PaulBuz
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| posted on 27/4/07 at 06:58 PM |
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fuel pump, DHLA's & timing issues
I have finally got my engine running.
After 5 long years, believe me, it was a long time coming.
However, I seem to be having a few problems. Is anyone else running a fast road facet pump (4.5-6psi) WITHOUT a pressure regulator?.
I seem to have fuel weeping very slowly from the carbs.
They have been fully rebuilt with a kit,but I'm wondering if I should have bought the standard road item.
This brings me to the second problem, IF the pressure is too high,would this cause problems setting the idle mixture?...because its a mare to get
decent tickover...which brings me nicely to my final problem.
Does the timing needs for an engine alter when twin carbs are fitted?
I'm thinking that maybe the standard ecu is'nt giving the needed advance with the new carbs & this is the reason I cannot get it to
idle without dying.
My long term plan is to use mega jolt.
Maybe I will have to get a decent idle.
Anyone have any ideas?
ATB
Paul
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RobBrown
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| posted on 27/4/07 at 07:32 PM |
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I had a similar problem with my Dellorto's where I had fuel dripping out of the trumpet. It was down to the floats in the float chamber not
closing off the fuel inlet valve, so took the lid off the affected carb and bent the float down slightly to make the gap slightly bigger (between the
float and the lid) when in the seated position. This then means that when the float chamber is near enough full, the valve is closed properly and it
doesn't overflow.
Hope that helps.
regards
Rob
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chriscook
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| posted on 27/4/07 at 07:52 PM |
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You will need pressure regulator suitable for using with carbs.
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Dusty
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| posted on 27/4/07 at 10:01 PM |
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Absolutely fit a pressure regulator otherwise the float chambers overfill and it runs way too rich at tickover. Fuel pressure must be low enough to
allow the float valves to control the fuel level in the chambers accurately or you will never get the DHLA's to work well.
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bracey
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| posted on 28/4/07 at 12:33 AM |
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get the book mate on dellortos and webbers its a god send loads of info and how to set propally tells you seat & droop hights etc and all about
the timing advance needed and total advance to avoid detonation etc
best thing ive bought for carbs ., but still remember will need setting up on rollers
cheers
bracey
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PaulBuz
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| posted on 28/4/07 at 05:32 PM |
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cheers for the replies.
I had suspected that I would need a regulator, but the supplier in bought the kit off, swore that I did'nt need one.
Doe anyone know if a different ignition map is required.?
I know a 3D system will improve matters, but I wondered if radically diferent ignition settings are required when swopping to twin carbs?
ATB
Paul
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gottabedone
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| posted on 28/4/07 at 10:27 PM |
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Hey PaulBuz,
maybe a silly question but do you have a return in your fuel line? The engine will take what it needs and the excess will return to the tank or pre
pump. I had an overfuelling problem on my Alfa with twin 38 downdraughts until I noticed that the previous owner had plugged the fuel return. Max
flow from the pump was flowing though the carbs all of the time.
regards
Steve
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gazza285
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| posted on 28/4/07 at 11:35 PM |
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My old Mexico ran fine with a Facet pump into 45s with no regulator. However I will be using one on my Westfieldish using the same carb and pump on a
1300 Crossflow, just for peace of mind, and the filter that it comes with.
DO NOT PUT ON KNOB OR BOLLOCKS!
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flak monkey
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| posted on 29/4/07 at 10:56 AM |
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It depends on the pump, the std facet road pump only supplies about 3psi, which carbs can cope with. But the fast road pump supplied 4.5-6psi, which
it way too much for carbs. The main thing is carbs need fuel volume, not pressure. Ideally you want to regulate the pressure down to between 1.5 and
2.5psi.
Just changing the carbs doesnt mean you need to change the advance, only if you change the cam as well.
Heres how i set my carbs up (twin 40s)
1. Set the fuel pressure to 2 psi
2. Wind the idle screws out equal amounts (i think its 4.5turns on DHLAs as they have a really fine thread, but cant remember. I know its 1.5 turns on
DCOEs)
3. Back off the idle speed screw until the throttle spindle doesnt move anymore, then wind on a couple of turns (not sure how many on DHLAs) to let
the engine get some air. Then adjust the balance screw until its holding the second carb open the same amount roughly (back it off then wind it up to
touch the balance lever)
4. Start the engine up (it will run like a bag of bolts) and balance the carbs with a synchrometer. This should give you a reasonably smoothish idle
alone. The main reason you have a very rough idle is normally due to the carbs being out of synch.
5. Let the engine warm up to operating temp.
6. Wind in the idle screws 1/4 turn at a time until the revs peak, and then drop off (too lean). Take note of the setting.
7. Wind out the idle screws until the revs significantly fall (too rich) and take note of the setting
8. Set all of the idle screws to halfway between the settings from 6 & 7. This gives you a good starting point, but expect it to be well up on CO
emmissions!
9. Hold the revs at about 2000 or so, if you are getting a misfire/spitting back through one choke richen it up half a turn. Similarly at idle. This
should solve the problem.
10. Your engine should be running quite smoothly by now. If it isnt, chances are you have the wrong jets in the carbs.
Starting point for jets on a 2 litre, with DHLA 40s would be:
Chokes - 34mm
Main Jets - 140
Emulsion Tubes - 7772.6/7772.5
Air Correctors - 180
Idle Jets - 50/7850.2
Pump Jets - 40
Aux Venturis - 7848.2
As for your fuel dripping problem:
If the fuel is running out of the float chamber air intake (on the front of the carbs) then they are flooding due to too much fuel pressure.
If they are dripping from around the tumpets then its fairly common. The fuel being passed through the aux venturis finds its way out via capillary
action, especially if theres no load on the engine. Take the trumpets off and seal them with hylomar. Had to do it on mine, and totally solved the
problem
Hope some of thats useful.
David
[Edited on 29/4/07 by flak monkey]
Sera
http://www.motosera.com
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PaulBuz
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| posted on 30/4/07 at 06:39 PM |
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Thanks again for the info.
It looks like a regulator is on cards then!
In true locost fashion, does anyone know of a carbed tintop that has one I could rob?
ATB
Paul
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flak monkey
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| posted on 30/4/07 at 06:43 PM |
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You really might as well buy something that right for the job. They are under a tenner.
Carbed engines tend to be fitted with mechanical pumps, which dont need to be regulated.
Have a look on ebay. Usually some cheap on there. They only start getting pricey if you want a filter king or something fancy.
David
Sera
http://www.motosera.com
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