Twin carbie issues
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Twin carbie issues
So having a bit of a drama with a twin carby setup (su single throat carbies). First of all, it's not on a Gemini but on an old 4cyl MG A.
Carbies have just been rebuilt by a shop.
The MG motor has the inlet and exhaust all on one side, with 3 exhaust ports and 2 inlet ports. Cylinders 2 and 3 go into the middle exhaust port and 1 and 4 have their own individual ones. Inlets are feed 1 & 2 and 3 & 4 respectively.
So, bolted the exhaust manifold, carby manifold and carby all up using new gaskets and gasket compound. However, the thing is only running on cylinders 3 and 4. Take the leads off 1 and 2 and there is practically no noticeable difference. There is plenty of spark and I have switched plugs to make sure it's not the unlikely case of dead plugs. After the car has been running for a while, taking the plugs out of no1 & 2 you notice that they are wet so there is fuel getting in there just not going bang. Spraying aerostart down the throat while the car is running seems to make some difference but not a lot. Ideas are appreciated.
I'll try and get some pictures to help out.
Cheers guys.
Carbies have just been rebuilt by a shop.
The MG motor has the inlet and exhaust all on one side, with 3 exhaust ports and 2 inlet ports. Cylinders 2 and 3 go into the middle exhaust port and 1 and 4 have their own individual ones. Inlets are feed 1 & 2 and 3 & 4 respectively.
So, bolted the exhaust manifold, carby manifold and carby all up using new gaskets and gasket compound. However, the thing is only running on cylinders 3 and 4. Take the leads off 1 and 2 and there is practically no noticeable difference. There is plenty of spark and I have switched plugs to make sure it's not the unlikely case of dead plugs. After the car has been running for a while, taking the plugs out of no1 & 2 you notice that they are wet so there is fuel getting in there just not going bang. Spraying aerostart down the throat while the car is running seems to make some difference but not a lot. Ideas are appreciated.
I'll try and get some pictures to help out.
Cheers guys.
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Im confident it's not a spark issue as we have switched the plugs from 1 and 2 into 3 and 4 with no change and when you take the leads off while the engine is running you can see plenty of spark leaping to the spark plug.
I've tried turning the mixture screw on no 1 carbie from all the way from lean to rich and vis versa whilst running with no change.
I'll check the slide thing later. After I figure out what exactly that is. I assume it is the thing that the choke moves up and down on. There oil levels in the carbies are fine.
keep the ideas coming guys, they are all welcome. trouble shooting seems to be the only way Im gonna get past this.
I've tried turning the mixture screw on no 1 carbie from all the way from lean to rich and vis versa whilst running with no change.
I'll check the slide thing later. After I figure out what exactly that is. I assume it is the thing that the choke moves up and down on. There oil levels in the carbies are fine.
keep the ideas coming guys, they are all welcome. trouble shooting seems to be the only way Im gonna get past this.
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Yer, I suspected maybe a break between 1 and 2. We did a bush mechanic compression test by cranking it and holding a finger over the spark plug hole, there was still compression so not all lost. Would have to get the guage to know for sure though.marksegec wrote:How about a fked head gasket or worse, rings / pistons are gone?
No xplosion, plenty of fuel, ...
says to me do a compression test.
There is a mechanism that allows you to manually move the slide up from underneath. I have moved this up slowly whilst it's running and has made no difference.GEMI79 wrote:Check to see when you have it going that the slide is moving to allow air in. Also check for any vacuum leaks.
Cheers Steve.
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Hurp a durp durp durp.Gem WRC wrote:Stupid question Are the plug leads on in the
correct firing order?
We have a winna. Im such an idiot. So this is what happened. In an effort to fix the problem I replaced the points in the dissy but when I put it back in I plugged the leads back in coz they'd fallen out and I must have got 1 and 2 back to front.
The actual problem in the first place was that the mixture screws were full in (lean) and thats why it would only run on choke. The points were also screwed but it was a secondary problem.
Now I've just got to figure out every other problem it has. Thanks for the help guys.
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Yer, I've heard a bit about these, never used one. I have also heard the old 'hose to your hear" trick.TURGEM wrote:its absolutely important that they are syncronised...
google; carby syncronisers and you will see what im on about and what theiir purpose is
So far Ive just been adjusting the mixture screws to the same position on each. i.e. 3 flats out on the rear, 3 flats out on the front. then idle speed, same deal. Definitely far from a good tune atm. Doesn't help its overheating while idling, so need to sort that out too.
Im getting contradicting clues though as to the tune. Plugs are fouling up (carbon) but the test with the SU's push the choke open just a tad and see if the engine increases revs, increases then drop to same, or drops.
It drops indicating lean mixture tho. More investigating to be done.
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To be honest...
I dont think its really worth reading spark plugs much anymore, unless your still running the old (leaded)... Which I doubt,
Temp wise just make sure your timing isnt too retarded as this can cause overheating...
It mite be worth asking if there other SU owners out there, asking whats jets they have to give you a ball park...
P.s. Just because the mixture screws are the same doesn't mean they are... Id definately have a crack at the Hose in your ear trick.
I dont think its really worth reading spark plugs much anymore, unless your still running the old (leaded)... Which I doubt,
Temp wise just make sure your timing isnt too retarded as this can cause overheating...
It mite be worth asking if there other SU owners out there, asking whats jets they have to give you a ball park...
P.s. Just because the mixture screws are the same doesn't mean they are... Id definately have a crack at the Hose in your ear trick.
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WASTEGATES - WASTE 8S
IF YOU WANNA FLY, GIVE IT MORE P.S.I
WASTEGATES - WASTE 8S
IF YOU WANNA FLY, GIVE IT MORE P.S.I