Setting up my H1

[Tatenlyle]

Hello again. I had my 33 RP out last week, after fitting a H1 SU carb. It ran quite well, with, I believe, a bit more oomph.But it did seem quite thirsty, and I could smell petrol in the exhaust fumes. Now I believed I had it set up right, new jet kit, AN needle, but it still burns rich. There was oil in the dashpot, no spring, and the weight on the dashpot damper had been turned down to give 160g. So I removed the dashpot oil, a bit more power, but still rich. So I refitted the spring, (no colour visible) runs well, but still runs rich, but ticks over well. I may try a weaker needle. Any other ideas?

[Ian McGowan]

Are you sure that you don't have the fuel level set too high???

[Reckless Rat]

My RP is fitted with an H1 SU and it has no spring. I have found that very little oil is needed in the dashpot damper, otherwise there is hardly any piston lift . The car regularly returns 45mpg. Try setting mixture with a colourtune.

[Tatenlyle]

Hi Ian, dont think its too high, its a new fork and needle valve. Besides that, the tickle doesnt touch the float, so if anything, its low

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I have the mixture screw turned right up, and the plugs are still black. but, there is no soot out the exhaust, its white. I'll give it a good blast tomorrow

[Reckless Rat]

If the exhaust pipe is white then the mixture is not over-rich. If your plugs are black it may be that the engine is burning oil. Does the car have a late Ruby head? If so, plug oiling can be a problem. Try a set of hotter plugs. I find NGK B5HS are good for this set-up.

[Tatenlyle]

Thanks for that, there is the odd puff of blue smoke now and again, I shall try new plugs

[Peter Clayton]

Has the main jet gone oval over the years, allowing fuel to leak through?

[John Cornforth]

Hi.  I run an SU H1 with a HC head.  This carb came originally from a Morris 8 series E.  As standard the piston weight is used alone, there is no spring.  I presume springs were a later refinement to allow a lighter piston for reduced inertia, and also to cater for carbs that weren't vertical.  Did a previous owner modify your carb ?

I seem to recall that the needle has a deliberately accentuated taper near the idling position, so that you can set idle mixture with only a small variation in jet height and therefore avoid changing the mixture too much at greater speeds and loads.  All the standard tuning advice is slanted towards getting the idle mixture right, as there is an assumption that the needle is the one developed (not without some effort) for the precise needs of the engine and will therefore not need altering. Of course for an A7 such a needle was never officially developed, so choosing the best one is down to experiment.

SU carbs aren't very sensitive to float chamber fuel level, and springs and damper oil will hardly affect idle, so the fact that your jet adjustment needs to be right up one end is a puzzle.  Is the choke linkage all OK, are all the washers and glands in the right place ?

[jansens]

Is the needle centered in the jet and not dragging? And also check that the returns springs on the jet/choke mechanism are fully returning the jet when the choke is off. I had one once where even with the choke off the jet wasn't fully returning to the normal position until I adjusted it.

Simon

[Bob Culver]

The dashpot piston needs be only submeged at rest. Is the dashpot cover vented as no internal vent on originals. There has been extensive on here with tables of jet contours etc if you can find. I found the EK needle as fitted in morris 8 from which most of the carbs come was OK if not esp economical but the "'weak"" recommendation MOV (intended fro high altitude) was hopelessly so. Dunno how AN compares. Weak mixtures are proven by partly opening the ""choke"" substitute. A problem is that  bodies and pistons are interchangeable and early heavy pistons find their way onto later carbs. Is the piston free to lift fully?