Hi All,
I'm new to the forum and have had a '74 BGT for about 18 months which I have been re commissioning with the hope to get her on the road shortly. I bought the car partly dismantled and with a modified engine (bored out, racing cam etc) which I have since changed out for a standard engine in order to get back to factory spec. I am now just trying to set up the running, and when warm she starts well and runs beautifully. I've used the John Twist videos on the web to set up the carbs etc, so warm running is great. Idles about 800 rpm.
I was hoping someone could help me or point me in the right direction as the cold starting and running is terrible. She starts (eventually) on full choke and revs very high at about 3000 rpm, but falters and misfires if I try pressing the throttle. I'm able to gradually push the choke in over a few minutes without stalling, but any attempt to press the throttle results in misfires, backfires etc until she warms up. I certainly couldn't drive off until warm. I'm guessing that I have an issue with the choke balance/mechanism, but it looks to me to pull down the black plastic pipes on the bottom of the carbs evenly. Is there a guide anywhere to setting up the chokes please? Many thanks in advance for any advice.
Dylan
Choke and cold running
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Dylan Roberts
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Vic Butler
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Re: Choke and cold running
The choke is linked to the throttle linkage and yours needs adjusting to slow it down. There is a cam on the choke linkage which activates the throttle.
I had trouble starting my BGT from cold a little while ago and although the carburettor jets were moving they weren't lowering fully (I've got HS6's not the HIF4's.) In this case I adjusted the choke cable, make sure there is some free play but not too much.
Hope this helps.
. Vic Butler
I had trouble starting my BGT from cold a little while ago and although the carburettor jets were moving they weren't lowering fully (I've got HS6's not the HIF4's.) In this case I adjusted the choke cable, make sure there is some free play but not too much.
Hope this helps.
. Vic Butler
Last edited by Vic Butler on Mon Jan 15, 2018 5:33 pm, edited 1 time in total.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Dylan Roberts
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Re: Choke and cold running
Thanks Vic - I'll take a look at that. I did read somewhere about the cam, and that the choke should slightly open the throttle. I thought it was just barely doing that, but I suppose my idea of 'slightly opening' may be greater than it should be! I'll have a go at adjusting this morning.
Dylan
Dylan
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Peter Cresswell
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Re: Choke and cold running
Hi Dylan,
This article will help you whilst under the bonnet to ties up the John Twist video. The adjustment for the choke idle speed is item 3 in the third picture.
http://www.mgexp.com/article/su-tune.html
Another thought - did you use the carbs off the original engine? If so they are unlikely to have standard needles in them. The standard ones for the (18V engine which is the correct one for your car) should be:
for HS4 SUs the standard needle is AAL and for HIF carbs (with the fuel bowl underneath the carb), it is AAU or ABD. This is stamped on the top (the thick end) of the needle. The workshop manuals don't quote a richer needle for 1974 cars, so if you are not using the standard air filter cans, but something like K&N filters, then give Burlen a ring for them to suggest an alternative. All their details are here: http://burlen.co.uk/
This article will help you whilst under the bonnet to ties up the John Twist video. The adjustment for the choke idle speed is item 3 in the third picture.
http://www.mgexp.com/article/su-tune.html
Another thought - did you use the carbs off the original engine? If so they are unlikely to have standard needles in them. The standard ones for the (18V engine which is the correct one for your car) should be:
for HS4 SUs the standard needle is AAL and for HIF carbs (with the fuel bowl underneath the carb), it is AAU or ABD. This is stamped on the top (the thick end) of the needle. The workshop manuals don't quote a richer needle for 1974 cars, so if you are not using the standard air filter cans, but something like K&N filters, then give Burlen a ring for them to suggest an alternative. All their details are here: http://burlen.co.uk/
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965
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Vic Butler
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Re: Choke and cold running
Evening Dylan.
The factory carburettors for your MG are HIF4's. There are 2 types, the earlier ones are AUD 616F & R, the later ones are FZX 1001F & R. There is should be an attached tag showing the number. The standard needles are CUD1018AAU and CUD1051ACD. However it's unlikely that anyone would fit HIF4's to a modified engine. If you can let me know the number on the tag on your carburettors I can check my SU Reference Catalogue. No alternative needles are shown in the catalogue so you would need to contact Burlen but this can be hit and miss and needles are expensive but you have said that it runs fine when warmed up so that seems OK. The best way to set up if you have to is a rolling road session.
If you can let me know the needle numbers too I can check these.
The needles in the HIF4's are biased (spring loaded) and rub against the side of the jet over time wearing it. This was for ECE15 emission rules and the throttle discs have troublesome overrun valves.
. Vic Butler
The factory carburettors for your MG are HIF4's. There are 2 types, the earlier ones are AUD 616F & R, the later ones are FZX 1001F & R. There is should be an attached tag showing the number. The standard needles are CUD1018AAU and CUD1051ACD. However it's unlikely that anyone would fit HIF4's to a modified engine. If you can let me know the number on the tag on your carburettors I can check my SU Reference Catalogue. No alternative needles are shown in the catalogue so you would need to contact Burlen but this can be hit and miss and needles are expensive but you have said that it runs fine when warmed up so that seems OK. The best way to set up if you have to is a rolling road session.
If you can let me know the needle numbers too I can check these.
The needles in the HIF4's are biased (spring loaded) and rub against the side of the jet over time wearing it. This was for ECE15 emission rules and the throttle discs have troublesome overrun valves.
. Vic Butler
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Vic Butler
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Re: Choke and cold running
Just a thought Dylan. Are your carburettors 2 or 4 stud fitting on the manifold ?
Pete. ABD needles are for the USA spec B's.
. Vic Butler.
Pete. ABD needles are for the USA spec B's.
. Vic Butler.
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Michael Barclay
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Re: Choke and cold running
Hello Dylan
1974 was a change over year for the factory when they switched from SU4 to HIF carburetors. So which type would depend on build date. However the standard needle fitted to both types of carbs was AAU . If you are fitting K and N air filters the recommendation is to change to AAA needles.
I have a document (very tatty) from the Nuffield press that may help with setting up the throttle and choke on your carburetors. I used it to set mine up and had the car put on rolling road. The garage told me they were spot on so hopefully it may help you.
Tried to attach it but no luck so if you let me have your email address I will send it to you
Best regards
Mike Barclay
1974 was a change over year for the factory when they switched from SU4 to HIF carburetors. So which type would depend on build date. However the standard needle fitted to both types of carbs was AAU . If you are fitting K and N air filters the recommendation is to change to AAA needles.
I have a document (very tatty) from the Nuffield press that may help with setting up the throttle and choke on your carburetors. I used it to set mine up and had the car put on rolling road. The garage told me they were spot on so hopefully it may help you.
Tried to attach it but no luck so if you let me have your email address I will send it to you
Best regards
Mike Barclay
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Dylan Roberts
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- Joined: Sat Jan 13, 2018 10:52 am
- Forename: Dylan
- Surname: Roberts
Re: Choke and cold running
Hi Michael Vic and Peter,
Many thanks for all your replies and sorry it took me a while to take a look at it. And yes - she's now running much better! The throttle was opening too much, and so as I pushed the choke back in to slow the revs, this then caused too lean a mixture for cold running. Thank you.
There are many other points you have raised which I need to look at too, such as the needles. Yes I used the carbs from the modified engine, so yes there could well be non standard needles - I'll take a look this weekend.
Many thanks again - I will report back!
Dylan
Many thanks for all your replies and sorry it took me a while to take a look at it. And yes - she's now running much better! The throttle was opening too much, and so as I pushed the choke back in to slow the revs, this then caused too lean a mixture for cold running. Thank you.
There are many other points you have raised which I need to look at too, such as the needles. Yes I used the carbs from the modified engine, so yes there could well be non standard needles - I'll take a look this weekend.
Many thanks again - I will report back!
Dylan
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Vic Butler
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- Joined: Wed Dec 21, 2016 6:07 pm
- Forename: Vic
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Re: Choke and cold running
Evening Dylan.
Are you using the standard air filter assembly or something else eg K & B's?
. Vic Butler
Are you using the standard air filter assembly or something else eg K & B's?
. Vic Butler
1977 Stage 2 MGB GT
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
1975 SWB Series 3 Land Rover with a later 2.5 petrol engine
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Dylan Roberts
- Posts: 5
- Joined: Sat Jan 13, 2018 10:52 am
- Forename: Dylan
- Surname: Roberts
Re: Choke and cold running
Hi Vic,
I have the orignal filter housings with new filters (which were surprisingly expensive!).
I didn't go into much detail regarding the modified engine as I didn't think it relevant, but it actually blew up on me when I was trying to get it running properly in my garage. It looks like the big end came apart on cylinder 1 and the con rod punched a couple of holes either side through the block. Made quite a bang! The other 3 pistons look ok and the oil pump looks new, so if anyone can use it for parts they're welcome to have it - just needs collecting from Woking area. There's no head though as its on the replacement engine.
Regards, Dylan
I have the orignal filter housings with new filters (which were surprisingly expensive!).
I didn't go into much detail regarding the modified engine as I didn't think it relevant, but it actually blew up on me when I was trying to get it running properly in my garage. It looks like the big end came apart on cylinder 1 and the con rod punched a couple of holes either side through the block. Made quite a bang! The other 3 pistons look ok and the oil pump looks new, so if anyone can use it for parts they're welcome to have it - just needs collecting from Woking area. There's no head though as its on the replacement engine.
Regards, Dylan