9 replies to this topic

[CharlieNZ]

I'm running a very standard 998 with hs2 carb and struggling with what I think is a fueling issue.

 

On the road, the car runs pretty well. It revs ok and pulls cleanly enough from low down. However, at tickover it chugs badly, puffs black smoke and generally seems to be running very rich. Plugs are very sooty. If I sit at the lights too long, or don't get going quickly enough in the morning, it fouls the plugs. 

 

I've tried leaning out the main jet to the point where it starts to misbehave, but even then it seems choked up at tickover, puffing black smoke.

 

I would welcome any other thoughts, but at the moment I'm taking an interest in float height. According to the late, lamented Mr Haynes, I should have an 8mm gap between float and lid. Mine is much lower, more like about 5.5. Because this difference is measured quite close to the needle, this would make a significant difference to the float height. I have a couple of other, junky hs2 carbs and they seemed about the same as the one I've got in there.

 

The floats are solid plastic - no brass tang to bend. It seems I have to adjust float height by putting a washer under the base of the needle valve? I've tried putting a washer made from 0.4mm gasket material under there, raising the height to roughly 7mm, and I think it's slightly better, although I could be kidding myself.

 

Anyone got experience of these solid plastic floats, and able to say what the correct height should be? Or any other thoughts about what else I should look at?

 

Thanks in advance...

[nicklouse]

sounds like you have the wrong figures

http://sucarb.co.uk/...ng-float-height

HS carbs with the later all nylon float and delrin type needle. The gap between the float and the lid face should be between 0.062" and 0.187" with the float resting on the needle but not depressing it. This type is non adjustable.

 

[CharlieNZ]

 

sounds like you have the wrong figures

http://sucarb.co.uk/...ng-float-height

HS carbs with the later all nylon float and delrin type needle. The gap between the float and the lid face should be between 0.062" and 0.187" with the float resting on the needle but not depressing it. This type is non adjustable.

 

 

Thanks, I hadn't seen that page. For some reason the SU site never loads on my phone, and when I'm in the garage my phone is all I've got.

 

So measuring the gap there makes sense, and all the floats I've got would be about there. This isn't the one on the car, but it looks about the same as the one that is on there.

 

Interestingly, when I popped the float off to take a photos of the needle, this one had a coating - is this delrin? The one that is on the car is brass and seems a little worn, so I'll probably swap them at some point.

 

I'm a little surprised that this is the "later" type - I had thought these were all relatively early carbs. I guess if the float height is right, I'm back to banging my head against something of a brick wall...

[unburntfuelinthemorning]

That looks like a viton tipped needle.  Try using that if it's in good condition - especially if the old brass one is worn, it could well solve your problem.  You might need to use the matching seat or just change the hole float chamber lid over complete with float and valve.

[Ethel]

Float vent clear? Float pivot smooth and unworn?

[Spider]

Also, check your fuel pressure at the float bowl.

[CharlieNZ]

That looks like a viton tipped needle.  Try using that if it's in good condition - especially if the old brass one is worn, it could well solve your problem.  You might need to use the matching seat or just change the hole float chamber lid over complete with float and valve.

I think that will be my next step. And although it seems like my float height is probably about right, I might try dropping it a bit. I can always change it back.

 

I'll also be checking my float pivot, float vent and fuel pressure as per the other suggestions. Thanks guys!

[GraemeC]

Float height on those types was altered by changing the bowl lid - the holes for the pivot shaft were drilled at various different heights.

[Mito]

I had the same problem with a hs4 carb. I never did get to the bottom of it before I took the car off the road.

I was starting to think it was either float height or main jet and I've since seen somewhere else that the main jet should be replaced after 40k miles if its the swing needle type, as the needle wears the inside of the jet.
Like you I checked the flat height and it seemed okay, so replacing the jet was the next step. I didn't check fuel pressure though!

I did bend a jet once when I forgot to put the top engine steady back on. Is your jet straight and returning fully?

Edited by Mito, 15 February 2019 - 05:06 PM.

[CharlieNZ]

I had the same problem with a hs4 carb. I never did get to the bottom of it before I took the car off the road.

I was starting to think it was either float height or main jet and I've since seen somewhere else that the main jet should be replaced after 40k miles if its the swing needle type, as the needle wears the inside of the jet.
Like you I checked the flat height and it seemed okay, so replacing the jet was the next step. I didn't check fuel pressure though!

I did bend a jet once when I forgot to put the top engine steady back on. Is your jet straight and returning fully?

 

Thanks for everyone's suggestions. The needle and jet are pretty much new, and I took some care to centre the needle as per Haynes instructions. The main jet returns nicely after using choke (although I don't use any choke at the moment) and the piston falls with a satisfying click when I use the lifting pin, so I don't think the problem is there.

 

I put an extra washer under the jet, replaced the needle with the viton-coated one, and made sure the float was moving smoothly. I think it made it slightly better, but didn't solve the problem. 

 

I haven't checked the fuel pressure yet.

 

I did put in some hotter plugs (BP5ES), and raised the tickover a bit. It seems a lot better, although you can smell that it is still running rich. I think by doing this I'm treating the symptoms rather than the underlying problem.

 

I think I'm just going to keep driving it for a while, in the hope that it either gets worse or better. I'm also taking it to a show on Sunday, where apparently there will be 70 other minis, so I'll see if I can get someone to have a physical look and advise...

Edited by CharlieNZ, 27 February 2019 - 11:02 PM.