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M4Rob1987

Member
Hi all,

Have recently purchased a RR classic/series 3/90 hybrid with a 3.5 v8 with twin strombergs. Ugh.

Took it for a test drive about 4 days ago, ran smoothly and well.

Got it home yesterday, and have no end of issues with it. I’ve replaced ALL of the fuel lines, and put a new fuel pump on (1st one that arrived was a duff)! And fuel is merrily pumping in the engine bay, although I’m unsure at what pressure (gauge is coming tomorrow). The problem seems to be that it will run for perhaps half a mile, and then the power just entirely drops, barely makes it up small hills and sounds like it’s running on half of its cylinders. Now don’t seem to be able to get in running smoothly again. I’ve got a Filterking in line filter and pressure reg, and have adjusted the adjustment screw, which does absolutely nothing what so ever.

Does anyone have any ideas as I’m really losing my patience with something that was supposed to be fun.

Cheers all

Rob
 
Why change all the fuel lines if it's running well? Sounds like you've done something wrong or there's air getting in/petrol getting out!
 
Fuel new and clean? Filter blocked? Fuel pickup working properly?

If you've only had it four days, I'd do a full service, timing, filters, oils/fluids and go from there.
 
By way of an experiment loosen the fuel filler cap, take it for a run &see what happens.
DON'T go fast round any corners with the cap off as you might chuck fuel all over the road! (Guess how I know & in my case it was right handers cos that's the side my filler is on....)
 
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Does the return have a restriction in the pipe still?
Otherwise your just pumping fuel straight back to the tank
 
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I had similar on a 3.5 V8 with SU HIF carbs. It turned out one of the jet needles had dropped out of its mount, so only running on 4 cylinders. I would check the needles first. What pressure is the new pump meant to deliver?
 
Hi all - thanks for the replies!

Paul - Fuel is brand new, have got a Mapassi Filterking which seems to work ok, but am going to purchase some service parts for it just to make sure. Fuel pick up seems to be ok too - taking the hose off just before the carbs and it spurts out pretty swiftly.

Ratae - I’ll give it a go! Because it’s a non-standard fuel tank though, the filler cap is only a sort of “bodge” job anyway so seems to let a bit of air in.

Hicap - My RR doesn’t seem to have a fuel return, is this something I should DEFINITELY have? If so, where do I connect the hose on the carbs?

Landyman - How would I go about checking the needles? Do I have to completely remove the carbs to check that? The pump is an external 12v pump (http://www.paddockspares.com/prc3901-fuel-pump-ecternal-electric.html) Facet type which seems to work ok. If personally rather something a little more...professional, but I guess it does the job. Supposed to provide pressure between 4.0-5.5 psi, but can’t get exactly. Have got a in line pressure gauge turning up tomorrow.

Something I forgot to add was that when it’s running on what sounds like less than 8 cylinders, there is a very different “sound” coming from the carb air intakes - very hard to describe, but a suction noise but almost like it’s got something stuck in the airway, sort of noise. Coming from both carbs. I hope that makes sense to someone!

Cheers all.
 
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To check the jet needles just remove the top of the carb. The needles should lift out with the piston if still attached. All v8 carb setups I've seen have a fuel return pipe that tees of the second carb and is a smaller diameter then the feed pipe. It helps to eliminate overpressure and flooding the float chambers. It also means fuel is flowing continuously thus reducing the likeliehood of fuel vapour block.
 
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v8landyman said:
To check the jet needles just remove the top of the carb. The needles should lift out with the piston if still attached. All v8 carb setups I've seen have a fuel return pipe that tees of the second carb and is a smaller diameter then the feed pipe. It helps to eliminate overpressure and flooding the float chambers. It also means fuel is flowing continuously thus reducing the likeliehood of fuel vapour block.
Click to expand...
Ah ok - that sounds a relatively simple job - I’m sure even I can manage that! Is there anything specific I should be looking for? I don’t suppose you could find a picture of a carb )or have one of your own) that shows where the return pipe connects do you? I think I read that the feed pipe should be 8mm and the return 6mm - does that sound right?
 
IMG_20180226_171437.jpg

This is the return on my 101FC V8...rubber hose on left is the choke hose connecting the carbs...clear blue is return to tank....threaded end is carb connection... How does the fuel get to pump...I had a problem with mine the in tank strainer was blocked gave same symptoms as yours...sounds like fuel starvation...
 
Shippers said:
View attachment 153319
This is the return on my 101FC V8...rubber hose on left is the choke hose connecting the carbs...clear blue is return to tank....threaded end is carb connection... How does the fuel get to pump...I had a problem with mine the in tank strainer was blocked gave same symptoms as yours...sounds like fuel starvation...
Click to expand...
The fuel is drawn up a copper pipe and into a union that an 8mm fuel hose is then connected to. The hose is about 70cm long, which then connects to the fuel pump which I’ve mounted under the rear tub on the rear chassis rail. I still think it’s the filterking pressure reg/filter that’s causing the issues, but oddly, removing it and connecting the carbs directly to the fuel pump, doesn’t do anything either!
 
M4Rob1987 said:
Ah ok - that sounds a relatively simple job - I’m sure even I can manage that! Is there anything specific I should be looking for? I don’t suppose you could find a picture of a carb )or have one of your own) that shows where the return pipe connects do you? I think I read that the feed pipe should be 8mm and the return 6mm - does that sound right?
Click to expand...

This link gives a simple description of a Stromberg carb with good diagrams. Unlike the SU carbs, the Stromberg uses a rubber diaphragm at the top of the piston (illustrated in the link) that is prone to perishing and failure. This could be another cause of the symptoms. 6mm sounds correct for the return pipe. A workshop manual for your model will show everything you need.
https://www.howacarworks.com/fuel-systems/adjusting-a-stromberg-carburettor
 
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v8landyman said:
This link gives a simple description of a Stromberg carb with good diagrams. Unlike the SU carbs, the Stromberg uses a rubber diaphragm at the top of the piston (illustrated in the link) that is prone to perishing and failure. This could be another cause of the symptoms. 6mm sounds correct for the return pipe.
https://www.howacarworks.com/fuel-systems/adjusting-a-stromberg-carburettor
Click to expand...
Great stuff, thank you. When I’ve disassembled the top of the carb, and am looking at the needle, is there anything in particular that I should be looking for? I.e what sort of movement (if any) should it have?
 
Does it start and tick over OK then when under load IE driving it misfires and then loses power?
 
M4Rob1987 said:
Great stuff, thank you. When I’ve disassembled the top of the carb, and am looking at the needle, is there anything in particular that I should be looking for? I.e what sort of movement (if any) should it have?[/QUOTE

The needle is attached to the bottom of the piston with a screw. So when you lift the piston out the needle should come with it. If not then make sure the needle isn't bent and reattach to the piston. The later models have a spring biased mount that eliminates the need to centre the jet.
Click to expand...
 
M4Rob1987 said:
Great stuff, thank you. When I’ve disassembled the top of the carb, and am looking at the needle, is there anything in particular that I should be looking for? I.e what sort of movement (if any) should it have?
Click to expand...

The needle is attached to the bottom of the piston with a screw, so lifts out of the jet when you remove the piston. Check the needles are straight and reattach if necessary. Later models have a spring biased mount that eliminates the requirement to centre the jet.
 
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