Daimler running rich
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trampintransit
- Posts: 4
- Joined: Sat Sep 21, 2013 10:15 am
Daimler running rich
I have a '67 Daimler 2.5L V8. Bit of a barn find and still to go on the road. We've been struggling with carburation for a while. It ticked over but wouldn't rev.Stripping the carbs revealed them to be all gummed up. So a good clean and the car seems a lot happier. But, the strip revealed that both floats were set low. by the same amount. So we set them correctly. Although the car sounds ok now and ticks over smoothly and picks up OK, but it just seems too rich. Weve back off the adjustment but it still starts on a warm day without choke and even on a cold day it'll come off the choke almost instantly. Anybody else had similar problems with this engine? I'm now wondering if it's got the wrong needle jets in it. Are they too short and somebody had dropped the floats to compensate. Now the floats are 'correct' the over short needle valves are allowing over fuelling...or is that just a rubbish idea?
Re: Daimler running rich
I am assuming SU's right?
Problem could be worn needles, unleaded is harsher on them apparently, and they erode.
You set the mixture OK at idle but as the needles rise in the jet the worn taper allows too much fuel through.
You can get new needles at Burlens and they can also advise on the correct needles for your installation so you can check if you have the right ones fitted.
Problem could be worn needles, unleaded is harsher on them apparently, and they erode.
You set the mixture OK at idle but as the needles rise in the jet the worn taper allows too much fuel through.
You can get new needles at Burlens and they can also advise on the correct needles for your installation so you can check if you have the right ones fitted.
Re: Daimler running rich
It's normally the jet tubes that wear rather than the needles, although for the sake of the extra cost it would be worth replacing both.
Currently over 35 years worth of fixing 35 boxes.
Hoping to reach 65 years worth of fixing 65 boxes.
Hoping to reach 65 years worth of fixing 65 boxes.
Re: Daimler running rich
I thought you have to be rich to be running a Daimlertrampintransit wrote:Daimler running rich
....sorry,I just couldn't resist 
Re: Daimler running rich
sierra3dr wrote:I thought you have to be rich to be running a Daimlertrampintransit wrote:Daimler running rich
Is "Daimler running rich" above or below "filthy, stinking rich" in the order of chapters in the current edition of The Rich List?
And surely being Rich means that you run a JCB and have a fondness for the Nissan Micra?
J
"Home is where you park it", so the saying goes. That may yet come true..
"Home is where you park it", so the saying goes. That may yet come true..
Re: Daimler running rich
OK, some random thoughts, but firstly an apology if I’m stating the bl**ding obvious:
The needles for early cars should be type CI, for later cars type TZ: I don't know what year your car is, so suggest you check your needle. The jet needle MUST be positioned with the shoulder flush with the bottom face of the piston. The jet needle type is stamped on the side or top face of the parallel position of the needle. You can replace needles on earlier cars with the TZ needle without any problem. CI needles should not be used with later cars.
The jet size should be 0.100 inches (2.54mm). If they are worn it would contribute to rich running.
These engines are not very tolerant to a wide variation in float levels: I have mine set at the recommended 11mm gap between the top of the pronged fork and the lip of the float chamber lid.
Is the jet properly centred? It's not uncommon for misalignment to occur due to ageing of the diaphragm: this misalignment can wear needles and jets.
From the perspective of the driving seat, the LHS carb primarily feeds RHS cylinders 2 & 3 and LHS cylinders 1 & 4. The RHS carb primarily feed RHS cylinders 1 & 4 and LHS cylinders 2 & 3 (there is a balancing tube linking the two primary flows). Can you tell from plug colouration if one carb is running richer than the other?
The rubber diaphragm jet mounting in the HD6 carb plays a key role in their performance. It isn’t uncommon for diaphragms to “misbehave” if left dry for a long time. They can also be affected by high ethanol content in petrol. If the diaphragm is too stiff, the jet might not rise sufficiently with the sudden venturi effect caused by opening the throttle & this could cause rich running at higher revs. If it is too flexible it could rise too far and have the opposite effect. In the past I also had a tiny pin hole in one of the diaphragms causing all sorts of mayhem.
At tick-over with a hot engine, if you raise the piston 1/32” (0.8mm) the engine speed should momentarily increase slightly indicating a correct setting. If the engine speed decreases, the mixture is too weak. If it rises and continues to run faster, it is too rich. I have found this to be a much more reliable system than using Colourtune plugs! It should be the same momentary rev rise for each carb. If one is out of tune more than the other this might help you diagnose the culprit.
Is the choke return spring doing its job properly? Sometimes play in the linkages coupled with a weak spring can cause odd mixture settings.
In very cold weather I set the choke about 2/3 of the way between “Hot” and “Cold”. In warmer weather I set it about ¼ of the way above Hot. I have never had to use full choke.
Hope these comments help!
Best wishes, Dave B
The needles for early cars should be type CI, for later cars type TZ: I don't know what year your car is, so suggest you check your needle. The jet needle MUST be positioned with the shoulder flush with the bottom face of the piston. The jet needle type is stamped on the side or top face of the parallel position of the needle. You can replace needles on earlier cars with the TZ needle without any problem. CI needles should not be used with later cars.
The jet size should be 0.100 inches (2.54mm). If they are worn it would contribute to rich running.
These engines are not very tolerant to a wide variation in float levels: I have mine set at the recommended 11mm gap between the top of the pronged fork and the lip of the float chamber lid.
Is the jet properly centred? It's not uncommon for misalignment to occur due to ageing of the diaphragm: this misalignment can wear needles and jets.
From the perspective of the driving seat, the LHS carb primarily feeds RHS cylinders 2 & 3 and LHS cylinders 1 & 4. The RHS carb primarily feed RHS cylinders 1 & 4 and LHS cylinders 2 & 3 (there is a balancing tube linking the two primary flows). Can you tell from plug colouration if one carb is running richer than the other?
The rubber diaphragm jet mounting in the HD6 carb plays a key role in their performance. It isn’t uncommon for diaphragms to “misbehave” if left dry for a long time. They can also be affected by high ethanol content in petrol. If the diaphragm is too stiff, the jet might not rise sufficiently with the sudden venturi effect caused by opening the throttle & this could cause rich running at higher revs. If it is too flexible it could rise too far and have the opposite effect. In the past I also had a tiny pin hole in one of the diaphragms causing all sorts of mayhem.
At tick-over with a hot engine, if you raise the piston 1/32” (0.8mm) the engine speed should momentarily increase slightly indicating a correct setting. If the engine speed decreases, the mixture is too weak. If it rises and continues to run faster, it is too rich. I have found this to be a much more reliable system than using Colourtune plugs! It should be the same momentary rev rise for each carb. If one is out of tune more than the other this might help you diagnose the culprit.
Is the choke return spring doing its job properly? Sometimes play in the linkages coupled with a weak spring can cause odd mixture settings.
In very cold weather I set the choke about 2/3 of the way between “Hot” and “Cold”. In warmer weather I set it about ¼ of the way above Hot. I have never had to use full choke.
Hope these comments help!
Best wishes, Dave B
1937 Daimler 15 Mulliner Sports & 1969 Daimler V8 250
Re: Daimler running rich
To add to my last comment: today I was cleaning up my spare set of carbs, the needles measure 42mm from the base of the piston to the point of the chamfered tip. Hope this is useful.
Also, I tried to reply to your private message, but the reply sticks in my outbox, I can't find a send button!
Best wishes, Dave B
Also, I tried to reply to your private message, but the reply sticks in my outbox, I can't find a send button!
Best wishes, Dave B
1937 Daimler 15 Mulliner Sports & 1969 Daimler V8 250
Re: Daimler running rich
If it's in your outbox then you sent it already and all that it takes is for the recipient to open it, at which point the flag will change to sent.
When the O/P has sufficient posts, he'll be able to see it or you could use the email button instead of the PM one.
When the O/P has sufficient posts, he'll be able to see it or you could use the email button instead of the PM one.
J
"Home is where you park it", so the saying goes. That may yet come true..
"Home is where you park it", so the saying goes. That may yet come true..