smudge88
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| posted on 26/7/09 at 09:34 AM |
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Weber settings
Hi
I am running a 1300cc ford crossflow (Kent) engine in a Locost. This is a standard engine, with the exception of, the Twin 40 Weber’s, a free flow
exhaust and a high torque camshaft.
Below are the sizes of the parts I have within my carbs
Mains 110
Air Jets 155
Choke 30
Accelerator 35
Idle 45 F9
Aux venture 4.5
Emulsion tube ??
Having passed all the legal requirements my car is now on the road but not running correctly, it’s using lots of fuel, the exhaust pipe & plugs
are black, it backfires through number 2 cylinder/exhaust, it doesn’t seem to want to pull and there is a fuel mist around the end of the trumpet (if
you put your hand over the end of the trumpet neat fuel runs out of the trumpet)
I believe that it is running rich and have been told I need 26mm chokes (but I cant seem to find any anywhere) but I am wondering if I also need to
come down a size or two on the Mains or Air Jets for tuning of the carbs,
Any advice would be greatly received
Best regards
Grant
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britishtrident
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| posted on 26/7/09 at 10:41 AM |
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Back firing through a single cylinder indicates something is wrong with that cylinder ---- if nothing obvious ie an HT ignition fault or choked idle
jet then check the valve clearances and do a compression test or cylinder leakdown test,
My gut feeling is valve isn't sealing
Important to check the float levels, fuel pressure and the carbs are in synch ---- and all the jets are tight.
Tthe idle jets look too big more appropriate to a 1600 engine ---- a 1300 engine will run on the idle jets to quite a way up the rev range.
Mains also look more appropriate to a 1600 engine.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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austin man
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| posted on 26/7/09 at 11:36 AM |
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Talk to Anthony at Fast Road CArs, I bought my jets from him Via ebay he is very helpfull, and has a vast knowledge of webbers.
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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tomprescott
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| posted on 26/7/09 at 11:55 AM |
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I second Austin Man, Fast Road Cars are great, but as above, if its just on one cylinder its likely to be a problem with that cylinder. Do a google
search for jet sizes and compare what you have with what other people are saying is working for them.
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robocog
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| posted on 26/7/09 at 12:27 PM |
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Afternoon Grant :-)
Just to add..
I think Grant did a compression test and all looked consistant?
The carbs, though looking clean on the inside did need some persuading to get them all to run (accel jets were a bit gummy? and airline and pokey wire
cleared them so there was finally a jet of fuel on prodding the accel)
I am failrly sure we did check the float heights on both carbs
also deffo carbs were as close to balanced as we could get according to the Gunsons pea in a tube jobbie
I helped try and get the mixtures as close as poss for idle using a Gunsons colourtune, and with the idle adjusters barely left with a thread left
holding them in -they were still running damned rich, so they are deffo on the large size as we had run out of adjustment there
Using megajolt for ignition and it seems to be doing what it says on the tin (went for a spin and did some logging on lappy and no unusual spikes or
anything)
Checked that it was indeed doing what the jolt was instructing by monitoring with lappy and strobe, so think the ign side is tickety boo and its just
mixtures being inconsistent and overly rich
...
my money is on it just being wrong sized jets/chokes and other Webber voodoo
Fastroadcars was pretty good when I had my DGAV issues and wanted to know what jets I needed, but I think I mentioned this and you said he had not got
back to you when you emailed him??
- alternately get Chippy to sell you the megasquirt brain and get those TB's hooked up...go on ..you know it makes sense, esp as it will pretty
much all be plug and play for when you pick up a Zetec/Duratec/4AGE just involving some minor twiddling on the lappy to get it running good on
whatever you end up running
Laters
Rob
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davidwag
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| posted on 26/7/09 at 02:20 PM |
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Hi,
Its worth checking that the cold start mechanisms are working properly, they are prone to the pistons sticking and giving rich mixtures. Used to run a
pair of 45's with 36mm chokes on my 1300 Xflow fiesta hillclimber, but that was a 10,000 Rpm 150bhp monster.
David
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britishtrident
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| posted on 26/7/09 at 04:19 PM |
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The idle mixture screws turn in to make the mixture weaker.
It might be an idea to check the ignition timing on 2 different cylinder ie 1 and 4, if the timing is different you have a bent or worn distrubuter
shaft.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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robocog
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| posted on 26/7/09 at 05:56 PM |
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BT you sure about the idle mix screw direction?
If so I think we were going the opp way!
(worth checking again Grant?...I have the colourtune handy ish so just gimme a shout and I'll drop it round/have it ready for you)
Not sure why we did that if it was the case, unless it was too weak and we had to richen up till we were on last thread of adjuster?...either way that
was where we left it, due to running out of adjustment IIRC
(it was some time ago...pre SVA and much has happened since then..in my defense!)
The ignition is megajolt and running off a toothed wheel on crank and an EDIS module to coilpack...so cannot be dissy related unfortunately, but good
suggestion :-)
Regards
Rob
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smudge88
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| posted on 26/7/09 at 06:28 PM |
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Thanks for stepping in Rob, the compressions are 115-120 across the board, with a squirt of oil they all go up by 5psi. I was worried the backfire
could be air getting in, but I will try Fast Road Cars for information many thanks for the responses I think the carbs were set up for a 1700cc
crossflow.
Regards
Grant
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britishtrident
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| posted on 26/7/09 at 06:34 PM |
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For sure something is far wrong --- the idle jets look more appropriate for a fairly warm 1600 engine.
This might help with idle mixture setting
http://www.carburetion.com/Weber/adjust.htm
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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