David Jenkins
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| posted on 4/5/08 at 12:29 PM |
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Running on bike carbs - but now I need advice!
I've finally managed to get out and about in my car since converting to bike carbs. The tick-over is excellent, the acceleration is good (but
I'm not sure it beats the Weber down-draft yet) but it mis-fired really badly on WOT above 4500rpm and all power disappeared. It felt like the
Megajolt system rev limiter had cut in, but that's set to 6300rpm.
Trouble is, as part of this conversion, I've also changed from from MAP to TPS and replaced the entire fuel supply system from mechanical to an
electric fuel pump - any of these could be causing my problem!
I know it's not a great check, but I had a look at the plugs after an energetic run and they look OK. I also did a temp check on the exhaust
manifolds after the run and they all match each other (and similar to when I had the down-draft carb). I don't think the carbs are very far
wrong.
I've made a guess at the ignition map, but that's still a bit of a question mark - I did a datalog and I can see that I'm at around
30 degrees BTDC at WOT and 4500rpm - does that sound reasonable?
Finally, I've set the fuel regulator to 2psi for the time being, and I'm wondering if that's enough to meet the demand? The fuel
pump has enough capacity for the BHP according to specs, and the fuel regulator/filter is supposed to be a high-volume jobbie.
Apart from this wee problem, the car starts much more easily, has a really good and reliable tick-over and does sound lovely on acceleration, with a
rather impressive intake roar every time I touch the throttle! 
All hints & tips appreciated.
cheers,
David
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miikae
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| posted on 4/5/08 at 01:01 PM |
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My first thoughts on reading your post was fuel starvation , so try to up to 3psi and give it good run to see if this sorts it out .
Mike
If it can be done it i will be done .
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whitestu
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| posted on 4/5/08 at 01:09 PM |
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It may not help much, but I'm using the matching fuel pump from the bike the carbs came from and it works perfectly.
My pump was £10 off ebay.
Stu
[Edited on 4/5/08 by whitestu]
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triumphdave
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| posted on 4/5/08 at 02:14 PM |
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Yeh 2psi does sound a tad low,3 would be better.
If you always do what you have always done you will always get what you have always got
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David Jenkins
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| posted on 4/5/08 at 02:16 PM |
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Now set it to 3psi - but had a beer or 3 down my local, so can't try it out until the next dry day!
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ReMan
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| posted on 4/5/08 at 03:16 PM |
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Do they have an airbox?
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David Jenkins
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| posted on 4/5/08 at 03:23 PM |
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No - a filter box with a BIG filter across the front!
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Surrey Dave
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| posted on 4/5/08 at 03:53 PM |
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Jets?
Have you enlarged the main jets to 150 -180 , I think my car is set and runs at 2psi with no return.
Any more than that and the float needles flood.
Have a bike pump to fit but too lazy at the mo.
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Jon Ison
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| posted on 4/5/08 at 04:33 PM |
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A lot of bike carbs do not run well on regulators, by the time the pressure is down low enough flow is crap.
Fit a bike pump, better still bolt the carbs to a bike engine......... 
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David Jenkins
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| posted on 4/5/08 at 04:49 PM |
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quote:
Originally posted by Surrey Dave
Have you enlarged the main jets to 150 -180 , I think my car is set and runs at 2psi with no return.
Any more than that and the float needles flood.
Have a bike pump to fit but too lazy at the mo.
Currently my jets are 1.6mm.
Flooding is my main concern when increasing to 3psi.
I also have a bike pump, but I wasn't sure that it was man enough - it's from a 600cc bike. Mind you, if the weather's as bad
tomorrow as they predict, I might have a go at fitting it...
[Edited on 4/5/08 by David Jenkins]
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David Jenkins
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| posted on 4/5/08 at 04:55 PM |
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quote:
Originally posted by Jon Ison
Fit a bike pump, better still bolt the carbs to a bike engine.........
No thanks! I like to have reverse...
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westf27
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| posted on 4/5/08 at 04:58 PM |
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Honda Goldwing engine
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whitestu
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| posted on 4/5/08 at 06:24 PM |
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quote:
I also have a bike pump, but I wasn't sure that it was man enough - it's from a 600cc bike. Mind you, if the weather's as bad
tomorrow as they predict, I might have a go at fitting it...
My ZX6R pump works fine on my Zetec and has loads of flow.
Stu
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David Jenkins
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| posted on 4/5/08 at 06:48 PM |
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Thanks Stu - that may be my best option 
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DarrenW
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| posted on 4/5/08 at 08:37 PM |
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Im running bike carbs and bike pump, no regulator and no problems. Id change that first.
During rolling road Boggs determined my initial settings were too weak, took some fiddling to get good mixture through rev range.
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David Jenkins
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| posted on 4/5/08 at 08:41 PM |
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quote:
Originally posted by DarrenW
Im running bike carbs and bike pump, no regulator and no problems. Id change that first.
Boot box came out this evening, ready for the swap-over first thing tomorrow. Shouldn't be too painful as I had already modified the bracket to
take the bike pump ages ago - I'd changed my mind at the last minute!
quote:
During rolling road Boggs determined my initial settings were too weak, took some fiddling to get good mixture through rev range.
Doug (garage19) is coming over with his AFR meter tomorrow afternoon so maybe we'll see if I'm in the right ball-park.
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DarrenW
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| posted on 4/5/08 at 08:49 PM |
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You should get a good set up with the AFR. I hope it goes well.
Boggs were happy with my 1.6mm jets on my set up and mainly concentrated on needle position after basic checks were completed. I think they aimed for
about 2.5% CO across the rev range under load. Not sure what ratio that would correspond to.
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jacko
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| posted on 4/5/08 at 09:10 PM |
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I dont no if this will help but Boggs blocked some air holes in line with the needles to stop the fuel / air mix going week above 3ooo- on my car
jacko
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iscmatt
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| posted on 4/5/08 at 09:48 PM |
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just to add to the general theme, i have baike carbs and a bike pump and no probs, i also got bigger jets after a rolling road session at boggs.
cheers
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Dingz
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| posted on 4/5/08 at 11:20 PM |
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Just a thought, have you tried to link the carbs together with a vacuum line for servo?
2psi should be plenty, upping the pressure does nothing for the flow.
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