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Hi all,

just got round to fitting my cbr600 carbs onto my 1.4 8v (AEX) polo 6n.

Im trying to fuel it using a t piece with the standard injection pump, however when I switch on the ignition it pours fuel out from the bowl overflow hose, doesn’t start and when I stop cranking it pours more fuel out. 
I’m pretty sure the floats work ok, could the pressure just be too high from the t piece? 
Tearing my hair out a bit so any wisdom would be much appreciated,

thanks :)

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Unbalanced throttles usually gives a shaky engine, rather than regular small pulses on the flywheel.   But It's really hard to get mixture correct if one cylinder is doing the most work, bec

Hole in a single float so it sinks slowly. Float rubbing on side wall. Float hinge damaged. Dirt at valve. Worn needle valve tip or seat. Damaged body gasket.

Yep the pump does that for a couple of seconds. After draining bowls it takes a few goes of this to fill them again and get the engine started, however I think this is because it’s wired to the origin

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I'm no expert on such conversions, but I believe carbs need far less fuel pressure than injection systems. Not sure what the fix is for you though.

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14 hours ago, Pete1 said:

I'm no expert on such conversions, but I believe carbs need far less fuel pressure than injection systems. Not sure what the fix is for you though.

Cheers yeah that’s definitely the case. Was wondering if I’d *somehow* plumbed the t piece in wrong. Maybe that only works on mk2s

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dvderlm

The mechy head mk2 pump is fine up to about 80ish hp but won't fit on hydro head.

 

The return line might be blocked, but carbs need high volume at low pressure

or the incoming fuel overcomes the needle valve(s) held closed by the float's buoyancy.

 

I assume the floats are not stuck on a side wall or holed... 

 

Bigger t-piece and fatter return line and clamped inlet pipe might work with just the tank lift pump and no high pressure pump but that risks fuel starvation on corners without a swirl pot/accumulator mounted higher than the carbs.

 

I'd suggest either a motorbike fuel pump, or a Huco suction pump or an injection to carb fuel pressure regulator with the high pressure injection pump.

 

Use a good quality item from Malpassi, not cheap rubbish that risks an engine fire.

https://www.ebay.co.uk/itm/FUEL-PRESSURE-REGULATOR-FOR-INJECTION-TO-CARB-CONVERSIONS-REDUCES-60-TO-5PSI-FP-/401381251704

 

 

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16 minutes ago, dvderlm said:

The mechy head mk2 pump is fine up to about 80ish hp but won't fit on hydro head.

 

The return line might be blocked, but carbs need high volume at low pressure

or the incoming fuel overcomes the needle valve(s) held closed by the float's buoyancy.

 

I assume the floats are not stuck on a side wall or holed... 

 

Bigger t-piece and fatter return line and clamped inlet pipe might work with just the tank lift pump and no high pressure pump but that risks fuel starvation on corners without a swirl pot/accumulator mounted higher than the carbs.

 

I'd suggest either a motorbike fuel pump, or a Huco suction pump or an injection to carb fuel pressure regulator with the high pressure injection pump.

 

Use a good quality item from Malpassi, not cheap rubbish that risks an engine fire.

https://www.ebay.co.uk/itm/FUEL-PRESSURE-REGULATOR-FOR-INJECTION-TO-CARB-CONVERSIONS-REDUCES-60-TO-5PSI-FP-/401381251704

 

 

Thankyou, in fairness The widest fuel line on the t is the one that goes to the carbs so makes sense that more fuel would be taking that route. 
I’ve ordered a bike pump, how do these work while keeping the fuel level sender working?

 Different People are telling me you can/can’t drag through the original fuel pump, sender somehow works without being plugged in (odd) and other mad stuff

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dvderlm

The fuel level sender and the pump in the tank are surely two separate electrical circuits in one unit with a common earth.

 

Me, I'd use the lift pump to feed the motorbike pump via a large inline fuel filter with a T piece return (small side back to tank) and big to new pump. Use the motorbike pump (which has an auto shut-off single outlet) to feed the carbs with correct pressure and flow rate. Keep pipes as short as you can without stressing them. 

 

Use SAE J30 R7 or PTFE or Teflon hose. 

 

Wire the motorbike pump on a switched fused spur with an inertia impact switch.

 

https://fastroadcars.co.uk/store/index.php?route=product/product&product_id=502

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10 minutes ago, dvderlm said:

The fuel level sender and the pump in the tank are surely two separate electrical circuits in one unit with a common earth.

 

Me, I'd use the lift pump to feed the motorbike pump via a large inline fuel filter with a T piece return (small side back to tank) and big to new pump. Use the motorbike pump (which has an auto shut-off single outlet) to feed the carbs with correct pressure and flow rate. Keep pipes as short as you can without stressing them. 

 

Use SAE J30 R7 or PTFE or Teflon hose. 

 

Wire the motorbike pump on a switched fused spur with an inertia impact switch.

 

https://fastroadcars.co.uk/store/index.php?route=product/product&product_id=502

Nice one that was the plan. Do you think there’d be any way I could mount the new pump in the space the old injection pump occupies?  Thus cutting down on additional wiring and using the original pump circuit off the key?  Cheers 

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dvderlm

Depends on the pump design (head pressure) and the case. Most motorbike pumps have the tank above so always run with fuel for the vanes. So low is good.

 

This one needs to be mounted near car fuel tank.

https://danstengineering.co.uk/Bike-Carb-Fuel-Pump 

 

But I have seen Facet style low pressure pump on inner wing about 30cm above bottom of tank. One with long looped untidy plumbing to carb ran poorly. Shortening the pipe route helped. New owner might have also switched to larger internal diameter.

 

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On 11/11/2020 at 03:24, dvderlm said:

Depends on the pump design (head pressure) and the case. Most motorbike pumps have the tank above so always run with fuel for the vanes. So low is good.

 

This one needs to be mounted near car fuel tank.

https://danstengineering.co.uk/Bike-Carb-Fuel-Pump 

 

But I have seen Facet style low pressure pump on inner wing about 30cm above bottom of tank. One with long looped untidy plumbing to carb ran poorly. Shortening the pipe route helped. New owner might have also switched to larger internal diameter.

 

Got it to run today using a cbr pump, it idles ok (intermittently), however whenever i give it any throttle at all it either dies completely, or revs up and stays at that speed for maybe 30 seconds. Cant see any black smoke from the exhaust. Any idea what this could be? Fuel pressure too low as its currently pulling through the old pump? I've not balanced them yet but surely balance wouldn't cause that obvious of a problem.

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dvderlm

vacuum leak, Falschluft (false air)  the Germans call it.

 

Air is being sucked in unmetered by the carb, not inhibited by the throttle plate.

 

Try shaving foam on cold engine where carbs mount to inlet tubes and tubes to cylinder head. It'll bubble where the air is sucked.

 

Or Cold start spray (diethyl ether) it will speed up from idle when leak hole sprayed.

Or Carb cleaner might slow it down.

 

 

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19 hours ago, dvderlm said:

vacuum leak, Falschluft (false air)  the Germans call it.

 

Air is being sucked in unmetered by the carb, not inhibited by the throttle plate.

 

Try shaving foam on cold engine where carbs mount to inlet tubes and tubes to cylinder head. It'll bubble where the air is sucked.

 

Or Cold start spray (diethyl ether) it will speed up from idle when leak hole sprayed.

Or Carb cleaner might slow it down.

 

 

Carb cleaner sped it up on a couple of cylinders? I am Fairly certain my manifold isn’t up to task though, it’s an awful flux core welded diy job 

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dvderlm

Might depend on the cleaner content I suppose. 

If it is flammable isopropanol or benzene it will speed up.

Think most cleaners are xylene or toluene based...

 

Whatever, it should not affect the engine speed when sprayed on the outside.

You could maybe braze the joints with silver solder or fill with exhaust putty?

 

If the plate that meets head is warped because an amateur welded it will need planing, filing, machining flat. You might be able to use some chunky gasket material like cork sheet to seal better.

 

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Sounds like the carbs need setting up correctly, unbalanced and untuned carbs can cause a lot of randomness to occur, especially if the air/fuel, spring rate and jetting are all wrong. 

 

You could "seal" the the welds with a putty of some sort to test for air leaks, but if they are completely out of sync it would make minimal difference.  

 

Any pictures of the setup you have at present? 

 

just to note. It is possible to balance the butterflies off the engine with the right kit.  

 

Check out this link: 

 I know the links contained within this are a bit long and in depth but there may be something to help somewhere in main carb thread. 

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15 hours ago, Cymro said:

Sounds like the carbs need setting up correctly, unbalanced and untuned carbs can cause a lot of randomness to occur, especially if the air/fuel, spring rate and jetting are all wrong. 

 

You could "seal" the the welds with a putty of some sort to test for air leaks, but if they are completely out of sync it would make minimal difference.  

 

Any pictures of the setup you have at present? 

 

just to note. It is possible to balance the butterflies off the engine with the right kit.  

 

Check out this link: 

 I know the links contained within this are a bit long and in depth but there may be something to help somewhere in main carb thread. 

I bench balanced them as best as I could using a bit of very thin wire, also tried to balance them with my gunson carbalancer yesterday which improved things somewhat. Whatever I do the readings are definitely worse on the cylinders with the two most bodged runners on.

 

I sealed the manifold and welds with instant gasket before fitting and it was airtight,  but I think this has broken down  due to petrol contact so I’ve given up on that manifold before I suck any big pieces into the engine. Could exhaust assembly paste or something work temporarily? Just want to get it useable until my new manifold arrives (really long lead times at the moment from danst engineering)

 

all I’ve got is this short video from before I connected the throttle cable or cleaned the blocked idle circuits:

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Should be able to use the inlet manifold gasket to seal, then put the sealant around the outside portion of the welds. 

 

If you've got access to a blow torch, you could use brass or lead to seal the welds. 

 

It doesn't sound to be running took bad once revved. 

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Turbobandit

Hi rusty how did you mount and take the feed to the bike pump ? I’m in the middle of fitting bike carbs and have become stuck on this thanks in advance any pics would be appreciated 

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On 20/11/2020 at 18:15, Cymro said:

Should be able to use the inlet manifold gasket to seal, then put the sealant around the outside portion of the welds. 

 

If you've got access to a blow torch, you could use brass or lead to seal the welds. 

 

It doesn't sound to be running took bad once revved. 

Very nice, my nice aluminium inlet has just arrived so I’ll be fitting that tomorrow fingers crossed

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1 minute ago, Turbobandit said:

Hi rusty how did you mount and take the feed to the bike pump ? I’m in the middle of fitting bike carbs and have become stuck on this thanks in advance any pics would be appreciated 

Very easily done, my current setup has the line that would normally go into your fuel rail straight to the “IN” connection on the pump in the engine bay, then a length of hose and an inline fuel filter going to the carbs. 
Pump is cable tied securely onto the little plastic bracket that normally  holds the charcoal canister breather valve. It should be just in front of your strut tower. I’d add some foam or rubber between the pump and the bodywork of your car as insulation. The pump’s sound is loud and annoying inside the cabin otherwise.

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Turbobandit

Thanks rusty and that is with the original pump connected ? Could you post a pic of your set up please just so I can see it ? Also what did you do with the fuel return hose ? 

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Just now, Turbobandit said:

Thanks rusty and that is with the original pump connected ? Could you post a pic of your set up please just so I can see it ? Also what did you do with the fuel return hose ? 

Yep, original pump is still in, just with its 12v feed pulled out of the plug. Seems to work ok so far and I’ve since replaced the injection system so doesn’t seem to have caused any damage (I hope).

At first I connected the Fuel return on a t piece with the carbs and fuel send but it’s disconnected a bolt clamped in the end to blank it off now.

The t piece Seemed to make the pump run constantly as it never got to pressure, shouldn’t be needed with a decent motorbike pump.

 

not got any photos at the moment, I’ll try and remember to stick one up for you tomorrow

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Turbobandit

Brilliant thank you mate !! So you removed the 12v signal to original pump . Fitted the motorcycle pump in the engine bay and have the other side going to carbs . It still pulls the fuel through the original pump and to the carbs fine ? Also what did you do for the wiring of the bike pump ? Is it on a switch in the cabin ? 

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Turbobandit
16 hours ago, rusty said:

Very easily done, my current setup has the line that would normally go into your fuel rail straight to the “IN” connection on the pump in the engine bay, then a length of hose and an inline fuel filter going to the carbs. 
Pump is cable tied securely onto the little plastic bracket that normally  holds the charcoal canister breather valve. It should be just in front of your strut tower. I’d add some foam or rubber between the pump and the bodywork of your car as insulation. The pump’s sound is loud and annoying inside the cabin otherwise.

Hi rusty any chance of a couple pics please ? Don’t mean to hassle just I am going to attempt to fit again soon and just wanna see how yours is !! Have you ran a power supply on a switch for the pump ? 

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2 hours ago, Turbobandit said:

Hi rusty any chance of a couple pics please ? Don’t mean to hassle just I am going to attempt to fit again soon and just wanna see how yours is !! Have you ran a power supply on a switch for the pump ? 

Here’s one of the full bay:  https://ibb.co/2qtVCXP

Couldn’t upload on here as the file limit is too small

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Turbobandit
20 hours ago, rusty said:
6 minutes ago, rusty said:

Here’s one of the full bay:  https://ibb.co/2qtVCXP

Couldn’t upload on here as the file limit is too small

Hi rusty thanks for that . I’ve been and had another go at fitting today but my pump won’t pull the fuel through original pump with the power supply disconnected. I see the put on your pump goes to something else before carbs what is that mate ? I’m thinking of looping the in and return together with  at-piece and fitting the pump after and try that with original pump still connected 

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