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Hif38 Questions


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#1 mkw

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Posted 05 July 2019 - 05:11 PM

Hello,

 

A couple of years ago I picked up a HIF38 carb that had been sat on a shelf for years, my car then came off the road and is now back up and running so I want some advice.

 

I've given the carb a clean up and put it on my car. Had a mobile tuning guy come to tweak and fiddle and sort the timing out. He told me that there doesn't seem to be much resistance on the piston. After setting up the mix to around 3% I took the car for a drive round, a bit lumpy, then came back and he retested it and it was 0.5%. Another fiddle and drive, strong fuel smell, then the retest was 9%! He said there must be an issue with the carb and we left it at that.

 

Now, i've been playing about with the mixture and a colourtune and got it much better to drive but it's still got a flat spot when accelerating and every now and then there is a pop from the carb.

 

When I got the carb it hadn't been touched at all, to the extent that the plug was still in the mixture screw hole. My question is, assuming it was fitted to a 1275 in a previous life is, will the spring be right for my car? And how do I identify it? Any other tips for tuning it? I'm after a fun weekend drive on the twisty bits. 

 

I've got a 998 A+, Stage 1, standard air filter box, ABD needle, SW5 cam.

 

Thanks!

 



#2 cal844

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Posted 05 July 2019 - 06:17 PM

I'd take the dashpot off and check to see if there's a spring fitted, while it's off check to see what needle is fitted.


Did you put oil in the dashpot? What grade did you use?

Is the fuel fresh or old?

#3 mkw

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Posted 05 July 2019 - 07:20 PM

There is definitely a spring in, I just can’t tell what type as there is no colour on it. Dashpot oil is 20w50, ABD needle as above and fuel is brand new full tank.

#4 cal844

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Posted 05 July 2019 - 07:27 PM

There is definitely a spring in, I just can’t tell what type as there is no colour on it. Dashpot oil is 20w50, ABD needle as above and fuel is brand new full tank.


Sounds good, what I'd now do is run the car and get it to misbehave, when it does give the choke a tug, bury the throttle and see what happens.. if the car doesn't pull like a train I'd push the choke in then get it to misbehave (in a safe spot) then turn the engine off and remove no 1 and 3 spark plugs, are they lean(ehute or biscuit colour... or rich (wet and sooty)

#5 mkw

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Posted 05 July 2019 - 07:46 PM

I’ll try that tomorrow, so if pulling the choke helps I need to richen it up? If not check the plugs and maybe lean it off?

#6 cal844

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Posted 05 July 2019 - 08:10 PM

I’ll try that tomorrow, so if pulling the choke helps I need to richen it up? If not check the plugs and maybe lean it off?


Yes that is what needs to happen, I usually set the CO to the highest value for the year of car, then adjust the needle and jet as needed

#7 Ethel

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Posted 05 July 2019 - 09:30 PM

The choke on a Hif won't do much at full throttle. That's one reason it's a separate drilling instead of holding down mainjet like a HS. It is a possible cause though if it's sat for years the O ring seal in the choke may well have perished.

#8 cal844

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Posted 05 July 2019 - 09:54 PM

It worked for me on my 1275 to clean the rubbish out just enough to get the car running good enough to drive home. I then stripped carb off the car to give it all a clean

#9 Ethel

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Posted 06 July 2019 - 02:41 PM

You might even manage to drive on just the choke jet ,but it doesn't have a venturi so relies on manifold depression alone. Meaning it flows less fuel the wider the throttle is open.



#10 Boycie

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Posted 06 July 2019 - 02:53 PM

I don't think you'll ever get that carb right unless you strip and rebuild it. Unless it was brand new/ never seen fuel before it was put on a shelf, the whole thing will be full of deposits, corrosion and, as said above, the (very important) rubber parts will be split and causing the crazy mixture changes you're experiencing.
I have a Range Rover V8 with two HIF carbs and a long period of rest, both carbs were almost ruined. I managed to salvage the bodies and one piston, but that was it. The HIF is much worse in this respect compared to the older HS type.
The good news is, a strip and rebuild is simple and all parts are cheap and available.




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