14 replies to this topic

[tomgale]

hi all,

 

I recently changed my carb from wax stat to standard jet, as there wasn't really enough room for the waxstat jet, causing it to hit the bulkhead and become bent, preventing it from moving fully into the body of the carb (sticking out about 5mm), however the mini was running just fine.

 

after changing the jet, I've encountered odd problems, It seems to be running very rich, any revs at all cause the exhaust to pop and splutter, (like some kind of bastard hybrid between a rally car and a 2-stroke scooter), as well as a huge cloud of black smoke. It also occasionally detonates the fuel air mix still in the manifold (big pop and smoke out of the carb inlet).

 

now the reason i'm surprised about that, is that the adjustment nut is wound all the way up (fully lean) compressing the spring between the nut and the locknut, plus using the piston lifting pin causes the revs to decrease, implying its running too lean. It also seems incapable of any running at all with the choke all the way in, 2mm or so out is fine, but the moment I push it all in it just dies.

 

What on earth is it doing? I wish I'd just left the horribly bent waxstat jet in now

 

thanks for your help, Tom

 

(oh, car is a stage 1 998, RC40 exhaust, 12g295 head and a HS4 carb)

[ACDodd]

Have you fitted the correct jet with 0.090" orifice, and not one for the larger hs6 carb with .100" orifice?

Ac

[tomgale]

Have you fitted the correct jet with 0.090" orifice, and not one for the larger hs6 carb with .100" orifice?

Ac

yup, at least I hope so, the bag from minispares said HS4 on it

[AlexMozza]

Setting the jet height at around 6 flats from flush usually gets the mixture to somewhat the correct amount.
Have you checked the timing too? Also what needle did you fit?

[tomgale]

Setting the jet height at around 6 flats from flush usually gets the mixture to somewhat the correct amount.
Have you checked the timing too? Also what needle did you fit?

 

when you say flush, do you mean the end of the jet from the bearing, in the carb throat itself? haven't touched the timing, might have to have a fiddle with that tomorrow, as for the needle, I didn't change it, I suspect it's either the one from the stage 1 kit, or possibly another one if the rolling road guy changed it. thanks!

[AlexMozza]

I mean the Jet. Get it sat flush with the iside of the carb, the area where the damper sits at rest if that makes sense

[tomgale]

i think im with you, shall try that tomorrow! 

[tomgale]

hi all, timing adjustment didn't cause much change, I spoke to the local mini expert,and reckoned that the new (old style) jet is supposed to run with the fixed needle rather than the self centering one, which is shorter and hence the fuelling is completely off. does that sound about right? and if that is the case, which needle should I be running?

 

Thanks

[Spider]

Needle and Seat in the Float Bowl Lid not jammed open or incorrectly set or just plain worn is it?

 

<Edit: Remove the Bell Cover and look in the Jet to see where the fuel level is, should be about 5 - 8 mm down the Jet (though it's more of a guess as it's quite hard to tell). Get the fuel pump working while it's like this and just check fuel isn't pouring out of the Jet. None should flow out at all. >

Edited by Moke Spider, 20 January 2016 - 07:55 PM.

[jaydee]

I spoke to the local mini expert,and reckoned that the new (old style) jet is supposed to run with the fixed needle rather than the self centering one, which is shorter and hence the fuelling is completely off. does that sound about right? 

 

No

[tomgale]

I was a little suspicious, shall do the check Moke Spider recommended 

[tomgale]

Looks like fuel is about where it should be, and it's not coming out when the engine is turning over. Could a bent needle cause these symptoms? It's possible that the needle got bent when the old jet did

[Spider]

Looks like fuel is about where it should be, and it's not coming out when the engine is turning over. Could a bent needle cause these symptoms? It's possible that the needle got bent when the old jet did

 

 

Yes and Yes.

 

I think that was suggested earlier?

 

<Edit: If you remove the dashpot damper and then lift the piston all the way with your finger, it should rise fairly easy and then should drop with a light 'clunk'. >

Edited by Moke Spider, 21 January 2016 - 06:25 PM.

[tomgale]

It has been easy to raise and clunking as expected, so I've been assuming the needle is still alright, I have a spare from a stage one kit, so I'll try that in it. The jet is sticking a little though, there's a small amount of resistance with the jet about 10mm out, the Spring can't pull it closed, put a little poke with a finger and it clicks home, I've been assuming this was due to a bit of damage to the jet bearing, but I suppose it could be affecting the running quite a lot? It's not a result of a bent needle though, does it without the piston on too

[Dusky]

Maybe th emixture needs adjustment now? I can imagine that it 'll be a lot different than when the jet was bent..