8 replies to this topic

[alpder]

This HIF38 came to me 'refurbished'.

 

Been trying today to track down a bogging-down problem. Took the chamber off and worked the piston... and I could hear and feel weird noises as the spring would unevenly apply pressure to the piston... for example, as the piston drops it moves quickly at first, then it slows down, then the spring breaks loose from its grip against the side of the chamber with a 'scrape...clunk' noise, and then the piston speeds up again.

 

This is the first time the chamber has been apart (in my ownership).

 

And I'm guessing the spring shouldn't be this shape? It has shiny rub-marks where it's pushed its middle coils firmly sideways against the sidewall of the chamber - clearly causing it to bind.

 

 IMG_20250301_143631.jpg   39.92K   3 downloads

[nicklouse]

That’s been abused.

[alpder]

Can't have been! I paid YorkshireClassicParts £235 for a "fully rebuilt Hif 38". Their description, not mine. Oh, hang on, silly me... they're on ebay. That explains it. (And those were 2022 ££s... that's... well... "lots" in today's money.)

 

So what spring should I fit so that the carb behaves at least something like it did when I paid a fortune for a rolling-road to hand-make a needle for me... which is probably going to need doing again when I fit an un-abused spring :-(

 

Edit: No paint on it at all. But using Burlen's spring measuring method I get 5.1oz spring force at 1.5" compressed length. Guess that makes it a 'red' then. Or one that's been made up by the seller from an old coat-hanger, to emulate a red.

Edited by alpder, 01 March 2025 - 03:29 PM.

[Lplus]

Can't have been! I paid YorkshireClassicParts £235 for a "fully rebuilt Hif 38". Their description, not mine. Oh, hang on, silly me... they're on ebay. That explains it. (And those were 2022 ££s... that's... well... "lots" in today's money.)

 

So what spring should I fit so that the carb behaves at least something like it did when I paid a fortune for a rolling-road to hand-make a needle for me... which is probably going to need doing again when I fit an un-abused spring :-(

 

Edit: No paint on it at all. But using Burlen's spring measuring method I get 5.1oz spring force at 1.5" compressed length. Guess that makes it a 'red' then. Or one that's been made up by the seller from an old coat-hanger, to emulate a red.

The correct spring for the HIF38 on a standard 1275 is the red AUD 4355.   Since that's the weakest large diameter spring it would have to do for a 998 as well. The weight is 4.5 oz at 1.53".  The next up is a yellow at 8 oz at 1.53"

[nicklouse]

If you want to know what  a spring should look like.

 

https://sucarb.co.uk...ring-red-1.html

[alpder]

Thanks everyone. Have ordered a red. And, for now, I've reshaped this mangled one so that the piston moves much more smoothly. Might even choose to leave it in place: because it is the one the needle was tuned for and it seems a tadge firmer than a red is supposed to be - probably because it's been stretched.

[timmy850]

Does it move smoothly up and down with the spring removed? The ball bearing race can also break up over time and it’ll be a bit stiff

[NLinPEN]

Are you sure that that needle is straight? It might be optical illusion, but it could be bent.

[alpder]

This is sorted now, thanks. Straightening the spring allows the piston to move freely. And half a tankful of fuel has been through the carb this morning on a trip all around Pembs, engine behaving nicely.