Fuel Injection swap to carbs - a conundrum!

[Nick Fairweather]

I'm thinking about swapping the injection system to carbs and am weighing up the pros and cons. The current system has a Bosch pump and filter kit in the boot. I've fitted new spindles and throttle linkage (from Malcolm Prestige injection),metering unit/injectors overhauled by Neil Fergusson and new injection pipes. The car has been tuned and set up at Revingtons on a rolling road. Reasons for considering a change: I need to replace the fuel pump as it got severely overheated (stopped 2x) in Germany (36c +)and is not running as smoothly as it did so I figure it is on the way out. I ran the car in high temps before but had the previous pump in the wheel arch and had no problem. But I'm thinking maybe it is time to ditch fuel injection and go for carbs. In the main the car runs well 23 to 25 mpg but it has always been lumpy on tickover probably due in part to being a CP model with a fast road cam, and takes longer to start than I'd like. I was also thinking I may be able to run it on E10 with carbs if it becomes necessary and I understand it will be more economical (up to 30 mpg I think).

Not to be undertaken lightly. I understand  I'll need 2 HS6 carbs, an inlet manifold to mount the HS6 carbs  dizzy/pedestal/MU and drive gear and fit the drive gear from a saloon including the pedestal along with the pinch clamp, then refit the distributor + new fuel pump.

Loads of you will have done this; is it a good idea or stick with the simpler solution of fitting a new Bosch pump in the wheel arch?

 

Thanks

Nick

[Macleesh]

Sounds like you've invested quite a lot of time money and effort on PI already, I'd be just changing the pump if it were me.

If you were ever to sell a car on carbs will be less desirable than one with PI

I'd imagine it would be even more lumpy on carbs. FI can tolerate a wilder cam than carbs 

Sean

[cp25616]

As Sean has stated just change the Bosch pump.

Alan G

[Malbaby]

I can appreciate your concern with a fuel pump failure.

As others have stated, fit a new pump, rather than change to carbs.

Also consider fitting an additional pump in the boot space as a back up....More fuel line/electrical work, but not difficult.

[Mike C]

Bit of an overkill to fix a pump problem.Potential cures for overheating PI fuel systems have been extensively discussed in this forum. I have a Bosch pump fitted on the wheel arch fed buy a Carter booster pump and have has  no PI system overheating problems even on 40 deg C days ( not that I drive around as much on extremely hot days now I'm a bit older).

I personally wouldn't do it but if I switched to carbs it would be to Weber's , not SU's,  or maybe a totally modern, programmable injection system.

[Mk2 Chopper]

Wouldn't you lose power doing this change? I suppose we need to hear from the "loads" of people that have already done this, to see if it was a good idea. 

I think the newer pumps are the cause of the overheating fuel, the original Bosch conversions don't seem to have been an issue. 

Gareth

[cp25616]

I think the newer pumps are the cause of the overheating fuel, the original Bosch conversions don't seem to have been an issue.

Gareth I think you might be correct with your assumption the original Bosch fuel pump which ended in 996 seems to go on forever. The more modern Sytec replacement would appear to have more problems.

Alan G

[roy53]

Move your pump back to the wheel arch. Is it the same type that you had ? as it worked fine.

There are lots of posts regarding the repositioning of pumps and also the fitting of fuel coolers which i like the idea of.

To make it clear i am a Lucas pump as original but with the feeder pump fitted.

Depending on your location i have an SU carb setup that you could borrow if you want to try.

Always said that if i ever gave up on PI it would be webers.

Roy

[Nick Fairweather]

Thanks for your responses and offer of borrowing carbs, much appreciated. As I was asking the question I was leaning towards a replacement pump, but your comments have reinforced this decision............thanks again., The Bosh pump I had under the wheel arch developed a leak so I replaced it in 2015 I think with the Moss kit with the filter with it. I'll use the original filter this time and fit a replacement pump in the wheel arch. I've heard of problems with new pumps so  any suggestions of the best pump to fit, or is it a lottery?

 

 

[roy53]

Look at those who have fitted both pump and filter outside the boot 

[Nick Fairweather]

Will do thanks

[TRTOM2498PI]

I would certainly persevere with the Lucas system Vs carbs, especially since you have it all there & already fitted.  Once you have resolved the fuel pump issue, you should be fine.  For the record, my Bosch pump is in the boot, and has done over 10 trips abroad over the last 20 years, in all climates, and not missed a beat.  Depending on the fast road cam spec, you may also find the carbs are insufficient to deliver the fuel requirements, so that then you pose another problem or cost.

 

 

Good luck.

[astontr6]

On 12/2/2023 at 10:23 PM, Mike C said:

Bit of an overkill to fix a pump problem.Potential cures for overheating PI fuel systems have been extensively discussed in this forum. I have a Bosch pump fitted on the wheel arch fed buy a Carter booster pump and have has  no PI system overheating problems even on 40 deg C days ( not that I drive around as much on extremely hot days now I'm a bit older).

I personally wouldn't do it but if I switched to carbs it would be to Weber's , not SU's,  or maybe a totally modern, programmable injection system.

In my view a bad choice to go to SU,s, as this would in pact the value of your car. I agree with what is stated above. 

Bruce.

[Mk2 Chopper]

22 hours ago, Nick Fairweather said:

Thanks for your responses and offer of borrowing carbs, much appreciated. As I was asking the question I was leaning towards a replacement pump, but your comments have reinforced this decision............thanks again., The Bosh pump I had under the wheel arch developed a leak so I replaced it in 2015 I think with the Moss kit with the filter with it. I'll use the original filter this time and fit a replacement pump in the wheel arch. I've heard of problems with new pumps so  any suggestions of the best pump to fit, or is it a lottery?

 

 

I have read that the Bosch 0 580 464 126 is a good choice, but unfortunately I can't find specs on its operating pressures and volumes.

Gareth

[Andy Moltu]

There have been a few reports of issues recently with pumps overheating and "cavitating"

One theory is that E10, which has notionally existed for a while, now contains nearer to the maximum 10% ethanol than was than case for the past few years. It a relatively low boiling point, especially the winter petrol formulations which are the most volatile and are perhaps being sold in the summer at times!

After a long stint in warm weather, tank gets low, fuel in the tank has been heated by passing through the pump & prv a few times and the problems that seemed to disappear when many switched to Bosch pumps after the late 80s may be returning.

Solutions - mount the pump as low as possible (possibly outside) with an unrestricted flow to it with only a coarse mesh to protect the pump, and a fine post filter to protect the metering unit. Or go truly retro and fit a lift pump to make sure there is a decent head of pressure to feed the Bosch or Sytec pump. Someone mentioned a Carter but the Bosch Red top is another readily available option in the UK, put between the tank and the Bosch. The red top has an inbuilt, replaceable crud filter built in.
(I used to run with this when I had a Walbro roller vane pump which used to overheat and cavitate in the 6 without the lift pump, however was unnecessary when I put Sytec (044 equivalent in years ago) but wont until unless I have problems.

Would I put the carbs back on - No chance. The car was meant to be injected so should I deviate from Lucas PI it would be efi which can retain the existing inlet manifolds and bar the fuel rail and injectors will look much the same. (Unless you go single throttle body)

[TR NIALL]

When I contacted Glencoe regarding a replacement Pump for a TR6 this was their recommendation.

[BlueTR3A-5EKT]

Go engine driven fuel pump using the Bosch electric to start the engine only.

 

more reading

http://www.lucasinjection.com/bosch_and_lucas_fuel_pumps.htm

 

Edited December 4, 2023 by BlueTR3A-5EKT

[Mk2 Chopper]

37 minutes ago, BlueTR3A-5EKT said:

Go engine driven fuel pump using the Bosch electric to start the engine only.

 

more reading

http://www.lucasinjection.com/bosch_and_lucas_fuel_pumps.htm

 

That's really good! Interesting is also listed the flow rate and psi and amps of a number of Bosch pumps. The 413 pump is listed at 200l/ph and runs at 8 bar (116psi) although no chart is listed for that model on its amps, only the 044 variant which is rated at 6.5 bar which would be around 14 amps.

So the question is, would that pump (413) be better as it runs at a little over the pressure we require (approx 7.5 bar)? Another model (909) rated at 148l/ph at 5 bar shows the amps to be under 9 when it outputs at 7.5 bar. 

So it's a bit confusing to know which is best for our application. I can imagine higher amps could mean a warmer motor, not good for cavitation. Perhaps longevity won't be a good if the pump is running closer to its maximum? And what actually controls what the pump puts out? Why the range of values on these charts?  

Gareth

[Tom Fremont]

As others have posted, Webers are the top choice for carbs, preserving (6) throttles and delivering unsurpassed reliability and immunity to altitude sickness. PI needs closed loop monitoring and dynamic fuel regulation to address said altitude sickness where carburetors don't. To my knowledge they leave no performance on the table relative to PI.

First hand, my driver's engine has clocked 143,000 miles since its last rebuild on a very old set of 40DCOE18s with brass shafts. I repacked the bearings with grease once and clean the air filters every few years, otherwise no maintenance, adjustment or troubles. It's got a CP cam and uses the original type AC fuel pump. In the quarter mile it did 16.2 seconds, faster than the TR5 test times of the day - and I'm an amateur driver so it might have done better in a pro's hands. It lives at 500 ft above sea level but has climbed to 11,150ft with no running issues and clean spark plugs.

I do have another trick engine ready to fit to my concourse '250 which had a little trouble with the mechanical pump though it made 189.6 BHP. With a tweak to the air correctors and an electric pump it made 201 BHP ( corrected, not raw values ).

After 27 blissful years with them I'll never consider anything but Webers for my TRs. Here in the 'States where P.I. wasn't sold ( or legal/ compliant with pollution regs ) they're the only fueling conversion which increases the values rather than depress them. For an original P.I. that may not be the case, vintage originality trumping all.

In the UK you are spoiled for choice in rolling road shops who know Webers inside and out. Here it's a desert!

Tom

[Andy Moltu]

Perhaps Webers are an option but the altitude concerns are probably spurious. Why would you go Efi and not run closed loop so it can adapt to altitude for the cost of a wideband  sensor? The costs are similar to a triple Weber set up and can be set up by any rolling road rather than finding a Weber expert. A good solution but probably yesterday’s? Ditches the restrictions of worn distributors too.

The existing PI manifolds can be adapted to modern injectors and throttle position sensors. 

The expensive bit is the ECU but most of the other bits are common to many modern cars.

Go for a single throttle body and wilder cams struggle, but why do that when your existing manifolds provide an individual throttle body option?

[SteveBaker]

I was going down the road of fitting SU’s onto my CP but ended up selling the car.  It never seemed to run smoothly at lower speed, I’d replaced everything, it had a Revingtons pump fitted and set up by them. When you had your foot down it was great but much as I’d like to, you can’t always drive like that. Everyone I speak to agrees that lower speeds are a little lumpy but they love the system and are sticking with it. I’ve now bought a 4a with a well worked CP 6 pot up front and it’s running poorly on triple webbers, if you want those Nick they will be available very soon! 

[Andy Moltu]

They shouldn't be lumpy at low speeds. Only at tickover.

Usually rough low speed running is related to throttle imbalance.

[Tom Fremont]

32 minutes ago, Bakes said:

I’ve now bought a 4a with a well worked CP 6 pot up front and it’s running poorly on triple webers, if you want those Nick they will be available very soon! 

The cast-off Webers stories are legion; that's why I never had to pay even new price for NOS vintage Italian let alone excellent used carbs. They're not for everyone and it seems I'm an outlier in that I've had success with them on several 6-pot TR engines without professional or expert assistance - scarce here but plentiful on your side of the pond.

With over 4 billion permutations there are several recipes that exist for each application with indistinguishable results. I'd say the range for these engines is a couple of hundred - not a few but doable for those who persevere.

Agreed, Andy but " spurious " is not perhaps apt here; the LUCAS P.I. issues with altitude are what I meant, assuming all EFI systems have such monitoring. 

Finally, these cars are ~60 years old now and their vintage cachet goes out the window with EFI. What amazes me is the Jenvey EFI systems which imitate the real thing. On BAT this year the former didn't make 1/3 of what the latter made on TR6 auctions of otherwise comparable cars. All of the performance of Webers with the added complexity of electronics which have little likelihood of being available years from now at no extra charge  

 

Tom

[Roadrunner Paul]

+1 for Andy’s suggestion to check throttle imbalance. It only needs one - 1/8 turn on my Revington underslung throttle mechanism on the rear throttle adjuster cured jerky running below 1800 rpm.  Thanks to Dennis Hobbs!

[DRD]

1 hour ago, Bakes said:

I was going down the road of fitting SU’s onto my CP but ended up selling the car.  It never seemed to run smoothly at lower speed, I’d replaced everything, it had a Revingtons pump fitted and set up by them. When you had your foot down it was great but much as I’d like to, you can’t always drive like that. Everyone I speak to agrees that lower speeds are a little lumpy but they love the system and are sticking with it. I’ve now bought a 4a with a well worked CP 6 pot up front and it’s running poorly on triple webbers, if you want those Nick they will be available very soon! 

I switched from SUs to Webers on one of my previous classic cars and setup by an alleged expert on a RR but it never ran as well as it did on the SUs. I certainly wouldn't go there again myself.