16 replies to this topic

[alpder]

Having endless problems getting my "professionally rebuilt" carb set up by the book (i.e. so that when the piston is raised by the lifter-button, the RPMs rise very slightly).
If I set the jet low enough that lifting the piston causes a slight RPM increase, then the idle is super-rich and it picks-up very poorly when the throttle is pressed. If I lean it out at idle, so that it picks-up nicely, then lifting the piston 1mm kills the engine dead instantly. And all this is still occurring even after a rolling-road set-up.

 

Gut feeling is this is indicative of a manifold air-leak, but it all looks tight in that area and I used plenty of Hylomar Blue when I assembled the engine.

 

Plus, despite being an old codger of a driver, I'm getting under 30mpg. And occasionally the car just cuts out and takes 30 seconds of cranking to start again - happens when I pull away with a quick pulse of power but then quickly de-clutch ready to stop immediately after.

 

One problem is, I have no faith in the quality of the carb rebuild by Yorkshire Classic Parts. I've done the least-possible to the carb but so far I've...

 

...straightened a bent spring...

 IMG_20250301_143631.jpg   39.92K   0 downloads

 

...removed a stash of metallic dirt from the bowl and jet...

 post-131677-0-86585700-1740864262.jpg   90.61K   3 downloads

 

...and, today, dealt with a hugely wrong float level...

 IMG_20250322_104227_HDRx.jpg   30.98K   1 downloads

 

Am loath to take it completely apart to look for any further "professional" foul-ups, but not seeing much alternative now. Unless someone's seen these symptoms before and can point me to something simpler?

 

Edit: having dismantled, I find the shaft seals were both fitted inverted. Did I mention this was "professionally rebuilt"? Oh I did? Sorry to bang on about it, then. Pics here: https://www.theminif...n/#entry3783521

 

1310cc, freeflow manifold and Maniflow exhaust, MiniSpares inlet manifold, K&N air filter, mild cam, 65DM4 distributor.

Edited by alpder, 22 March 2025 - 06:52 PM.

[Gaz66]

That spring is unbelievable 😳

[alpder]

That spring is unbelievable

Yeah, that's why I haven't even bothered to contact the seller. Any pro who sells a recon carb with that inside it, is hardly likely to have customer satisfaction at the top of their priority list.

Edited by alpder, 22 March 2025 - 02:09 PM.

[Lplus]

There should be a 20 - 40 thou gap below the ruler to the centre of the float.  I've given up with the lift the piston business, the amount of lift needed is minimal anyway.  Personally I find the mixture for the fastest idle speed and weaken until the engine slows obviously  then re-richen a tad.so it speeds up a bit.

[alpder]

There should be a 20 - 40 thou gap below the ruler to the centre of the float.  I've given up with the lift the piston business, the amount of lift needed is minimal anyway.  Personally I find the mixture for the fastest idle speed and weaken until the engine slows obviously  then re-richen a tad.so it speeds up a bit.

 

Cheers.

 

I have tried this technique too (before and after correctly setting the float). No dice... there is no consistent relationship between jet height and idle speed/smoothness. But this may have something to do with it: https://www.theminif...n/#entry3783521 . So I'll rebuild with the seals fitted properly, and try again.

 

[nicklouse]

Won’t answer all your questions

https://sucarb.co.uk...pe-carburetters

they also have book on rebuilding I think.

[Lplus]

 

There should be a 20 - 40 thou gap below the ruler to the centre of the float.  I've given up with the lift the piston business, the amount of lift needed is minimal anyway.  Personally I find the mixture for the fastest idle speed and weaken until the engine slows obviously  then re-richen a tad.so it speeds up a bit.

 

Cheers.

 

I have tried this technique too (before and after correctly setting the float). No dice... there is no consistent relationship between jet height and idle speed/smoothness. But this may have something to do with it: https://www.theminif...n/#entry3783521 . So I'll rebuild with the seals fitted properly, and try again.

 

Bearing in mind that HS carbs had no seals at all but still react consistently, I'm not convinced it's those seals causing that problem.  Have you rebuilt the choke mechanism?

[alpder]

Have you rebuilt the choke mechanism?

 

Having now seen how many mistakes went into this carb, I'm taking the whole thing apart and starting from scratch. It does look like many of the parts are new. And yet there's that spring, and the back-to-front seals, which suggest a careless chuck-it-together attitude. It is (or it was until today) the only part of the car I didn't nut-and-bolt strip myself for the rebuild. And, yes, the cold-start mechanism appears to have been correctly assembled (I guess some parts had to fall into their correct positions, just by law of probability).

 

I'll have the manifold off too, and double-check for leaks.

[timmy850]

The lift pin method for setting idle can give you poor results. It’s best to measure the fuel mixture with an afr gauge

I wouldn’t bother with that spring either, just replace it with a known new one (or buy a red and yellow at the same time so you have options)

[bpirie1000]

Should not be as much or any junk in the fuel bowl.. that could not have been the reconditioning process.. that will most certainly have come from the tankmas a source..

Consider fuel tank clean out or an inline filter... or both..

[Cheeser]

What spec was the engine before the rebuild, was it running well previously? Are the manifolds exhaust distributor and cam used in the engine before the rebuild, why was it rebuilt? Just trying to establish where you’re starting from!

[alpder]

Should not be as much or any junk in the fuel bowl.. that could not have been the reconditioning process.. that will most certainly have come from the tankmas a source..

Consider fuel tank clean out or an inline filter... or both..

Tank and fuel line and pump are new. There is a mesh in the tank and there's an inlet mesh on the carb which would have caught them anyway. Unfortunately there's no possibility that those chunks of metal got in there from the fuel. They can have only been there from the time I bought it... newly "reconditioned". So many other disasters in this carb that it's hardly surprising.

[alpder]

What spec was the engine before the rebuild, was it running well previously? Are the manifolds exhaust distributor and cam used in the engine before the rebuild, why was it rebuilt? Just trying to establish where you’re starting from!

The Metro A+ 1275 was new to me (and arrived in pieces). I had it rebored, crank ground, new pistons, shells, cam (Kent 246 - very much a sensible everyday road cam), valve guides, fixed duplex chain. CR increased supposedly to 10.5 advised by the engineering firm that did the work (which now seems a bit high to me) but I haven't measured it. Otherwise standard. Then I reassembled it myself. Essentially just renewing it, not tuning it.

 

Been set up on a rolling-road, who hand-made a needle for it. Trouble is, they did this before this disaster of a carb "refurb" was discovered. So the needle is now probably wrong.

 

Even so, it runs on E5 and E10 equally well and pulls like a train even from low RPM. Less than 30mpg though even with old-fart driving style, so that's a hint that fueling is wrong. And sometimes it'll die in very specific circumstances: pull away sharply from a standstill (after a long-ish idle), then de-clutch almost immediately: one time in ten of doing that it'll just quit, and then needs a long cranking to restart.

[Lplus]

 

Have you rebuilt the choke mechanism?

 

Having now seen how many mistakes went into this carb, I'm taking the whole thing apart and starting from scratch. It does look like many of the parts are new. And yet there's that spring, and the back-to-front seals, which suggest a careless chuck-it-together attitude. It is (or it was until today) the only part of the car I didn't nut-and-bolt strip myself for the rebuild. And, yes, the cold-start mechanism appears to have been correctly assembled (I guess some parts had to fall into their correct positions, just by law of probability).

 

I'll have the manifold off too, and double-check for leaks.

 

Trying to think of anything else that could make the idle erratic other than fuelling/air leaks - one thing that occured was something loose/worn/broken in the distributor allowing the timing to wander at idle.  What distributor are you using and where did it come from?

[timmy850]

If the float is set too low like the picture the fuel level will also be low and it won't run as it's designed to do. 

 

With all the issues present in this carb there's plenty of things that will cause poor running