Carb Troubles

[mcbride]

Hi
Trying without success to get my 1275 running without a poor midrange misfire that I think is carb related. Previous HS4 was completely worn out and replaced with a brand new old stock HS4 FZX 1189 with the dreaded Waxstat.

Car runs fine at idle then hits flatspot and splutters like a bad one around 300 rpm in top, if you floor to gull throttle the car pulls well enough without a problem. back of the throttle things remain smooth until a hill appears then same routine.... boot the baws off it otherwise, severe misfire again.

Intrigingly, if you let the misfire develop and pull out the choke, all is fine, car instantly improves and sorts itself out.

No other work done and engine condition and history is unknown to me apart from it is a Gold Seal motor.

Accuspark unit fitted which makes no difference as I thought it was a worn dizzy originally.Wee tuned 4 branch exhaust of unknown origin.

Was thinking next job should be conversion to normal jet from wax stat. Any idea what would be the best needle?

What do you think?

Thanks guys in advance.

Scotty

[MarinaCoupe]

It sounds like too weak a mixture to me. Richen the mixture by one complete turn of the mixture screw and see how she goes.


Chris
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[david painter]

Is the Carb definatley off a 1275 it could have the wrong needle and spring in it. What grade of oil is in the dashpot. Does it have an overrun valve in butterfly if so solder it shut. You can try richening the mixture but will alter it everywhere rather than just light throttle. Do you have you an air leak throttle spindle carb face manifold face brake servo hose etc ?
Dave

[david painter]

SU list that number as Marina 1275 Should have a ADG needle with a Red spring
Dave

[mcbride]

Guys, thanks for the replies. Will sort out and get a red spring and correct jet. I am thinking the fuel pump may be the culprit if it is weak or no longer pumping as required. I changed the inline filter the other day and it only quarter fills. Will let you know how I get on.

[ronecc]

These people should help.
http://sucarb.co.uk/carbspec/carburetto ... s/id/1992/

[david painter]

The Majority of carburettor fuel filters only tend to fill 1/4 to 1/3 full even when fitted on pressure side of the pump
Dave

[Kilroy]

I think the answer is with the dashpot.

I would try cleaning it out and using normal engine oil in it.

If the car runs ok full throttle then there is adequate fuel supply.

If the piston rises too quickly - as in a dry dashpot - the mixture will go really lean - and pulling the choke out will rectify it to some extent.

Any foreign material that has entered via the fuel and then partially blocks the main jet will have a similar effect - but as you have a filter that should not be happening.