Hi guys

So I spent the morning changing my carb and managed to achieve 2 things.
1) Got comfortable removing and installing carbs (stock CVK and new FCR35)
2) Change air screw on the stock carb to the kouba screw

Anyway, it seems the mounting flanges on my eBay special FCR35 carb (that supposedly came off a mid 90's KLX250) aren't quite right. The airbox side is a little bigger diameter than the stock one, but the airbox boot fits over it so there isn't too much of a problem there.

On the engine side, things aren't quite as rosey. as the flange diameter is a few mm too small, and it seems a little too short too. Now, the rubber boot is supple enough to be able to clamp to the neck tight enough to not leave any noticeable gaps. With it being too short though, it means the carb doesn't quite mount up correctly as it rests on the starter, and I cannot seem to be able to mount the throttle cables. (I followed NoBrakes advice given in this thread to try and prevent the carb sitting on the starter - but it still didn't work). Before I order a new neck I thought I would just see how the engine runs though, and again things are not rosey



Would you guys mind watching the video below and telling me what you think the problem with the carb is? Per advice given by AgoosSS and RaceGass in the Pumper carb thread (https://www.kawasakiforums.com/forum...9&postcount=34) I have the following setup:
Pilot: #52
Main: #152
Fuel screw: 1.5 turns out
Needle: OCDVR with 3rd clip from the top

Video: http://www.youtube.com/watch?v=LlEx5xB9Y6U

It seems on the initial blip of the accelerator the bike chokes and/or backfires then recovers. My first thought is that the accelerator pump (AP) is squirting too much fuel into the engine which chokes it. This is where the Taffy mod comes in to play I believe. Looking at 2k1w=no$ mod, perhaps that would fix my problem (https://www.kawasakiforums.com/forum...hlight=taffy)?

Any advice would be welcome.

 

are you sure you don't have a vacuum leak at the intake manifold?
Spray some carb cleaner around it while it is idling and see if the RPM's change, then look to the AP.
Also,,as an after thought,,, was the bike warmed up? choke on or off?

 

By "intake manifold" I assume you mean where the carb feeds into the cylinder head? There quite possibly is a leak there as the spigot does not fit all the way in and leaves about a 1mm gap between the manifold seal and the spigot before I tighten the clamp. I thought I had tightened the clamp enough to seal it off, but quite possibly (probably even) didn't get a perfect seal. The carb cleaner test is a good one - I will try that next time I try fit the carb again.

I think I have sourced a spigot for a DR350 that is 6mm longer, and has a 2mm larger outer diameter than the current spigot at the engine end that might sort that problem out.

After some advice from kbekus I have done an AP mod that should limit the length of the pump on acceleration nicely. It is basically a collar for an RC car (got it from a habby shop for a couple of $) that fits over the wire shaft that pushes the pump. Brilliant in its simplicity - just hope it works.



Yeah, the bike was warmed up. There is no choke on the carb from what I can see - which could make things interesting in the cold, but I'll cross that bridge when I come to it.

Thanks for the advice. I'm still open to more advice and opinion.

 

I looked at nobrakes thread and it apears that you have your carb fitted closer to the motor than HE was able to, so i guess you have it in the "Spigot" far enough. from the video i can't tell if it is lean or rich. no choke????? hmmm i don't think i would have done that model carb.

 

that sounds lean to me the more i listen and watch your hand moving the throttle.
try blocking off the airbox partially and see what happens since you dont have a choke.
if you wick the throttle several times it should stall if it is rich, and you will smell it, and your plug will be dirty.

 

I'm glad you mentioned that coz it made me take a closer look at how his fitted up. I reckon his spigot was longer than mine coz if you look at the gap between the cylinder head and the cable mount (green arrow) there is a smaller gap on mine than his. So although my spigot gap (yellow arrow) is smaller than Nobrakes, I think his carb is further back than mine - so your original suggestion is still possible.


Yeah, I find it strange too. If you look at the pics in the links below and can spot a choke please point it out:
http://i629.photobucket.com/albums/u.../aDSC_0092.jpg
http://i629.photobucket.com/albums/u.../aDSC_0094.jpg
Can't even see one on the exploded view of the carb: http://www.showandgo.com.au/carbie/hfcrexp.htm

OK, thanks. Would that be lean on the pilot or the main jet? If it is idling OK, the pilot and air/fuel screw setting would be about right, wouldn't they? So that would mean it's lean on the main... is my logic correct? If it's sucking extra air in at the manifold then you are probably right about it being lean and causing that pop.

I've just run into another problem - I tried to remove the current spigot nd couldn't. On closer inspection it looks like the previous owner kindly used red loctite so the spigot will never come off. I need to think about how I am going to tackle this a bit more. I am loving learning more, but getting frustrated now, and beginning to wonder whether I have wasted money on this carb

 

So I have spent some time thinking about how to mount the carb up. Because I cannot remove the spigot that is too short by about 20mm, what I am thinking of doing is making up an "adaptor".

Something like this:


The spigot is currently about 17mm long with an outer diameter of 40mm. It needs to be about 35mm long and have an outer diameter of 42mm to fit up to the engine mount properly. So if I can find a pipe with an outer diameter of 42mm that is about 20mm long and has an inner diameter about the same as the spigot, it will fit up nicely to the engine mount where I can clamp it. Then if I can find a rubber tube with an inner diameter of 40mm I can stretch it over the spacer (42mm) with a light clamp, and fit it up nice and snug to the spigot.

The bush mechanic in me says that it might work, but it certainly won't be optimal as extra turbulence will probably be introduced with the changing inner diameters of the tubes, and the extra length of the intake. But I would like to know what you guys think.

Thanks in advance.

 

Gezz that carb is big and looks like a pain to fit………… I was looking at an FCR originally but now I am glad I stuck with the Mikuni.

As I am not really familiar with a FCR carb and I cant really tell from the video but agree that it would be stalling if too rich so I am thinking lean as well……….. Do that air leak test with some carb cleaner take make sure there are no leaks causing it.

Also if idle is ok then it won’t be you pilot....... I also doubt that it’s your main jet as this circuit is more for 3/4 throttle to WO throttle. Because your probably blipping the throttle between ¼ - ¾ it would more likely be your needle setting so if there is no leak try raising your needle 2 x positions.

 

To release the locktite, the part needs to be heated to about 250f. It can be done with a propane torch. Have the new "spigot" before you start because you may toast the old one. Don't get carried away with the torch. Just heat it until the bolts can be removed.

Remove the connector to the air box, cover about 1/2 the carb with your hand. Blip the throttle. See if it still backfires.

Don't guess, Be sure you know what you want to change.


David

 

When you DO find it is lean,,,, don't go changing jets until you sort out the AP.
make sure it is squirting like it should.