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tonight - backfire

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JPSmit

JPSmit

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well, even though there is lots of snow and it is only 8 deg C (46F) I had to move the car from one garage to another. So, decided to do so by going around the block. Good news - she starts and idles strongly. Bad news, I'm driving (slight uphill incline) she starts to backfire. I loose some power, get around the curve and going slight downhill - no backfire.

any ideas?
 
I think MS Triss has a gas problem. Take two Beano and call the doctor in the
morning.

Cheers

Mark
 
Judging from your other post and this backfire situation I would say that you are running lean and not rich. When you taped off a portion of your air cleaner you cut the volume of the air getting to the carb. What you have done is enriched your mixture by adjusting the amount of air not fuel. Now for the backfire, if it sounds as if it is coming from under the hood it is a lean burn backfire which occurs in the intake runner. Under certain lean conditions hot gases remain in the combustion chamber after the intake valve opens and causes the fresh charge to ignite early thus creating the backfire. This almost always happens under load.
Of course this is just my non professional opinion but I had a similar experience with my TR 6 when I re carburetored it.
Hope you get the bugs worked out.
 
I think Roman may be right.

Be sure you don't have a vacuum leak (manifold gasket or carb gasket). Run the car at idle and spray WD-40 near these gaskets. If there's a leak, the Wd-40 will get in and cause the engine to slow down a bit.

Be sure float isn't stuck or fuel filter isn't clogged.

You should be able to raise or lower the needle in the damper piston slightly....may want to raise it to richen slightly.

If none of this helps, have a look at ignition wires (crossfiring?). This is easiest to see in the dark while revving the engine.

And you may want to look at ignition timing.
 
I suspect Roman might be right

sprayed all with WD40 te other day and nothing changed
timing recently ( 2 weeks ago) set
float has been done/ redone so often, that, while it might be sticking I doubt it.
fuel filter certainly looks clear

will peel some tape off the air filter and try again. anyone have a percentage coverage for a longflo cleaner?
 
JP

What do you need to get rid of this carb setup?

Mark
 
I keep meaning to contact a guy from the British Saloon club who had a bunch of SU's for sale. I really don't want to go Weber but I understand from another recent post that a rear MGB carb is what I need
 
What do you need??

Need to check stock in the barn.

MD
 
According to this

https://tinyurl.com/aujv6k

I need a 1 1/2" rear MGB carb. diagonal flange rear lower/ front higher

thanks for checking
 
Don't give up now, JP! You got her on the ropes! She's runnin' <span style="font-style: italic">lean</span>! You're almost there! :jester:

If it's a lean backfire, that means you're on the right track and blocking the air cleaner is working. The next time you run her around the block, when she backfires, pull the choke a little and see if that cures it, to verify that <span style="font-style: italic">is </span>actually a lean condition. If it's running lean under load (that is, under acceleration,) try a little thicker oil in the dashpot first. It'll richen the acceleration slightly without changing any other settings. If it's still popping after that, try nibbling back on the air cleaner a little to fine-tune that vacuum balance. You may have to sacrifice idling a little rich to get it "right" at speed. Zeniths would usually idle rich, and (theoretically) you'll spend more time driving than idling anyway. :thumbsup:

(Actually, JP, you're kinda encouraging me to try puttin' the old Zenith back on Nigel sometime and see if I can't get <span style="font-style: italic">mine </span>in tune!)
 
:winner1: thank you - took it around the block and when she started to backfire again - pulled out choke and tada! hurray, we're on the right track
 
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