurements but mine require 28.46mm to be removed.

The shaft is easily cut with a hack saw and de-burred with a file.

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Next a cover has to be made for the end of the throttle shaft.

The hole is 17.50 in diameter

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and 28.41 long

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I made the cover from 3mm aluminium and cut it out on the band saw. hand tools could also be used.

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and cleaned it up on a sander.

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then used the existing screw to fix it in place.

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This covers the TPS housing removal and throttle shaft modifications

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With the TPS housing removed the carb has lost its idle adjustment, this needs to be replaced in the usual spot under the throttle wheel.

this part is very tricky with the potential to ruin the carb if it goes wrong. no specialized tools are necessary apart from a 0.5mm metric tap.

Take your time and it should all go smoothly.

First center punch and drill a 2mm hole directly above the boss at the top of the throttle housing. You need to be very accurate when doing this.

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The ideal is hit dead center of the boss in the casting directly below. This is the part where you need to be spot on. If you drill the boss off center there is a chance that when tapping the hole the casting will crack and not support a thread.

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With the 2mm drill bit drill all the way through the boss.

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then increase the hole size to 4.5mm going up in 0.5mm drill bit sizes.

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You may need to increase the hole size at the top of the housing to give you better access as you increase drill bit sizes. its safe to drill a larger hole in the housing as long as it does NOT protrude into the slide plate well.

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Next you will need a metric M5x0.5 tap. This is a fine thread pitch not to be confused with the more common M5x0.8

You will need a M5x0.5 tap that is at least 70mm long.

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you can now tap the 4.5mm hole. take your time doing 1/4 turns at a time.

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You can now use the idle adjuster from the stock mikuni carb.

You will need to cut away some of the rubber hosing and also file down the metal shaft so it clears a casting on the carb body.

I did this by wrapping masking tape around the end of the adjuster and inserting it into a cordless drill. I then used files and sand paper to reduce the shaft diameter.

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You can see how close the adjuster is to the casting.

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lastly add some springs to hold the adjuster in position.

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This concludes the idle stop adjuster.

 

 

The last modification you need to do to the carb body is to remove some material around the throttle wheel housing. 

This part of the housing hits against the bikes frame so it needs to be removed.

I used the disk sander again but a file will do the job too.

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the shiny part is what needs to be removed.

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the casing needs to be taken down very thin to give as much room later as possible.

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A lot of work has gone into the carb by this point, I'm still unsure of the internal condition of the carb, what jets it has etc but its cost me nothing but time so far.

fingers crossed it works out in the end.

 

The last thing that's needed to get this carb working is a velocity stack.

This is the part that a lot of people will struggle with. I've spent many nights trying to think of ways to make this part with basic tools but due to the precision needed I just don't see its feasible.

Ideally this part needs to be milled on a milling machine. I managed to do it on an overhead router but its not particularly safe however with care it can give very precise results.

I was tempted to try cutting the external sizes with hole saws and use a dremel tool to carve out the center as a DIY approach but I've not got round to that yet, Like I say its probably not feasible.

However I have noticed a lot of adapters turning up on e-bay from fellow thumper talk users so if you are unable to make your own thats always an option.

For me I didnt want to spend a single penny on an unknown carb that was still uncertain to work so I made my own.

 

From the dimensions I took at the start I mocked one out of some birch ply to test the shape and fit.

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Rough dimensions

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First was too large, second was much better.

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Once I was happy with the wooden mock ups I started thinking of what to make the proper one from.

Aluminium was my first thought but buying a single billet is quite expensive. Then I thought about nylon but again just as expensive as ally.

I then searched for thermo plastics and stumbled upon HDPE which can be made at home for FREE!

 

Google it to find out more but essentially its melting down HDPE (which is normally used for making milk bottles) and pressing it into a billet.

 

So after collecting about 10 large milk bottles and cutting them into small pieces I put them in a baking try and popped them into the oven at 180c 

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Before that I made a press to put the HDPE into once it had all melted together.

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After cramping it into the press and left to cool for a few hours you get a billet of HDPE.

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Which then machines very well indeed.

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After a few hours work it started to take shape.

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And finally after a few more it was done.

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I'm not advising any one else use HDPE to make their velocity stack I'm simply using it as I don't want to spend any money on this carb until I know it will or will not work.

HDPE seemed to be the best thing to hand. 

I do have a few concerns about it. We know its melting point is 180C (around 360F) but I'm hoping that as its on the cold side of the carb with constant air flow through it, it should never get any where near those temperatures.

 

The next concern is durability. I made a few billets of it and believe me this stuff is strong. I hit it as hard as I could with a 12oz hammer and it didn't even leave a mark. so again hopefully it will stand up to the task.

As for chemical resistance I don't know. I haven't checked its resistance to petrol or any other chemical.

 

If the carb does work I intend to replace the HPDE version with either a nylon or aluminium one. However if it seems the HDPE is holding up fine it will stay in there :)

 

So finally All the mods are done and the carb is almost ready to be tried in the bike.

 

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Oh while I was at it I also made a vacuum port nipple.......You didn't think I was going to buy one :)

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Or 3!

 

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Lastly I opened up the carb to give it a clean internally and check jet sizes.

 

the inside of the carb was pretty clean. the o-rings and gaskets where a bit crusted up but I cleaned them with silicone spray.

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and applied hylomar blue when reassembling. You only need a very small amount of hylomar. there should be minimal squeeze out when reassembling. 

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Lastly you need to remove the coast enricher.

All that needs to be done is to remove the diaphragm and insert an o-ring in its place. You also need to block the vacuum line. I used a piece of o-ring to seal the hole.

a smear of hylomar blue again and seal it back up.

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As far as jets go its running

155 main

45 pilot

90 main air jet

I dont know what the starter or pilot air jets are.

it has an emn needle on the 3rd clip.

2 turns out on the mixture screw.

 

I used hylomar blue on the velocity stack as its a non setting sealer so when I need to remove the carb it should make it a little easier.

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The YZF carb went in easy, I put the front boot onto the engine first and then pushed the carb into it. there is just enough room to slide the velocity stack up from the bottom to get it into place.

I should also mention that I used the rubber boot from the YZF carb onto the engine. it is a perfect fit over the engine side and the drz clamp can be used. the YZF clamp needs to be used on the carb side.

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and with the carb fitted

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Getting the air boot into place was a right PITA, its so stiff with zero access to get your fingers in there. It took a while but I think it got it sealed all around.

 

lastly I attached the throttle cables, I should have done this earlier to make life easier for me. 

And here it shows the clearance on the throttle wheel housing. As you can see it was important to remove that materiel earlier, there is only a few mm clearance.

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I totally forgot to drill the return cable hole so the nut and bolt can be pushed in from the side so I had to drill and file it in situ. Don't do it like this make sure you remember to do it before fitting the carb!

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And she is finally in!

I do have an issue with the throttle not returning. It seems to be sticking. I tried adjusting the cable at the lever end but its made no difference. can any one advise on this.

 

I also need to get a piece of fuel line as I'm using the bit from the mukuni carb which is a bit short and kinking.

 

So i primed the carb gave the throttle a few blips and fired her up. she burst straight into life :)

 

Idle was a bit low so i raised that. Also to mention the mukuni idle adjuster sits perfectly on top of my manual cam chain tensioner for easy access.

 

I left her to idle for a bit and all seemed fine.

 

So i went and grabbed my riding gear.

Wow what a difference. I have -1 +2 gearing but it now power wheelies so easy in first i nearly fell off the back!

Riding around it feels great. 

Though I dont think its running at its best yet. I'm getting a lot of popping on declaration.

I have e cams and an open end exhaust but stock header.

When I'm giving it lots of throttle its great pulls nicely in all gears however when i'm going slow at lower revs its feels a bit jerky. not stuttering as such just not smooth.

 

I was only out for about 30 mins or so but I'm over the moon so far. Obviously I need to ride it more to see how things go but if any one can give me some advice on the throttle cables and jetting that would be great.

I'm ok at making stuff but not to good one the technical side :)

 

I'll keep you posted with how its going. 

 

 

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Thanks for the likes guys :thumbsup:

 

I've been doing some research and came across this post.

Quote

if you get a lot of popping at chopped throttle... your pilot is too small... you get one pulse going through being too lean for spark ignition... and the next pulse richens it up so it can light...but then that lights the lean mix that made it to the exhaust without the spark lighting it... pop..pop..pop

 

Which sounds like whats happening to mine, as I close the throttle from quick revs there is a LOT of popping.

 

So I know it has a 45 pilot jet am I right in saying I need to increase the size of this to a 48-50?

I still need to adjust the idle mixture screw as I dont know if the bike bogs down when it is fully screwed in so I guess that is where I start.

 

Also does any one know what this nipple is for? I'm guessing its just a fuel overflow but I remember I had to take the tube off when fitting the tank and I forgot to reconnect it.

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and lastly does any one know the fuel line hose size as I have to order a new bit?

 

Cheers.

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Vent line maybe? Every carb vehicle I've ever owned has had a little pop on deceleration.

Edited by Bermudacat

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A little pop I like, this is a LOT of pop with the occasional loud bang!

 

Doing a little more reading it seems removing the coast enricher doesn't help with decel pop either.

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2 hours ago, -=fusion=- said:

A little pop I like, this is a LOT of pop with the occasional loud bang!

 

Doing a little more reading it seems removing the coast enricher doesn't help with decel pop either.

Quite the opposite. :)

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Oh really? thats reassuring. from what I was reading it was the other way round but that was info from a YZF forum.

 

Had another quick play around with the throttle cables, I opened up the housing at the bar end and lubed every thing up well but they are still sticking. 

Would it make any difference if I re routed the cables to try and take some flex out of them?

 

Also there is no way in hell im going to be able to adjust the stock idle mixture screw so going to order an aftermarket one.

 

lastly the bike starts right up strong with no choke but if I pull the choke out the bike will stall. What does this mean?

 

oh and fuel line hose is 12mm OD x 7mm ID if any one needs to know :)

cheers. 

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4 minutes ago, -=fusion=- said:

Had another quick play around with the throttle cables, I opened up the housing at the bar end and lubed every thing up well but they are still sticking. 

Would it make any difference if I re routed the cables to try and take some flex out of them?

 

 

lastly the bike starts right up strong with no choke but if I pull the choke out the bike will stall. What does this mean?

 

cheers. 

Routing is tricky. Make sure that they are not binding down the tank region to the throttle wheel.

Your idle is too rich. We're talking cold, right?

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yeah from cold. 

It's hard to tell as the throttle cable issue is holding the throttle in different positions every time I turn it.

I have to remember to twist it fully shut every time.

I also learnt not to twist the throttle too much when the bikes not running with a pumper carb, must have squirted a load of fuel into the engine when I was messing around with the throttle.

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Had another quick play with the bike after work.

Still cant get the throttle right. I've ordered a new idle mixture screw so when that comes I'll take the carb out again and have a proper go.

 

Took it for a quick spin and it seems to be running pretty well. I think the sticking throttle is the main cause of issues at the moment.

She pulls really well in all gears.

I think it might be a bit rich at idle as she starts right up with no choke. Would I be able to sort this with the new mixture screw or do I need to install different jets too?

If so I'd like to do that when I have the carb out next.

 

Also does any one have any tips for sorting the throttle cables. So far my plan is to remove the tube from that bar and give it a good clean and lube, then possibly re route the cables if I can.

I also need to move the engine mounts to the left side of the bike as I  forgot to do that when installing the carb and I noticed that the return cable is just hitting it.

Is it safe to remove both mounts? I don't have to brace the engine or any thing?

I also checked the temp of the HDPE velocity stack when I got home and it was cold to the touch so thats a good sign.

Other than the throttle I'm really pleased so far. Its a big improvement over the stock carb.

Cheers.

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I know when I disturb the cables, they can be a little fiddly to get set back. Here is how mine route.

 

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12 hours ago, -=fusion=- said:

Had another quick play with the bike after work.

Still cant get the throttle right. I've ordered a new idle mixture screw so when that comes I'll take the carb out again and have a proper go.

 

Took it for a quick spin and it seems to be running pretty well. I think the sticking throttle is the main cause of issues at the moment.

She pulls really well in all gears.

I think it might be a bit rich at idle as she starts right up with no choke. Would I be able to sort this with the new mixture screw or do I need to install different jets too?

If so I'd like to do that when I have the carb out next.

 

Also does any one have any tips for sorting the throttle cables. So far my plan is to remove the tube from that bar and give it a good clean and lube, then possibly re route the cables if I can.

I also need to move the engine mounts to the left side of the bike as I  forgot to do that when installing the carb and I noticed that the return cable is just hitting it.

Is it safe to remove both mounts? I don't have to brace the engine or any thing?

I also checked the temp of the HDPE velocity stack when I got home and it was cold to the touch so thats a good sign.

Other than the throttle I'm really pleased so far. Its a big improvement over the stock carb.

Cheers.

You can remove both of the cylinder head stays at once and transfer to the left side without issues.The motor is still braced in 3 other places;at the swingarm pivot shaft,underneath the sump to the frame and at the front of the frame downtube at the oil tank.

 

You may want to remove the bodywork and observe the throttle cables for binding.It should be bind-free when turning the handlebars from lock to lock.Route and secure then slowly put the bodywork back on piece by piece and when finished double check for binding.The throttle should always move freely and snap back smartly regardless of how the bars are positioned.

Edited by bumtarder
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Cheers for the tips. Your routing looks identical to mine. 

A friend has a cable lube tool so going to give that a go as well.

I'll let ya know how I get on.

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Afternoon again chaps.

 

So I was able to have another go at the throttle cables this morning. I took the throttle tube right off and was surprised at just how much crap there was around the bar! I'm surprised the thing moved at all.

So after cleaning all the gunk off and giving the throttle cables a good lube with a tool a friend let me borrow (which made life a lot easier I also did the clutch cable while I was at it) the throttle tube moves a whole lot easier.

I had to taker the carb out again and I found that heating the ruber air boot with the wifes hair dryer made getting it off and on a million times easier! just make sure she doesn't find out about the hair dryer.

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I fitted a new extended fuel screw. A word of warning spend a little extra when buying one of these. I got a cheaper one at first and it was total junk. the machining was well over size on the tip and it didn't fit into the carb at all.

 

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I also drilled a hole in the velocity stack

 

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and tapped it for a m4 grub screw

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This is because it's much easier to get the carb in place on the front boot then slide the velocity stack in from the bottom after.

 

I drilled a small divot in the carb that the grub screw locates in, this way I know the velocity stack is sitting in the right place.

 

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I also moved the upper motor mounts, damn where those nuts tight! I didn't think I'd get them off to start with.

The last thing I did was to add a washer to the return cable.

I found that the nut for the cable was falling into a recess in the carb housing so I couldn't do the nut up properly. 

I cut a notch out of a washer so it fitted over the 6mm thread then once in place I squashed down the gap with some pliers so it doesn't fall off.

Now the washer sits up against the out side of the throttle housing the the nut goes up to it.

 

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With those mods done I tired the throttle and thankfully it's snapping shut like brand new. 

 

I had to fit a new piece of fuel line as I wasn't happy with the one I used off the mikuni carb as it was pinching.

I tried several different positions but ended up like this. Because the nipple on the yfz carb points up its difficult to get the line in place with out it kinking.

 

Does this look ok? I know it look poo but will it function ok?

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I actually cut it down a little more after this picture and now it tucks up right under the petcock.

 

Lastly I think its still a bit rich at idle and 1/4 throttle. I got a 48 pilot jet but I think I should have gone the other way with a 42?

I'm still running the 45 at the moment.

 

any advice on the jetting?

 

cheers.

 

 

Edited by -=fusion=-

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Just been out for a little while to see how she's running.

At WOT  it's great pulls really hard in all gears. 

at lower revs it feels a bit rough.

 

I had a go at adjusting the idle mixture screw. 

When i turn it all the way in the revs get higher, then when i back it out they drop down. 

I turned it to 2 turns out and it seemed to idle fine however if I back it out to 3 or even 4 turns out there is no change.

 

Am I right in saying the idle is too rich and I need to go to a smaller pilot jet?

I have a 45 pilot in at the moment, should I try a 42 or even a 40?

 

I also have the EMN needle on the 3rd clip, would it be a good idea to go to the second clip from the top?

 

thanks guys.

Edited by -=fusion=-

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Hey all,

It's been a while since I updated this post and I wanted to make a final conclusion of this carb conversion.

As of writing this I'm very happy with the results. The carb is performing very well and I think I've finally got on top of the jetting.

The HDPE boot adapter is holding up very well too, No problems with it at all. I Just use a little hyomlar blue every time I install it which helps make a nice seal on the carb.

 

The final jetting I've settled on for my bike which is an SM with E cams, k&N air filter, 3x3, open exhaust with stock headers.

main jet 148

pilot jet 40

pilot air jet 100

starter jet 70

leak jet is stock.

extended fuel screw 2 turns out.

Bike starts with choke and idles well and has good power through out the rev range in all gears. 

 

a couple of follow up threads here also.

thanks to all that helped along the way. Happy riding :)

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