joining the backfire club it seems......

:think
After finally getting my ratty green bug running with twin 40 dellortos i’ve suffered a couple of mishaps:

  1. one of the rubber seals on the fuel union disintegrated - I suspect the carb may have lunched on some small flakes of rubber which exaggerated the situation
  2. after running well but with a lot of backfiring on the overun (but loads of power the rest of the time) a bit of a chronic misfire started - restricting top speed to about 65 - and taking about a day and a strong tailwind to get there!

Checked all the timing etc but to no avail - so ended up going back to basics.

I’m now back with the 32/36 at the moment, and it runs ok (a bit down on power) but spits pops and barks like a rally car as soon as you lift your foot off.

Having checked everything else, I’ve spotted that one of the plugs is running a bit oily (presuming valve guides worn or piston rings) - other than that, the only thing I can think of is that the J tube section of the heat exchanger is holed (the car was sat in quite a damp garage without being run for about 6 weeks).
I think this is quite likely as I’ve a bit of a burning oil smell inside the car when lifting off the throttle sharply at speed (yes its presumably burning oil from worn valve guides and/or piston rings - but the only way the smell should be getting in the car is from inside the heat exchangers?)

Any other suggestions before I stop cursing and start stripping the engine?
Any help greatly appreciated as its been quite traumatic giving up the lovely power increase I briefly enjoyed!

All I can suggest for now is, while the shiny Dells are off the car, strip them to bits and clean them out thoroughly. If you reckon some bits of fuel hose rubber have got into them, chances are, a jet or two is blocked!
They’re damn sensitive those jets ya know! My 1966 motor ran slower than the 1776 I had when I last raced you because the main jet tubes weren’t fully screwed down (Ian Evans was right as usual!)
While you’re at it, check the main jet size. I replaced the 136 jets with 140’s and had a noticeable increase in power. You might get away with my old 136 jets if yours are smaller.
Dunno about the oily plug though - that’s not lookin’ too good…

cheers Alex - planning on a full strip down of the dell’s before they go back on the car.

Pretty certain that the exhaust is blowing inside one of the heat exchangers too - been driving around with the heater off and the oily smell goes away… Is there any way to check this other than replacing them? Thinking of borrowing a pair of straight j tubes my bro has lying around to see what difference this makes before I do anything else.

Oily plug is still a bit worrying - it isn’t really grotty, but think I might have the head off on that side and see what’s happening. Got stainless valves so presuming its most likely the guides or piston rings needing doing - which might be an idea anyway to get the compression back up to scratch.

Will check the main’s in the carbs, but if anything I reckon they’re probably a wee bit on the large side for my tiny engine…!

If there’s ANY doubt your heaters are leaking exhaust gasses - replace them a.s.a.p!
I had this gassing effect in my Beetle years ago - smell, headache, tiredness, etc.
The next phase is too close to coma, accident, DEATH!, for comfort.
Hell, even driving down south for 5 hours with a fuel leak inside the car AND smoking fags is less dangerous!
J - tubes are fine for a quick repair this time of year, but by October, you’ll be wanting full heat exchangers back there again…

block the exhaust the engine should stall if it doesnt you have an exhaust leak

not dead yet…
heat exchangers are off, waiting on some new ones to arrive. They didnae look to bad inside - but it also appears that they the traditional leaky joint from the back of the exchangers to the header was blowing back (forward?) into the exchanger (a bit rotten around this end!), which may explain the smell in the car…

Figure tis best to replace them anyway to be on the safe side, and the outsides are getting a few holes in now anyway (creating a turkish bath effect in the rain…)

Going to see what difference sorting this out will make before taking the head off to check valves etc. Hopefully this’ll sort out the backfiring with the 32/36, then I can get the dell’s rebuilt and finally make it down the strip!!!