BCPCEC = Bike carb powered car engine cars

Managed to get car ticking over quite happily tonight. Not managed to road test yet sono idea how it will behave on the road. I may take it to work in the morning.

Anyway - question is this - It ticks over and revs up OK stationary. Ihave noticed however that with DGAS when i let of the throttle it settled down quite quickly. The bike carbs take a while longer to get back to tick over speed. Has anyone else noticed this? Im wondering if it is a characteristic of CV slide carbs - ie when engine draws air the slides lift up and car revs up, so when you let off the throttle the engine still draws air and it takes longer to get back to tick over. Either that or i need to fine tune the set up.

Id also like to test my theory ref needle set up. If i find it runs slightly lean or rich can this be adjusted by altering needle height? ie lift needle to richen and lower them to weaken?


Thanks in advance,
Darren.

[Edited on 7/9/07 by DarrenW]

[Edited on 10/9/07 by DarrenW]

You can raise or lower the needle to adjust the fuel mixture at a given level of needle lift but the needle profile will control what happens either side of that given, adjusted, position.

the movement of the piston up and down the CV carb will mean the RPM change is slightly slower than a system without moving parts... but only slightly....

i would try balancing the carbs first darren
just to ensure their all open the same amount then recheck the idle/ settleing back situation afterwards.
just a thought aswell if the mixture screws are set as per the bike standard settings then will the pinto pull to much fuel through due to the strong manifold vaccuum so may need weaker screw settings than stock bike?
do you have vac gauges/gauge to check the balance and does your manifold have ports/drillings for vac connections etc?

I had the same problem, slow to return to tick over.
Cured by fitting a spring to aid the return.
Bill

Likewise - couple of springs neeeded.....Oli.

Any air leaks on the inlet manifold?

Great replies everyone, many thanks.

Just arrived at work (only a 3 mile drive).

The slow return to idle is a problem for gear changing (in that the engine races slightly when clutch is depressed but i expected that to happen).

OK -firstthe settings.
Cable is brand new and may need some fine tuning (Mac#1 cable kit).
Pump is ZX1000 and seems to run as expected.
Main jets are drilled to 160 (1.6mm drill put through carefully by hand - nice fit afterwards so i dont suspect it drilled oversize).
Air screws were wound in until seated then out 3 full turns each.
Needles are in central position as a starting point.
Carb balance has never been touched so its feasible it could need adjustment.
No vacuum take off's on Manifold.
Carb tops are the de-restricted types. Slides move right to the top and seem to be smooth and drop down easily.



Ref balance - i can see how one carb slightly open too far could cause slow return to idle. Can i use a simple cheap gunson balancer (the type you see in Halfords) or is a better one more advantageous?

I also noticed this morning that i have the Subaru effect. Im going to check plugs and leads etc. i noticed the exhaust popping a touch which indicates unburnt fuel getting through - maybe a symptom of one cylinder not firing correctly.

Ref springs - i had to raid my box of bits to find a spring but its not ideal. Attached at the carb. Seems to work but maybe not perfect. I may need to find a smaller diameter and shorter spring today and maybe also attach one to the pedal.

First time i got the cxar running for over 5 mins was last night at 22:00 so i couldnt do too many checks etc. I have a few checks to run through today.

[Edited on 7/9/07 by DarrenW]

[Edited on 7/9/07 by DarrenW]

Has anyone used this type? Any good?

ill second the return spring i was having the same problem fitted a good stiff spring and sorted it. I tried a couple before i got one suitable for the job (from my local factors)

The spring seems to be doing its stuff. Ive just checked it again. Its not great but is working.


Editted to remove 000's of words!! i had a problem earlier that the vacuum pistons werent lifting on 2 carbs = subaru effect (ie flat sounding). Root cause = rubber diaphragms not seated correctly. Countermeasure - smear of red rubber grease in the grooves, sticky enough to hold the seal in place whilst tops are placed on. Now pistons move OK.


Latest theory on revs not returning to idle - seems to be OK when i operate throttle link at carbs - not when i press pedal. I reckon ive tightened the pedal pivot just a touch too much. Will sort it tonight.


On the road it pops and quietly ish bangs from exhaust quite a bit. Assuming no air leaks at manifold etc - is this indicative of too much fuel and possibly needing to adjujst the ignition timing a tad???.(Megajolt). Also some farting noises from filter
[Edited on 7/9/07 by DarrenW]

[Edited on 7/9/07 by DarrenW]

Have you tried adjusting the air screws in a bit? I reckon 3 turns out may be a touch too much, 2 1/2??

My engine starts and blips up and down no problem, although thats without any load, and no exhaust! My carbs are also just as they came off the bike. I haven't drilled the jets yet.

The silencer and coolant pipes are going on next so I'll be able to make a better assessment.

Checked carb balance tonight. They were quite close but even closer now.

Checked pedal and it was loose enough. ive lubed up anyway.

Fired her up and still took a while to drop to idle. Revs drop quickly to around 1500 or so then take a little longer to reach tickover.

Could the idle screw position really change this? Ill try again to adjust to 2.5 turns (from 3) but they are a bugger to get access to. Is my assumption correct that screwing out richens / in weakens?

Darren as you know my carbs are zx9r but my air screws are only 1 turn out the air screws are only in use at low tick over .

Graham

Managed to balance carbs up at weekend, they were close but now better.

Reset mixture screws to 2.5 turns (interesting what you say Graham, ill bear that in mind for further tweeks or just let Boggs sort it out).

Bought a boxed set of springs. Fitted better sized and strength spring. Pedal nice and positive. Now revs return very nicely indeed.

Just been for a little blast up the road. All i can say is when i got back i sat in car giggling!!! I cant believe how much better it is now. Cant wait to get them tuned up properly. Ive got an adrenalin rush off it. Rather happy indeed.

You've probably released 30 + BHP so it should feel better

Cheers

Mark

I did have a moment earlier. car has always been twitchy when downshifting from too fast and braking. Cause is rear camber not correctly set up yet. There is a stretch of road to where i work that ive travelled many times. Today however the turn in for the car park seemed to come forward to meet me, i had to brake a bit harder and when i downshifted i got the back end to do a bit of a shuffle. Great fun. Previously i would have been on full throttle down this bit, however today i had more to go so surprised myself a touch.


The sound is sooooo nice as well. Ive always like webers for that, these arent too dissimilar.


30BHP - nice thought but maybe not that much yet. Hopefully that will be the gain after they are set up and ignition is tweeked. Im not bothered about RR though so may never know true output, it does feel good though.

I always liked my M3 for the adrenalin buzz it used to give me. This car has been close but not quite as the same - UNTIL TODAY

quote:

---

Originally posted by DarrenW
I did have a moment earlier. car has always been twitchy when downshifting from too fast and braking. Cause is rear camber not correctly set up yet. There is a stretch of road to where i work that ive travelled many times. Today however the turn in for the car park seemed to come forward to meet me, i had to brake a bit harder and when i downshifted i got the back end to do a bit of a shuffle. Great fun. Previously i would have been on full throttle down this bit, however today i had more to go so surprised myself a touch.


The sound is sooooo nice as well. Ive always like webers for that, these arent too dissimilar.


30BHP - nice thought but maybe not that much yet. Hopefully that will be the gain after they are set up and ignition is tweeked. Im not bothered about RR though so may never know true output, it does feel good though.

I always liked my M3 for the adrenalin buzz it used to give me. This car has been close but not quite as the same - UNTIL TODAY

---

Darren it needs a R/Road it may be running week for all you know mine was at top end revs you dont want to melt a piston do you
Graham

When i say no RR i still mean to go to Boggs. They have a rolling road but im not chasing the figures - just want the carbs set up.


Edit - 9th Oct - Managed 110bhp at just 5K revs on Boggs RR - im well happy. Probs would be more if we took the revs a touch higher but there was no need to.

[Edited on 9/10/07 by DarrenW]