those with carbs, stop spitting.....

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Andrew Gilbert
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those with carbs, stop spitting.....

I have a HPC c20xe on 45's, been set up nice but there's an issue.

Light throttle in any gear results in spitting back through the carb, a bit more throttle its fine, on track its fine, full throttle its fine.

Carbs have been rejetted, chokes replaced, rolling road dynoed and set up but low revs on the road in traffic can be a pain. New misabs and the things are not tight the manifold.

I don't know what I'm looking at, and although I have a set of TB's to go on I'd like to retain the carbs if I can.

Thoughts?

Geoff Brown
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Seems to be a common problem as when following a Seven with 45s in traffic conditions one always gets covered in a thin film of fuel!

MADMALC
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I think it is all part of the charm. My 1700 X-Flow did it and also left the black gooey stuff dripping from the carbs. The air is far too clean these days, can't beat a few noxious fumes to enhance the drive.

R.I.P. SLR No.27.

Andrew Gilbert
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lol, yes I love the sound but it can be a pain to make smooth progress in traffic, I think I'll pull the idle jet and see what is fitted.

Love a HPC

1992 HPC vx2.0 c20xe goodness....

https://www.facebook.com/groups/caterham7c20xevariants

Roger King
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It might be the idle jets being a little too small - this is extremely common on a Supersprint engine with 40DCOEs where a change from 45F9 jets to 50F9s often makes a huge difference - but with 45DCOEs it is more usually a problem with the progression holes. 

These are located under the round brass caps near to the mixture screws (two per carb.) and the problem is usually that there aren't enough of them. The most common case is that you need one more small hole just a little nearer to the top edge of the butterfly when it is in its closed position. This gets the fuel flowing just a tiny bit sooner when you open the throttle a minute amount. Effectively this is filling in a dead spot in the fueling where the fuel/air ratio is far too weak.

Two caveats: I can't be certain that this is the problem because I haven't seen the vehicle (although it is usually the first thing I investigate with 45DCOEs), and unless you really know what you are doing this modification needs to be done by someone who does.

Andrew Gilbert
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thanks Roger, oddly enough I was reading another post where you mention the same so I'll pull the jets and see whats in at present.

Yes, these 45's are from 1992 so 3 prog holes I think, but I wouldn't want to drill a 4th (or 5th) as per the newer DCOE's, So its possibly a toss up between a new set and set up or going to TB's and set up. If so then this may have to wait a while I think as funds will have to be deviated to elsewhere.

 

Love a HPC

1992 HPC vx2.0 c20xe goodness....

https://www.facebook.com/groups/caterham7c20xevariants

Colin Cooper
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I had a similar problem when I had fitted a 2ltr Blacktop Zetec, and retained the 45's from the old crossflow, but it didn't bother me to much. Part of the charm.

I looked into fuel injection, and the cost of the injectors, etc, was manageable, but I balked at the extra fuel line, new tank and pump.

I took the car to Northampton Motor Sport, for a rolling road tune up, where Troy did drill extra progression holes. Much more drivable, not cheap, but a better option.

Col     

 

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many many moons back I did a set, for a long cockpit 1700, owner wanted to use his hillclimb car on the road, made a jig to mount the body on a vertical miller using the mounting holes,